Authors: Rundong Yuan, Wojciech J. Jankowski, Ka Shen, Robert-Jan Slager
Magnons with momentum-dependent chirality are a key signature of altermagnets. We identify bicircular light as a smoking-gun optical probe for chiral altermagnetic magnons, selectively targeting their quantum geometry induced by an alteration of magnonic chirality. We show that in $d$-wave altermagnets, under a canting magnetic field, the altermagnetic magnons realize a nontrivial quantum geometry, resulting in an enhancement of the nonlinear second-order light-magnon interactions. We find that the scattering of bicircular pulses probes the present magnon quantum geometry, even if the magnonic topology is trivial. Hence, our findings establish bicircular Raman response as an optical effect of choice to identify altermagnetic magnons. As such, we propose a universal experimental protocol to distinguish altermagnets from antiferromagnets by detecting their magnon chirality patterns with light, independently of the underlying magnon topology.
Authors: Szu-Cheng Cheng, Yu-Wen Wang, Wen-Hsuan Kuan
We investigate the nonlinear Bloch dynamics and Landau-Zener tunneling of quantum droplets in optical lattices, where the interplay between mean-field repulsion and beyond-mean-field attraction from Lee-Huang-Yang corrections introduces a localization impedance that inhibits dynamical dispersion. This self-stabilizing mechanism is crucial to droplet mobility and nonlinear dephasing under external driving. In the deep-lattice regime, simulation in tight-binding reduction reveals breathing modes, self-trapping, and nonlinear Bloch oscillations. In the shallow-lattice regime, we reformulate the problem in momentum space and map the dynamics onto a nonlinear two-level model with time-dependent detuning. The adiabatic spectrum features looped bands and multiple fixed points, parallelly captured by the phase-space structure through a classical Josephson analogy. Applying Hamilton-Jacobi theory, we quantify the tunneling probabilities and demonstrate nonreciprocal Landau-Zener tunneling. The transition probability from the lower to upper band differs from that of the reverse process, even under the same sweeping protocol. This asymmetry arises from nonlinearly induced band gap modulation, highlighting rich dynamical behavior beyond the linear and adiabatic regimes.
Authors: Katherine Chea, Erin S. Grant, Kevin J. Rietwyk, Hiroshi Abe, Takeshi Ohshima, David A. Broadway, Jean-Philippe Tetienne, Gary Bryant, Philipp Reineck
The nitrogen-vacancy (NV) center in diamond is emerging as a powerful tool for imaging magnetic and electric signals at the microscale and below. However, most imaging demonstrations thus far have relied on costly, millimeter-sized bulk diamond substrates, which cannot be easily scaled or integrated with other materials. Here, we report a scalable method for fabricating NV-containing dense and homogenous fluorescent nanodiamond (FND) layers through electrostatic self-assembly and demonstrate the utility of the FND layers for magnetic imaging. We investigate the effect of FND concentration in suspension, substrate immersion time, and solvent pH on the FND density on the substrate. We identify optimized self-assembly conditions that maximize the FND density while minimizing aggregation. Using FND layers on a quartz substrate, we demonstrate magnetic field and magnetic noise imaging at the microscale, based on NV optically detected magnetic resonance magnetometry and T$_1$ relaxometry, respectively. Our results provide a direction for the development of cost-effective and scalable FND layers and surface coatings. This paves the way for on-demand quantum sensing and imaging on a broad range of surfaces based on NV centers and other diamond quantum emitters.
Authors: Han Wu, Jianwei Huang, Chaowei Hu, Lei Chen, Yiqing Hao, Yue Shi, Paul Malinowski, Yucheng Guo, Bo Gyu Jang, Jian-Xin Zhu, Andrew F. May, Siqi Wang, Xiang Chen, Yaofeng Xie, Bin Gao, Yichen Zhang, Ziqin Yue, Zheng Ren, Makoto Hashimoto, Donghui Lu, Alexei Fedorov, Sung-Kwan Mo, Junichiro Kono, Yu He, Robert J. Birgeneau, Pengcheng Dai, Xiaodong Xu, Huibo Cao, Qimiao Si, Jiun-Haw Chu, Ming Yi
Quantum materials with bands of narrow bandwidth near the Fermi level represent a promising platform for exploring a diverse range of fascinating physical phenomena, as the high density of states within the small energy window often enables the emergence of many-body physics. On one hand, flat bands can arise from strong Coulomb interactions that localize atomic orbitals. On the other hand, quantum destructive interference can quench the electronic kinetic energy. Although both have a narrow bandwidth, the two types of flat bands should exhibit very distinct spectral properties arising from their distinctive origins. So far, the two types of flat bands have only been realized in very different material settings and chemical environments, preventing a direct comparison. Here, we report the observation of the two types of flat bands within the same material system--an above-room-temperature van der Waals ferromagnet, Fe$_{5-x}$GeTe$_2$, distinguishable by a switchable iron site order. The contrasting nature of the flat bands is also identified by the remarkably distinctive temperature-evolution of the spectral features, indicating that one arises from electron correlations in the Fe(1) site-disordered phase, while the other geometrical frustration in the Fe(1) site-ordered phase. Our results therefore provide a direct juxtaposition of the distinct formation mechanism of flat bands in quantum materials, and an avenue for understanding the distinctive roles flat bands play in the presence of magnetism, topology, and lattice geometrical frustration, utilizing sublattice ordering as a key control parameter.
Authors: Ricardo Ortiz, Karol Strutyński, Manuel Melle-Franco
Altermagnetism stands as a third type of collinear magnetic order, whose band structure combines a net zero magnetization with a non-relativistic spin-splitting caused by a broken time reversal symmetry. So far, the strategy to design platforms displaying altermagnetism has relied mostly on inorganic crystals with d-metals as spin centers, where a representative example is the two-dimensional square lattice with antiparallel D2h magnetic blocks related by a pi/2 rotation. Despite the fact that there is no strong requirement for the magnetic atoms to be metals, the construction of an altermagnetic framework with light elements like carbon is challenging due to symmetric constrictions. We show how it is possible to overcome this by including non-alternant rings in pi-conjugated nanographenes. More specifically, dibenzo[ef,kl]heptalene, an S = 1 pi-conjugated hydrocarbon consisting of a graph of two fused heptagons and hexagons, represents a suitable building block for an altermagnetic 2D crystal. In this work, we confirm this hypothesis with DFT calculations of the spin polarized band structure, presenting a spin compensated ground state with broken time reversal symmetry, and a d-wave symmetry of the first valence and conduction bands. Consistent results are obtained for covalent organic frameworks based on dibenzo[ef,kl]heptalene units connected by linkers, paving the way for the realization of organic altermagnetic materials.
Authors: Jiaming Hu, Zhichao Guo, Wenbin Li, Hua Wang, Kai Chang
Light-induced coherent phonons provide a powerful platform for ultrafast control of material properties. However, the microscopic theory and quantum geometric nature of this phenomenon remain underexplored. Here, we develop a fully quantum-mechanical framework based on Feynman diagrams to systematically describe the generation of coherent phonons by light. We identify a dominant second-order, double-resonant process in noncentrosymmetric semiconductors that efficiently couples light to both electronic and phononic excitations. Crucially, we uncover the quantum geometric origin, encoded in the electron-phonon coupling (EPC) shift vector and the EPC quantum geometric tensor. Applying our theory to ferroelectric BaTiO$_3$ and SnSe, we demonstrate the potential for light-induced modulation of ferroelectric polarization driven by coherent phonons. This work provides fundamental insights for designing efficient optical control strategies for both coherent phonons and ferroelectric polarization.
Authors: Bo Lu, Phillip Mercebach, Pablo Burset, Keiji Yada, Jorge Cayao, Yukio Tanaka, Yuri Fukaya
We investigate the realization and control of subgap states by tailored altermagnetic fields on unconventional superconductors. When the symmetries of altermagnetism and unconventional superconductivity align, we demonstrate the emergence of bulk zero-energy flat bands, giving rise to a zero-bias conductance peak. The symmetry and strength of $d$- and $g$-wave altermagnets strongly affect the surface Andreev states from $d$-wave and chiral $d$- and $p$-wave superconductors. As a result, distinct types of subgap states are realized, including curved and flat bands, that can be detected by tunneling spectroscopy. Furthermore, we find that the altermagnetism-induced subgap states give rise to a large spin conductance at zero net magnetization which helps identify the strength of the underlying altermagnetism and superconductivity. Our results offer a solid route for designing and manipulating subgap states in superconducting systems, which can be useful for functionalizing superconducting spintronic devices.
Authors: Zhiyu Chen, Fangyang Zhan, Da-Shuai Ma, Dong-Hui Xu, Rui Wang
Conventional topological classification theory dictates that time-reversal symmetry confines the quantum spin Hall (QSH) effect to a $\mathbb{Z}_2$ classification, permitting only a single pair of gapless helical edge states. Here, we utilize the recently discovered altermagnetism to circumvent this fundamental constraint. We demonstrate the realization of a unique QSH phase possessing multiple pairs of gapless helical edge states in altermagnetic multilayers. This exotic QSH phase, characterized by a mirror-spin Chern number, emerges from the interplay of spin-orbit coupling and $d$-wave altermagnetic ordering. Moreover, using first-principles calculations, we identify altermagnetic Fe$_2$Se$_2$O multilayers as promising material candidates, in which the number of gapless helical edge states scales linearly with the number of layers, leading to a correspondingly large, exactly quantized, and experimentally accessible spin-Hall conductance. Our findings unveil a new mechanism for stabilizing multiple pairs of gapless helical edge states, significantly expanding the scope of QSH effects, and provide a blueprint for utilizing altermagnetism to engineer desired topological phases.
Authors: Zi-Hao Ding, Lei Wang, Zhen-Feng Ouyang, Jingsi Qiao, Ze-Feng Gao, Wei Ji, Kai Liu, Peng-Jie Guo, Zhong-Yi Lu
Exploring the intricate interplay between magnetism and charge density waves has long been a fundamental pursuit at the forefront of condensed matter research. In this letter, based on symmetry analysis and first-principles calculations, we propose for the first time that anomalous charge density wave can be realized in two-dimensional altermagnetic WO. The anomalous charge density wave is characterized by three key features: (i) Unlike conventional charge density wave, whose stabilization is driven by the opening of a gap near the Fermi level, the anomalous charge density wave is stabilized by the occupied states with energies shifting lower far away from the Fermi level; (ii) the anomalous charge density wave increases the density of states near the Fermi level and then enhances-rather than diminishes-the metallicity of materials; (iii) altermagnetism plays a crucial role in stabilizing anomalous charge density wave. Thus, our work offers a pathway for exploring both the realization and the underlying mechanisms of anomalous charge density waves in magnetic systems.
Authors: Shengpu Huang, Zheng Qin, Fangyang Zhan, Dong-Hui Xu, Da-Shuai Ma, Rui Wang
Recent studies have drawn growing attention on non-relativistic odd-parity magnetism in the wake of altermagnets. Nevertheless, odd-parity spin splitting is often believed to appear in non-collinear magnetic configurations. Here, using symmetry arguments and effective model analysis, we show that Floquet engineering offers a universal strategy for achieving odd-parity magnetism in two-dimensional (2D) collinear antiferromagnets under irradiation of periodic driving light fields such as circularly polarized light, elliptically polarized light, and bicircular light. A comprehensive classification of potential candidates for collinear monolayer or bilayer antiferromagnets is established. Strikingly, the light-induced odd-parity spin splitting can be flexibly controlled by adjusting the crystalline symmetry or the polarization state of incident light, enabling the reversal or conversion of spin-splitting. By combining first-principles calculations and Floquet theorem, we present illustrative examples of 2D collinear antiferromagnetic (AFM) materials to verify the light-induced odd-parity magnetism. Our work not only offers a powerful approach for uniquely achieving odd-parity spin-splitting with high tunability, but also expands the potential of Floquet engineering in designing unconventional compensated magnetism.
Authors: T. Karabassov, I. V. Bobkova, A. M. Bobkov, A. S. Vasenko, A. A. Golubov
We develop a linear response theory for the dynamical proximity effect in topological superconductor/ferromagnetic insulator (TS/FI) hybrid structures. Our approach combines the nonequilibrium quasiclassical Keldysh-Usadel equations for the electronic Green's functions in the TS with the Landau-Lifshitz-Gilbert equation governing the magnetization dynamics in the FI. Within this framework, we study the proximity-induced coupling between magnons and superconducting collective excitations. We find that the spin-momentum locking intrinsic to the surface state of the TS leads to a hybridization between the superconducting Nambu-Goldstone (phase) collective mode and magnons, resulting in the emergence of composite magnon-Nambu-Goldstone excitations. The dependence of the coupling strength on relevant physical parameters is analyzed both analytically and numerically. In contrast, we show that the Higgs (amplitude) mode does not couple to magnons at linear order and therefore does not participate in the formation of hybrid collective excitations.
Authors: Stephon Alexander, Heliudson Bernardo, Humberto Gilmer
We present a model of dark matter as a superconducting fluid of Cooper pairs of right handed neutrinos or of vector-like quarks. The superconducting dark matter is induced by attractive channels in the Standard Model Higgs and color sectors of the Standard Model, respectively. We show that, for each case, the solution to the gap equation provides viable dark matter candidates for suitable chemical potential values. The mechanism yields an ultra-light neutrino condensate with a mass of $m_{\rm DM} \sim 10^{-19} \text{eV}$ or a vector-like quark condensate with wide range of possible masses. Both cosmological and particle physics constraints on the model lead to a connection between the number of effective relativistic species $N_{\rm eff}$, and the chemical potential and CMB temperature at the time of fermion creation. We also find a relation between the superconducting fermion and baryon densities, with implications for the coincidence between the dark matter and baryon densities in standard cosmology. Given the natural $\text{eV}$ scale of neutrinos, this mechanism may have implications for the Hubble tension.
Authors: Kazuki Doi, Tadashi Takayanagi
We consider the evolution of entanglement entropy in a two-dimensional conformal field theory with a holographic dual. Specifically, we are interested in a class of excited states produced by a combination of pure-state (local operator) and mixed-state local quenches. We employ a method that allows us to determine the full time evolution analytically. While a single insertion of a local operator gives rise to a logarithmic time profile of entanglement entropy relative to the vacuum, we find that this growth is heavily suppressed in the presence of a mixed-state quench, reducing it to a time-independent constant bump. The degree of suppression depends on the relative position of the quenches as well as the ratio of regularization parameters associated with the quenches. This work sheds light on the interesting properties of gravitational scattering involving black holes.
Authors: Amichay Vardi, Doron Cohen
We consider a minimal model for quantum thermalization of coupled chaotic subsystems. The route towards ergodicity is explored as a function of the coupling strength. The results are contrasted with the predictions of standard Random Matrix Theory (RMT) and the Eigenstates Thermalization Hypothesis (ETH). We highlight a coupling regime of disparity between the spectral statistics that indicates chaos, and ergodicity measures that indicate lack of ETH thermalization. The analysis involves a revision of the energy shell concept, in a way that is consistent but independent of the semiclassical perspective.
Authors: Haydar Sahin
Electrical circuits offer a unique platform to explore physical phenomena, from topology to non-Hermitian effects. Investigations of the fundamental properties of this metamaterial platform are crucial to distinguish observed/measured quantities from intrinsic circuit responses. In this thesis, we delve into the analysis of voltage and impedance responses and their role in unveiling complex dynamics and profound physical principles. We reveal that even the simplest one-dimensional circuits exhibit intriguing voltage profiles. Our study of multi-dimensional and multi-structural lattice models shows size-dependent impedance responses, which challenge our current textbook knowledge. Building on these insights, we will present non-linear and non-Hermitian circuit applications, showcasing how electrical circuits provide a suitable platform for realizing intriguing physical phenomena.
Authors: Guillermo Parra-Martínez, Alejandro Jimeno-Pozo, Jose Angel Silva-Guillén, Francisco Guinea
Rhombohedral graphene systems with different number of layers feature an abundance of correlated phases and superconducting states in experimental measurements with different doping and displacement fields. Some of the superconducting pockets can emerge from - or close to - one of the correlated states. Therefore, studying the phase diagram of the correlated phases for varying number of layers could be useful to interpret the experimental observations. To achieve this, systematic Hartree-Fock calculations have been performed to build the phase diagram of rhombohedral (ABC-stacked) graphene for different number of layers, in the presence of long-range Coulomb interactions. By varying the external displacement field and carrier density, a cascade of metallic partially-isospin-polarized phases that spontaneously break spin and/or valley (flavor) symmetries is found. In addition, these states can present nematicity, stabilized by electron-electron interactions, exhibiting rich internal complexity. Polarized states are more stable for electron doping, and they are found for systems with up to 20 layers. Moreover, the tunability of the phase diagram via substrate screening and spin-orbit coupling proximity effects has been studied. Our results offer new insights into the role of correlations and symmetry breaking in graphitic systems which will motivate future experimental and theoretical works.
Authors: Francesco Parisen Toldin, Fakher F. Assaad, Max A. Metlitski
The interplay of topology and correlations defines a new playground to study boundary criticality in quantum systems. We employ large scale auxiliary field quantum Monte Carlo simulations to study a two-dimensional Kane-Mele-Hubbard model on the honeycomb lattice with zig-zag edges and the Hubbard U-term tuned to the three-dimensional XY bulk critical point. Upon varying the Hubbard-U term on the edge we observe a boundary phase transition from an ordinary phase with a helical Luttinger liquid edge decoupled from the critical bulk to an extraordinary-log phase characterized by a logarithmically diverging spin stiffness. We find that the spectral functions exhibit distinct features in the two phases giving potential experimental signatures.
Authors: Soumyaditya Das, Soumyajyoti Biswas, Bikas K. Chakrabarti
We study a quantum annealing approach for estimating the ground state energy of the Sherrington-Kirpatrick mean field spin glass model using the Suzuki-Kubo dynamics applied for individual local magnetization components. The solutions of the coupled differential equations, in discretized state, give a fast annealing algorithm (cost $N^3$) in estimating the ground state of the model: Classical ($E^0= -0.7629 \pm 0.0002$), Quantum ($E^0=-0.7623 \pm 0.0001$) and Mixed ($E^0=-0.7626 \pm 0.0001$), all of which are to be compared with the best known estimate $E^0= -0.763166726 \dots$ . We infer that the continuous nature of the magnetization variable used in the dynamics here is the reason for reaching close to the ground state quickly and also the reason for not observing the de-Almeida-Thouless line in this approach.
Authors: Ziyu Liu, Emil Viñas Boström, Dihao Sun, Jordan Pack, Matthew Cothrine, Kenji Watanabe, Takashi Taniguchi, David G. Mandrus, Angel Rubio, Cory R. Dean
Hysteretic gate responses of two-dimensional material heterostructures serve as sensitive probes of the underlying electronic states and hold significant promise for the development of novel nanoelectronic devices. Here we identify a new mechanism of hysteretic behavior in graphene/$h$BN/$\alpha$-$\mathrm{RuCl_3}$ charge transfer field effect devices. The hysteresis loop exhibits a sharp onset under low temperatures and evolves symmetrically relative to the charge transfer equilibrium. Unlike conventional flash memory devices, the charge transfer heterostructure features a transparent tunneling barrier and its hysteretic gate response is induced by the dynamic tuning of interfacial dipoles originating from quantum exchange interactions. The system acts effectively as a ferroelectric and gives rise to remarkable tunability of the hysteretic gate response under external electrical bias. Our work unveils a novel mechanism for engineering hysteretic behaviors via dynamic interfacial quantum dipoles.
Authors: Rohin Sharma, Diem Thi-Xuan Dang, Lilia M. Woods
Magnetism in doped transition metal dichalcogenide monolayers and van der Waals interfaced materials have motivated the search for sustainable magnetic states at the nanoscale with the prospect of building devices for spintronics applications. In this study, we report the existence of magnetism in a heterostructure made up of an $MoSe_2$ transition metal dichalcogenide monolayer and a $V_2O_5$ substrate. Using density functional theory simulations, we find that ferromagnetic ordering can be found in the $MoSe_2/V_2O_5$ heterostructure even though the individual components are nonmagnetic. By examining the electronic structure and magnetic properties of this system we find how the occurring ferromagnetism evolves if the transition metal dichalcogenide or the $V_2O_5$ substrate can host point defects. Our study suggests that the balance between charge transfer and spin reorganization can lead to interface magnetism in novel hybrid materials.
Authors: Xiangqi Liu, Chen Xu, Jing Jiang, Haonan Wang, Shaobo Liu, Gan Liu, Ziyi Zhu, Jian Yuan, Wei Xia, Lianbing Wen, Jiawei Luo, Yixuan Luo, Xia Wang, Na Yu, Peihong Cheng, Leiming Chen, Rui Zhou, Jun Li, Yulin Chen, Shiwei Wu, Ke Qu, Wei Li, Guangming Zhang, Chungang Duan, Jianhao Chen, Xiaoxiang Xi, Zhenzhong Yang, Kai Liu, Yanfeng Guo
Superconductivity in the two-dimensional (2D) limit is a fertile ground for exotic quantum phenomena-many of which remain elusive in their 3D counterparts. While studies of 2D superconductivity have predominantly focused on mono- or few-layer systems, we demonstrate an alternative route-interlayer sliding in bulk crystals. Through a precisely controlled growth strategy, we engineer interlayer sliding in bulk 3R-NbSe2, deliberately disrupting [001] mirror symmetry and drastically suppressing interlayer coupling. Remarkably, this structural manipulation stabilizes Ising-type superconductivity coexisting with an unconventional charge-density-wave (CDW) state akin to that of monolayer 2H-NbSe2. The sliding phase exhibits a pronounced suppression of the upper critical field at low temperatures, revealing a delicate competition between Ising and Rashba spin-orbit coupling (SOC) in the globally noncentrosymmetric lattice. Intriguingly, the superconducting state displays two-fold symmetry, a signature that may arise from asymmetric SOC or a multi-component pairing order parameter. Our work establishes interlayer sliding as a symmetry-breaking tool to promote 2D superconductivity in bulk materials-without resorting to extrinsic intercalation or doping. More broadly, this approach sets a paradigm for unlocking hidden quantum states in layered materials, offering a new dimension in design of quantum matter.
Authors: Mohammad Alipourzadeh, Davood Afshar, Yaser Hajati
Unconventional $p$-wave magnets (UPMs) with odd-parity spin textures have attracted interest for their zero net magnetization and anisotropic spin-split Fermi surfaces. Here, we explore a non-Hermitian open quantum system composed of a ferromagnet and a UPM, subjected to an external magnetic field and off-resonant circularly polarized light (CPL), serving as tunable control parameters. We demonstrate the emergence of exceptional points (EPs) in the proposed junction, whose locations can be modulated by the intrinsic properties of the UPM. These EPs exhibit different multiplicities and formation conditions compared to those in even-parity magnets (dubbed $d$- wave altermagnets), a distinction attributable to the preserved time-reversal and broken inversion symmetries characteristic of UPMs. We find that both the unidirectional magnetic field (with adjustable strength and orientation) and the CPL induce momentum-direction-dependent modifications to the EPs, such as their shifting, tilting, merging, or annihilation, supported by analyses of spin projection and eigenvector overlap. Although both perturbations influence the EP structure, they operate via distinct mechanisms: CPL induces a global Floquet re-normalization, enabling dynamic tunability through light, whereas the unidirectional magnetic field selectively alters orientation-aligned terms, lacking such tunability. Beyond revealing EP dynamics in UPM-based junctions, our results highlight UPMs as promising platforms for non-Hermitian phenomena in future spintronics.
Authors: Dawei Zhai, Hongyi Yu, Wang Yao
The moiré superlattices formed by stacking 2D semiconducting transition metal dichalcogenides (TMDs) with twisting angle or lattice mismatch have provided a versatile platform with unprecedented tunability for exploring many frontier topics in condensed matter physics, including optical, topological and correlation phenomena. This field of study advances rapidly and a plethora of exciting experimental and theoretical progresses have been achieved recently. This review aims to provide an overview of the fundamental properties of TMDs moiré superlattices, as well as highlight some of the major breakthroughs in this captivating field.
Authors: H. Y. Yuan
Recent experiments demonstrate that spin dynamics may acquire an inertial effect in a few metallic magnets, deviating from the traditional inertia-free dynamics. It remains an open question to ascertain the physical mechanisms and universality of the spin inertia across diverse magnetic systems. Here, we show that spin inertia generates nutation spin waves in the terahertz regime, which can hybridize with the surface plasmons in two-dimensional (2D) conducting materials such as graphene. By exciting hybrid spin wave-plasmon modes and analyzing the reflection spectrum of a 2D material$|$magnet heterostructure, we propose a method to quantitatively determine the strength of spin inertia in magnetic layers. Our approach is universally applicable to all types of magnetic insulators and could advance the future exploration of the magnitude and physical mechanism of spin inertia.
Authors: Victor Gondret, Rui Dias, Clothilde Lamirault, Léa Camier, Amaury Micheli, Charlie Leprince, Quentin Marolleau, Scott Robertson, Denis Boiron, Christoph I. Westbrook
By exciting the transverse breathing mode of an elongated Bose-Einstein condensate, we parametrically produce longitudinal collective excitations in a pairwise manner. This process also referred to as Faraday wave generation, can be seen as an analog to cosmological particle production. Building upon single particle detection, we investigate the early time dynamics of the exponential growth and compare our observation with a Bogoliubov description. The growth rate we observe experimentally is in very good agreement with theoretical predictions, demonstrating the validity of the Bogoliubov description and thereby confirming the smallness of quasiparticle interactions in such an elongated gas. We also discuss the presence of oscillations in the atom number, which are due to pair correlations and to the rate at which interactions are switched off.
Authors: Remy Adderton, Murray T. Batchelor
The Hamiltonian of the $N$-state clock model is written in terms of a coupled Temperley-Lieb (TL) algebra defined by $N-1$ types of TL generators. This generalizes a previous result for $N=3$ obtained by J. F. Fjelstad and T. Månsson [J. Phys. A {\bf 45} (2012) 155208]. The $\mathbb{Z}_{N}$-symmetric clock chain Hamiltonian expressed in terms of the coupled TL algebra generalizes the well known correspondence between the $N$-state Potts model and the TL algebra. The algebra admits a pictorial description in terms of a planar algebra involving parafermionic operators attached to $n$ strands. A key ingredient in the resolution of diagrams is the string Fourier transform. The pictorial presentation also allows a description of the Hilbert space. We also give a pictorial description of the representation related to the staggered XX spin chain. Just as the pictorial representation of the TL algebra has proven to be particularly useful in providing a visual and intuitive way to understand and manipulate algebraic expressions, it is anticipated that the pictorial representation of the coupled TL algebra may lead to further progress in understanding various aspects of the $\mathbb{Z}_{N}$ clock model, including the superintegrable chiral Potts model.
Authors: Tista Banerjee
Ultracold atoms in optical lattices are versatile testbeds to study and manipulate equilibrium and out-of-equilibrium aspects of quantum many-body systems whose behavior can be described by Hubbard-type Hamiltonians. In this paper, we consider an ansatz wave-function which respects total particle-number conservation for such systems and goes beyond mean-field theory; this wave-function has the same complexity in the number of parameters as the mean-field Gutzwiller ansatz, and captures quantum correlations and entanglement via projection onto an effective low-energy manifold. This ansatz can be exploited to study quantum phases observed in a large class of systems realizable in such experimental platforms and is useful to study quantum dynamics. We show that the relaxation dynamics of various out-of-equilibrium initial states under sudden quench of Hamiltonian parameters can be studied with this ansatz wavefunction within the framework of time-dependent variational principle. We present a quantitative comparison with small-scale exact diagonalization results in the 1D Bose-Hubbard model with and without external trapping potentials.
Authors: Wei-Cheng Peng, Hsien-Yang Liu, Cheng-Yu Yu, Artur Useinov, Tian-Li Wu
Ferroelectric Hf0.5Zr0.5O2 (HZO) thin films are promising for next-generation memory and logic devices due to their CMOS compatibility and scalability. The spatial uniformity of the orthorhombic (O) phase is crucial for optimizing ferroelectric properties like remnant polarization. This work introduces a novel piezoresponse force microscopy (PFM) approach for 2D mapping of O-phase uniformity in HZO films (5 nm, 9 nm, and 20 nm), further quantifing O-phase distribution by distinguishing polarized O-phase regions from non-polarized tetragonal/monoclinic (T/M) phases. Our results reveal that the 9 nm film exhibits the most uniform O-phase and highest remnant polarization. This PFM-based method enables comprehensive phase characterization without requiring complicated facilities, broadening access to phase analysis and advancing ferroelectric thin-film research for memory and logic applications.
Authors: Krishnayan Basuroy, Jose de Jesus Velazquez-Garcia, Sreeju Sreekantan Nair Lalithambika, Argha Barman, Torben Reuss, Guillaume Pompidor, Alexander Grebentsov, Önder Akçaalan, Simone Techert
We report on the photoinduced spin crossover (SCO) transition from a 2HS-2LS to a 3HS-1LS state in a [2x2] Fe(II) metallogrid complex using molecular crystals with static photocrystallography at a first ever attempt in the beamline P11 of the PETRA III synchrotron, DESY. A class 3B diode laser was used to induce the transition under controlled irradiation conditions. Structural characterization was achieved through single-crystal X-ray diffraction (SCXRD) measurements post-irradiation, revealing significant changes in average Fe-N distances, consistent with SCO behavior. Our experimental setup enables precise alignment necessary for photo-excitation using a class 3B diode laser along with a compact focusing optics. The longest dimension of the combined setup of the diode head and the focusing optics is not more than 32cm. The setup showcasing the utility of a compact diode laser system which can even be conveniently used in synchrotron-based pump-probe photocrystallography experiments for a wide range of molecular crystals.
Authors: Renato Colle, Pietro Parruccini, Andrea Benassi, Carlo Cavazzoni
We present absorption coefficient {\alpha}({\omega}), transverse dielectric function {\epsilon}({\omega}), optical conductivity {\sigma}({\omega}), and reflectance R({\omega}) calculated for an emeraldine salt conducting polymer in its crystalline three-dimensional polaronic structure. We utilize Kohn-Sham DFT electronic wavefunctions and energies implemented in the expression of the macroscopic transverse dielectric function in the framework of the band theory without the electron-hole interaction. Contributions of intra-band transitions are taken into account by adding a Drude-like term to the dielectric function calculated ab-initio. Comparison with optical properties, recently measured on high-quality emeraldine salts (Nature 441(2006)65-68), and with optical absorption spectra, recorded on other emeraldine salts, is very satisfactory. The calculated spectra are discussed in terms of energy-band structure, density of states, inter- and intra-band transitions and transverse dielectric function.
Authors: Alice Bellettini, Vittorio Penna
Recently, cold atoms mixtures have attracted broad interest due to their novel properties and exotic quantum effects with respect to single-component systems. In this paper the focus is on massive many-vortex states and their dynamics. Vortex configurations characterized by the same discrete rotational symmetry are investigated when confined within topologically nonequivalent geometries, and the relative stability properties at varying number of vortices and infilling mass are highlighted. It is numerically shown how massive many-vortex systems, in a mixture of Bose-Einstein condensates, can host the bosonic tunneling of the infilling component both in a disordered way, with tunneling events involving two or more close vortices, or in an almost-periodic way when the vortices are organized in persisting necklaces or star-lattices. The purpose is to explore a variety of situations involving the interplay between the highly-nonlinear vortex dynamics and the inter-vortex atomic transfer, and so to better understand the conditions for the onset of Josephson supercurrents in rotating systems, or to reveal phenomena that could be of interest for a future application e.g. in the context of atomtronics.
Authors: Sudheer Anand Sreedhar, Matthew Staab, Mingkun Chen, Robert Prater, Zihao Shen, Giuseppina Conti, Ittai Sidilkover, Zhenghong Wu, Eli Rotenberg, Aaron Bostwick, Chris Jozwiak, Hadas Soifer, Slavomir Nemsak, Sergey Y. Savrasov, Vsevolod Ivanov, Valentin Taufour, Inna M. Vishik
The multiple crystalline terminations in magnetic Weyl semimetal Co$_3$Sn$_2$S$_2$ display distinct topological and trivial surface states, which have successfully been distinguished experimentally. However, a model of pure terminations is known to be inadequate because these surfaces exhibit a high degree of spatial heterogeneity and point disorder. Here we perform a spectromicroscopy study of the surface chemistry and surface electronic structure using photoemission measurements in combination with first-principles calculations of core levels. We identify an intermediate region with properties distinct from both the sulfur and tin terminations, and demonstrate that the spectral features in this region can be associated with a disordered tin termination with a varying density of surface tin-vacancies. Finally, we show how a combination of algorithmic and machine learning analysis of photoemission data can be used to extract identifying features, classify spatial regions, and correlate local chemistry with local electronic structure.
Authors: Stuart N. Holmes, Jonathan Gough, Ethan Dommett, Gavin R. Bell
Low temperature transport measurements are presented of ferromagnetic MnSb devices with the magnetic properties patterned using a Ga focused ion beam FIB system at 30 keV. FIB patterning introduces disorder and this is quantified in this paper through measurements of the longitudinal resistivity and the anomalous Hall effect contribution to the Hall conductivity. The MnSb structural phase is the niccolite phase with a surface state in addition to bulk states. FIB doses up to 1E16 Ga ions per square cm reduces the anisotropic magnetoresistance signal but increases the size of the anomalous Hall effect signal in out of plane magnetic fields, B. The anomalous Hall effect contribution to the Hall conductivity is e squared divided by h in the undamaged devices, where e is the electronic charge and h is Plancks constant. This quantity is sensitive to the level of disorder induced by the Ga ion beam, reducing to zero at dose levels greater than 1E16 Ga ions per square cm. The resistivity shows a logarithmic B dependence after the magnetization has saturated with the low field anisotropic magnetoresistance contribution of 0.12 percent. The conductivity change is e squared divided by h in the magnetic field range of logarithmic B behavior. The resistivity shows a reduced fit to a logarithmic B dependence at high FIB dose levels and is dependent on the damage uniformity. Patterning nanostructured magnetic behavior in MnSb, with compatibility to altermagnetic materials, in particular the niccolite phase of CrSb and non trivial Berry phase contributions to transport make this ferromagnetic material and patterning technique useful for future spintronic device development.
Authors: Xuan Bai, Yu Lu, Tianhao Yu, Kangjie Lv, Cai Yao, Feng Shi, Andong Liu, Kai Wang, Wenshou Wang, Chris Lai
Lipid nanoparticles (LNPs) are a leading platform in the delivery of RNA-based therapeutics, playing a pivotal role in the clinical success of mRNA vaccines and other nucleic acid drugs. Their performance in RNA encapsulation and delivery is critically governed by the molecular structure of ionizable lipids and the overall formulation composition. However, mechanistic insight into how these factors govern LNP architecture and function remains limited, primarily owing to the challenges of capturing nanoscale assembly and organization using experimental techniques. Here, we employ coarse-grained molecular dynamics simulations to systematically investigate how ionizable lipid chemistry influences LNP self-assembly, internal organization, and surface properties. We further explore the effects of formulation ratios and pH-dependent deprotonation on both the internal structure and surface morphology of LNPs. Leveraging these insights, we demonstrate how in silico structural characteristics can inform the rational design of novel ionizable lipids and optimization of formulation ratios, supported with experimental validations. Our findings offer a molecular-level understanding of LNP assembly dynamics and architecture, thereby establishing a computational framework linking lipid chemistry and LNP formulation to the structure and performance of LNP, to advance the rational design of novel LNP delivery systems.
Authors: Raphael Blumenfeld
Recent observations of coordinated self-organisation (SO) of stress and structure in granular systems provide insight into the fundamental principle underlying this phenomenon. It is first argued here that SO emerges when a minute subset of configurations are significantly more stable than the rest and therefore survive the noise in the system much longer to be observed. This principle goes deeper than recently proposed energy considerations. Guided by this principle, a statistical mechanics model is formulated then for SO in these systems and its extension to three dimensions is outlined. The principle holds beyond granular systems and the model is extended next to describe emergence of SO in more general systems. The application of the model is illustrated for the specific example of laning. Parallels of the modelling approach to traditional statistical mechanics provide useful insight that should assist in modelling SO in other out-of-equilibrium systems.
Authors: Mingpeng Liu, Peizhi Zhuang, Raul Fuentes
This study integrates a data-driven model for estimating the unfrozen water content into the thermo-hydraulic coupling simulation of frozen soils. An artificial neural network (ANN) was employed to develop this data-driven model using a dataset from the literature. Thereafter, a numerical algorithm was developed to implement the data-driven model into the thermo-hydraulic simulation. In the numerical algorithm, the frozen and unfrozen zones are distinguished first according to the freezing temperature, where the unfrozen water at frozen nodes is updated using the ANN model. Subsequently, discretized hydraulic and thermal equations are solved sequentially and iteratively using Newton-Raphson method until the temperature and unfrozen water content satisfy the tolerance simultaneously. Horizontal and vertical freezing experiments are used to verify the reliability of the proposed algorithm. The computed variations in temperature, total water, unfrozen water, and ice content achieve good agreements with measured data. Some key features of frozen soils, such as water migration and ice formation, and the increase in total water content, are reproduced by the developed algorithm. Additionally, the comparison between the ANN model and existing empirical equations for determining unfrozen water content demonstrates that the ANN model offers a better performance.
Authors: Vladimir L. Safonov, Derek A. Bas, Andrew Franson, Piyush J. Shah, Michael E. McConney, Michael Newburger, Michael R. Page
This study presents a simple theoretical model describing narrow envelope surface acoustic waves (phonons) and spin waves (magnons) in an ultrathin ferromagnetic film. Based on the general principles of weak wave turbulence, the model considers interactions between beams of an ideal phonon gas and a weakly non-ideal magnon gas, which represent magnetoacoustic oscillations in the system. Equations for the wave envelopes of phonons and magnons, along with their harmonics, are derived, incorporating nonlinear effects from three- and four-particle interactions. In the general non-resonant case, linear stationary envelope simulations are sufficient. These clarify the experimentally observed angular dependence of the transmitted acoustic signal with respect to the orientation of the magnetic field. The study highlights increased energy losses associated with enhanced magnetoacoustic coupling. Given the broad interdisciplinary interest in weak turbulence phenomena within condensed matter physics and nonlinear wave dynamics, our model offers significant predictive capabilities and greatly simplifies calculations of quasiparticle beam interactions.
Authors: Sara Sarbaz, Zhi Xin Liu, Heidi Feigenbaum, Samaneh Bayati, Winston Wang, Jennifer Wade, Husain Mithaiwala, Matthew D. Green
A new direct air capture (DAC) technology uses a moisture swing (MS) process with anion exchange membranes, potentially offering a more energy-efficient way to remove CO2 from the air. In this MS process, the membrane absorbs CO2 as it dries and releases it when water is added. Understanding the mechanical behavior of these membranes is essential for improving the design and efficiency of DAC systems and prolonging sorbent lifetime. This study tested one anion exchange membrane, Fumasep FAA-3, under mechanical loading and various temperature and humidity conditions to measure its swelling, stiffness, strength, plastic deformation, and stress relaxation. Experimental results were used to identify a mechanical model for FAA-3 that can be used to predict the material's nonlinear viscous behavior under various loads and environments.
Authors: Timur Weber (1), Daniel Jetter (2), Jan Ullmann (1), Simon A. Koch (1), Simon F. Pfander (1), Katharina Kress (2), Andriani Vervelaki (2), Boris Gross (2), Oliver Kieler (3), Ute Drechsler (4), Priya R. Baral (5), Arnaud Magrez (5), Reinhold Kleiner (1), Armin W. Knoll (4), Martino Poggio (2 and 6), Dieter Koelle (1) ((1) University of Tübingen, (2) University of Basel, (3) PTB Braunschweig, (4) IBM Reserach Europe Zürich, (5) EPFL Lausanne, (6) Swiss Nanoscience Institute Univ. Basel)
Superconducting quantum interference devices (SQUIDs) are exceptionally sensitive magnetometers capable of detecting weak magnetic fields. Miniaturizing these devices and integrating them onto scanning probes enables high-resolution imaging at low-temperature. Here, we fabricate nanometer-scale niobium SQUIDs with inner-loop sizes down to 10 nm at the apex of individual planar silicon cantilevers via a combination of wafer-scale optical lithography and focused-ion-beam (FIB) milling. These robust SQUID-on-lever probes overcome many of the limitations of existing devices, achieving spatial resolution better than 100 nm, magnetic flux sensitivity of $0.3~\mu\Phi_0/\sqrt{\rm{Hz}}$, and operation in magnetic fields up to about 0.5 T at 4.2 K. Nanopatterning via Ne- or He-FIB allows for the incorporation of a modulation line for coupling magnetic flux into the SQUID or a third Josephson junction for shifting its phase. Such advanced functionality, combined with high spatial resolution, large magnetic field range, and the ease of use of a cantilever-based scanning probe, extends the applicability of scanning SQUID microscopy to a wide range of magnetic, normal conducting, superconducting, and quantum Hall systems. We demonstrate magnetic imaging of skyrmions at the surface of bulk Cu$_2$OSeO$_3$. Analysis of the point spread function determined from imaging a single skyrmion yields a full-width-half-maximum of 87 nm. Moreover, we image modulated magnetization patterns with a period of 65 nm.
Authors: Velimir Labinac, Jiayu David Cao, Gaofeng Xu, Igor Žutić
Adding spin-polarized carriers to semiconductor lasers strongly changes their properties and, through the transfer of angular momentum, leads to the emission of the circularly polarized light. In such spin-lasers the polarization of the emitted light can be modulated an order of magnitude faster than its intensity in the best conventional lasers. This ultrafast operation in spin-lasers relies on the large linear birefringence, usually viewed as detrimental in spin and conventional lasers, which couples the two linearly-polarized emission modes. We show that the dynamical properties of birefringent spin-lasers under intensity and polarization modulation are accurately described as coupled harmonic oscillators. Our model agrees with the intensity-equation description which, unlike the common complex field components describing the role of birefringence in laser dynamics, uses simpler real quantities and allows analytical solutions. We further predict unexplored operation regimes and elucidate the difference between the weak and strong coupling in spin-lasers.
Authors: Gabriel Cardoso, Erlend Syljuåsen, Alexander V. Balatsky
We report two light-induced orbital magnetization effects in quantum Hall (QH) fluids, stemming from their transverse response. The first is a purely transverse contribution to the inverse Faraday effect (IFE), where circularly polarized light induces a DC magnetization by stirring the charged fluid. This contribution dominates the IFE in the QH regime. The second is the orbital inverse Cotton-Mouton effect (ICME), in which linearly polarized light generates a DC magnetization. Since the applied field in the ICME does not break time-reversal symmetry, the induced magnetization directly probes the chiral orbital response of the fluid at the driving frequency. We estimate that the resulting magnetization lies in the range of 0.5-10 Bohr magnetons per charge carrier in materials such as graphene and transition-metal dichalcogenides (TMDs) in the QH regime. Finally, we show that the induced magnetization is accompanied by a local correction to the static particle density, enabling optical quantum printing of density profiles into the QH fluid.
Authors: Okan Köksal
Harnessing the interplay of symmetry breaking and spin-orbit coupling, we investigate Rashba spin splitting in buckled honeycomb (SrHfO$_3$)$_2$/(LaAlO$_3$)$_4$(111) superlattices using density functional theory (DFT) calculations with a Hubbard $U$ term and a Wannier-based tight-binding (TB) model. In the non-centrosymmetric $P1$ phase, pronounced Rashba-type splitting emerges near the $M$ and $K$ points accompanied by a helical in-plane spin texture, while the centrosymmetric $P321$ phase remains spin-degenerate. A Wannier-based tight-binding Hamiltonian, extended analytically with on-site spin-orbit coupling, reproduces the DFT results. A Rashba coefficient of $\alpha_R = 0.34$ eV$ \cdot$ Angstrom and energy $E_R = 29$ meV are extracted directly from the DFT band structure placing the system among moderately strong oxide Rashba materials. $\Gamma$-phonon calculation confirms the dynamical stability of the $P1$ structure and the results reveal the critical role of symmetry breaking and inter-orbital hybridization in enabling Rashba effects, supported by enhanced imaginary second-nearest-neighbor hoppings and Berry curvature. These findings establish SrHfO$_3$-based buckled heterostructures as a promising platform for engineering Rashba effects in oxide-based spintronic devices.
Authors: Lórien MacEnulty, João Paulo Almeida de Mendonça, Roberta Poloni, David D. O'Regan
The effect of the Hund's J terms in various DFT+U+J corrections to semi-local spin-density functional theory is assessed for a series of four octahedrally coordinated Fe(II) spin-crossover molecules spanning the covalent end of the ligand field spectrum. We report values and analyze trends for the Hubbard U and Hund's J parameters determined via minimum-tracking linear response for all valence atomic subspaces and relevant spin states in these molecules. We then methodically apply them via simplified rotationally-invariant Hubbard functionals in search of the simplest combination to yield reliable adiabatic energy differences with respect to those obtained using CASPT2/CC. The observed failure of canonical, positively-signed Hund's J terms in furthering the already robust capacity of DFT+U to obtain accurate energetics prompts an evaluation of their limitations when seeking to account for the static correlation phenomena in such strongly covalent systems and suggests directions for their improvement.
Authors: Polina Matveeva, Dmitri Gutman, Sam T. Carr
We study the interplay of spontaneous symmetry breaking and topological properties in interacting one-dimensional models. We solve these models using bozonization and identify topologically non-trivial phases by counting the additional degeneracy (affiliated with the edge modes) of a finite-size system relative to the infinite one. We find even if the mean-field solution is topological, this may not be true when it arises from spontaneous symmetry breaking, including in the Su-Schrieffer-Heeger (SSH) model. This implies that the original SSH model, as presented by Su, Schrieffer, and Heeger, is topologically trivial, as opposed to its mean-field version. A spinful version, on the other hand, does exhibit a topologically non-trivial phase. In that state, both mean-field solutions are topologically non-trivial and correspond to non-interacting SSH chains in the opposite phases with the winding number $\nu=1$. We show that this phase is protected by a chiral symmetry, similar to the non-interacting phases.
Authors: Toma Yoneya, Kazuya Fujimoto, Yuki Kawaguchi
The Monte Carlo (MC) trajectory sampling of stochastic differential equations (SDEs) based on the quasiprobabilities, such as the Glauber-Sudarshan P, Wigner, and Husimi Q functions, enables us to investigate bosonic open quantum many-body dynamics described by the Gorini-Kossakowski-Sudarshan-Lindblad (GKSL) equation. In this method, the MC samplings for the initial distribution and stochastic noises incorporate quantum fluctuations, and thus, we can go beyond the mean-field approximation. However, description using SDEs is possible only when the corresponding Fokker-Planck equation has a positive-semidefinite diffusion matrix. In this work, we analytically derive the SDEs for arbitrary Hamiltonian and jump operators based on the path-integral formula, independently of the derivation of the Fokker-Planck equation (FPE). In the course of the derivation, we formulate the path-integral representation of the GKSL equation by using the $s$-ordered quasiprobability, which systematically describes the aforementioned quasiprobabilities by changing the real parameter $s$. The essential point of this derivation is that we employ the Hubbard-Stratonovich (HS) transformation in the path integral, and its application is not always feasible. We find that the feasible condition of the HS transformation is identical to the positive-semidefiniteness condition of the diffusion matrix in the FPE. In the benchmark calculations, we confirm that the MC simulations of the obtained SDEs well reproduce the exact dynamics of physical quantities and non-equal time correlation functions of numerically solvable models, including the Bose-Hubbard model. This work clarifies the applicability of the approximation and gives systematic and simplified procedures to obtain the SDEs to be numerically solved.
Authors: Le Tri Dat, Tran Trong Tai, Truong Van Tuan, Vo Van Tai, Nguyen Duy Vy
We demonstrate that coupled AlGaN/GaN quantum wells with asymmetric widths ($L_1-L_2<30 $ A achieve up to 4.5 times higher mobility than single wells at optimal separation (d = 100 A). Crucially, mobility surpasses single wells when d>40 A reversing the trend at smaller distances. This enhancement stems from double-layer screening that suppresses remote/background impurities and dislocations, while LO phonon scattering remains unaffected. For identical wells, coupled systems underperform single wells at d<40 A but exceed them beyond this threshold. Peak gains occur at cryogenic temperatures (77 K). Our results provide a robust theoretical framework to optimize mobility in AlGaN/GaN heterostructures, reducing experimental trial-and-error in quantum device engineering.
Authors: Xiao-Bin Qiang, Tianyu Liu, Zi-Xuan Gao, Hai-Zhou Lu, X. C. Xie
Over the years, Berry curvature, which is associated with the imaginary part of the quantum geometric tensor, has profoundly impacted many branches of physics. Recently, quantum metric, the real part of the quantum geometric tensor, has been recognized as indispensable in comprehensively characterizing the intrinsic properties of condensed matter systems. The intrinsic second-order nonlinear conductivity induced by the quantum metric has attracted significant recent interest. However, its expression varies across the literature. Here, we reconcile this discrepancy by systematically examining the nonlinear conductivity using the standard perturbation theory, the wave packet dynamics, and the Luttinger-Kohn approach. Moreover, inspired by the Dirac model, we propose a toy model that suppresses the Berry-curvature-induced nonlinear transport, making it suitable for studying the quantum-metric-induced nonlinear conductivity. Our theory can be further extended to include disorder effects and higher-order quantum geometric contributions, paving the way for a more comprehensive and systematic understanding of nonlinear transport.
Authors: Koki Satow, Ai Yamakage
Multifold fermions, quasiparticles with multiple degeneracy protected by crystalline symmetries, exhibit a variety of intriguing phenomena stemming from their large topological charges and unique band structures. A comprehensive understanding of their response to external stimuli remains challenging, especially for types protected by nonsymmorphic symmetries where various degrees of freedom are intricately coupled. Here, we systematically construct effective models for multifold fermions that incorporate external fields based on crystalline symmetry. Specifically, we develop a $\boldsymbol{k} \cdot \boldsymbol{p}$ model for the threefold fermion protected by space group I2$_1$3 (No.~199) in the presence of spin--orbit coupling, and derive the terms for external fields. By complementing this with a tight-binding model, we investigate the magnetic field response and reveal the pair annihilation of magnetic monopoles. Furthermore, we construct a $\boldsymbol{k} \cdot \boldsymbol{p}$ model for the eightfold fermion in space group P$\bar{4}3n1'$ (No.~218), including its coupling to external fields. This work provides a robust theoretical foundation for advancing the study of external field responses and transport phenomena in multifold fermions, opening new avenues to explore their rich physics.
Authors: Adhinarayan Naembin Ashok, Sanjam Bedi, Taha Ashraf Ali Shaikh, Jai Aadhithya Ramesh, Adarsh Ganesan
This paper presents the possibility for inertial imaging of spatially patterned annular mass distributions of a circular graphene nanodrum resonator. By placing two distinct analytes in concentric annular regions, we harness the vibrational mode-specific sensitivities of the nanodrum to estimate their respective mass densities. An analytical formulation based on the Rayleigh-Ritz principle is developed to relate radial mass loading to modal frequency shifts. Finite element simulations are performed in COMSOL Multiphysics to obtain the shifts in the resonance frequency of vibrational modes under varying geometrical configurations of annular rings. By processing these frequency shifts through a transformation matrix, we estimate the concomitant mass distributions of annular rings. The results indicate that the estimation errors are lower for analytes placed near the antinodal regions of the dominant vibration mode, with the lowest error being 1.82 % for analyte A and 2.03 % for analyte B. Furthermore, thinner annular rings demonstrate enhanced detection accuracy due to reduced modal overlap. This study demonstrates an analytical strategy for mass detection using a graphene nanodrum by providing insights into optimal analyte placement and structural design for high-precision multi-target mass sensing applications.
Authors: Vineet Barwal, Hirofumi Suto, Yuya Sakuraba
Spin-transfer torque (STT) in magnetoresistance devices has enabled key applications such as STT-magnetoresistive random access memory, spin torque oscillators, and energy-assisted magnetic recording. In the device structures, where a free layer (FL) magnetization is manipulated by spin injection from a spin injection layer (SIL), the critical current density required for operation is directly proportional to the damping ($\alpha$) constant of FL and inversely proportional to the STT efficiency, which depends on the spin polarization ($P$) of the materials. Here, we investigate the effect of low $\alpha$ and high $P$ of $Co_2FeGa_{0.5}Ge_{0.5}$(CFGG) Heusler alloy on the operation current required for STT-induced magnetization reversal in current perpendicular-to-plane giant magnetoresistance devices. Devices with CFGG as a FL material achieved a large reduction in the operation current, as compared to those with conventional NiFe-FL owing to the very low $\alpha$ of CFGG, demonstrating the advantage of CFGG as a FL material. As the advantage of high spin polarization CFGG for SIL, we analyzed the effect of bilayer SIL consisting of CoFe and thin CFGG layers, focusing on utilizing the spin scattering asymmetry at the CoFe/CFGG interface. Devices with the CoFe/CFGG-SIL exhibited the lowest critical current, demonstrating enhanced STT efficiency. In addition, the correlation of STT efficiency with magnetoresistance ratio were comprehensively investigated, showing that device-to-device distribution in STT-efficiency was smaller in CoFe/CFGG-SIL. These findings highlight the potential of CFGG Heusler alloy and CoFe/CFGG bilayer structures as key components for the development of efficient and stable STT-based spintronic devices.
Authors: Paul Lafourcade, Nicolas Bruzy, Paul Bouteiller, Jean-Bernard Maillet, Christophe Denoual
Recent developments dedicated to the building of multiscale mechanical and chemical constitutive laws for energetic molecular crystals are presented and discussed. In particular, various tools have been specifically incorporated in molecular dynamics codes to facilitate the subsequent information transfer to the continuum, i.e. finite elements simulation codes. Atomistic simulations have been augmented with the capability to follow specific deformation paths as well as local Lagrangian mechanical metrics, enabling the computation of materials flow stress surface. This mechanistic library allowed the construction of a comprehensive non-linear hyperelastic continuum model including crystal plasticity and twinning for TATB. Besides, recent advances in analyzing reactive molecular dynamics simulations with unsupervised learning algorithms has enabled the identification and calibration of chemical decomposition kinetics for RDX and TATB single crystal. In the present work, the procedure is applied to $\beta$-HMX and extended with the calibration of a multi-components equation of state. These two ingredients are implemented in a finite-element code in order to model the shock-to-detonation transition at the mesoscale level and to study dimensionality effects in quasi-static hotspots. Finally, these dedicated efforts towards a comprehensive multiscale modeling of explosives has also given rise to the need for new prospective experiments, discussed throughout the paper.
Authors: Jacob Svane, Kim-Khuong Huynh, Yong P. Chen, Bo Brummerstedt Iversen
InSe is a van der Waals semiconductor in which mechanical flexibility, high electronic mobility, and non-trivial electronic structures converge, making it an attractive platform for both intriguing fundamental studies and promising device developments. However, the nucleation and growth of phase-pure, intrinsic InSe crystals require stringent thermodynamical conditions, and have therefore remained elusive. Since InSe melts incongruently, the widely used synthesis methods based on cooling of a 1:1 In-Se mixture will produce either aggregates of multiphase crystallites or uncontrolled In-rich, heavily electron-doped InSe. This fundamental thermodynamic constraint provides a compelling explanation for the large discrepancies observed in the reported physical properties of InSe. We overcome these limitations by utilizing the traveling solvent floating zone (TSFZ) method to produce high quality, centimeter-size InSe single crystals. Electrical, thermal, and thermoelectric transport measurements demonstrate that TSFZ-InSe single crystals closely approach the intrinsic limit, establishing it as a benchmark material for the future studies of this important material.
Authors: Keishi Sunami, Sachio Horiuchi, Yoriko Sonoda, Naomi Fujiki, Toshiki Higashino, Yuki Atsumi, Shoji Ishibashi, Jun'ya Tsutsumi
The rapid advancement of communication technology necessitates the development of hybrid optical modulators that integrate silicon photonics with electro-optic (EO) materials to enable ultrafast, low-power, and compact photonic devices. However, no existing material simultaneously meets the requirements for high EO performance, process compatibility, and thermal stability, which are essential for practical optoelectronic integration. Here, we present 4-(4'-nitrophenylazo)diphenylamine (NDPA) and its derivative, novel nonlinear optical molecular crystals discovered through materials screening incorporating crystal habit prediction. They demonstrate crystallization into high-quality aligned thin films and ultrafine silicon slot fillings through the capillary action of melts. The resulting EO performance much exceed that of conventional lithium niobate and are comparable to state-of-the-art EO polymers, with excellent thermal stability maintained for over 1000 hours at 393 K. The present EO materials satisfying all the requirements above are promising candidates for silicon-organic hybrid optical modulators, opening a significant step toward scalable and high-performance optoelectronic technologies.
Authors: Mahdi Tavakol, Kislon Voïtchovsky
Aqueous solid-liquid interfaces (SLI) are ubiquitous in nature and technology, often hosting molecular-level processes with macroscopic consequences. Molecular dynamics (MD) simulations offer a tool of choice to investigate interfacial phenomena with atomistic precision, but there exists a large number of water models, each optimised for a different purpose. Here we compare the ability of common water models to accurately simulate the interface between a charged silica surface and an aqueous solution containing NaCl. We first compare the bulk dielectric constant of water and its dependence on salt concentration for SPC/Fw, SPC/e, TIPS3p, H2O/DC, TIP3P-Fw, OPC3, TIP3P, TIP3P-FB, TIP3P-ST, FBA/e, and TIPS3p-PPPM, revealing large variations between models. Simulating the interface with silica for the most suitable water models (SPC/Fw, H2O/DC, TIP3-ST and TIPS3p-PPPM) show some intrinsic consistency with continuum predictions (Poisson-Boltzmann) whereby the free energy minima obtained from MD and the analytical model are in agreement, provided the latter includes the MD-determined total charge of ions in the Stern layer and dielectric constant. This consistency stands even for water models with a dielectric constant off by 10%. For salt concentrations higher than 0.21 M NaCl, the formation of random ion-ion pairs limits the reproducibility of the MD results and the applicability of the analytical method. The results highlight the applicability of the analytical model down to the nanoscale, provided a priory knowledge of the Stern layer charge is available. The findings could have significant implications for MD simulations of SLIs, especially at charged or electrified interfaces.
Authors: D. Maroulakos, A. Wal, A. Ugulava, O. Kharshiladze, L. Chotorlishvili
Since the pioneering work Lohani et. al., Phys. Rev. X 9, 041063 (2019), it became clear that quantum skyrmions have highly unusual properties as compared to the classical skyrmions and, due to their quantumness, cannot be described by continuous magnetic textures akin to the classical skyrmions. Competing nearest-neighbor and next-nearest-neighbor ferromagnetic and antiferromagnetic interactions in triangular spin-frustrated magnets lead to the formation of quantum skyrmion states. In frustrated magnets, skyrmions are characterized by the helical degree of freedom, which can store quantum information. In the limit of a weak electric field, the system can be described as a two-level system, i.e., a skyrmion qubit. Here, we propose a more general formulation of the problem and obtain general analytic solution of the model previously introduced in Psaroudaki et. al., Phys. Rev. Lett. 127, 067201 (2021). Our solution is valid not only for small barrier but for the arbitrary electric field. In the case of a significant barrier, we prove that the system's state is not a Skyrmion qubit as it was thought before, but a Skyrmion qudit. We constructed the density matrix of the Skyrmion qudit and studied its evolution in time. The obtained results suggest that the proposed model can be exploited further to meet the needs of quantum information theory and quantum skyrmionics. We showed that the $l_1$ norm of coherence of the skyrmion quantum qudit is a thousand times larger than the coherence of the skyrmion quantum qubit. The obtained result opens new perspectives for quantum skyrmion-based resource theory.
Authors: Nicolo Tormena, Teuta Pilizota, Kislon Voïtchovsky
Biological membranes are complex, dynamic structures essential for cellular compartmentalization, signaling, and mechanical integrity. The molecular organization of eukaryotic membranes has been extensively studied, including the lipid raft-mediated lateral organization and the influence of the specific molecular interactions. Bacterial membranes were traditionally viewed as compositionally simpler and structurally uniform. Recent evidence, however, reveals that they possess significant lipid diversity and can form functional microdomains reminiscent of eukaryotic lipid rafts, despite lacking sterols and sphingolipids. Yet, the impact of unspecific physical contacts on the local molecular organization and evolution of the prokaryotic membranes remains poorly understood. Here we use a model lipid membrane mimicking the composition of Escherichia coli's inner membrane to investigate the impact of contacting substrates on the membrane nanoscale evolution, when close to its transition temperature, $T_m$. As expected, the presence of a substrate lowers the $T_m$ by $\sim$10 °C and induces a differential leaflet transition. However, it also slows down the phase transition kinetics by almost 2 orders of magnitude while simultaneously enabling a spinodal-like lateral molecular reorganization. This creates local alterations of the phase of the membrane, with the emergence of mechanically stiffer, yet still fluid nanodomains evolving over substrate-dependent timescales, consistent with a substrate-biased lipid flip-flop mechanism. The results verify previous theoretical predictions and demonstrate that a general physical mechanism -- driven by membrane-surface interactions -- can spontaneously induce lipid domain formation in bacterial membranes. This is bound to have notable consequences for its function and mechanical role, including in processes like osmotic pressure regulation.
Authors: J. L. Allen, L. Heinze, R. A. Mole, S. Süllow, O. Janson, S. Nishimoto, R. A. Lewis, K. C. Rule
We report inelastic neutron scattering (INS) measurements on the magnetically frustrated $S=\frac12$ sawtooth-chain compound atacamite Cu$_2$Cl(OH)$_3$ featuring inequivalent Cu(1) and Cu(2) sites. Transverse to the sawtooth chains, INS reveals two dispersive spin-wave modes and a gap of at least 0.75 meV. This behavior is rationalized within a zigzag-chain model of Cu(2) spins in an effective magnetic field of Cu(1) spins. The model is compatible with first-principles calculations and accounts for INS dispersions within linear spin-wave theory calculations. Our results reveal a unique case of an effective separation of energy scales between two differently oriented one-dimensional chains, with the zigzag-chain model being essential to fully characterize atacamite's low-energy magnetism.
Authors: Simone Fratini
I present a theory of strange metals that is based on the following asumptions: (i) wavelike coherence is lost at each hop between neighboring atoms in the solid, i.e. the metal is bad, (ii) the carriers move independently from one another and (iii) the motion of the charge carriers obeys the correspondence principle, i.e. the quantum-mechanically averaged carrier diffusion in time is the same as in the classical case. The theory explains $T$-linear resistivity with apparently Planckian scattering rates as well as both the stretched Drude and displaced Drude peaks that are commonly observed in optical absorption experiments. The present framework might also indicate a solution to the problem of universal dielectric relaxation in insulators.
Authors: Julien Bauland, Thomas Gibaud
In recent years, significant effort has been devoted to developing smart materials whose mechanical properties can adapt under physical stimuli. Particulate colloidal gels, which behave as solids but can also flow under stress, have emerged as promising candidates. Resulting from the attractive interaction between their constituents, their network architecture exhibit solid-like properties even at very low volume fractions. This structural flexibility allows them to adopt various configurations and store structural information making them highly susceptible to memory effects. Shear flow, applied through rheometry, offers a simple and effective way to tune their properties and imprint a ``rheological memory'' of the flow history. However, the precise relationship between flow history and viscoelastic response remains elusive, largely due to the limited structural characterization of these systems during flow and after flow cessation. Here, we use ultra-small angle X-ray scattering (USAXS) to reveal a strong structural memory in the solid state, where the microstructure formed under shear is retained after flow cessation. We identify two distinct mechanisms of structural memory, as governed by the ratio of viscous to attractive forces, namely, the Mason number. Using recently developed fractal scaling laws, we show that the rheology is fully determined by the gel microstructure. Notably, these gels exhibit a double-fractal architecture, highlighting the remarkably broad range of length scales over which these disordered materials are structured. By clarifying how memory is encoded, our results offer strategies to tune shear sensitivity of colloidal gels and design smart materials.
Authors: Stefan Porfir, Bram F. Haverkort, Federico Sbravati, Aida Todri-Sanial
This paper explores the application of Oscillatory Neural Networks (ONNs) to solving Sudoku puzzles, presenting a biologically inspired approach based on phase synchronization. Each cell is represented by an oscillator whose phase encodes a digit, and the synchronization is governed by the Kuramoto model. The system dynamically evolves towards a valid solution by having the puzzle constraints encoded into the weight matrix of the network, and through a proposed novel phase mapping of the Sudoku digits. Experimental results show that ONNs achieve high performance for puzzles with moderate difficulty and outperform Hopfield Neural Networks, particularly in cases with up to 20 initially unknown values. Although the performance decreases with increased ambiguity, ONNs still produce correct solutions in some of the iterations, cases in which the baseline Hopfield Neural Network algorithm fails. The findings support ONNs as a viable alternative for solving constraint optimization problems and reinforce their relevance within emerging non-von Neumann computing paradigms.
Authors: Thomas Gawne, Zhandos A Moldabekov, Oliver S Humphries, Motoaki Nakatsutsumi, Sebastian Schwalbe, Jan Vorberger, Ulf Zastrau, Tobias Dornheim, Thomas R Preston
We compare the predictions of the dynamic structure factor (DSF) of ambient polycrystalline aluminium from time-dependent density functional theory (TDDFT) in the pair continuum regime to recent ultrahigh resolution x-ray Thomson scattering measurements, collected at the European XFEL. TDDFT predicts strong anisotropy in the DSF at the wavenumber examined here, even with $q$-blurring accounted for. The experimental spectrum has more than sufficient resolution and signal-to-noise levels to resolve these orientation dependencies, and therefore the orientational averaging of the polycrystalline sample is observed rigorously. Once the orientation averaging is accounted for, TDDFT is able to reproduce the experimental spectrum adequately. Finally, comparisons of predicted DSFs from jellium to experiment demonstrates the importance of accounting for lattice effects in modelling the spectrum from a polycrystal.
Authors: Xinnan Peng, Marco Lozano, Jie Su, Lulu Wang, Diego Soler-Polo, Thomas Tuloup, Junting Wang, Shaotang Song, Ming Wah Wong, Jiangbin Gong, Junzhi Liu, Franz J Giessibl, Pavel Jelínek, Jiong Lu
Peierls theorem postulates that a one-dimensional (1D) metallic chain must undergo a metal-to-insulator transition via lattice distortion, resulting in bond length alternation (BLA) within the chain. The validity of this theorem has been repeatedly proven in practice, as evidenced by the absence of a metallic phase in low-dimensional atomic lattices and electronic crystals, including conjugated polymers, artificial 1D quantum nanowires, and anisotropic inorganic crystals. Overcoming this transition enables realizing long-sought organic quantum phases of matter, including 1D synthetic organic metals and even high-temperature organic superconductors. Herein, we demonstrate that the Peierls transition can be globally suppressed by employing lattice topology engineering of classic trans-polyacetylene chains connected to open-shell nanographene terminals. The appropriate topology connection enables an effective interplay between the zero-energy modes (ZMs) of terminal and the finite odd-membered polyacetylene (OPA) chains. This creates a critical topology-defined highest occupied molecular orbital (HOMO) that compensates for bond density variations, thereby suppressing BLA and reestablishing their quasi-1D metallic character. Moreover, it also causes the formation of an unconventional boundary-free resonance state, being delocalized over the entire chain with non-decaying spectral weight, distinguishing them from traditional solitons observed in polyacetylene. Our finding sets the stage for pioneering the suppression of material instability and the creation of synthetic organic quantum materials with unconventional quantum phases previously prohibited by the Peierls transition.
Authors: Yuto Hosogi, Koichiro Furutani, Yuki Kawaguchi
We investigate coupled dynamics of spinless fermions on a one-dimensional lattice and spins on the links. When the hopping integral and the on-site potential of the fermions depend on the direction of the link spins, the low-energy effective theory predicts that the link spins behave as a dynamical axion field in 1+1 dimensions. The axion field $\theta$ is coupled to the electric field $E$ as $\theta E$, through which the link spins rotate in response to the applied electric field or the chemical potential gradient for charge-neutral fermions. This is the inverse phenomenon of Thouless pumping in the Rice-Mele model. After analyzing the dynamics by approximating the link spins with the classical ones and utilizing the axion Lagrangian, we show the full-quantum dynamics using the tensor network method. Even though we do not explicitly introduce the axion Lagrangian in solving the fermion-spin coupled many-body dynamics, the full-quantum results agree well with those with the classical spin approximation, including the dynamics of the axion field and fermion transport. In addition, we find that the quantum correlation between spins accelerates the dynamics of axion fields as the suppression of the expectation values of the link spins allows them to rotate easily. We also propose a possible experimental setup for cold-atomic systems to implement the Hamiltonian in this study.
Authors: Zhenhua Zhu, Gu Zhang, Dong E. Liu
Measuring entanglement entropy in interacting, multipartite systems remains a significant experimental challenge. We address this challenge by developing a protocol to measure von Neumann entropy (VNE) and mutual information in quantum transport systems with both many-body interactions and multiple subsystems. Our analysis indicates that the vital connection between VNE and two-point correlation functions persists under these realistic conditions. The measurement is shown to be feasible for systems with boundary interactions and, critically, for bulk-interacting systems subject to a quantum quench of their internal couplings. Our work provides a pathway to experimentally quantify entanglement in complex interacting systems and establishes mutual information as an experimentally accessible indicator for system-environment entanglement.
Authors: Yu-Chang Chen, Ken-Ming Lin
Two-dimensional transition metal dichalcogenides present compelling prospects for next-generation low-power and high-frequency field-effect transistors. However, scaling 2D TMD FETs into the sub-10 nm regime remains challenging due to technical complexity. Moreover, short-channel effects in this length scale are not yet fully understood. In this work, we investigate the transport properties of 2D TMD nanojunctions with channel lengths from 12 down to 3 nm, using first-principles calculations that integrate the nonequilibrium Green function formalism implemented in density functional theory (NEGF-DFT) and an effective gate model. Our simulations reveal a classical-to-quantum crossover in electron transport during transistor downscaling, governed by two critical temperatures: Tc, which marks the crossover from thermionic emission to quantum tunneling, and Tt, beyond which thermionic emission dominates and the subthreshold swing approaches its classical limit. The shortest 3 nm junction exhibits pronounced quantum tunneling up to 500 K and achieves a subthreshold swing superior to the Boltzmann tyranny, enabled by the steep energy dependence of the transmission coefficient. This quantum-tunneling-enhanced switching behavior demonstrates the potential of ultra-scaled 2D FETs to surpass classical efficiency constraints, offering a promising route toward energy-efficient, quantum-enabled computing technologies. This study presents a predictive, atomistic methodology for quantifying quantum transport and identifies the transition in electron transport mechanisms from semiclassical thermionic current in long-channel to quantum tunneling in short-channel 2D TMD FETs, offering critical design insights for leveraging quantum-classical hybrid transistor technology.
Authors: Francesco Troisi, Hannes Hübener, Angel Rubio, Simone Latini
We propose an all-optical Moiré-like exciton confinement by means of spatially periodic optical cavities. Such periodic photonic structures can control the material properties by coupling the matter excitations to the confined photons and their quantum fluctuations. We develop a low energy non-perturbative quantum electro-dynamical description of strongly coupled excitons and photons at finite momentum transfer. We find that in the classical limit of a laser driven cavity the induced optical confinement directly emulates Moiré physics. In a dark cavity instead, the sole presence of quantum fluctuations of light generates a sizable renormalization of the excitonic bands and effective mass. We attribute these effects to long-range cavity-mediated exciton-exciton interactions which can only be captured in a non-perturbative treatment. With these findings we propose spatially structured cavities as a promising avenue for cavity material engineering.
Authors: Pawel Koczanowski, Paolo Nicolini, Hesam Khaksar, Enrico Gnecco
We have investigated nanoscale wear on multilayered MoS2, the flagship transition metal dichalcogenide, by elastically driving sharp diamond tips under normal loads sufficient to induce in-plane fracture. The accompanying friction and the resulting wear structures were first characterized by atomic force microscopy (AFM), revealing a stick-slip regime that drives progressive exfoliation of MoS2 chips. At high normal forces, the slip phase displays hallmark signatures of avalanche dynamics, observed for the first time at the nanoscale, evidenced by a Generalized Extreme Value distribution of friction force drops. The AFM characterization is corroborated by molecular dynamics simulations, which reproduce experimental trends and uncover atomistic details of the wear process, including local amorphization, layer curving, and the involvement of distinct dissipative channels. Notably, it appears that only one-fifth of the energy inputted into the system is used to damage the MoS2 surface irreversibly. These results offer new insight into the physical mechanisms governing friction and wear in layered solids and provide a framework for precision cutting and nanomachining in van der Waals materials, relevant to next-generation devices at sub-micrometer scales.
Authors: Smitarani Mishra, Shaon Sahoo
We revisit the J1-J2 frustrated Heisenberg spin-1/2 chain with dimerization ({\delta}) or modulation in the nearest-neighbor couplings to investigate its thermalization behavior. While the dimerization tends to induce localization, the next-nearest-neighbor interaction J2 generally favors thermalization, making the assessment of the model's compliance with the Eigenstate Thermalization Hypothesis (ETH) particularly subtle. The challenge is further compounded by the model's SU(2) symmetry; the study of ETH compliance is necessarily done for each symmetry sector but separating different sectors of this symmetry is known to be a computationally demanding task. The current study is driven by two main motivations: first, to explore whether the well-known ground-state phases of the model have any bearing on its thermalization properties; and second, to understand how the interplay between two competing factors, namely, the non-uniformity (via {\delta}) and the beyond-nearest-neighbor interactions (via J2) governs the system's approach to thermal equilibrium. A systematic analysis shows that the ETH is most strongly satisfied for intermediate values of {\delta} (~ 0.5) with J2 ranging from intermediate (~ 0.5) to large (~ 1)- a parameter regime falls within the spiral ground-state phase. It is also found that when the system is in the gapless ground-state phase (which falls within the N'eel phase), the ETH is more prone to violation. In the regime of large {\delta} and small J2, the system is seen to enter a localized phase (characterized here by modulation in density-of-states; assessing ETH compliance is less meaningful for this phase.
Authors: Joseph J. Webber, Thomas D. Montenegro-Johnson
Responsive hydrogels can sense environmental stimuli and respond as actuators by expelling water and changing shape. In this article, we develop theory to demonstrate that groups of responsive hydrogels can also communicate with each other, by utilising the effect of elastic deformation on chemical reaction dynamics. Specifically, we consider a system of two spatially-separated chemically responsive hydrogels suspended in a solution in which a Belousov-Zhabotinsky (BZ)-type reaction occurs. Solving for the gel dynamics with the transport of solvent through the poroelastic network and the chemical kinetics, we show how the periodic swelling-deswelling oscillations of each gel can become coupled, and how this coupling can be exploited to send signals from one gel to the other via mechanical manipulation of the sender that affect the local (and thus global) frequency of oscillation.
Authors: Surya N. Panda, Ning Mao, Nikolai Peshcherenko, Xiaolong Feng, Yang Zhang, Anastasios Markou, Claudia Felser, Edouard Lesne
The generation and control of spin currents are crucial for advancing next-generation spintronic technologies. These technologies depend on materials capable of efficiently sourcing and interconverting spin and charge currents, while overcoming some limitations associated with conventional ferromagnets and heavy metals. Kagome topological antiferromagnetic Weyl semimetals, such as Mn$_3$Sn, present unique advantages owing to their distinct magnetic order and significant Berry curvature-driven transport phenomena. In this study, we systematically investigate spin current generation and spin-to-charge conversion phenomena in epitaxial (0001)-oriented Mn$_3$Sn thin films. Our findings reveal a spin Hall angle of 0.9$\%$ and a nearly isotropic in-plane spin Hall conductivity of 44.4~($\hbar$/e) $\Omega^{-1}$.cm$^{-1}$ at room temperature, originating from a combination of intrinsic and extrinsic contributions, as discussed in light of first-principle calculations. Furthermore, in Mn$_3$Sn(0001)/Ni$_{81}$Fe$_{19}$ heterostructures, we observe a high spin-mixing conductance of 28.52 nm$^{-2}$ and an interfacial spin-transparency of approximately 72$\%$. Notably, we also find that the spin diffusion length in Mn$_3$Sn(0001) epitaxial films exceeds 15 nm at room temperature. Our results highlight the potential of the topological Weyl noncollinear antiferromagnet Mn$_3$Sn as an efficient material for spin transport and conversion in prospective spintronic applications.
Authors: Ke Sun, Jack R. Panter, Alvin C. M. Shek, Yonas Gizaw, Kislon Voïtchovsky, Halim Kusumaatmaja
The removal of liquid droplets from solid surfaces is central to cleaning, coatings and oil recovery. Here we investigate liquid droplets capillary lifted by an immiscible working liquid. The rising working liquid triggers the formation of a capillary bridge between the solid and the air interface, which can lead to full, partial, or no droplet dewetting. Our theoretical model predicts, and experiments confirm, that the effectiveness of droplet removal can be tuned by manipulating the droplet contact angle with the solid and the interfacial tensions at play. Significantly, dewetting can be enhanced by employing working liquids with high interfacial tension, in contrast to common surface cleaning strategies where surfactants are used to reduce interfacial tension. Our findings can open new avenues for droplet manipulation with reduced resources and more sustainable environmental impact.
Authors: Julia Kharlan, Roman Verba, Krzysztof Sobucki, Paweł Gruszecki, Maciej Krawczyk
Three-wave scattering is a fascinating phenomenon with many applications in various technologies. Reducing the system symmetry greatly affects three-wave scattering, which, in this case, goes beyond the simple momentum conservation law. In this study, we examine three-magnon scattering at the edge of a thin ferromagnetic film, when a bulk spin wave interacts with an edge-localized propagating spin-wave upon the reflection. This creates new bulk spin waves at mixed frequencies by means of three-magnon confluence or stimulated splitting processes. Using our developed analytical theory, which has been confirmed by full micromagnetic simulations, we demonstrate that the amplitude of the wave generated in the stimulated splitting process is several times larger than that generated in the confluence process, primarily due to the lower group velocity. Furthermore, intensity of inelastically scattered waves exhibit a pronounced dependence on the incidence angle and frequency of the edge spin wave that goes beyond existing qualitative models. We show that the observed behaviors can only be explained by taking into account, that the scattered waves are created by several elementary three-magnon processes involving the incident and reflected waves. The complex nature of the scattered wave creation results in a strong sensitivity of its amplitude to the phase accumulation of spin waves upon reflection.
Authors: Oliver Franke, Piet W. Brouwer
Heterostructures of normal metals (N) and magnetic insulators (F) show paradigmatic effects, such as spin-Hall magnetoresistance and electric drag currents. These effects are linear in the applied electric field $E(\omega)$. Normal-metal $-$ magnetic-insulator heterostructures also exhibit a characteristic nonlinear response quadratic in $E(\omega)$, referred to as unidirectional spin-Hall magnetoresistance or spin-torque diode effect. In this article, we develop a theory of the bilinear response of FN bilayers and NFN trilayers for finite frequencies $\omega$ of the driving field and for four contributions that have been previously considered in the literature: Joule heating, phonon-mediated unidirectional magnetoresistance, the spin-torque diode effect, and magnonic unidirectional spin-Hall magnetoresistance. We identify their distinct dependencies on frequency and the magnetization direction of the magnetic insulator and examine their scaling with magnetic field and system geometry, providing a framework for experimental differentiation.
Authors: A. Imparato
We investigate the thermalization of a stochastic system with discrete phase space, initially at equilibrium at temperature $T_i$ and then termalizing in an environment at temperature $T_f$ , considering both cases $T_i > T_f$ and $T_i < T_f$. For the simple case of a system with constant energy gaps, we show that the relation between the time scales of the cooling and heating processes is not univocal, and depends on the magnitude of the energy gap itself. Specifically the eigenvalues of the corresponding stochastic matrix set the time scales of the relaxation process and for large energy gaps the cooling process is found to exhibit the shortest relaxation times to equilibrium while the heating process is found to be faster at all scales for small gaps. We consider both the Kullback-Leibler divergence and the Fisher information and its related quantities to quantify the degree of thermalization of the system. In the intermediate to long time regime both quantities are found to bear the same type of information concerning the rate of thermalization, and follow the ordering predicted by the dynamic eigenvalues. We then consider a more complex system with a more intricate stochastic matrix, namely a 1D Ising model, and confirm the findings on the existence of two regimes, one in which cooling becomes faster than heating. We make contact with a previous work where an harmonic oscillator was used as working fluid and the heating process was always found to be faster than the cooling one.
Authors: Hernán A. Ritacco, Macos D. Fernández Leyes, Zulma Quirolo, M. M. Soledad Lencina, Cecilia del Barrio, Rafael Márquez, Jaqueline Fernández, Jhon Sánchez Morales
Responsive drug delivery vectors can be designed using oppositely charged polyelectrolyte-surfactant complexes. As a model, we created a brush-type copolymer (PECop), combining alginate and Poly(N-isopropylacrylamide) (PNIPAAm), whose side chains respond to temperature. Aggregation of PECop with the cationic surfactant dodecyltrimethylammonium bromide (DTAB) was examined versus surfactant concentration and temperature. We used surface tension, electrophoretic mobility, zeta potential, potentiometry, light scattering, and atomic force microscopy to analyze the complexes. PECop/DTAB complexes form spherical, monodisperse aggregates in certain surfactant ranges, even though the copolymer itself is polydisperse. The binding isotherms combine features of oppositely charged polyelectrolyte/surfactant systems and hydrophobically modified polymers. Compared to alginate alone, PECop binds six times more DTAB at 1 mM surfactant concentration. Temperature responsiveness depends on surfactant concentration (cs). The surfactant triggers progressive collapse of polymer chains, maximized at cs = 2.8 mM, where thermo-responsiveness is lost. For cs 10 mM, size increases above LCST. This inversion in thermal response with rising surfactant concentration suggests changing aggregate structure, offering new avenues for drug delivery system design using these polymer-surfactant complexes.
Authors: Tongshuai Zhu, Di Zhou, Huaiqiang Wang, Jiawei Ruan
Altermagnets (AMs), recently discovered unconventional magnets distinct from ferro- and antiferromagnets, have rapidly emerged as a prominent frontier in condensed matter physics. AMs are characterized by alternating collinear magnetic moments with zero net magnetization in real space, and spin splittings with even-parity symmetry in momentum space. However, their counterparts exhibiting odd-parity spin splitting remain largely unexplored. Here, based on symmetry argument, we show that such unconventional odd-parity magnets can be induced from collinear antiferromagnets. Remarkably, using effective model analysis within Floquet-theory framework, we demonstrate that circularly polarized light irradiation of conventional antiferromagnetic lattices induces both $p$- and $f$-wave magnets, realizing novel magnetic states dubbed Floquet odd-parity collinear magnets. Moreover, we also uncover light-induced antiferromagnetic Chern insulating states in the $f$-wave magnets. The proposed Floquet odd-parity magnet is confirmed by first-principles calculations of MnPSe$_{3}$ under circularly polarized light. Our work not only proposes a new class of unconventional magnets, but also opens an avenue for light-induced magnetic phenomena in spintronic applications.
Authors: Ganesh Narasimha, Mykola Telychko, Wooin Yang, Arthur P. Baddorf, P. Ganesh, An-Ping Li, Rama Vasudevan
Manipulating matter with a scanning tunneling microscope (STM) enables creation of atomically defined artificial structures that host designer quantum states. However, the time-consuming nature of the manipulation process, coupled with the sensitivity of the STM tip, constrains the exploration of diverse configurations and limits the size of designed features. In this study, we present a reinforcement learning (RL)-based framework for creating artificial structures by spatially manipulating carbon monoxide (CO) molecules on a copper substrate using the STM tip. The automated workflow combines molecule detection and manipulation, employing deep learning-based object detection to locate CO molecules and linear assignment algorithms to allocate these molecules to designated target sites. We initially perform molecule maneuvering based on randomized parameter sampling for sample bias, tunneling current setpoint and manipulation speed. This dataset is then structured into an action trajectory used to train an RL agent. The model is subsequently deployed on the STM for real-time fine-tuning of manipulation parameters during structure construction. Our approach incorporates path planning protocols coupled with active drift compensation to enable atomically precise fabrication of structures with significantly reduced human input while realizing larger-scale artificial lattices with desired electronic properties. To underpin of efficiency of our approach we demonstrate the automated construction of an extended artificial graphene lattice and confirm the existence of characteristic Dirac point in its electronic structure. Further challenges to RL-based structural assembly scalability are discussed.
Authors: Mohammad M. Rahaman, Jose Flores, Mohamed Y. Noor, Md Mohsinur R. Adnan, Alex Blackston, Enam Chowdhury, Roberto C. Myers, Michael Newburger, Pelagia-Irene Gouma
A unique polymorph of binary tungsten trioxide, the epsilon phase of WO3, has non-centrosymmetric ferroelectric structure, typically stable below -43 degree C in bulk. We have stabilized the epsilon-WO3 at room temperature (RT) and nanostructured powders via flame spray pyrolysis synthesis. These nanopowders are drop cast into uniform thin films to enable RT measurement of ferroelectric and optoelectronic properties. We report ferroelectric hysteresis, nanoscale domains, and dipole switching measured via Piezo-response force microscopy (PFM). The epsilon-WO3 films also display optical second harmonic generation (SHG) and anticlockwise ferroelectric butterfly capacitance versus voltage hysteresis, further demonstrating the ferroelectric nature of epsilon-WO3. Remarkably, epsilon-WO3 shows ferroelectric polarization responses to optical stimuli and form bipolaron at RT, a spin-zero quasiparticle previously found only in cryogenic temperatures. The bipolaron formation and its interaction with electro-optical stimuli results in a single layer solid-state blue coloration, a ferrochromic effect. A mechanism of the ferrochromic effect is discussed. In summary, epsilon-WO3 appears to be a ferroelectric with the simplest structure, forming bosonic spin-zero bipolaron at RT, and it's dipoles respond to opto-electrical signals; therefore, this material holds significant promise for transforming the field of optoelectronics.
Authors: Cody L. Milne, Hector Gomez, Adway Gupta, A. Glen Birdwell, Sergey Rudin, Elias J. Garratt, Bradford B. Pate, Tony G. Ivanov, Arunima K. Singh, Mahesh R. Neupane
Heterointerfaces of cubic boron nitride (cBN) with diamond have garnered significant interest due to their ultra-wide bandgaps and small lattice mismatch ($\sim1.5$\%), offering promising advancements in high-power and high-frequency electronic devices. However, the realization of this heterointerface has been limited by challenging growth conditions and insufficient understanding of interfacial properties. In this work, we employ density-functional theory to investigate the structural and electronic properties of diamond/cBN heterostructures as a function of interfacial stoichiometry, cBN thickness, and surface termination and passivation. Formation energies and interfacial bond lengths reveal that boron-terminated heterojunctions are the most stable while abrupt nitrogen-terminated heterojunctions are least stable, but can be stabilized by carbon-mixing. Bandstructures are computed for the heterostructures using hybrid functionals, where we find the abrupt boron-terminated and nitrogen-terminated heterojunctions exhibit $p$-type and $n$-type conductivity, respectively, while carbon-mixed heterojunctions retain wide insulating bandgaps ($4.2-4.4$ eV). The effective masses of the abrupt interfaces are found to vary strongly with stoichiometry. Intriguingly, charge analysis reveals two-dimensional electron or hole gas regions with ultra-high densities on the order of $10^{14}$ cm$^{-2}$, with distinct spatial localization on either side of the interface. Band alignments show type-I and type-II band offsets tunable by interfacial composition. Further analysis of the band alignments reveals that the diamond valence bands consistently lie above the cBN valence bands by $0.25-2.1$ eV. Interestingly, the interface termination type switches the relative conduction band position of diamond relative to the cBN conduction band, exhibiting a type-I to type-II band alignment transition.
Authors: Justin Flory, Samantha Taylor, Shuqin Li, Sunil Tiwari, Garrett Cole, Amory Lowe, Lindsey Hamblin, Samuel Piorkowski, Matthew Ryan, Thiago Stangherlin Barbosa, Jason Kmon, Nick Lowery, Joel Eliston, Jason C. Quinn, John McGowen, Matthew D. Green, Klaus Lackner, Wim Vermaas
A moisture-driven air capture (DAC) system was designed and demonstrated. A laboratory-scale system delivering ~1 g CO2 per day was demonstrated in a laminar flow hood and a small pilot-scale system that could deliver ~100 g CO2 daily was operated outdoors in a 4.2 m2 (areal surface area) raceway pond. Elongated mesh tube packets were designed to contain AER beads with high surface area for contacting the air and were found to reduce drying and CO2 loading time ~4-fold over larger mesh bags. Whereas this system was designed for CO2 delivery for cultivating photosynthetic microbes, its potential uses are much broader and include CO2 use in the food and beverage industry, conversion to fuels and chemicals, and sequestration. Techno-economic assessments for a practical scenario based on current results are \$670/tonne to capture CO2 into an alkaline solution and an additional \$280/tonne to extract CO2 from solution, purify and compress to 15 MPa for sequestration. An aspirational scenario modelling reasonable improvements to develop AER sorbents with a capacity of 4 mmol CO2 per gram of sorbent and water uptake of 50 wt.%, which leads to sorbent drying and loading within 1 h, shows a potential to reach \$51/tonne to capture CO2 into an alkaline solution and an additional \$109/tonne to get to 15 MPa for sequestration. Life cycle analysis shows the aspirational moisture-driven process uses up to 87% less energy than thermal and/or vacuum swing DAC by using energy from water evaporation; however, ~330 wt.% water uptake by the sorbent contained in a hydrophilic mesh packets leads to ~33-fold higher water use than the thermodynamic limits, which emphasizes future research is needed to increase sorbent hydrophobicity while maintaining and further increasing ion exchange capacity needed to bind CO2.
Authors: Masafumi Fukuma, Yusuke Namekawa
The Worldvolume Hybrid Monte Carlo (WV-HMC) method [arXiv:2012.08468] is an efficient and versatile algorithm that simultaneously mitigates both the sign problem and the ergodicity problem -- the latter being intrinsic to algorithms based on Lefschetz thimbles. We consider a situation in which the maximum flow time can be set to a small value, as occurs when WV-HMC is applied to the doped Hubbard model using a nonphysical redundant parameter. An optimal choice of this parameter significantly reduces the sign problem on the original integration surface and allows the maximum flow time to remain small, a feature that facilitates increasing the system size while keeping the computation time modest. However, as the worldvolume becomes a thin layer, it becomes increasingly difficult to explore it efficiently, leading to potential ergodicity issues. To overcome this limitation, we propose embedding the Generalized-thimble HMC (GT-HMC) into the WV-HMC framework. GT-HMC performs HMC updates on a deformed surface at a fixed flow time. Although it suffers from ergodicity issues due to infinitely high potential barriers at the zeros of the Boltzmann weight, it enables more efficient exploration within the allowed region. Furthermore, its molecular dynamics step size can typically be taken to be larger than in WV-HMC. GT-HMC is thus better suited for sampling regions where ergodicity issues are not serious. We provide a proof that GT-HMC can be embedded within the WV-HMC algorithm, and verify that the two methods -- the pure WV-HMC and the combined version -- yield consistent results within statistical errors for the two-dimensional doped Hubbard model on a $6 \times 6$ spatial lattice at $T/\kappa = 1/6.4\simeq 0.156$ and $U/\kappa = 8.0$ with Trotter number $N_t = 20$ ($\kappa$: hopping parameter).
Authors: Sarvesh Srinivasan, Jian-Hao Zhang, Yang Qi, Zhen Bi
We investigate a novel class of topological superconducting phases protected by exact fermion-parity symmetry and average crystalline symmetries. These phases belong to the broader class of average crystalline symmetry-protected topological (ACSPT) states and include numerous examples of intrinsic ACSPTs -- topological phases that arise only in the presence of disorder or decoherence. Unlike conventional symmetry-protected topological (SPT) phases, which require exact symmetry protection, average SPT (ASPT) phases remain robust as long as the symmetry is restored on average across disorder realizations or mixed-state ensembles. To classify these phases, we extend the real-space block state construction framework to account for average crystalline symmetries. In this generalized setting, lower-dimensional cells are decorated with ASPT phases, and the obstruction-free conditions are reformulated to incorporate the constraints imposed by average symmetry at block intersections. This provides a physically transparent and systematic method for classifying ASPTs with spatial symmetries that are only preserved statistically. We further validate our classification using a generalized spectral sequence analysis, which serves as an independent consistency check. Our results demonstrate that many crystalline topological superconductors remain well defined under realistic imperfections, and they uncover a rich landscape of intrinsically average-symmetry-protected phases that have no analog in clean systems.
Authors: Yiyu Xia, Zhongdong Han, Jiacheng Zhu, Yichi Zhang, Patrick Knüppel, Kenji Watanabe, Takashi Taniguchi, Kin Fai Mak, Jie Shan
The emergence of high transition temperature (Tc) superconductivity in strongly correlated materials remains a major unsolved problem in physics. High-Tc materials, such as cuprates, are generally complex and not easily tunable, making theoretical modelling difficult. Although the Hubbard model--a simple theoretical model of interacting electrons on a lattice--is believed to capture the essential physics of high-Tc materials, obtaining accurate solutions of the model, especially in the relevant regime of moderate correlation, is challenging. The recent demonstration of robust superconductivity in moiré WSe2, whose low-energy electronic bands can be described by the Hubbard model and are highly tunable, presents a new platform for tackling the high-Tc problem. Here, we tune moiré WSe2 bilayers to the moderate correlation regime through the twist angle and map the phase diagram around one hole per moiré unit cell (v = 1) by electrostatic gating and electrical transport and magneto-optical measurements. We observe a range of high-Tc phenomenology, including an antiferromagnetic insulator at v = 1, superconducting domes upon electron and hole doping, and unusual metallic states at elevated temperatures including strange metallicity. The highest Tc occurs adjacent to the Mott transition, reaching about 6% of the effective Fermi temperature. Our results establish a new material system based on transition metal dichalcogenide (TMD) moiré superlattices that can be used to study high-Tc superconductivity in a highly controllable manner and beyond.
Authors: Andrea Gayon-Lombardo, Ehecatl A. del Rio-Chanona, Catalina A. Pino-Munoz, Nigel P. Brandon
The generation of multiphase porous electrode microstructures with optimum morphological and transport properties is essential in the design of improved electrochemical energy storage devices, such as lithium-ion batteries. Electrode characteristics directly influence battery performance by acting as the main sites where the electrochemical reactions coupled with transport processes occur. This work presents a generation-optimisation closed-loop algorithm for the design of microstructures with tailored properties. A deep convolutional Generative Adversarial Network is used as a deep kernel and employed to generate synthetic three-phase three-dimensional images of a porous lithium-ion battery cathode material. A Gaussian Process Regression uses the latent space of the generator and serves as a surrogate model to correlate the morphological and transport properties of the synthetic microstructures. This surrogate model is integrated into a deep kernel Bayesian optimisation framework, which optimises cathode properties as a function of the latent space of the generator. A set of objective functions were defined to perform the maximisation of morphological properties (e.g., volume fraction, specific surface area) and transport properties (relative diffusivity). We demonstrate the ability to perform simultaneous maximisation of correlated properties (specific surface area and relative diffusivity), as well as constrained optimisation of these properties. This is the maximisation of morphological or transport properties constrained by constant values of the volume fraction of the phase of interest. Visualising the optimised latent space reveals its correlation with morphological properties, enabling the fast generation of visually realistic microstructures with customised properties.
Authors: Bakhtiyar Mammadli, Casim Yazici, Muhammed Gürbüz, İrfan Kocaman, F. Javier Dominguez-Gutierrez, Fatih Mehmet Özkal
In this study, we present a machine learning (ML) framework to predict the axial load-bearing capacity, (kN), of cold-formed steel structural members. The methodology emphasizes robust model selection and interpretability, addressing the limitations of traditional analytical approaches in capturing the nonlinearities and geometrical complexities inherent to buckling behavior. The dataset, comprising key geometric and mechanical parameters of steel columns, was curated with appropriate pre-processing steps including removal of non-informative identifiers and imputation of missing values. A comprehensive suite of regression algorithms, ranging from linear models to kernel-based regressors and ensemble tree methods was evaluated. Among these, Gradient Boosting Regression exhibited superior predictive performance across multiple metrics, including the coefficient of determination (R2), root mean squared error (RMSE), and mean absolute error (MAE), and was consequently selected as the final model. Model interpretability was addressed using SHapley Additive exPlanations (SHAP), enabling insight into the relative importance and interaction of input features influencing the predicted axial capacity. To facilitate practical deployment, the model was integrated into an interactive, Python-based web interface via Streamlit. This tool allows end-users-such as structural engineers and designers, to input design parameters manually or through CSV upload, and to obtain real-time predictions of axial load capacity without the need for programming expertise. Applied to the context of steel storage rack columns, the framework demonstrates how data-driven tools can enhance design safety, streamline validation workflows, and inform decision-making in structural applications where buckling is a critical failure mode
Authors: Mohammad Azami, Pierre-Lucas Aubin-Fournier, Mehdi Hojjati, Krzysztof Skonieczny
As humanity advances toward long-term lunar presence under NASA's Artemis program, the development of lunar-based manufacturing and construction (LBMC) capabilities has become increasingly critical. The high cost of transporting materials from Earth makes in-situ resource utilization (ISRU) essential, with lunar regolith serving as a promising local feedstock. Additive manufacturing (AM) offers a compelling platform for LBMC due to its geometric flexibility, material efficiency, and capacity for on-demand, site-specific production. This study investigates material extrusion (MEX) AM of polyether-ether-ketone (PEEK) composites containing 10 to 50 wt% lunar regolith simulant (LRS). PEEK and LMS-1D powders were melt-compounded via twin-screw extrusion, printed using a high-temperature chamber, and annealed at 300 degrees C. The samples were characterized through density measurements, thermal analysis, tensile testing, and microstructural and elemental mapping. All filaments exhibited densities above 96%, though as-printed porosity increased from less than 1% in neat PEEK to 7.5% at 50 wt% LRS due to elevated melt viscosity. Regolith incorporation enhanced crystallinity (17.4 to 20.5%) and elastic modulus (by 6-41%), while reducing delamination and warping, which improved dimensional accuracy and print success rates. Tensile strength declined gradually from 107 MPa to 90 MPa up to 40 wt% LRS, then dropped sharply to approximately 70 MPa at 50 wt%. Annealing improved density and stiffness for composites containing up to 30 wt% LRS, with marginal benefit at higher contents. Microstructural and elemental analyses confirmed a continuous PEEK matrix with uniformly dispersed regolith particles. This work establishes processing windows and trade-offs for regolith-rich PEEK composites, supporting ISRU-enabled AM of future lunar infrastructure.
Authors: Hoang Hai Nam Nguyen, Minh Tien Tran, Hoheok Kim, Ho Won Lee
The effectiveness of machine learning in metallographic microstructure segmentation is often constrained by the lack of human-annotated phase masks, particularly for rare or compositionally complex morphologies within the metal alloy. We introduce PF-DiffSeg, a phase-fraction controlled, one-stage denoising diffusion framework that jointly synthesizes microstructure images and their corresponding segmentation masks in a single generative trajectory to further improve segmentation accuracy. By conditioning on global phase-fraction vectors, augmented to represent real data distribution and emphasize minority classes, our model generates compositionally valid and structurally coherent microstructure image and mask samples that improve both data diversity and training efficiency. Evaluated on the MetalDAM benchmark for additively manufactured multiphase steel, our synthetic augmentation method yields notable improvements in segmentation accuracy compared to standard augmentation strategies especially in minority classes and further outperforms a two-stage mask-guided diffusion and generative adversarial network (GAN) baselines, while also reducing inference time compared to conventional approach. The method integrates generation and conditioning into a unified framework, offering a scalable solution for data augmentation in metallographic applications.
Authors: Andrea Antinucci, Christian Copetti, Yuhan Gai, Sakura Schafer-Nameki
Matching 't Hooft anomalies is a powerful tool for constraining the low-energy dynamics of quantum systems and their allowed renormalization group (RG) flows. For non-invertible (or categorical) symmetries, however, a key challenge has been the lack of a precise framework to characterize and quantify anomalies. We address this by identifying tensor functors between UV and IR symmetry categories as central to capturing these constraints. To this end, we introduce Anomalous Simple Categories (ASCies) as fundamental building blocks of categorical anomalies. A given symmetry category may support multiple ASCies, each encoding distinct anomalous features. These structures naturally arise in the context of the Symmetry Topological Field Theory (SymTFT), where tensor functors correspond to RG-interfaces between UV and IR SymTFTs, and ASCies are realized as particular such interfaces satisfying simple, universal criteria. We demonstrate the utility of this framework through examples involving anomalous 0-form, higher-form, and crucially, non-invertible symmetries in various spacetime dimensions.
Authors: Joseph D. Broz, Jesse C. Hoke, Edwin Acuna, Jason R. Petta
In conventional exchange-only (EO) spin qubit demonstrations, quantum gates have been implemented using sequences of individually pulsed pairwise exchange interactions with only one exchange coupling active at a time. Alternatively, multiple non-commuting exchange interactions can be pulsed simultaneously, reducing circuit depths and providing protection against leakage. We demonstrate high-fidelity quantum control of an always-on exchange-only (AEON) qubit, operated using simultaneous exchange pulses in a triangular quantum dot (QD) array. We use blind randomized benchmarking to characterize the performance of the full AEON single-qubit Clifford gate set, achieving an average Clifford gate fidelity $F_{\rm C1}$ = 99.86\%. Extensions of this work may enable more efficient EO two-qubit entangling gates as well as the implementation of native $i$-Toffoli gates in Loss-DiVincenzo single-spin qubits.
Authors: Filippo Bigi, Michele Ceriotti
The equations of classical mechanics can be used to model the time evolution of countless physical systems, from the astrophysical to the atomic scale. Accurate numerical integration requires small time steps, which limits the computational efficiency -- especially in cases such as molecular dynamics that span wildly different time scales. Using machine-learning (ML) algorithms to predict trajectories allows one to greatly extend the integration time step, at the cost of introducing artifacts such as lack of energy conservation and loss of equipartition between different degrees of freedom of a system. We propose learning data-driven structure-preserving (symplectic and time-reversible) maps to generate long-time-step classical dynamics, showing that this method is equivalent to learning the mechanical action of the system of interest. We show that an action-derived ML integrator eliminates the pathological behavior of non-structure-preserving ML predictors, and that the method can be applied iteratively, serving as a correction to computationally cheaper direct predictors.
Authors: Massimo Solinas, Brandon Barton, Yuxuan Zhang, Jannes Nys, Juan Carrasquilla
Non-Hermitian quantum many-body systems exhibit a rich array of physical phenomena, including non-Hermitian skin effects and exceptional points, that remain largely inaccessible to existing numerical techniques. In this work, we investigate the application of variational Monte Carlo and neural network wavefunction representations to examine their ground-state (the eigenstate with the smallest real part energy) properties. Due to the breakdown of the Rayleigh-Ritz variational principle in non-Hermitian settings, we develop a self-consistent symmetric optimization framework based on variance minimization with a dynamically updated energy estimate. Our approach respects the biorthogonal structure of left and right eigenstates, and is further strengthened by exploiting system symmetries and pseudo-Hermiticity. Tested on a two-dimensional non-Hermitian transverse field Ising model endowed with a complex longitudinal field, our method achieves high accuracy across both parity-time symmetric and broken phases. Moreover, we propose novel optimization routines that address the challenges posed by exceptional points and provide reliable convergence to the ground state in regimes where standard variational techniques fail. Lastly, we show, through extensive numerical evidence, that our method offers a scalable and flexible computational tool to investigate non-Hermitian quantum many-body systems, beyond the reach of conventional numerical techniques such as the density-matrix renormalization group algorithm.
Authors: Yi-Ting Cheng, Hsien-Wen Wan, Wei-Jie Yan, Lawrence Boyu Young, Yen-Hsun Glen Lin, Kuan-Hui Lai, Wan-Sin Chen, Chao-Kai Cheng, Ko-Hsuan Mandy Chen, Tun-Wen Pi, Yen-Hsiang Lin, Jueinai Kwo, Minghwei Hong
Long-term stability of superconducting microwave resonators is essential for scalable quantum technologies; however, surface and interface degradation continue to limit device stability. Here, we demonstrate exceptional stability in microstrip resonators fabricated from epitaxial tantalum and aluminum films, protected by in situ deposited Al2O3 under ultra-high vacuum. These resonators initially exhibit internal quality factors (Qi) exceeding one million and maintain high performance with minimal degradation after up to fourteen months of air exposure. In contrast, devices relying on native surface oxides show substantial declines in Qi over time, indicating increased microwave losses. X-ray photoelectron spectroscopy reveals that the in situ Al2O3 effectively suppresses interfacial oxidation and preserves the chemical integrity of the underlying superconducting films, whereas native oxides permit progressive oxidation, leading to device degradation. These findings establish a robust, scalable passivation strategy that addresses a longstanding materials challenge in the development of superconducting quantum circuits.
Authors: Stefan Löffler, Peter Schattschneider
Elastic electron scattering is one of the primary means of investigating materials on the atomic scale. It is usually described by modeling the sample as a fixed, static, perturbative potential, thereby completely neglecting the quantum nature of the atoms inside. In this work, we present a quantum treatment of elastic electron scattering. We show that the interaction of the probe beam and the sample results in entanglement between the two systems, which can have far-reaching consequences, particularly on coherence and image contrast. As a timely example, we discuss decoherence in Bragg scattering on nanoparticles. We also investigate under which conditions the conventional scattering theory is recovered.
Authors: Sebastián Bahamondes
In this thesis we build a phenomenological, strongly coupled quantum field theory in $2+1$-dimensions through AdS/CFT holography, by building a $3+1$-dimensional, negatively curved gravity theory with a $SU(2)$ gauge field, and a scalar field in the adjoint of $SU(2)$. We locate a phase transition between two distinct phases at zero and finite temperature, which are characterized through the dispersion relation of quasi-normal modes of probe fermions in the bulk, and correspond either to a Dirac semimetal or a band insulator. These phases are separated by a critical phase/critical point (depending if $T>0$ or $T=0$, respectively) where the band structure of boundary fermions exhibits semi-Dirac anisotropy. We characterize each phase at $T=0$ by explicit solutions to the bulk equations of motion in the infra-red, and determine that the critical point's spacetime is a Lifshitz geometry, whose dynamical critical exponent is approximately equal to $2$. We also find that this anisotropy induces a non-trivial scaling of the shear viscosity-entropy density ratio with respect to temperature in the $T\to 0$ limit, and find evidence that the anisotropic phase of the system corresponds to a finite-temperature quantum critical phase.
Authors: Shah Ishmam Mohtashim
We introduce RinQ, a hybrid quantum-classical framework for identifying functionally critical residues in proteins, utilizing techniques in quantum optimization. To that end, protein structures are modeled as residue interaction networks (RINs), and the centrality detection task is cast as a Quadratic Unconstrained Binary Optimization (QUBO) problem. Solved using D-Wave's simulated annealing, this approach is applied to a diverse set of proteins, including small peptides and biologically significant regulatory proteins. RinQ consistently finds residues that align with classical centrality benchmarks, underscoring the accuracy and reliability of the approach. This work highlights the promise of near-term quantum and quantum-inspired methods for advancing protein network analysis and lays the groundwork for future extensions to larger systems using real quantum hardware.
Authors: Sebastian De Haro, Jeremy Butterfield
This monograph discusses dualities in physics: what dualities are, their main examples--from quantum mechanics and electrodynamics to statistical mechanics, quantum field theory and string theory--and the philosophical questions they raise. Part I first conceptualises dualities and discusses their main roles and themes, including how they are related to familiar notions like symmetry and interpretation. It also discusses the main simple examples of dualities: position-momentum, wave-particle, electric-magnetic, and Kramers-Wannier dualities. Part II discusses advanced examples and their inter-relations: particle-soliton dualities, electric-magnetic dualities in quantum field theories, dualities in string theory, and gauge-gravity duality. This Part ends with discussions of the hole argument, and how string theory counts the microstates of a black hole. Part III is an in-depth discussion of general philosophical issues on which dualities bear: theoretical equivalence (two theories 'saying the same thing, in different words'), scientific realism and the under-determination of theories by data, theory succession and the M-theory programme, explanation, and scientific understanding. It proposes a view of scientific theories that it dubs 'the geometric view of theories'. The book's treatment of the examples is at the advanced undergraduate and graduate level, starting from elementary and progressing to more advanced examples. The discussions of philosophical topics, such as referential semantics, theoretical equivalence, scientific realism and scientific understanding, are both self-contained and in-depth. Thus the book is aimed at students and researchers with an interest in the physical examples and philosophical questions about dualities, and also in how physics and philosophy can fruitfully interact with each other.
Authors: Moongul Byun, Taewon Yuk, Young-Kwon Han, Debabrata Ghorai, Sang-Jin Sin
We investigate topological invariants in strongly interacting many-body systems within holographic mean-field theory (H-MFT) framework. Analytic expressions for retarded Green's functions are obtained for all possible fermionic bilinear interactions in the limit of probe background limit $\mathrm{AdS}_4$, from which we construct topological Hamiltonians. Integrating Berry curvature over the momentum domain for the gapped spectra yields well-defined and quantized Chern numbers, enabling a systematic classification of them across interaction types. These topological invariants remain robust under deformation parameters like interaction and temperature, indicating that H-MFT encodes effective single-particle-state topology near a quantum critical point in strongly correlated systems. We point out why topological number is defined in the holographic theories while it is not in the perturbative field theory.
Authors: Philipp Benjamin Aretz, Manfred Salmhofer
We provide a mathematically rigorous Keldysh functional integral for fermionic quantum field theories. We show convergence of a discrete-time Grassmann Gaussian integral representation in the time-continuum limit under very general hypotheses. We also prove analyticity of the effective action and explicit bounds for the truncated (connected) expectation values of the non-equilibrium system. These bounds imply clustering with a summable decay in the thermodynamic limit, provided these properties hold at time zero, and provided that the determinant bound and decay constant of the fermionic Keldysh covariance are bounded uniformly in the volume. We then give bounds for these constants and show that uniformity in the volume indeed holds for a general class of systems. Finally we show that in the setting of dissipative quantum systems, these bounds are not necessarily restricted to short times.
Authors: Elizabeth Bradley, Adilson E. Motter, Louis M. Pecora
Nonlinear science has evolved significantly over the 35 years since the launch of the journal Chaos. This Focus Issue, dedicated to the 80th Birthday of its founding editor-in-chief, David K. Campbell, brings together a selection of contributions on influential topics, many of which were advanced by Campbell's own research program and leadership role. The topics include new phenomena and method development in the realms of network dynamics, machine learning, quantum and material systems, chaos and fractals, localized states, and living systems, with a good balance of literature review, original contributions, and perspectives for future research.
Authors: Ho Truong Nam Hai, Jacqueline Hidalgo-Jiménez, Kaveh Edalati
The formation of green energy carriers such as hydrogen (H2) and methane (CH4) via photocatalytic processes provides a clean method for addressing environmental and energy issues. To achieve highly efficient photocatalysts for H2 and CH4 generation, the present work introduces the P/N heterojunctions in a high-entropy oxide (HEO) with d0/d10 electronic junctions. The study uses CuO as a P-type semiconductor and the HEO containing d0 (Ti, Zr, Nb, Ta) and d10 (Zn) cations as an N-type semiconductor. The material exhibits improvements in optical properties, such as light absorption, charge mobility and reduced electron-hole recombination. The integration of two concepts, atomic-scale d0/d10 electronic junctions and micro-scale P/N heterojunctions, leads to enhanced H2 and CH4 production. Particularly after the partial removal of vacancies in the heterojunction, H2 production from photocatalytic water splitting reaches 0.71 mmol/g.h, and CH4 evolution from CO2 conversion reaches 2.40 umol/g.h with 72% selectivity for methanation. The integrated strategy of this study has a high potential in developing active heterostructured catalysts for clean fuel production.
Authors: Qidong He
Building on an earlier work by Alm, we consider a model of weighted self-avoiding walks on a generic lattice and develop a systematic method for deriving upper bounds on the corresponding weighted connective constant. These bounds are obtained as the dominant eigenvalues of certain matrices and provide detailed information about the domain of convergence of the model's multivariate generating function. We discuss potential applications of this framework to developing Peierls-type estimates for contour models in statistical physics with anisotropic weights, generalizing a technique recently introduced by Fahrbach--Randall.
Authors: Bryan Li, Mengxuan Yang
For the chiral limit of two sheets of $n$-layer Bernal-stacked graphene established in the Physical Review Letters arXiv:2109.10325 and arXiv:2109.11514, we prove a trichotomy: depending on the twisting angle, we have either (1) generically, the band crossing of the first two bands is of order $n$; or (2) at a discrete set of magic angles, the first two bands are completely flat; or (3) for another discrete set of twisting parameters, the bands exhibit Dirac cones. This new mathematical discovery disproves the common belief in physics that such a twisted multilayer graphene model can only have higher order band crossings or flat bands, and it leads to a new type of topological phase transition.
Authors: Yixuan Li, Linhu Li, Zhihao Xu
Non-Hermitian systems exhibit unique boundary phenomena absent in their Hermitian counterparts, most notably the non-Hermitian skin effect (NHSE). In this work, we explore a lattice model consisting of two coupled non-reciprocal chains, focusing on the interplay between system size, inter-chain coupling, and spectral topology. Using both analytical and numerical approaches, we systematically examine the evolution of the complex energy spectra and spectral winding numbers under periodic and open boundary conditions. Our results uncover a variety of size-dependent localization transitions, including the emergence and instability of concurrent bipolar skin effects (CBSE) in the $W=0$ region, and their crossover to unipolar and conventional bipolar NHSE as the system size increases. Notably, we demonstrate that these size-dependent behaviors persist even beyond the weak-coupling regime, highlighting their universality in non-Hermitian systems with complex spectral structures. This study provides new insights into the mechanisms governing skin effects and offers practical guidelines for engineering non-Hermitian topological phases in synthetic lattices.
Authors: Shanyue Li, Mengying Hu, Jing Lin, Chen Fang, Zhensheng Tao, Kun Ding
Solitons, typically resulting from a competition between band dispersion and nonlinearity, occur in lattices featuring the non-Hermitian skin effect as nonlinearity increases, accompanied by a transition in localization from linear skin modes to solitons. However, localization does not disentangle the role of skin modes in the soliton formation from that of band dispersion. Here, in such lattices, we uncover two distinct soliton phases, skin-mode-assisted solitons (SMASs) and nonreciprocity-dressed solitons (NRDSs). Rooted in fundamentally different mechanisms, SMASs originate from skin effect, while NRDSs stem from band nonreciprocity, each exhibiting unique spatial profiles. Using a stacked Su-Schrieffer-Heeger-like model as a prototype, we delineate the phase diagram of SMASs and NRDSs, each having clear phase boundaries. To interpret them, we formulate a Wannier-function-based nonlinear Hamiltonian, showing that soliton formation depends critically on how skin-mode localization and band nonreciprocity suppress or enhance wave dispersion. For SMASs, skin-mode localization reduces wave broadening at the localization sites, thereby lowering the formation threshold. This soliton phase is observable from edge dynamics and accompanied by a dynamical stability reentrance when transitioning from linear skin modes. In contrast, NRDSs, as well as their thresholds, originate from bulk band nonreciprocity and persist under periodic boundary conditions. Our framework offers predictive tools for characterizing and engineering solitons in experimentally realizable non-Hermitian systems, spanning optics to mechanics.
Authors: José M. Cruz, Masafumi Udagawa, Pedro Bicudo, Pedro Ribeiro, Paul A. McClarty
Higher rank gauge theories are generalizations of electromagnetism where, in addition to overall charge conservation, there is also conservation of higher rank multipoles such as the total dipole moment. In this work we study a four dimensional lattice tensor gauge theory coupled to bosonic matter which has second rank tensor electric and magnetic fields and charge conservation on individual planes. Starting from the Hamiltonian, we derive the lattice action for the gauge fields coupled to $q=1,2$ charged scalars. We use the action formulation to carry out Monte Carlo simulations to map the phase diagram as a function of the gauge ($\beta$) and matter ($\kappa$) couplings. We compute the nature of correlators at strong and weak coupling in the pure gauge theory and compare the results to numerical simulations. Simulations show that the naive weak coupling regime (small $\kappa$, large $\beta$) does not survive in the thermodynamic limit. Instead, the strong coupling confined phase, spans the whole phase diagram. It is a proliferation of instantons that destroys the weak coupling phase and we show, via a duality transformation, that the expected strong confinement is present in the analog of Wilson line correlators. For finite matter coupling at $q=1$ we find a single thermodynamic phase albeit with a first order phase transition terminating in a critical this http URL $q=2$ it is known that the the X-cube model with $\mathbb{Z}_2$ fractonic topological order is recovered deep in the Higgs regime. The simulations indeed reveal a distinct Higgs phase in this case.
Authors: Zhian Jia
In this work, we present a construction of a cluster state lattice Hamiltonian that exhibits the symmetry of the Ising fusion algebra. This construction is formulated within the framework of weak Hopf symmetry topological field theory (SymTFT), where we assign smooth and rough boundaries to the weak Hopf quantum double model, thereby extending the conventional cluster state model. Central to our construction is the weak Hopf Ising boundary tube algebra $\mathcal{T}_{\mathsf{Ising}}$, whose representation category is equivalent to the Ising fusion category $\mathsf{Ising}$. We take this algebra as the input data for the weak Hopf quantum double model. The resulting model exhibits Ising fusion symmetry on both open and closed $1\text{d}$ manifolds. On open manifolds, the symmetry is governed by $\mathcal{T}_{\mathsf{Ising}} \otimes \mathcal{T}_{\mathsf{Ising}}^{\vee}$; on closed manifolds, it reduces to $\operatorname{Cocom}(\mathcal{T}_{\mathsf{Ising}}) \otimes \operatorname{Cocom}(\mathcal{T}_{\mathsf{Ising}}^{\vee})$. Since the Ising fusion algebra embeds into $\operatorname{Cocom}(\mathcal{T}_{\mathsf{Ising}}^{\vee})$, the model faithfully realizes the symmetry of the Ising fusion category.
Authors: Gianluca Di Natale, Francesco Pio De Cosmo, Leandro Cieri
Ice clouds, particularly cirrus clouds, significantly influence Earth's radiative balance but remain poorly characterized in current climate models. A major uncertainty arises from the variability of their microphysical properties, especially the evolution of ice crystal habits under depositional growth. We propose a heuristic method to describe habit evolution based on four fundamental shapes identified in the literature and from in situ observations: droxtals, plates, columns, and rosettes. These represent the primary forms that are relevant under depositional growth, excluding aggregation. In this study, we employ a non-Abelian gauge theory within a field-theoretical framework, imposing an SU(2) $\otimes$ U(1) symmetry on the fields associated with each habit probability growth. This symmetry enables the derivation of a modified system of coupled Fokker-Planck equations, capturing the stochastic growth dynamics of ice crystals while incorporating phenomenological mutual influences among habits. This framework outlines a novel theoretical direction for integrating symmetry principles and field-theoretical tools into the modelling of habit dynamics in ice clouds.
Authors: Linus Andersson, Benjamin Olsson, Simone Gasparinetti, Robert Rehammar
A stepped-impedance low-pass filter with integrated hollow waveguide absorbers is presented. The filter combines low insertion loss in the passband with strong attenuation at high frequencies, making it well suited for superconducting quantum computing applications, where qubits are sensitive to both near-band and far out-of-band radiation. The structure is implemented in a rectangular coaxial geometry, with inductive sections coupled to circular hollow waveguides oriented orthogonally to the transmission axis. Above their cutoff frequency, these waveguides efficiently couple to radiation inside the stepped-impedance filter, absorbing energy that would otherwise cause Cooper pair breaking in conventional superconductors. Optimal dimensions were obtained using a differential evolution algorithm applied to interpolated electromagnetic simulation data. A prototype was fabricated and characterized using a calibrated vector network analyzer up to 67 GHz. Measurements confirm a 3 dB cutoff frequency at 13.5 GHz, insertion loss below 0.45 dB for frequencies under 8 GHz, and more than 52.7 dB rejection above 17.3 GHz. The design offers a compact, low-loss solution for near-band filtering and suppression of quasiparticle-generating radiation in cryogenic quantum systems.
Authors: Alessio Miscioscia
Conformal Field Theories (CFTs) are special classes of quantum field theories that find applications ranging from critical phenomena to theories of quantum gravity via holography. Understanding thermal effects in CFTs is crucial: criticality is experimentally probed at finite temperature, and, from the holographic perspective, the study of thermal CFTs is dual to the study of black holes in Anti-de Sitter space. In this thesis, we explore the kinematics and dynamics of finite-temperature CFTs by analyzing broken and unbroken symmetries and adapting various analytical and numerical bootstrap approaches to finite-temperature correlation functions. These methods are non-perturbatively valid and can be tested against exactly solvable models, such as free theories and two-dimensional systems, as well as compared with perturbative calculations. The main applications discussed in this thesis concern one- and two-point functions and the free energy density in the O(N) models in three dimensions, with particular focus on the 3d Ising, XY, and Heisenberg models (N = 1,2,3).
Authors: Anton Montag, Jordan Isaacs, Marcus Stålhammar, Flore K. Kunst
Exceptional points (EPs) are non-Hermitian spectral degeneracies marking a simultaneous coalescence of eigenvalues and eigenvectors. Despite the fact that multiband $n$-fold EPs (EP$n$s) generically emerge as special points on manifolds of EP$m$s, where $m
Authors: Jerome Lloyd, Dmitry A. Abanin, Sarang Gopalakrishnan
The Markov length was recently proposed as an information-theoretic diagnostic for quantum mixed-state phase transitions [Sang & Hsieh, Phys. Rev. Lett. 134, 070403 (2025)]. Here, we show that the Markov length diverges even under classical stochastic dynamics, when a low-temperature ordered state is quenched into the high temperature phase. Conventional observables do not exhibit growing length scales upon quenching into the high-temperature phase; however, the Markov length grows exponentially in time. Consequently, the state of a system as it heats becomes increasingly non-Gibbsian, and the range of its putative "parent Hamiltonian" must diverge with the Markov length. From this information-theoretic point of view the late-time limit of thermalization is singular. We introduce a numerical technique for computing the Markov length based on matrix-product states, and explore its dynamics under general thermal quenches in the one-dimensional classical Ising model. For all cases, we provide simple information-theoretic arguments that explain our results.
Authors: Luca Di Carlo, Francesca Mignacco, Christopher W. Lynn, William Bialek
Recent advances in experimental techniques enable the simultaneous recording of activity from thousands of neurons in the brain, presenting both an opportunity and a challenge: to build meaningful, scalable models of large neural populations. Correlations in the brain are typically weak but widespread, suggesting that a mean-field approach might be effective in describing real neural populations, and we explore a hierarchy of maximum entropy models guided by this idea. We begin with models that match only the mean and variance of the total population activity, and extend to models that match the experimentally observed mean and variance of activity along multiple projections of the neural state. Confronted by data from several different brain regions, these models are driven toward a first-order phase transition, characterized by the presence of two nearly degenerate minima in the energy landscape, and this leads to predictions in qualitative disagreement with other features of the data. To resolve this problem we introduce a novel class of models that constrain the full probability distribution of activity along selected projections. We develop the mean-field theory for this class of models and apply it to recordings from 1000+ neurons in the mouse hippocampus. This 'distributional mean--field' model provides an accurate and consistent description of the data, offering a scalable and principled approach to modeling complex neural population dynamics.
Authors: Jacques R. Eone
The magnetic and surface properties of some transition metals have been investigated within the tight-binding approximation, including Coulomb correlations. These surface properties are calculated after applying a charge neutrality rule that is restricted to the d-band. This formalism gives a charge distribution containing delocalized sp-states in agreement with a linear muffin-tin orbital calculation. It enables the description of local magnetism, surface energies, and work functions without recourse to the total energy. The present investigation is focused on the study of fcc cobalt, bcc iron, fcc nickel, and fcc platinum surfaces, as well as an exploration of fcc cobalt nanoparticles.
Authors: Jacques R. Eone
The electronic structure, when restricted to the d-band approximation, is a computational model that is both efficient and useful for describing transition metals. In the absence of considering delocalized sp-states, this approximation gives rise to incorrect surface energies, binding energies, and an inaccurate description of ferromagnetic transition metals. The present work compares the complexity of implementing corrections with the possibility of using an accurate sp-d approach. Basic force fields based on the second moment approximation continue to be utilized for the description of interactions in transition metals. In contrast, the present study proposes an elementary and more accurate interatomic potential based on hopping parameters depending on distances. The charge distribution and the Stoner model are also analyzed to provide appropriate corrections to the tight-binding picture used to describe ferromagnetic metals and alloys.
Authors: Konstantin V. Grigorishin
By analogy with the Ginzburg-Landau theory of multi-band superconductors with inner (interband) Josephson couplings we formulate the three-band Glashow-Weinberg-Salam model with weak Josephson couplings between strongly asymmetrical condensates of scalar (Higgs) fields. Unlike usual single-band model, we found three Higgs bosons corresponding to three generations of particles, moreover the heaviest of them corresponds to the already discovered H-boson and decays into fermions of only the third generation through Yukawa interaction. The other two decay into fermions of the first and second generations accordingly, but they are difficult to observe due to very poor conditions for production. We found two sterile ultra-light Leggett bosons, the Bose condensates of which form the dark halos of galaxies and their clusters (i.e so called "dark matter"). The masses of the Leggett bosons are determined by the coefficient of the interband coupling and can be arbitrarily small ($\sim 10^{-20}\mathrm{eV}$) due to non-perturbativeness of the interband coupling. Since propagation of Leggett bosons is not accompanied by current, these bosons are not absorbed by gauge fields unlike the common-mode Goldstone bosons. Three coupled condensates of the scalar fields are related to the existence of three generations of leptons, where each generation interacts with the corresponding condensate getting mass. The interflavour mixing between the generations of active neutrinos and sterile right-handed neutrinos in the three-band system causes the existence of mass states of neutrino without interaction with the Higgs condensates.
Authors: Yining Hu, Xu Wang, Chen Chen, Qingle Zhang, Dongming Zhao, Tianzhen Zhang, Chenxi Wang, Qiang-Hua Wang, Donglai Feng, Tong Zhang
Conventional magnetic domain walls are characterized by reorientation of local spins. However, what occurs at the boundary of itinerant magnets is largely unknown. Here using spin-sensitive scanning tunneling microscopy, we investigated the microscopic domain wall structure of the spin-density-wave (SDW) state in a prototypical itinerant antiferromagnet - chromium (Cr). At the boundary of two incommensurate SDW domains, we found the spins undergo finite-scale decay rather than reorientation. This generates a double-Q SDW state, which is further evidenced by an accompanying second-order charge modulation. In the commensurate SDW domains, a clear SDW energy gap is observed. Interestingly, the screw dislocations induced half vortex and anti-vortex of SDW, paired by antiphase domain wall. The spin density vanished at such antiphase domain walls. Remarkably, for the first time we observed the SDW quasiparticle states at the boundary, resembling the Andreev bound states in superconductors. These unique SDW boundary structures can be viewed as consequences of local interference of two SDWs, either with different Q or reversed phases. Our findings thus reveal a new type of domain wall distinct to that of local moment magnetism, with a mechanism rooted in the itinerant nature of SDW.
Authors: Yuri Fukaya, Maria Teresa Mercaldo, Daniel Margineda, Alessandro Crippa, Elia Strambini, Francesco Giazotto, Carmine Ortix, Mario Cuoco
We investigate supercurrent nonreciprocal effects in a superconducting weak-link hosting distinct types of vortices. We demonstrate how the winding number of the vortex, its spatial configuration, and the shape of the superconducting lead can steer the sign and amplitude of the supercurrent rectification. We find a general criterion for the vortex pattern to maximize the rectification amplitude of the supercurrent. The underlying strategy is the search for specific vortex core positions yielding a vanishing amplitude of the supercurrent first harmonic. We also prove that supercurrent nonreciprocal effects can be used to diagnose high-winding vortex and to distinguish between different types of vorticity. Our results thus provide a toolkit to control the supercurrent rectification by means of vortex phase textures and nonreciprocal signatures to detect vortex states with nonstandard phase patterns.
Authors: Christopher M. Langlett, Joaquin F. Rodriguez-Nieva
Our current understanding of quantum chaos in many-body quantum systems hinges on the random matrix theory(RMT) behavior of eigenstates and their energy level statistics. Although RMT has been remarkably successful in describing `coarse' features of many-body quantum Hamiltonians in chaotic regimes, such as the Wigner-Dyson level spacing statistics or the volume-law behavior of eigenstate entanglement entropy, it remains a challenge to describe their `finer' features, particularly those arising from spatial locality. Here, we show that we can accurately describe the statistical behavior of eigenstate ensembles in many-body Hamiltonians by using pure random states with physical constraints that capture the essential features of the Hamiltonian, specifically spatial locality and symmetries. We demonstrate our approach on local spin Hamiltonians with a scalar U(1) charge. By constructing ensembles of constrained random states that account for two commuting scalar charges playing the role of energy and magnetization, we describe the patterns of entanglement of mid-spectrum eigenstates beyond their average volume-law behavior, including $O(1)$ corrections and fluctuations, analytically and numerically. When defining the correspondence between quantum chaotic eigenstates in many-body Hamiltonians and RMT ensembles, our work highlights the important role played by spatial locality in describing universal features beyond the volume-law behavior.
Authors: Tobias Micklitz, Alexander Altland
Light scattering in random media is usually considered within the framework of the three-dimensional Anderson universality class, with modifications for the vector nature of electromagnetic waves. We propose that the linear dispersiveness of light introduces topological aspects into the picture. The dynamics of electromagnetic waves follow the same differential equations as those of a spin-$1$ Weyl semimetal. In the presence of disorder, this equivalence leads to a range of phenomena explored in this paper. These include topological protection against localization when helicity hybridization is weak, the emergence of exotic phases in weakly scattering media, and anomalies in optical transparency in the presence of synthetic `magnetic fields'. We argue that some of these effects should be visible and investigated already in weakly disordered optical materials.
Authors: J. Freedberg, D.L.Schlagel, R. L. Orbach, E. Dan Dahlberg
Aging in a single crystal spin glass ($\mathrm{Cu}_{0.92}\mathrm{Mn}_{0.08}$) has been measured using ac susceptibility techniques over a temperature range of $0.3 - 0.8 \, T_g$. In these studies, traditional aging experiments (or ``quench'' aging protocols) are compared to aging curves constructed from finite-cooling-rate curves. By comparing the growth rates of spin glass order between the two types of aging curves, it is determined that quantitative comparisons between protocols which are taken by quenching and protocols using a finite cooling rate are not possible without a deeper understanding of the interplay between aging and rejuvenation. We then demonstrate that the data presented indicate that rejuvenation, rather than cumulative aging, is the cause for the discrepancies between the two growth rates.
Authors: Cong Xiao, Jin Cao, Qian Niu, Shengyuan A. Yang
We show that the three commonly employed approaches that define the same dc (or low-frequency) intrinsic linear anomalous Hall response actually lead to different results for intrinsic nonlinear transport. The difference is due to an intrinsic anomalous distribution (IAD). It originates from a nonlinear field effect during scattering, but its value is completely independent of scattering, because it represents the local equilibration of electron wave packets with field corrected energy. The proper definition of intrinsic current that is detectable in experiment must incorporate the effect of IAD. We also show that IAD is indispensable for consistency with fundamental physical relations. In addition, we predict that under ac driving, the intrinsic reponses in rectified and double-frequency channels exhibit distinct frequency dependence, for which we estimate the signals that can be probed in antiferromagnetic CuMnAs.
Authors: Ewan Scott, Michal Kwasigroch
The local magnetic anisotropy of a typical crystalline compound is usually attributed to the combined effect of crystal electric fields and spin-orbit coupling. We show that this simple local picture is transformed in heavy-fermion compounds by the development of coherent electron scattering from local spin degrees of freedom. Provided the dominance of the coherence energy scale over the magnetic energy scale is strong enough, the fractionalisation and delocalisation of the spins destabilises their single-ion anisotropy by generating an opposing anisotropy in the exchange. Experimentally, this can manifest as competing splittings in the Curie-Weiss constants and effective moments. We show that in the presence of orthorhombic or tetragonal symmetry the destabilisation of the anisotropy can result in either ferromagnetic or antiferromagnetic order that is perpendicular to the high-temperature easy axis. In the absence of destabilisation, we show that the order is more likely to be antiferromagnetic. In agreement with our theory, we also observe that the temperature at which the anisotropy of the uniform magnetic response changes tracks the coherence energy scale in a wide range of actinide and lanthanide compounds.
Authors: Dmitrii V. Semenok, Boris L. Altshuler, Emil A. Yuzbashyan
Fundamental upper bounds on the electron-phonon interaction strength and superconducting transition temperature $T_c$ in metals are established based on the intrinsic instability of the equilibrium between electrons and the crystal lattice under strong interaction. This instability explains why observed electron-phonon coupling constants are limited to $\lambda \lesssim 4$. The theory also accounts for the mechanism of metastable superconductivity with enhanced $T_c$, which emerges near the instability threshold. Based on theoretical analysis and comparison with experimental data, room-temperature phonon-mediated superconductivity is found to be feasible exclusively in hydrogen compounds.
Authors: Eric Kochems, Gretel Quintero Angulo, Reinhold Egger, Carsten Müller, Selym Villalba-Chávez
Thermal radiation features of dynamical axion insulators, which are characterized by an antiferromagnetic order with simultaneously broken time-reversal and space-inversion symmetries, are investigated. Planck's radiation law is shown to exhibit remarkable anisotropic behavior as a result of the strong dispersion caused by the light-matter interaction. A crossover scenario at low temperature is identified and an associated phase highly populated by slow thermal photons is revealed. We show that the asymmetry degree of the heat radiation and its angular distribution can be controlled via a magnetic field, paving the way toward a directional-tunable mechanism for thermal quantum manipulation and storage. Analogies are drawn with the expected behavior of blackbody radiation in the core of neutron stars.
Authors: Xin Li, Guodong Ren, Haidong Lu, Kartik Samanta, Amit Kumar Shah, Kai Huang, Pravan Omprakash, Yu Yun, Pratyush Buragohain, Huibo Cao, Yan Wu, Jordan A. Hachtel, Andrew R. Lupini, Miaofang Chi, Juan Carlos Idrobo, Evgeny Y. Tsymbal, Alexei Gruverman, Rohan Mishra, Xiaoshan Xu
Antiferroelectricity is a material property characterized by alternating electric dipoles spontaneously ordered in antiparallel directions. Antiferroelectrics are promising for energy storage, solid-state cooling, and memory technologies; however, these materials are scarce, and their scalability remains largely unexplored. In this work, we demonstrate that single-crystalline hafnia, a lead-free CMOS-compatible material, exhibits antiferroelectricity under compressive-strain conditions. We observe antiparallel sublattice polarization and stable double-hysteresis in single-crystalline (111)-oriented epitaxial La-doped hafnia films grown on yttrium-stabilized zirconia and show that the antipolar orthorhombic phase of hafnia adheres to the Kittel model of antiferroelectricity. Notably, compressive strain strengthens the antiferroelectric order in thinner La-doped hafnia films, achieving an unprecedented 850 C ordering temperature in the two-dimensional limit, highlighting hafnia's potential for advanced antiferroelectric devices.
Authors: Thales F. Macedo, Julián Faúndez, Raimundo R. dos Santos, Natanael C. Costa, Felipe A. Pinheiro
We theoretically investigate criticality and multifractal states in a one-dimensional Aubry-Andre-Harper model coupled to electromagnetic cavities. We focus on two specific cases where the phonon frequencies are $\omega_{0}=1$ and $\omega_{0}=2$, respectively. Phase transitions are analyzed using both the average and minimum inverse participation ratio to identify metallic, fractal, and insulating states. We provide numerical evidence to show that the presence of the optical cavity induces a critical, intermediate phase in between the extended and localized phases, hence drastically modifying the traditional transport phase diagram of the Aubry-Andre-Harper model, in which critical states can only exist at the well-defined metal-insulator critical point. We also investigate the probability distribution of the inverse participation ratio and conduct a multifractal analysis to characterize the nature of the critical phase, in which we show that extended, localized, and fractal eigenstates coexist. Altogether, our findings reveal the pivotal role that the coupling to electromagnetic cavities plays in tailoring critical transport phenomena at the microscopic level of the eigenstates.
Authors: Oliver Franke, Duje Akrap, Piet W. Brouwer
Electron-magnon coupling at the interface between a normal metal and a magnetically ordered insulator modifies the electrical conductivity of the normal metal, an effect known as spin-Hall magnetoresistance. It can also facilitate magnon-mediated current drag, the nonlocal electric current response of two normal metal layers separated by a magnetic insulator. Additionally, spin and heat transport are coupled both in the magnetic insulator and across the interfaces to normal metals. In this article, we present a theory of these spintronic and spin-caloritronic effects for time-dependent applied electric fields $E(\omega)$, with driving frequencies $\omega$ up to the THz regime. Our model describes how the dominant transport mechanism, coherent or incoherent magnons, evolves with the driving frequency $\omega$.
Authors: Letizia Catalini, Javier del Pino, Soumya S. Kumar, Vincent Dumont, Gabriel Margiani, Oded Zilberberg, Alexander Eichler
The combination of a strong pump and a weak probe has been widely applied to investigate both optical and nanomechanical devices. Such pump-probe measurements allows for the exploration of nonlinear dynamics, driven by the large pump tone, by measuring the system response to a probe tone. In contrast, here we report on the dynamics of a mechanical Duffing resonator driven with a combination of two large tones at different frequencies. Our results indicate the presence of various distinct regimes with very different dynamics. We systematically investigate the impact of the relative strength and detuning between the two drives on the dynamical response. This provides an illustrative example of dynamical phase transitions in out-of-equilibrium systems.
Authors: David Ribar, Clifford E. Woodward, Jan Forsman
Recent experimental results by the Surface Force Apparatus (SFA) have identified a dramatic deviation from previously established theories of simple electrolytes. This deviation, referred to as anomalous underscreening, suggests that the range of electrostatic interactions increase upon a further addition of salt, beyond some threshold concentration (usually about 1M). In this theoretical work, we explore an extension of the Restricted Primitive Model (RPM) wherein a short-ranged pair potential of mean force (sPMF) is added to the usual Coulombic interactions so as to mimic changes of the hydration as two ions approach one another. The strength of this potential is adjusted so that the modified RPM saturates at a realistic concentration level (within a range 4-7M, typical to aqueous 1:1 salts). We utilise grand canonical simulations to establish surface forces predicted by the model and compare them directly with SFA data. We explore different sPMF models, which in all cases display significant clustering at concentrations above about 1M. In these models, we find significant double-layer repulsion at separations that significantly exceed those expected from standard RPM predictions. We do not, however, observe an increase of the screening length with salt concentration, but rather that this screening length seemingly saturates at a (rather high) value. The simulated long-ranged interactions are shown to correlate with ion cluster formation, implicating the important role of accompanying {\em cluster-cluster} interactions. In particular, steric interactions between clusters (manifested in density-density correlations) are quite relevant in these systems.
Authors: Zachariah Addison, Lauren Keyes, Mohit Randeria
We develop a theory for the electrical and thermal transverse linear response functions such as the Hall, Nernst and thermal Hall effects in magnetic materials that harbor topological spin textures like skyrmions. In addition to the ordinary transverse response that arises from the Lorentz force due to the external magnetic field, there is an anomalous and a topological response. The intrinsic anomalous response derives from the momentum space Berry curvature arising from the spin-orbit coupling (SOC) in a system with a nonzero magnetization, while the topological response arises from real space Berry curvature related to the the topological charge density of the spin texture. To take into account all these effects on an equal footing, we develop a semiclassical theory that incorporates all phase-space Berry curvatures. We show within a controlled, semiclassical approach that all conductivities -- electrical, thermoelectric, and thermal Hall -- can be written as the sum of three contributions: ordinary, anomalous and topological, when the conduction electron SOC is weaker than the exchange coupling to the spin texture. All other contributions, including those arising from mixed real-momentum space Berry curvature, are negligible in the regime where our calculations are controlled. We derive various general relations that remain valid at low temperatures including the Weidemann-Franz relation between the electrical and thermal conductivities and the Mott relation between the thermoelectric and electrical conductivities. We also discuss how an in-plane Hall response arises in three-dimensional materials with sufficiently low symmetry. Finally, the Hall response is qualitatively different when the conduction electron SOC is stronger than the exchange coupling to the spin texture, where we find that the anomalous term dominates and the topological term vanishes.
Authors: Ya-Jun Wang, Jun Zhang, Zheng-Yuan Zhang, Shi-Yao Shao, Qing Li, Han-Chao Chen, Yu Ma, Tian-Yu Han, Qi-Feng Wang, Jia-Dou Nan, Yi-Ming Yin, Dong-Yang Zhu, Qiao-Qiao Fang, Chao Yu, Xin Liu, Guang-Can Guo, Bang Liu, Li-Hua Zhang, Dong-Sheng Ding, Bao-Sen Shi
The dynamical trajectory of a dissipative Rydberg many-body system could be flipped under a microwave field driving, displaying an enhanced sensitivity. This is because the intersection of the folded hysteresis trajectories exhibits a sharp peak near the phase transition, amplifying the response to small changes in the microwave field. Here, we demonstrate an experiment of enhanced metrology through flipping the hysteresis trajectory in a cold atomic system, displaying an approach to improve sensitivity near the gap-closing points. By measuring the intersection points of hysteresis trajectories versus Rabi frequency of the microwave field, we quantify the equivalent sensitivity to be 1.6(5) nV cm-1 Hz-1/2. The measurement is also dependent on the interaction time, optical depth and principal quantum number since the long-range interaction between Rydberg atoms could dramatically change the shape of hysteresis trajectories. The reported results suggest that flipping trajectory features in cold Rydberg many-body systems could advance sensing and metrology applications.
Authors: Tommer D. Keidar, Shlomi Reuveni
First-passage processes are pervasive across numerous scientific fields, yet a general framework for understanding their response to external perturbations remains elusive. While the fluctuation-dissipation theorem offers a complete linear response theory for systems in steady-state, it fails to apply to transient first-passage processes. We address this challenge by focusing on rare - rather than weak - perturbations. Surprisingly, we discover that the linear response of the mean first-passage time (MFPT) to such perturbations is universal. It depends solely on the first two moments of the unperturbed first-passage time and the mean completion time following perturbation activation, without any assumptions about the underlying system's dynamics. To demonstrate the utility of our findings, we analyze the MFPT response of drift-diffusion processes in two scenarios: (i) stochastic resetting with information feedback, and (ii) an abrupt transition from a linear to a logarithmic potential. In both cases, our approach bypasses the need for explicit determination of the perturbed dynamics, unraveling a highly non-trivial response landscape with minimal effort. Finally, we show how our framework enables a new type of experiment - inferring molecular-level fluctuations from bulk measurements, a feat previously believed to be impossible. Overall, the newly discovered universality reported herein offers a powerful tool for predicting the impact of perturbations on kinetic processes - and, remarkably, for extracting hidden single-molecule fluctuations from accessible bulk measurements.
Authors: Vincenzo Alba
We investigate the dynamics of the Rényi Operator Space Entanglement ($OSE$) entropies $S_n$ across several one-dimensional integrable and chaotic models. As a paradigmatic integrable system, we first consider the so-called rule $54$ chain. Our numerical results reveal that the Rényi $OSE$ entropies of diagonal operators with nonzero trace saturate at long times, in contrast with the behavior of von Neumann entropy. Oppositely, the Rényi entropies of traceless operators exhibit logarithmic growth with time, with the prefactor of this growth depending in a nontrivial manner on $n$. Notably, at long times, the complete operator entanglement spectrum ($ES$) of an operator can be reconstructed from the spectrum of its traceless part. We observe a similar pattern in the $XXZ$ chain, suggesting universal behavior. Additionally, we consider dynamics in nonintegrable deformations of the $XXZ$ chain. Finite-time corrections do not allow to access the long-time behavior of the von Neumann entropy. On the other hand, for $n>1$ the growth of the entropies is milder, and it is compatible with a sublinear growth, at least for operators associated with global conserved quantities. Finally, we show that in finite-size integrable systems, $S_n$ exhibit strong revivals, which are washed out when integrability is broken.
Authors: Felipe Taha Sant'Ana, Hui Liu
We study the effects of the two-spinon excitations on the field-field correlator of the Tonks-Girardeau gas. While these excitations have been previously examined in the ground state of the system, their role at finite temperatures remains unexplored. Here, we extend the analysis to the one-dimensional interacting Bose gas at thermal equilibrium, focusing on the one-body correlation function of the infinitely repulsive Lieb-Liniger model. We demonstrate that two-spinon excitations, characterized by two holes within the rapidity distribution, constitute the dominant contribution to the field-field correlator at low temperatures. Furthermore, we analytically show that incorporating additional particle-hole excitations diminishes their contribution, highlighting the efficacy of the two-spinon framework in capturing the essential physics of the system. Numerical evaluations of both the Fredholm determinant and the spectral sum stemming from the two-spinon program, with the addition of particle-hole excitations, reveal convergence at low temperatures.
Authors: Hiroki Nakai, Chisa Hotta
We explore the quantum pseudospin-1 pyrochlore magnet featuring Fe$^{2+}$-based spinel oxides that addresses the formation of amplitude-modulated spin-density waves. We propose that the relatively small spin-orbit coupling and the small extra crystal field splitting in these materials create anisotropic exchange interactions and strong single-ion anisotropy, respectively, whose interplay becomes the source of quadrupolar moments selectively appearing on certain sublattices, leading to a spatially modulated hybrid of dipolar and quadrupolar moments. This mechanism represents the possibility of insulating magnets to form an exotic phase with coexisting liquid-solid properties.
Authors: Yongxin Zeng, Andrew J. Millis
Systems such as Wigner crystals and incommensurate charge density waves that spontaneously break a continuous translation symmetry have unusual transport properties arising from their ability to slide coherently in space. Recent experimental and theoretical studies suggest that spontaneous translation symmetry breaking in some two-dimensional materials with nontrivial quantum geometry (e.g., rhombohedral pentalayer graphene) leads to a topologically nontrivial electron crystal state called the anomalous Hall crystal and characterized by a vanishing linear-response dc longitudinal conductivity and a non-vanishing Hall conductivity. In this work we present a theoretical investigation of the sliding dynamics of this new type of electron crystal, taking into account the system's nontrivial quantum geometry. We find that when accelerated by an external electric field, the crystal acquires a transverse anomalous velocity that stems from not only the Berry curvature of the parent band but also the Galilean non-invariance of the crystal state (i.e., crystal states with different momenta are not related by simple momentum boosts). We further show that acceleration of the crystal modifies its internal current from the static crystal value that is determined by the Chern number of the crystal state. The net Hall conductance including contributions from center-of-mass motion and internal current is in general not quantized. As an experimentally relevant example, we present numerical results in rhombohedral pentalayer graphene and discuss possible experimental implications.
Authors: Chen-Xin Jiang, Zi-Xiang Hu, Bo Yang
Flat bands result in a divergent density of states and high sensitivity to interactions in physical systems. While such bands are well known in systems under magnetic fields, their realization and behavior in zero-field settings remain largely unexplored. Here we compare the behavior of electrons confined to a single flat band on the surface of a sphere to those in flat bands under a magnetic field. The zero-field flat band exhibits an additional C(2) symmetry, which causes electrons to symmetrically cluster on opposite sides of the sphere's center when a trapping potential is introduced, resulting in a unique form of long-range "entanglement". To explore these findings experimentally, we propose a feasible setup to explore the unique properties of zero-field flat bands on spherical substrates, offering a promising route for studying interaction-driven states in spherical geometry without external fields.
Authors: Attila Szabó
Based on the relationship between reduced and thermal density matrices in conformal field theory (CFT), we show that the entanglement spectrum of a conformal critical chain with exponentially decaying terms consists of conformal towers of the associated chiral CFT, with only weak finite-size effects. Through free-fermion and interacting examples, we show that these entanglement spectra present a reliable method to extract detailed CFT spectra from single wave functions without access to the parent Hamiltonian. We complement our method with a Wilsonian numerical renormalisation group algorithm for solving interacting, exponentially decaying chain Hamiltonians.
Authors: Amis Sharma, Chun-Chia Chen, Jordan McCourt, Mingi Kim, Kenji Watanabe, Takashi Taniguchi, Leonid Rokhinson, Gleb Finkelstein, Ivan Borzenets
We perform transport measurements on proximitized, ballistic, bilayer graphene Josephson junctions (BGJJs) in the intermediate-to-long junction regime ($L>\xi$). We measure the device's differential resistance as a function of bias current and gate voltage for a range of different temperatures. The extracted critical current $I_{C}$ follows an exponential trend with temperature: $ \exp(-k_{B} T/ \delta E)$. Here $\delta E = \hbar \nu_F /2\pi L $: an expected trend for intermediate-to-long junctions. From $\delta E$, we determine the Fermi velocity of the bilayer graphene, which is found to increase with gate voltage. Simultaneously, we show the carrier density dependence of $\delta E$, which is attributed to the quadratic dispersion of bilayer graphene. This is in contrast to single layer graphene Josephson junctions, where $\delta E$ and the Fermi velocity are independent of the carrier density. The carrier density dependence in BGJJs allows for additional tuning parameters in graphene-based Josephson Junction devices.
Authors: Yifan Liu, Zehan Chen, Qiming Shao
Realizing novel topological states in magnonic systems unlocks robust, low-power spin-wave devices. In this letter, we show that incorporating left-handed spin waves (antimagnons) fundamentally reorganizes band topology, and enables tunable spin-wave coupling and chirality. We proposed a two-dimensional Su-Schrieffer-Heeger like model, the 2D-SSH4 chain, where dipolar interactions between magnons and antimagnons generate topological bands with nonzero Chern numbers. This framework explains the origin of topological surface states in ferromagnetic multilayer and shows they share the same topological origin as classic magnetostatic surface spin waves. Our model also offers a straightforward framework for designing more complex magnetic multilayer connected by dipolar interactions, such as antiferromagnetic/ferromagnetic multilayer. In these dipolar-coupled multilayers, both coherent and dissipative interlayer spin-wave couplings together with the layer resolved chirality, are tunable via external magnetic fields and spin torques. Our results provide a practical platform for topological magnonics, enabling control of magnon chirality and coupling in future devices.
Authors: Jerome Garnier-Brun, Ruben Zakine, Michael Benzaquen
We study the hydrodynamics of a system of agents who optimize either their individual utility (self-interest) or the collective welfare (cooperation). When agents act selfishly, their interactions are non-reciprocal, driving the system out of equilibrium; by contrast, purely altruistic dynamics restore reciprocity and yield an equilibrium-like description. We investigate how mixtures of these two behaviors shape the macroscopic properties of the liquid of agents. For highly rational agents, we find that introducing a small fraction of altruists can suppress the sub-optimal clustering induced by selfish dynamics. This phenomenon can be attributed to altruists localizing at interfaces and acting as effective surfactants, shedding a new light on earlier findings in fixed neighborhood-based models [Phys. Rev. Lett. \textbf{120}, 208301 (2018)]. When agents are boundedly rational, we introduce a well-mixed approximation that reduces the two-population model to a single effective scalar field theory. This allows us to leverage state-of-the-art tools from active matter to analytically characterize how altruism modifies surface tension and nucleation dynamics.
Authors: Alba Viejo-Rodríguez, Andrea Rossetti, Marco Gandolfi, Yoav Urbina-Elgueta, Evgeny B. Modin, Svetlana Starikovskaia, Tat Loon Chng, Vasily Temnov, Maria Antonietta Vincenti, Daniele Brida, Paolo Vavassori, Nicolò Maccaferri
Single-shot picosecond (ps) laser induced delamination allows for the direct generation of suspended membranes from a continuous metallic film, offering a promising platform for control of ultrafast magnetization dynamics driven by acoustic waves. Using the picosecond-ultrasonics method, we demonstrate that long-lived low-frequency acoustic waves can be optically-excited in the delaminated cavities. At the same time, higher-frequency modes >60GHz exhibit a surprisingly fast damping, following a scaling law incompatible with the expected attenuation mediated by phonon-phonon scattering. Comparing measurements between delaminated cavities and a benchmark nickel film in contact with the substrate, we link our findings with structural modifications of the nickel crystal induced by the delamination process.
Authors: Jesse Balgley, Jinho Park, Xuanjing Chu, Ethan G. Arnault, Martin V. Gustafsson, Leonardo Ranzani, Madisen Holbrook, Yangchen He, Kenji Watanabe, Takashi Taniguchi, Daniel Rhodes, Vasili Perebeinos, James Hone, Kin Chung Fong
The narrow bandgap of semiconductors allows for thick, uniform Josephson junction barriers, potentially enabling reproducible, stable, and compact superconducting qubits. We study vertically stacked van der Waals Josephson junctions with semiconducting weak links, whose crystalline structures and clean interfaces offer a promising platform for quantum devices. We observe robust Josephson coupling across 2--12 nm (3--18 atomic layers) of semiconducting WSe$_2$ and, notably, a crossover from proximity- to tunneling-type behavior with increasing weak link thickness. Building on these results, we fabricate a prototype all-crystalline merged-element transmon qubit with transmon frequency and anharmonicity closely matching design parameters. We demonstrate dispersive coupling between this transmon and a microwave resonator, highlighting the potential of crystalline superconductor-semiconductor structures for compact, tailored superconducting quantum devices.
Authors: Julian Boesl, Yu-Jie Liu, Wen-Tao Xu, Frank Pollmann, Michael Knap
Topologically ordered phases exhibit further complexity in the presence of global symmetries: Their anyonic excitations may exhibit different transformation patterns under these symmetries, leading to a classification in terms of symmetry-enriched topological orders. We develop a generic scheme to study an analogous situation for three-dimensional fracton phases by means of isometric tensor network states (isoTNS) with finite bond dimension, which allow us to tune phase transitions between different symmetry fractionalization patterns. We focus on the X-Cube model, a paradigmatic fracton model hosting two types of excitations: lineons, which are mobile in a single direction only, and fractons that are immobile on their own. By deforming the local tensors of the fixed point ground state, we find a family of exact wavefunctions for which the symmetry fractionalization under an anti-unitary symmetry on both types of excitations is directly visible. These wavefunctions are non-stabilizer states and have non-vanishing correlation lengths. They even exhibit power-law correlations at criticality between two symmetry-enriched topological orders. Furthermore, the isoTNS description allows for the explicit construction of a linear-depth quantum circuit to sequentially realize these exotic 3D states on a quantum processor, including a holographic scheme using only a pair of two-dimensional qubit arrays alongside measurements. Our approach provides a construction to enrich phases with exotic topological or fracton order and to study 3D quantum phase transition with exact wavefunctions, and offers a tractable route to implement and characterize fracton order on quantum devices.
Authors: Titus Quah, Sho C. Takatori, James B. Rawlings
Active matter swarms -- collectives of self-propelled particles that could self-assemble, ferry microscopic cargo, or endow materials with dynamic properties -- remain hard to steer. In crowded systems, tracking or controlling individual agents becomes challenging, so strategies should operate on macroscopic fields like particle density. Yet predicting how density evolves is difficult due to inter-agent interactions. For model-based feedback control methods -- like Model Predictive Control (MPC) -- fast, accurate, and differentiable models are crucial. Detailed agent-based simulations are too slow, necessitating coarse-grained continuum models. However, constructing accurate closures -- approximations expressing the effect of unresolved microscopic states (e.g., agent positions) on continuum dynamics -- is challenging for active matter swarms. We present a learning-for-control framework that learns continuum closures from agent simulations, demonstrated with active Brownian particles under a controllable external field. Our Universal Differential Equation (UDE) framework represents the continuum as an advection-diffusion equation. A neural operator learns the advection term, providing closure relations for microscopic effects like self-propulsion, interactions, and external field responses. This UDE approach, embedding universal function approximators in differential equations, ensures adherence to physical laws (e.g., conservation) while learning complex dynamics directly from data. We embed this learned continuum model into MPC for precise agent simulation control. We demonstrate this framework's capabilities by dynamically exchanging particle densities between two groups, and simultaneously controlling particle density and mean flux to follow a prescribed sinusoidal profile. These results highlight the framework's potential to control complex active matter dynamics.
Authors: Da Ma, Zhi-Fan Zhang, Hua Jiang, X. C. Xie
The semiclassical Boltzmann equation is widely used to study transport effects. However, being semiclassical and borrowing heavily from classical mechanics, the formalism calls for verification from the perspective of quantum mechanics. Although previous works discussed the relation between the quantum density matrix and the semiclassical formalism, direct comparison, especially of disorder effects, including side jumps and skew scattering in the two approaches, has not been fully conducted. In this work, we systematically and directly compare the semiclassical Boltzmann equation and its counterpart arising from the density matrix. We find that there is an additional correction to the side-jump velocity, the longitudinal velocity, which is longitudinal in the leading order, and its resultant current does not require time-reversal symmetry breaking. Moreover, we find the semiclassical side-jump collision integral is an approximation of the quantum result at moderate temperatures, and it also contains a correction induced by the longitudinal velocity. We also show that the scattering rate obtained from the density matrix agrees with the semiclassical results. Our work illuminates the quantum roots of the semiclassical Boltzmann equation.
Authors: Yuri Fukaya, Bo Lu, Keiji Yada, Yukio Tanaka, Jorge Cayao
In this work we review the recent advances on superconducting phenomena in junctions formed by superconductors and unconventional magnets. Conventional magnets, such as ferromagnets and antiferromagnets, are characterized by broken time-reversal symmetry but only ferromagnets produce a finite net magnetization due to parallel spin alignment and spin-split bands in momentum. Very recently, a new type of magnets has been reported and here we refer to them as unconventional magnets because they exhibit special properties of both ferromagnets and antiferromagnets: they exhibit zero net magnetization (like antiferromagnets) and a nonrelativistic spin splitting of energy bands (like ferromagnets), both leading to anisotropic spin-polarized Fermi surfaces. An interesting property of unconventional magnets is that their magnetic order can be even or odd with respect to momentum, where $d$-wave altermagnets and $p$-wave magnets are the most representative examples. In this regard, $d$-wave altermagnets and $p$-wave magnets are seen as counterparts in magnetism of the unconventional $d$- and $p$-wave superconducting states, respectively. While the impact of conventional magnetism on superconductivity has been largely studied, the combination of unconventional magnets and superconductivity has only lately attracted considerably attention. This work provides a comprehensive review of the recent progress on the interplay between superconductivity and unconventional magnets. In particular, we focus on the fundamental emerging superconducting phenomena and also discuss the potential implications towards quantum applications.
Authors: Carlos Arauz-Moreno, Keyvan Piroird, Elise Lorenceau
In this study, we present an experimental work on bubble nucleation and growth using a model system comprised of viscoelastic polyvinyl butyral confined in a Hele-Shaw cell geometry that is decompressed at elevated temperatures. The appearance and growth of bubbles are connected to the temperature-induced shift in chemical equilibrium experienced simultaneously by two gases present in the bulk. The latter becomes simultaneously oversaturated with water vapor and slightly undersaturated in air. Our bubbles grow with various shapes and sizes depending on the initial morphology of the nucleus or the presence of neighboring bubbles. For large nuclei, bubbles grow anisotropically because of contact line pinning. The likelihood of nucleation is related to the amount of water dissolved in the bulk and the imposed temperature. Counter-intuitively, the number of nuclei whence a bubble can grow is inversely correlated with said temperature. In an analogy with champagne, we show that nucleation can either be natural, at trapped fibers or dust particles, or artificial, at crenels we purposefully made in the glass surface. Our results indicate that the growth rate of bubbles can be impacted by the nucleation mechanism.
Authors: Jongbae Hong
We investigate a quantum phase transition (QPT) in quantum point contacts by analyzing the gate-voltage-dependent quasiparticle energy at the Fermi level at zero temperature. This energy is computed using the local density of states at the site of the localized spin, which is extracted from the replicated gate-voltage-dependent differential conductance shaped by entangled-state tunneling. The QPT occurs between symmetric ($G \geq 0.7 G_0$) and asymmetric ($G < 0.7 G_0$) Kondo coupling states, where $G_0 = 2e^2/h$, and is driven by the migration of a localized spin in response to the side-gate voltage. The asymmetric state exhibits two distinct Kondo temperatures, while the symmetric state has only one. The existence of two Kondo temperatures in the $G < 0.7 G_0$ regime accounts for both the anomalous gate-voltage dependence of the zero-bias anomaly width and the inability to define a Kondo temperature in the $G < 0.7 G_0$ region.
Authors: Junyi Yang, Changjiang Liu, Xianjing Zhou, Hanyu Hou, Kaijun Yin, Jianguo Wen, John Pearson, Alexey Suslov, Dafei Jin, Jidong S. Jiang, Ulrich Welp, Jian-Min Zuo, Michael R. Norman, Anand Bhattacharya
Two-dimensional superconductors with spin-textured Fermi surfaces can be a platform for realizing unconventional pairing states and are of substantial interest in the context of quantum information science, and superconducting spintronics/orbitronics. We observed an unusual in-plane uniaxial anisotropy in the superconducting 2D electron gas (2DEG) formed at EuOx/KTaO3 (110) interfaces, where the EuOx is magnetic. This anisotropy is not evident in AlOx/KTaO3 (110) where the overlayer is non-magnetic. Our results are consistent with a highly anisotropic 'half-Rashba' spin-textured Fermi surface in 2DEGs formed at the KTaO3 (110) interface that is hidden from external magnetic fields due to a near cancellation between orbital and spin moments but revealed by exchange interactions of the electrons in the 2DEG with Eu moments near the EuOx/KTaO3 (110) interface. The interactions between the uniaxial spin texture and the magnetic overlayer offer new ways to explore the interplay between magnetism and 2D superconductivity.
Authors: Takao Morinari, Hibiki Takegami
We investigate the effect of a magnetic field on the Kitaev model using the equation of motion approach for the spin Green's function, considering both the case of suppressed magnetization ($m = 0$) and finite magnetization ($m \neq 0$). When magnetization is suppressed, the specific heat exhibits a clear $60^\circ$ periodicity in its angular dependence, with the locations of maxima and minima consistent with recent experimental observations in $\alpha$-RuCl$_3$. A qualitative difference in their temperature dependence is observed: the minima show gap-like behavior that may signal Majorana gap formation due to time-reversal symmetry breaking, while the maxima do not exhibit the expected gapless Majorana fermion signature. In addition, a linear-in-field effect -- distinct from magnetization -- emerges, with the characteristic temperature below which angular dependence appears increasing linearly with the magnetic field. Importantly, this directional dependence becomes quantitatively significant only at very low temperatures. When finite magnetization is included, the angular dependence of the specific heat remains, and the qualitative behavior is similar to the $m = 0$ case: the minima continue to exhibit gap-like features, while the maxima do not show signatures of gapless Majorana fermions. These results suggest that suppressing magnetization alone is insufficient to realize quantum spin liquid behavior in the Kitaev model under a magnetic field.
Authors: Xin Zhao, Mingzhe Liu, Yu Chen, Qi Zhang, Chang-Kui Duan
The PL6 color center in 4H-SiC, known for its excellent ambient-temperature spin and optical properties, has an unresolved microscopic origin. In this first-principles study, we systematically investigate potential structures to clarify its nature. We first rigorously examine the DV-antisite hypothesis (a divacancy paired with a carbon antisite, $\mathrm{C_{Si}}$), analyzing the energetic, electronic, and spin properties of various $V_\mathrm{Si}V_\mathrm{C}+\mathrm{C_{Si}}$ configurations. Two $\mathrm{C_{3v}}$-symmetric $\mathrm{kk+C_{Si}}$ complexes emerge as strong candidates within this framework. Subsequently, a critical comparison of hyperfine interaction signatures is performed between these candidates, the alternative OV model [specifically OV(hh) and OV(kk), an oxygen replacing C together with a Si vacancy], and experimental data. This analysis demonstrates that the OV(hh) structure more accurately reproduces PL6's hyperfine features. Furthermore, re-evaluation of the proposed OV(hk) model for the related PL5 center reveals zero-field splitting parameter $E$ inconsistencies with experimental results, suggesting that PL5 and PL6 may have distinct origins. These findings provide crucial theoretical insights and motivate targeted experimental validation for these quantum defects.
Authors: Ömer K. Büyükuslu, Fabrice Yang, Dierk Raabe, Moritz to Baben, Anna L. Ravensburg
Direct reduction of iron using hydrogen-rich gas is rapidly emerging as a key strategy for green steel production. This process involves complex, multiscale phenomena, encompassing solid-state phase transformations and gas transport through pores, that must be accurately represented for predictive industrial implementation. Here, we present a thermodynamically sound pellet-scale model that describes these mechanisms and can serve as a foundation for improving the understanding of pellet reduction kinetics in H$_2$/CO-containing atmospheres. The model assumes that the gas phase remains in thermodynamic equilibrium, meaning that the composition of the gas instantaneously adjusts to any changes in the system. This reduces the number of fitting parameters drastically compared to other existing models, while maintaining a strict thermodynamic upper bound estimate. A driving force term is included in the reaction rate equation based on the partial pressure of O$_2$ in the equilibrated gas phase. This constrained equilibrium-based approach ensures that the three iron oxide reduction steps and the formation of graphite and cementite in carbon-containing gases occur only if they are thermodynamically possible. It is demonstrated that fitting kinetic parameters based on conversion degree data alone leads to overfitting. This is true both for existing models and the model introduced here, despite the fact that the latter contains fewer parameters. To overcome this overfitting problem, spatially resolved microstructural data at key reduction stages can be considered, as shown here for recently reported data for a pellet reduced in H$_2$ atmosphere.
Authors: A. Tononi, G. E. Astrakharchik
We investigate the phenomenon of Bose-Einstein condensation in ideal bosonic gases confined to axially-symmetric surfaces of revolution. The single-particle Schrödinger equation is formulated on a general surface and then explicitly solved in the ellipsoidal and toroidal geometries to determine the one-body energy spectrum. We discuss how the curved geometry impacts the quantum statistical properties of ideal Bose gases confined on these surfaces. Specifically, we observe that Bose-Einstein condensation is suppressed when the surface aspect ratio is increased and, correspondingly, it becomes highly elongated and acquires a one-dimensional character. We also evaluate the Bogoliubov excitation spectrum, providing insights into the collective excitations of the condensate. Our results establish the conditions to achieve quantum degeneracy in curved manifolds, thus guiding forthcoming experiments with thin shells, and set the basis for solving the few-to-many body problem in general surfaces of revolution.
Authors: Puspita Parui, Bheema Lingam Chittari
We study the topological properties of Rashba spin-orbit coupling and exchange coupling induced pseudospin-$1$ system Dice lattice under the influence of a staggered electric potential and magnetization. The band structure and topological phases of the system are investigated and compared with the pseudospin-$\frac{1}{2}$ system honeycomb lattice. Under individual influence of the staggered electric field and magnetization, the system undergoes a distinct phase transition: (i) a staggered electric potential drives the system from a quantum anomalous Hall $(C_n = 2)$ to a valley polarized quantum anomalous Hall phase $(C_n = -1)$ associated with edge modes with a flip in the chirality; while (ii) a staggered magnetization changes the system to a topological metal associated with unconventional antichiral edge bands, from a topological insulator. These results are further supported by calculations of the Chern phase diagrams, Hall conductance, zigzag, and armchair edge states. Our findings enhance the understanding of new topological phases in the 2D pseudospin-$1$ system and open up a new platform to explore the anti-chiral edge states.
Authors: Taehun Kim, E. H. Hwang, Hongki Min
In multilayer structures, the coupling between layers gives rise to unique plasmon modes, but analytic solutions are typically available only for bilayers due to the increasing complexity as the number of layers increases. We investigate plasmons in multilayer structures, including the effects of interlayer tunneling. By introducing the Coulomb eigenvector basis for multilayer systems, which can be solved exactly using Kac-Murdock-Szegő Toeplitz matrices, we analytically derive the long-wavelength plasmon dispersions both with and without interlayer tunneling. In the $N$-layer systems, we find that, in the absence of interlayer tunneling, the out-of-phase acoustic or charge neutral plasmon modes with linear dispersions ($\omega_\alpha\propto q/\sqrt{{1-\cos{\left(\frac{\alpha-1}{N}\pi\right)}}}$ for $\alpha = 2, 3, \cdots, N$) exist, while the in-phase classical plasmon mode exhibits its conventional dispersion ($\omega_1\propto \sqrt{q}$). When interlayer tunneling is present, the out-of-phase modes develop plasmon gaps that are governed by specific interband transitions, whereas the classical mode remains unaffected. These findings have broad applicability to general coupled-layer structures.
Authors: Ivan Pasqua, Gregorio Staffieri, Michele Fabrizio
We analyze two simple model planar molecules: an ionic molecule with D3 symmetry and a covalent molecule with D6 symmetry. Both symmetries allow the existence of chiral molecular orbitals and normal modes that are coupled to each other in a Jahn-Teller manner, invariant under U (1) symmetry with generator a pseudo angular momentum. In the ionic molecule, the chiral mode possesses an electric dipole but lacks physical angular momentum, whereas, in the covalent molecule, the situation is reversed. In spite of that, we show that in both cases the chiral modes can be excited by a circularly polarized light and are subsequently able to induce rotational motion of the entire molecule.
Authors: Zhida Luo, Yurui Yang, Jiaxi Cui, Wenjuan Li, Miaoqian Lu, Xinzhou Guan, Wenhua Hai, Yunrong Luo
We study the stability of spin dynamics for a spin-orbit (SO) coupled boson held in a driven non-Hermitian double-well potential. Under high-frequency approximation, we analytically derive the Floquet states and complex Floquet quasienergies of the system and reveal a striking parity-dependent stability criterion: when the ratio of the Zeeman field strength to the driving frequency $\Omega/\omega$ is even, stable spin dynamics can be achieved for \emph{arbitrary} SO coupling strength. However, when $\Omega/\omega$ is odd, stability requires the SO coupling strength to be integer or half-integer values. Particularly, we find four types of stability boundary lines for non-zero bias field strength, in sharp contrast to the commonly observed stability regions. These results establish a tunable parity-governed mechanism for stabilizing spin dynamics in non-Hermitian cold atomic systems.
Authors: Yehonatan Tsubery, Hillel Aharoni
Topological defects, such as disclination lines in nematic liquid crystals, are fundamental to many physical systems and applications. In this work, we study the behavior of nematic disclinations in thin parallel-plate geometries with strong patterned planar anchoring. Building on prior models, we solve both the forward problem -- predicting disclination trajectories from given surface patterns -- and an extended inverse problem -- designing surface patterns to produce a tunable family of disclination curves under varying system parameters. We present an explicit calculation for pattern construction, analyze parameter limitations and stability constraints, and highlight experimental and technological applications.
Authors: Fabio Apruzzi, Francesco Bedogna, Salvo Mancani
We construct Symmetry Topological Field Theories (SymTFTs) for continuous subsystem symmetries, which are inherently non-Lorentz-invariant. Our framework produces dual bulk descriptions -- gapped foliated and exotic SymTFTs -- that generate gapless boundary theories with spontaneous subsystem symmetry breaking via interval compactification. In analogy with the sandwich construction of SymTFT, we call this Mille-feuille. This is done by specifying gapped and symmetry-breaking boundary conditions. In this way we obtain the foliated dual realizations of various models, including the XY plaquette, XYZ cube, and $\phi$, $\hat{\phi}$ theories. This also captures self-duality symmetries as condensation defects and provides a systematic method for generating free theories that non-linearly realize subsystem symmetries.
Authors: Pierre A. Haas
The flows of tissues of epithelial cells often involve T1 transitions. These neighbour exchanges are irreversible rearrangements crossing an energy barrier. Here, by an exact geometric construction, I determine this energy barrier for general, isolated T1 transitions dominated by line tensions. I~show how deviations from regular cell packing reduce this energy barrier, but find that line tension fluctuations increase it on average. By another exact construction, I prove that the nonlinear tensions in vertex models of tissues also resist T1 transitions. My results thus form the basis for coarse-grained understanding of cell neighbour exchanges for continuum descriptions of epithelia.
Authors: Steffen Wittrock, Christopher Klose, Salvatore Perna, Korbinian Baumgaertl, Andrea Mucchietto, Michael Schneider, Josefin Fuchs, Victor Deinhart, Tamer Karaman, Dirk Grundler, Stefan Eisebitt, Bastian Pfau, Daniel Schick
Magnons represent quantised collective motions of long-range ordered spins. For wavelength below 100 nm, exchange interactions dominate their physics, which gives rise to a so far unexplored regime of nonlinearities and couplings between magnons and other quasiparticles. Besides their selective excitation, also the detection of such short-wavelength spin waves remains a challenge of current research and technology. Here, we probe the intensity and wave vector of magnons by means of quasi-elastic, resonant soft-X-ray scattering. This Magnon Momentum Microscopy (MMM) can access magnons directly in momentum space with remarkable sensitivity and high photon efficiency up to THz frequencies and down to few-nanometre wavelengths. The two-dimensional information obtained by this light-scattering-based technique is especially valuable for studying the nonlinear interactions of exchange-dominated magnons within technologically relevant thin-film samples. In doing so, we uncover a rich variety of deeply nonlinear magnon interactions, highlighting their potential for applications in novel computing schemes. With its intrinsic element-selectivity and ability to probe also buried layers, soft-X-ray MMM has the potential to establish itself as an advanced tool for ultrabroadband studies of short-wavelength magnonics.
Authors: Ovidiu I. Patu, Gianni Aupetit-Diallo
Free expansion following the removal of axial confinement represents a fundamental nonequilibrium scenario in the study of many-body ultracold gases. Using the stationary phase approximation, we analytically demonstrate that for all one-dimensional spinor gases with repulsive contact interactions, whether bosonic or fermionic, the asymptotic density and momentum distribution can be directly determined from the quasimomentum distribution (Bethe rapidities) of the trapped gas. We efficiently obtain the quasimomentum distribution numerically by solving the integral equations that characterize the ground state of the integrable system within the local density approximation. Additionally, we derive analytical solutions for both weakly and strongly interacting regimes. Unlike in bosonic gases, where rapidity distributions and density profiles vary significantly across interaction regimes, fermionic gases maintain similar profiles in both weakly and strongly interacting limits. Notably, the gas expands self-similarly only when released from a harmonic trap. For other power-law trapping potentials, the asymptotic density profile is strongly influenced by the initial confinement geometry. Our results extend readily to Bose-Fermi mixtures and finite temperatures.
Authors: Kai Liu, Yating Sha, Bo Yin, Hongyun Zhang, Jinxi Lu, Shuhan Liu, Size Wu, Yulu Ren, Zhongxun Guo, Jingjing Gao, Ming Tian, Neng Wan, Kenji Watanabe, Takashi Taniguchi, Bingbing Tong, Guangtong Liu, Li Lu, Yuanbo Zhang, Weidong Luo, Zhiwen Shi, Shuyun Zhou, Quansheng Wu, Guorui Chen
Graphene multilayers exhibit electronic spectra that depend sensitively on both the number of layers and their stacking order. Beyond trilayer graphene, mixed stacking sequences (alternating Bernal and rhombohedral layers) give rise to multiple coexisting low-energy bands. Here we investigate ABCBC-stacked pentalayer graphene, a less-studied non-centrosymmetric mixed sequence. This stacking can be regarded as an ABC (rhombohedral) trilayer on top of an AB (Bernal) bilayer, so its low-energy band structure contains both a cubic band and a parabolic band that hybridize. In transport measurements, we observe an intrinsic band gap at charge neutrality whose magnitude changes asymmetrically under an applied perpendicular displacement field. This behavior reflects the spontaneous layer polarization inherent to the broken inversion symmetry and mirror symmetry. By tuning the displacement field and carrier density, we drive multiple Lifshitz transitions in the Fermi surface topology and realize Landau levels with different degeneracies arising from the multi-flatband system. Remarkably, a v = -6 quantum Hall state emerges at an exceptionally low magnetic field (~20 mT), indicating the interplay between spontaneous symmetry breaking and Berry curvatures. Our results establish mixed-stacked multilayer graphene as a tunable platform with various broken symmetries and multiple flatbands, suitable for exploring emergent correlated electronic states.
Authors: Franco Mayo, Nahual Sobrino, Rosario Fazio, Fabio Taddei, Michele Governale
We study the violation of thermodynamic uncertainty relations (TURs) in hybrid superconducting/normal metal leads coupled to a central region containing localized levels. We find violations of the TUR, also in its formulation recently derived for coherent conductors [Phys. Rev. Lett. 135, 046302 (2025)], due to the presence of macroscopic quantum coherence related to the superconducting condensate. To support our conclusion, we introduce a dephasing probe, demonstrating that the violation is directly correlated with the superconducting coherence, as measured by the pair amplitude in the central region. When the central region is a Cooper-pair splitter, crossed Andreev processes introduce nonlocal superconducting correlations that further enhance the violation. Finally, we derived a new inequality, fulfilled in hybrid superconducting - normal metal systems, in the limit in which quasi-particle tunneling can be ignored.
Authors: Diego Florez-Ablan, Carlos Mejuto-Zaera, Massimo Capone
Accurate and reliable algorithms to solve complex impurity problems are instrumental to a routine use of quantum embedding methods for material discovery. In this context, we employ an efficient selected configuration interaction impurity solver to investigate the role of bath discretization, specifically, bath size and parameterization, in Hamiltonian-based cluster dynamical mean field theory (CDMFT) for the one- and two-orbital Hubbard models. We consider two- and four-site clusters for the single-orbital model and a two-site cluster for the two-orbital model. Our results demonstrate that, for small bath sizes, the choice of parameterization can significantly influence the solution, highlighting the importance of systematic convergence checks. Comparing different bath parameterizations not only reveals the robustness of a given solution but can also provide insights into the nature of different solutions and potential instabilities of the paramagnetic state. We present an extensive analysis of the zero-temperature Mott transition of the paramagnetic half-filled single-band Hubbard model, benchmarking our findings against previous literature. We find that for the single-band model the dependence on parameterization is weak for the largest bath sizes accessible with ASCI, while a tendency towards a nematic solution can be seen when the bath size is small. Building on this, we extend our study to the multi-band regime, where we present the first systematic analysis at zero temperature for two orbitals and a two-site cluster. This setup allows us to assess the effect of nearest-neighbor dynamical correlations on the multi-orbital Mott transition. In this case, some quantitative dependence on the parameterization is retained for the two-orbital model, for instance in the value of the critical interaction for a Mott transition.
Authors: Fernando A. Garcia, Sushma Kumari, Juan Schmidt, Cris Adriano, Aashish Sapkota, Paul C. Canfield, Rebecca Flint, Raquel A. Ribeiro
Systematic investigations of rare-earth ($R$) based intermetallic materials are a leading strategy to reveal the underlying mechanisms governing a range of physical phenomena, such as the formation of a Kondo lattice and competing electronic and magnetic anisotropies. In this work, the magnetic, thermal and transport properties of $R$Co$_{2}$Al$_{8}$ ($R=$ La, Ce, Pr, Nd and Sm) single crystals are presented. LaCo$_{2}$Al$_{8}$ is characterized as a Pauli paramagnet and transport measurements, with the current along and perpendicular to the orthorhombic $c$-axis ($\rho_{c}$ and $\rho_{ab}$, respectively), reveal a clear electronic anisotropy, with $\rho_{ab }\approx(4-7)\rho_{c }$ at $300$ K. We show that CeCo$_{2}$Al$_{8}$ is a Kondo-lattice for which the Kondo coherence temperature $T_{\text{K}}^{*}$, deduced from broad maximums in $\rho_{c}$ and $\rho_{ab}$ at $\approx$ 68 and 46 K, respectively, is also anisotropic. This finding is related to a possible underlying anisotropy of the Kondo coupling in CeCo$_{2}$Al$_{8}$. The Pr- and Nd-based materials present strong easy-axis anisotropy ($c$-axis) and antiferromagnetic (AFM) orders below $T=4.84$ K and $T=8.1$ K, respectively. Metamagnetic transitions from this AFM to a spin-polarized paramagnetic phase state are investigated by isothermal magnetization measurements. The Sm-based compound is also an easy-axis AFM with a transition at $T=21.6$ K.
Authors: Hiroto Adachi, Fuyuki Ando, Takamasa Hirai, Rajkumar Modak, Matthew A. Grayson, Ken-ichi Uchida
Transverse thermoelectric effects interconvert charge and heat currents in orthogonal directions due to the breaking of either time-reversal symmetry or structural symmetry, enabling simple and versatile thermal energy harvesting and solid-state cooling/heating within single materials. In comparison to the complex module structures required for the conventional Seebeck and Peltier effects, the transverse thermoelectric effects provide the complete device structures, potentially resolving the fundamental issue of multi-module degradation of thermoelectric conversion performance. This review article provides an overview of all currently known transverse thermoelectric conversion phenomena and principles, as well as their characteristics, and reclassifies them in a unified manner. The performance of the transverse thermoelectric generator, refrigerator, and active cooler is formulated, showing that thermal boundary conditions play an essential role to discuss their behaviors. Examples of recent application research and material development in transverse thermoelectrics are also introduced, followed by a discussion of future prospects.
Authors: Grayson R. Frazier, Junyi Zhang, Yi Li
We demonstrate that coupling itinerant electrons to a noncollinear classical exchange field can induce anisotropic Josephson coupling between superconducting $d$-vectors, analogous to the Dzyaloshinskii-Moriya and $\Gamma$-type interactions in magnetism. Using perturbative methods, we analyze an $s$-$d$ model on a geometrically frustrated lattice. Noncollinear local spin textures generate spin triplet pairing correlations and can favor spatially varying superconducting order due to anisotropic Josephson couplings between $d$-vectors, endowing a ``pliability'' to the pairing order that competes with the superfluid stiffness. For nonunitary pairing, this spatial texture of $d$-vectors can give rise to anomalous vortices in the absence of an external magnetic field. We further predict a Josephson diode effect with efficiency proportional to the spin chirality of the underlying magnetic texture. These results establish a link between frustrated magnetism and spatial textures of triplet superconducting pairing, with implications for a range of materials such as Mn$_3$Ge and $4$Hb-TaS$_2$, where superconductivity can be proximity-induced or intrinsic.
Authors: Yongxin Zeng, Andrew J. Millis
Quantum geometry has been shown to make an important contribution to the superfluid stiffness of superconductors, especially for flat-band systems such as moiré materials. In this work we use mean-field theory to derive an expression for the superfluid stiffness of time-reversal symmetric superconductors at zero temperature by computing the energy of the mean-field ground state as a function of pairing momentum. We show that the quantum geometric contribution to superfluid stiffness is a consequence of broken Galilean invariance in the interaction Hamiltonian, arising from momentum-dependent form factors related to the momentum dependence of Bloch states. The effects of broken Galilean invariance are not fully parametrized by the quantum metric considered in previous work. We obtain general lower and upper bounds that apply to both continuum and lattice models and present numerical calculations of the precise value in several important cases. The superfluid stiffness of superconductivity in a Landau level saturates the lower bound and the superfluid stiffness of the other cases we consider is close to the general lower bound we derive. In multilayer rhombohedral graphene the geometric contribution is shown not to be the dominant contribution to the superfluid stiffness, despite the flat band behavior in the vicinity of the Fermi level. Finally, assuming contact interaction and uniform pairing, we show that the superfluid stiffness is proportional to the ``minimal quantum metric" introduced in previous work. We provide a continuum version of the minimal quantum metric and explain its physical origin.
Authors: M. H. Carvalho, D. Zau, A. P. Reyes, R. Cong, S. D. House, H. P. Pizzi, A. M. Caffer, D.S. Passos, R. C. Santos, G. S. Freitas, K. R. Pirota, R. R. Urbano, P. J. G. Pagliuso
In this work, we have explored the Metallic-Flux Nanonucleation method to synthesize single crystals and nanowires (diameter $\approx$ 170 nm) of CeIn$_{3}$ and compare their properties. The effects of reduced dimensionality were systematically investigated using Energy Dispersive Spectroscopy (EDS), Selected area electron diffraction (SAED), magnetic susceptibility, heat capacity, and Nuclear Magnetic Resonance (NMR). Semi-quantitative EDS analysis revealed a Ce:In ratio of 1:3.1(1), and the SAED results confirmed that the nanowires are polycrystalline with a cubic unit cell. Magnetic susceptibility, specific heat, and NMR data indicated a suppression of the antiferromagnetic transition to $T_N$ $\approx$ 2.4 K compared to the bulk value ($\approx$ 10 K). Furthermore, NMR analysis at temperatures below 2.8 K showed a reduced quadrupole frequency, $\nu_Q$ $\approx$ 1.77(2) MHz, and provided evidence of polycrystalline nanowires formed within the nanoporous alumina template, in agreement with SAED results. We attribute these findings to an increasing magnetic order frustration induced by dimensionality in CeIn$_{3}$ nanowires.
Authors: Byjesh N. Radhakrishnan, Francesco Serafin, Thomas L. Schmidt, Étienne Fodor
In many active systems, swimmers collectively stir the surrounding fluid to stabilize some self-sustained vortices. The resulting nonequilibrium state is often referred to as active turbulence, by analogy with the turbulence of passive fluids under external stirring. Although active turbulence clearly operates far from equilibrium, it can be challenging to pinpoint which emergent features primarily control the deviation from an equilibrium reversible dynamics. Here, we reveal that dynamical irreversibility essentially stems from singularities in the active stress. Specifically, considering the coupled dynamics of the swimmer density and the stream function, we demonstrate that the symmetries of vortical flows around defects determine the overall irreversibility. Our detailed analysis leads to identifying specific configurations of defect pairs as the dominant contribution to irreversibility.
Authors: Jihyung Kim, Dongchang Kim, Seung-Gi Lee, Yung-Cheng Li, Jae-Chun Jeon, Jiho Yoon, Sachio Komori, Ryotaro Arakawa, Tomoyasu Taniyama, Stuart S. P. Parkin, Kun-Rok Jeon
We report a significant reduction of low-temperature damping losses in tensile-strained, ultrathin Y3Fe5O12 (YIG) films grown by pulsed laser deposition, exhibiting ultralow damping constants and tunable magnetic anisotropy. Comparative broadband FMR measurements show that tensile-strained YIG films on Gd3Sc2Ga3O12 (GSGG) retain low damping even at nanometer thicknesses and cryogenic temperatures, outperforming relaxed films on Gd3Ga5O12. Based on static magnetometry measurements and microstructural characterization, we attribute these enhanced dynamic properties to the suppression of interdiffusion across the YIG/GSGG interface, resulting from enhanced chemical stability and favorable growth kinetics by the presence of Sc. Our findings highlight the importance of chemical and kinetic factors in achieving few-nanometer-thick YIG film with negligible low-temperature damping dissipation and perpendicular magnetic anisotropy for cryogenic spintronic applications.
Authors: Khachatur Nazaryan, Filippo Gaggioli, Yi Teng, Liang Fu
Neural networks (NNs) have great potential in solving the ground state of various many-body problems. However, several key challenges remain to be overcome before NNs can tackle problems and system sizes inaccessible with more established tools. Here, we present a general and efficient method for learning the NN representation of an arbitrary many-body complex wave function from its $N$-particle probability density and probability current density. Having reached overlaps as large as $99.9\%$, we employ our neural wave function for pre-training to effortlessly solve the fractional quantum Hall problem with Coulomb interactions and realistic Landau-level mixing for as many as $25$ particles. Our work demonstrates efficient, accurate simulation of highly-entangled quantum matter using general-purpose deep NNs enhanced with physics-informed initialization.
Authors: Jonas B. Profe, Jakša Vučičević, P. Peter Stavropoulos, Malte Rösner, Roser Valentí, Lennart Klebl
Solving the many-electron problem, even approximately, is one of the most challenging and simultaneously most important problems in contemporary condensed matter physics with various connections to other fields. The standard approach is to follow a divide and conquer strategy that combines various numerical and analytical techniques. A crucial step in this strategy is the derivation of an effective model for a subset of degrees of freedom by a procedure called downfolding, which often corresponds to integrating out energy scales far away from the Fermi level. In this work we present a rigorous formulation of this downfolding procedure, which complements the renormalization group picture put forward by Honerkamp [PRB 85, 195129 (2012)}]. We derive an exact effective model in an arbitrarily chosen target space (e.g. low-energy degrees of freedom) by explicitly integrating out the the rest space (e.g. high-energy degrees of freedom). Within this formalism we state conditions that justify a perturbative truncation of the downfolded effective interactions to just a few low-order terms. Furthermore, we utilize the exact formalism to formally derive the widely used constrained random phase approximation (cRPA), uncovering underlying approximations and highlighting relevant corrections in the process. Lastly, we detail different contributions in the material examples of fcc Nickel and the infinite-layer cuprate SrCuO$_2$. Our results open up a new pathway to obtain effective models in a controlled fashion and to judge whether a chosen target space is suitable.
Authors: Cristian Moreno-Pulido, Rachael Olwande, Tim Myers, Francesc Font
The shrinking core model describes the reaction of a spherical solid particle with a surrounding fluid. In this work, we revisit the SCM by deriving it from the underlying physical processes and performing a careful non-dimensionalisation, which highlights the limitations of the commonly used pseudo-steady-state approximation, particularly in liquid-solid systems where fluid and solid densities are comparable. To address these limitations, we derive approximate analytical solutions using a perturbation method that improves upon the pseudo-steady-state model. We also obtain a small-time solution capturing early transient behavior. A semi-implicit finite difference scheme is implemented to solve the full model numerically and benchmark the analytical approximations. We demonstrate that the perturbation solution provides significantly improved accuracy over the pseudo-steady-state model, especially in diffusion-limited regimes. Finally, we propose a simple fitting procedure combining the perturbation with the early-time solutions to estimate physical parameters from experimental data at minimal computational cost.
Authors: Eric V. Woods (1), Xinren Chen (1), Yuwei Zhang (1), J. Manoj Prabhakar (1), Patricia Jovičević-Klug (1), Matic Jovičević-Klug (1), Mahander P. Singh (1), Yujun Zhao (1), Siyuan Zhang (1), Stefan Zaefferer (1), Jian Liu (2), Yug Joshi (1), Baptiste Gault (1 and 3) ((1) Max Planck Institute for Sustainable Materials, Düsseldorf, Germany, (2) University of British Columbia, Kelowna, Canada, (3) Imperial College London, London, UK)
The role of Li-based batteries in the electrification of society cannot be understated, however their operational lifetime is often limited by the formation of dendrites, i.e. the localised deposition of Li that can cause shorts between the two electrodes leading to the failure of the battery. Nanocrystalline bimetallic current collectors can be used for anode-free Li-metal batteries, with improved Li plating and limited or suppressed formation of dendrites. Here, we demonstrate that the microstructure of an alpha-Brass current collector, Cu 63% Zn 37%, used in an anode-free Li-metal battery evolves during cycling. It initially had a nanocrystalline deformation layer approximately 80 nm in thickness after polishing. After 100 cycles, the initial deformed brass layer was partially converted to a ternary Laves phase Cu3ZnLi2 within a nanocrystalline brass matrix that grew to 200 - 250 nm in thickness. Upon Li stripping, the phase partially decomposes electrochemically, but what remains can sequester Li thus forming "dead Li" thereby contributing to capacity loss. We propose a mechanism for the microstructural evolution including dynamic recrystallization and phase formation. Since this ternary Laves phase emerges during electrochemical cycling alone, binary alloy current collectors must be assessed for metastable ternary phase formation under different cycling conditions to either stabilize and exploit such phases or electrochemically fully strip them.
Authors: Zesen Fu, Mengli Hu, Aolin Li, Haiming Duan, Junwei Liu, Fangping Ouyang
We present a theoretical and first-principles study of a two-dimensional altermagnet exhibiting spin-valley locking and strain-tunable topological phases. By constructing a minimal tight-binding model constrained by altermagnetic symmetry, we show that biaxial strain can drive a transition from a trivial insulator to a type-II quantum spin Hall (QSH) phase. Furthermore, we derive an analytical strain-induced perturbation theory that identifies two critical curves, dividing the phase space into four regions corresponding to a trivial insulator, a type-II QSH phase, and two quantum anomalous Hall phases with opposite Chern numbers. Remarkably, the Chern number can be reversed purely by changing the strain direction --without modifying magnetization or applying magnetic fields. The model reveals a universal phase diagram for materials with the same symmetry and valley structure. First-principles calculations on monolayer CrO confirm the predicted topological transitions, establishing strain engineering as an effective route for topological control in two-dimensional altermagnetic materials.
Authors: Masoumeh Davoudiniya, Jonas Fransson, Biplab Sanyal
$\beta_{12}$-borophene nanoribbons (BNRs) exhibit magnetic zigzag edges, while other edge configurations are nonmagnetic. However, when the source, central, and drain regions of a logic device are all composed of zigzag BNRs (ZBNRs), the resulting spin polarization remains weak, unless a high voltage is applied. In this work, we demonstrate that lattice vibrations-introduced for example, via a thermal bath coupled to the central BNR-can enhance spin polarization in ZBNRs. This enhancement manifests as marked changes in the current-voltage characteristics, enabling direct experimental probing. In contrast, nonmagnetic edge configurations exhibit phonon-enhanced charge transport. We employ a tight-binding approach augmented with local electron-phonon interactions described by the Holstein model, and compute the phonon-renormalized Green's functions and transport currents using the Landauer-Büttiker formalism. The mechanism is supported by analyzing both spinless and spinful electronic dispersions and the corresponding density of states. Compared to the phonon-free edges, structural distortions lead to anisotropic electron-phonon couplings, which significantly modify both charge and spin transport. These results position phonon as an effective tuning parameter for optimizing borophene-based logic devices via engineered edge configurations.
Authors: Ran-Chen He, Jia-Xi Zeng, Shu Yang, Cong Wang, Qi-Jun Ye, Xin-Zheng Li
To simulate indistinguishable particles, recent studies of path-integral molecular dynamics formulated their partition function $Z$ as a recurrence relation involving a variable $\xi$, with $\xi=1$(-1) for bosons (fermions). Inspired by Lee-Yang phase transition theory, we extend $\xi$ into the complex plane and reformulate $Z$ as a polynomial in $\xi$. By analyzing the distribution of the partition function zeros, we gain insights into the analytical properties of indistinguishable particles, particularly regarding the fermion sign problem (FSP). We found that at 0~K, the partition function zeros for $N$-particles are located at $\xi=-1$, $-1/2$, $-1/3$, $\cdots$, $-1/(N-1)$. This distribution disrupts the analytic continuation of thermodynamic quantities, expressed as functions of $\xi$ and typically performed along $\xi=1\to-1$, whenever the paths intersect these zeros. Moreover, we highlight the zero at $\xi = -1$, which induces an extra term in the free energy of the fermionic systems compared to ones at other $\xi=e^{i\theta}$ values. If a path connects this zero to a bosonic system with identical potential energies, it brings a transition resembling a phase transition. These findings provide a fresh perspective on the successes and challenges of emerging FSP studies based on analytic continuation techniques.
Authors: Rasmus S. Nielsen, Axel G. Medaille, Arnau Torrens, Oriol Segura-Blanch, Seán R. Kavanagh, David O. Scanlon, Aron Walsh, Edgardo Saucedo, Marcel Placidi, Mirjana Dimitrievska
Selenium is experiencing renewed interest as a elemental semiconductor for a range of optoelectronic and energy applications due to its irresistibly simple composition and favorable wide bandgap. However, its high volatility and low radiative efficiency make it challenging to assess structural and optoelectronic quality, calling for advanced, non-destructive characterization methods. In this work, we employ a closed-space encapsulation strategy to prevent degradation during measurement and enable sensitive probing of vibrational and optoelectronic properties. Using temperature-dependent Raman and photoluminescence spectroscopy, we investigate grown-in stress, vibrational dynamics, and electron-phonon interactions in selenium thin films synthesized under nominally identical conditions across different laboratories. Our results reveal that short-range structural disorder is not intrinsic to the material, but highly sensitive to subtle processing variations, which strongly influence electron-phonon coupling and non-radiative recombination. We find that such structural disorder and grown-in stress likely promote the formation of extended defects, which act as dominant non-radiative recombination centers limiting carrier lifetime and open-circuit voltage in photovoltaic devices. These findings demonstrate that the optoelectronic quality of selenium thin films can be significantly improved through precise control of synthesis and post-deposition treatments, outlining a clear pathway toward optimizing selenium-based thin film technologies through targeted control of crystallization dynamics and microstructural disorder.
Authors: Kaan Alp Yay, W. Joe Meese, Elliot Kisiel, Matthew J. Krogstad, Anisha G. Singh, Rafael M. Fernandes, Zahir Islam, Ian R. Fisher
Electronic nematic order is a correlated phase of matter in which low-energy electronic states spontaneously break a discrete rotational symmetry of a crystal lattice. Bilinear coupling between the electronic nematic and strains of the same symmetry yields a single pseudoproper ferroelastic phase transition at which both the nematic and lattice strain onset concurrently. To minimize elastic energy, the crystal forms structural twin domains, each with a distinct orientation of the nematic director (i.e. each with a specific sign of the induced shear strain). While the effects of externally induced strains on these domains are well established, the intrinsic behavior of spontaneous strain fields within individual domains has been hitherto unexplored, largely due to the lack of appropriate experimental tools. Here, we report the discovery of spontaneous mesoscopic strain waves within individual nematic domains of an underdoped iron-based superconductor, observed using dark-field X-ray microscopy (DFXM). This technique combines high spatial and reciprocal-space resolution with full-field, bulk-sensitive imaging, enabling direct visualization of subdomain strain modulations emerging concurrently with the onset of nematic order. The elastic compatibility relations that govern inhomogeneous strains in continuous solids provide a natural mechanism for the emergent strain waves that we observe. Our findings reveal a broadly relevant form of strain self-organization and position DFXM as a powerful tool for probing the local interplay between lattice strain and electronic order.
Authors: W. Joe Meese, Rafael M. Fernandes
Electronic nematicity is widely observed in quantum materials with varying degrees of electronic correlation, manifesting through charge, spin, orbital, or superconducting degrees of freedom. A phenomenological model capable of describing this broad set of systems must also account for nemato-elasticity, by which nematic and elastic degrees of freedom become intertwined. However, being a tensor gauge field theory, elasticity must satisfy the compatibility relations which guarantee the integrability of lattice deformations. Here, we develop a formalism for nemato-elasticity that manifestly respects the elastic compatibility relations. We show that these constraints bifurcate the phase space of nematic fluctuations into two orthogonal sectors: one compatible and thus critical, the other incompatible and therefore gapped. The suppression of the latter leads to universal direction-selective nematic criticality in any crystal lattice. Moreover, the critical nematic modes are protected from pinning effects induced by microscopic defect strains, which necessarily induce both longitudinal and transverse correlated random fields. Finally, our results also reconcile seemingly contradictory nematic phenomena, such as the mean-field character of the nematic transition and the widespread presence of domain formation.
Authors: W. Joe Meese, Rafael M. Fernandes
The defining property of electronic nematicity -- the spontaneous breaking of rotational symmetry -- implies an unavoidable coupling between the nematic order parameter and elastic strain fields, known as nemato-elasticity. While both quantities are rank-2 tensors, the strain tensor is constrained through the Saint Venant compatibility relations. These three coupled second-order partial differential equations arise from the lattice displacement vector's role as a potential field, and they reflect the underlying gauge invariance of geometric deformations which are violated only in the presence of crystalline defects. In this work, we develop a theory of nemato-elasticity that incorporates elastic compatibility explicitly through a co-rotating helical basis. With our formalism, we show elasticity bestows tensor compatibility upon the nematic order parameter by suppressing incompatible nematic fluctuations. As a result, nemato-elasticity is markedly different from bare nematicity. In ideal media devoid of defects, we show the suppression of incompatible nematicity underlies direction-selective criticality, even in the absence of crystalline anisotropy. In systems with defects, meanwhile, we show that elastic pinning fields emanate from quenched defects, generating random longitudinal and transverse conjugate fields for the local nematic order parameter. The coexistence of direction-selective nematic criticality with pinning effects from random fields is explained within our theory from the transformation to the helical basis, implying that local experimental probes of nematicity will be influenced by a linear -- but nonlocal -- combination of long-ranged and short-ranged helical nematic modes. Because the compatibility relations are gauge constraints endowed in the isotropic medium, our results constitute universal features of nemato-elastic criticality present in all crystalline systems.
Authors: M. Schuyler Moss, Alev Orfi, Christopher Roth, Anirvan M. Sengupta, Antoine Georges, Dries Sels, Anna Dawid, Agnes Valenti
Neural quantum states (NQS) provide flexible wavefunction parameterizations for numerical studies of quantum many-body physics. While inspired by deep learning, it remains unclear to what extent NQS share characteristics with neural networks used for standard machine learning tasks. We demonstrate that NQS exhibit the double descent phenomenon, a key feature of modern deep learning, where generalization worsens as network size increases before improving again in an overparameterized regime. Notably, we find the second descent to occur only for network sizes much larger than the Hilbert space dimension, indicating that NQS typically operate in an underparameterized regime, where increasing network size can degrade generalization. Our analysis reveals that the optimal network size in this regime depends on the number of unique training samples, highlighting the importance of sampling strategies. These findings suggest the need for symmetry-aware, physics-informed architecture design, rather than directly adopting machine learning heuristics.
Authors: Sascha Lill
Recently, Benedikter and the author proved an approximate formula for the momentum distribution of a 3d fermionic gas interacting by a short-range pair potential in the mean-field regime, within a trial state close to the ground state. Here, we derive an exact formula for the momentum distribution in this trial state, using a diagrammatic formalism due to Friedrichs. We further demonstrate how the formula of Benedikter and the author arises from a restriction of the contributing diagrams to those corresponding to a bosonization approximation.
Authors: Donghoon Kim, Tomotaka Kuwahara, Keiji Saito
The area law of the bipartite information measure characterizes one of the most fundamental aspects of quantum many-body physics. In thermal equilibrium, the area law for the mutual information universally holds at arbitrary temperatures as long as the systems have short-range interactions. In systems with power-law decaying interactions, $r^{-\alpha}$ ($r$: distance), conditions for the thermal area law are elusive. In this work, we aim to clarify the optimal condition $\alpha> \alpha_c$ such that the thermal area law universally holds. A standard approach to considering the conditions is to focus on the magnitude of the boundary interaction between two subsystems. However, we find here that the thermal area law is more robust than this conventional argument suggests. We show the optimal threshold for the thermal area law by $\alpha_c= (D+1)/2$ ($D$: the spatial dimension of the lattice), assuming a power-law decay of the clustering for the bipartite correlations. Remarkably, this condition encompasses even the thermodynamically unstable regimes $\alpha < D$. We verify this condition numerically, finding that it is qualitatively accurate for both integrable and non-integrable systems. Unconditional proof of the thermal area law is possible by developing the power-law clustering theorem for $\alpha > D$ above a threshold temperature. Furthermore, the numerical calculation for the logarithmic negativity shows that the same criterion $\alpha > (D+1)/2$ applies to the thermal area law for quantum entanglement.
Authors: Viviana Viggiano, Romain Bachelard, Fabio Deelan Cunden, Paolo Facchi, Robin Kaiser, Saverio Pascazio, Francesco V. Pepe, Antonello Scardicchio
In the collective photon emission from atomic clouds both the atomic transition frequency and the decay rate are modified compared to a single isolated atom, leading to the effects of superradiance and subradiance. In this article, we analyse the properties of the Euclidean random matrix associated to the radiative dynamics of a cold atomic cloud, previously investigated in the contexts of photon localization and Dicke super- and subradiance. We present evidence of a new type of phase transition, surprisingly controlled by the cooperativeness parameter, rather than the spatial density or the diagonal disorder. The numerical results corroborate the occurrence of such a phase transition at a critical value of the cooperativeness parameter, above which the lower edge of the spectrum vanishes exhibiting a macroscopic accumulation of eigenvalues. Independent evaluations based on the two phenomena provide the same value of the critical cooperativeness parameter.
Authors: Ali Mollabashi, Saleh Rahimi-Keshari
We investigate the dynamics of information scrambling in bosonic systems undergoing Gaussian unitary evolution associated with quadratic Hamiltonians. For initial Gaussian states, we observe the disappearance of the memory effect in the entanglement dynamics of disjoint blocks under Gaussian random local dynamics. In addition, we show that randomness in the Hamiltonian causes the tripartite mutual information to saturate at relatively large negative values. Therefore, despite being integrable, these systems exhibit information-scrambling diagnostics that mirror those observed in chaotic systems. We note, however, that random quadratic Hamiltonians can have a component exhibiting Wigner-Dyson energy-level statistics; for non-Gaussian states within the corresponding subspace, these systems can display chaotic behavior. Our results provide insight into the Gaussian dynamics of continuous-variable systems, which are useful and available resources for quantum information processing.
Authors: Qianyang Chen, Mikhail Prokopenko
Collective behaviours are frequently observed to self-organise to criticality. Existing proposals to explain these phenomena are fragmented across disciplines and only partially answer the question. This primer compares the underlying, intrinsic, utilities that may explain the self-organisation of collective behaviours near criticality. We focus on information-driven approaches (predictive information, empowerment, and active inference), as well as an approach incorporating both information theory and thermodynamics (thermodynamic efficiency). By interpreting the Ising model as a perception-action loop, we compare how different intrinsic utilities shape collective behaviour and analyse the distinct characteristics that arise when each is optimised. In particular, we highlight that thermodynamic efficiency -- measuring the ratio of predictability gained by the system to its energy costs -- reaches its maximum at the critical regime. Finally, we propose the Principle of Super-efficiency, suggesting that collective behaviours self-organise to the critical regime where optimal efficiency is achieved with respect to the entropy reduction relative to the thermodynamic costs.
Authors: Nakshatra Gangopadhay, Sayan Choudhury
Controlling the dynamics of quantum many-body systems is crucial for developing quantum technologies. This work demonstrates that counter-diabatic (CD) driving provides a powerful tool for steering collective spin systems along entangled trajectories for a long time. In particular, CD driving leads to approximate stroboscopic freezing and eternal entanglement oscillations for a large class of initial states in the periodically driven Lipkin-Meshkov-Glick model. Intriguingly, CD driving generates spin squeezing and its associated metrologically useful multipartite entanglement at the mid-point of every drive cycle, when the system is initially prepared in a fully x-polarized state. The CD driving induced non-ergodic dynamics is accompanied by a decrease in the average eigenstate entanglement and inverse participation ratio, thereby signalling greater eigenstate localization. Our work opens a new route to evade Floquet heating and control entanglement generation in collective spin systems.
Authors: Atsuhisa Ota
We conduct a mode analysis of a general $U(1)$-charged first-order relativistic hydrodynamics within the framework of effective field theory for dissipative fluids in flat Minkowski spacetime. We derive the most general quadratic action for hydrodynamic modes, including stochastic noise, and analyze the corresponding dispersion relations in a consistent gradient expansion. We argue that spontaneous breaking of spacetime symmetry arises in the presence of a local thermal state specified by a local timelike four-vector. We demonstrate that hydrodynamical perturbations can be identified as Nambu-Goldstone (NG) modes, analogous to their embedding in global $U(1)$-invariant theories. We find that frame-invariant combinations of hydrodynamic transport coefficients determine the first-order dispersion relations in the low-energy limit, making the mode analysis manifestly independent of the choice of hydrodynamic frame. Assuming local Kubo-Martin-Schwinger (KMS) symmetry and unitarity of the underlying UV theory, we show that first-order hydrodynamics is stable if the enthalpy density is positive.
Authors: Amaresh Sahu
An arbitrary Lagrangian--Eulerian finite element method and numerical implementation for curved and deforming lipid membranes is presented here. The membrane surface is endowed with a mesh whose in-plane motion need not depend on the in-plane flow of lipids. Instead, in-plane mesh dynamics can be specified arbitrarily. A new class of mesh motions is introduced, where the mesh velocity satisfies the dynamical equations of a user-specified two-dimensional material. A Lagrange multiplier constrains the out-of-plane membrane and mesh velocities to be equal, such that the mesh and material always overlap. An associated numerical inf--sup instability ensues, and is removed by adapting established techniques in the finite element analysis of fluids. In our implementation, the aforementioned Lagrange multiplier is projected onto a discontinuous space of piecewise linear functions. The new mesh motion is compared to established Lagrangian and Eulerian formulations by investigating a preeminent numerical benchmark of biological significance: the pulling of a membrane tether from a flat patch, and its subsequent lateral translation.
Authors: Lucia Vilchez-Estevez, Raul A. Santos, Sabrina Yue Wang, Filippo Maria Gambetta
Understanding low-energy excitations in fermionic systems is crucial for their characterization. They determine the response of the system to external weak perturbations, its dynamical correlation functions, and provide mechanisms for the emergence of exotic phases of matter. In this work, we study the spin excitation spectra of the 1D Fermi-Hubbard model using a digital quantum processor. Introducing a protocol that is naturally suited for simulation on quantum computers, we recover the retarded spin Green's function from the time evolution of simple observables after a specific quantum quench. We exploit the robustness of the protocol to perturbations of the initial state to minimize the quantum resources required for the initial state preparation, and to allocate the majority of them to a Trotterized time-dynamics simulation. This, combined with the intrinsic resilience to noise of the protocol, allows us to accurately reconstruct the spin excitation spectrum for large instances of the 1D Fermi-Hubbard model without making use of expensive error mitigation techniques, using up to 30 qubits of an IBM Heron r2 device.
Authors: Simon Becker, Zhongkai Tao, Mengxuan Yang
This paper provides a mathematical perspective on fragile topology phenomena in condensed matter physics. In dimension $d \leq 3$, vanishing Chern classes of bundles of Bloch eigenfunctions characterize operators with exponentially localized Wannier functions (these functions form convenient bases of spectrally determined subspaces of $L^2$). However, for systems with additional symmetries, such as the $C_{2}T$ (space-time reversal) or the $PT$ (parity-time) symmetry, a set of exponentially localized Wannier functions compatible with such symmetry may not exist. We show that for rank 2 Bloch bundles with such symmetry, non-trivial Euler classes are obstructions to constructing exponentially localized compatible Wannier functions. We also show that this obstruction can be lifted by adding additional Bloch bundles with the symmetry, even though the Stiefel--Whitney class of the total bundle is non-trivial. This allows a construction of exponentially localized Wannier functions compatible with the symmetry and that is referred to as topological fragility.
Authors: Guillaume Maitrier, Grégoire Loeper, Kiyoshi Kanazawa, Jean-Philippe Bouchaud
Understanding the impact of trades on prices is a crucial question for both academic research and industry practice. It is well established that impact follows a square-root impact as a function of traded volume. However, the microscopic origin of such a law remains elusive: empirical studies are particularly challenging due to the anonymity of orders in public data. Indeed, there is ongoing debate about whether price impact has a mechanical origin or whether it is primarily driven by information, as suggested by many economic theories. In this paper, we revisit this question using a very detailed dataset provided by the Japanese stock exchange, containing the trader IDs for all orders sent to the exchange between 2012 and 2018. Our central result is that such a law has in fact microscopic roots and applies already at the level of single child orders, provided one waits long enough for the market to "digest" them. The mesoscopic impact of metaorders arises from a "double" square-root effect: square-root in volume of individual impact, followed by an inverse square-root decay as a function of time. Since market orders are anonymous, we expect and indeed find that these results apply to any market orders, and the impact of synthetic metaorders, reconstructed by scrambling the identity of the issuers, is described by the very same square-root impact law. We conclude that price impact is essentially mechanical, at odds with theories that emphasize the information content of such trades to explain the square-root impact law.
Authors: Arman Duha, S. E. Begg, Thomas Bilitewski
We investigate phase transitions in the nonequilibrium dynamics of power-law interacting spin-1/2 bilayer XXZ models, which have recently been shown to allow generation of entanglement in the form of two-mode squeezing. We find a transition between a collective phase characterized by Heisenberg limited squeezing and a partially collective phase with scalable squeezing. We identify universal scaling of the squeezing dynamics in terms of system parameters and a divergent time-scale, establishing these as distinct dynamical phases within the framework of non-equilibrium critical phenomena. Our work demonstrates a novel dynamical phase transition with potential applications in quantum sensing and quantum simulation in cold-atomic, molecular or Rydberg platforms.
Authors: Claudio Bonati, Ivan Soler Calero
We numerically investigate the multicritical behavior of the three dimensional lattice system in which a SU(2) gauge field is coupled to two flavors of scalar fields transforming in the fundamental representation of the gauge group. In this system a multicritical point is present, where the global symmetry O(2)$\oplus$O(3) gets enlarged to O(5). Such a symmetry enlargement is hindered for generic systems by the instability of the O(5) multicritical point, but the SU(2) gauge symmetry prevents the appearance of the term triggering the instability. All the numerical results obtained in this lattice gauge model fully support the expectations coming from the O(2)$\oplus$O(3) multicritical Landau-Ginzburg-Wilson $\phi^4$ theory, and we discuss possible implications of these results for some models of deconfined quantum criticality.
Authors: John L. Weber, Rishabh D. Guha, Garvit Agarwal, Yujing Wei, Aidan A. Fike, Xiaowei Xie, James Stevenson, Biswajit Santra, Richard A. Friesner, Karl Leswing, Mathew D. Halls, Robert Abel, Leif D. Jacobson
Machine learning force fields (MLFFs) have emerged as a sophisticated tool for cost-efficient atomistic simulations approaching DFT accuracy, with recent message passing MLFFs able to cover the entire periodic table. We present an invariant message passing MLFF architecture (MPNICE) which iteratively predicts atomic partial charges, including long-range interactions, enabling the prediction of charge-dependent properties while achieving 5-20x faster inference versus models with comparable accuracy. We train direct and delta-learned MPNICE models for organic systems, and benchmark against experimental properties of liquid and solid systems. We also benchmark the energetics of finite systems, contributing a new set of torsion scans with charged species and a new set of DLPNO-CCSD(T) references for the TorsionNet500 benchmark. We additionally train and benchmark MPNICE models for bulk inorganic crystals, focusing on structural ranking and mechanical properties. Finally, we explore multi-task models for both inorganic and organic systems, which exhibit slightly decreased performance on domain-specific tasks but surprising generalization, stably predicting the gas phase structure of $\simeq500$ Pt/Ir organometallic complexes despite never training to organometallic complexes of any kind.
Authors: Mehran Z-Abyaneh
We write the Lagrangian of a time-reversal symmetry broken three dimensional Weyl superconductor in a covariant form. Then, based on an analogy with the Nambu Jona-Lasinio model and by employing the Fierz transformations, we demonstrate that new collective modes should exist in such a system, including a pseudo-scalar Nambu-Goldstone boson and its corresponding amplitude mode plus a vector and an axial-vector collective mode. It is also observed that the pseudo-scalar mode can become massive due to an explicit chiral symmetry breaking term in the Lagrangian. Analogous to pions in low-energy QCD, such a massive pseudo-scalar mode can decay via the axial anomaly.
Authors: Jonathan E. Moussa
The development of semiempirical models to simplify quantum mechanical descriptions of atomistic systems is a practice that started soon after the discovery of quantum mechanics and continues to the present day. There are now many methods for atomistic simulation with many software implementations and many users, on a scale large enough to be considered as a software market. Semiempirical models occupied a large share of this market in its early days, but the research activity in atomistic simulation has steadily polarized over the last three decades towards general-purpose but expensive ab initio quantum mechanics methods and fast but special-purpose molecular mechanics methods. I offer perspective on recent trends in atomistic simulation from the middle ground of semiempirical modeling, to learn from its past success and consider its possible paths to future growth. In particular, there is a lot of ongoing research activity in combining semiempirical quantum mechanics with machine learning models and some unrealized possibilities of tighter integration between ab initio and semiempirical quantum mechanics with more flexible theoretical frameworks and more modular software components.
Authors: Rui Guan, Junjie Liu
Correlated quantum systems can exhibit thermodynamic behaviors that defy classical expectations, with anomalous energy flow (AEF) against temperature gradients serving as a paradigmatic example. While AEF has been shown to arise from the consumption of initial quantum correlations, little is known about whether AEF can occur without correlation depletion, or if analogous anomalous transport exists for conserved quantities--dubbed charges--other than energy. Here, we develop a general global-local thermodynamic approach to describe charge exchange between arbitrary correlated quantum systems. For energy-conserving systems, we analytically rule out AEF in initially uncorrelated states, even with the involvement of quantum catalysts, thereby complementing existing studies. In contrast, in systems with multiple conserved charges, we uncover a mechanism for AEF that requires no initial correlations but is instead induced by a drag effect from normal flows of non-energy charges. Furthermore, by treating all conserved charges on equal footing, we generalize AEF to a broader concept of anomalous charge flow, applicable to any conserved charge. We confirm theoretical expectations with numerical examples. These findings deepen our understanding of nonequilibrium quantum thermodynamics and open new avenues for controlling transport phenomena in correlated quantum systems.
Authors: Emad Chaparian
A comprehensive Darcy-type law for viscoplastic fluids is proposed. Different regimes of yield-stress fluid flow in porous media can be categorised based on the Bingham number (i.e. the ratio of the yield stress to the characteristic viscous stress). In a recent study (Chaparian, J. Fluid Mech., vol. 980, A14, 2024), we addressed the yield/plastic limit (infinitely large Bingham number), namely, the onset of flow when the applied pressure gradient is just sufficient to overcome the yield stress resistance and initiate the flow. A purely geometrical universal scale was derived for the non-dimensional critical pressure gradient, which was thoroughly validated against computational data. In the present work, we investigate the Newtonian limit (infinitely large pressure difference compared to the yield stress of the fluid - ultra low Bingham number) both theoretically and computationally. We then propose a Darcy-type law applicable across the entire range of Bingham numbers by combining the mathematical models of the yield/plastic and Newtonian limits. Exhaustive computational data generated in this study (using augmented Lagrangian method coupled with anisotropic adaptive mesh at the pore scale) confirm the validity of the theoretical proposed law.
Authors: Pritam Chattopadhyay, Avijit Misra, Tanmoy Pandit, Goutam Paul
According to the Landauer principle, any logically irreversible process accompanies entropy production, which results in heat dissipation in the environment. Erasing of information, one of the primary logically irreversible processes, has a lower bound on heat dissipated into the environment, called the Landauer bound (LB). However, the practical erasure processes dissipate much more heat than the LB. Recently, there have been a few experimental investigations to reach this bound both in the classical and quantum domains. There has also been a spate of activities to enquire about this LB in finite time, with finite-size heat baths, non-Markovian and nonequilibrium environments in the quantum regime, where the effects of fluctuations and correlation of the systems with the bath can no longer be ignored. This article provides a comprehensive review of the recent progress on the Landauer bound, which serves as a fundamental principle in the thermodynamics of computation. We also provide a perspective for future endeavors in these directions. Furthermore, we review the recent explorations toward establishing energetic bounds of a computational process. We also discuss the thermodynamic aspects of error correction, which is an indispensable part of information processing and computations. In doing so, we briefly discuss the basics of these fields to provide a complete picture.
Authors: Daniel M. B. Lesko, Tobias Weitz, Simon Wittigschlager, Selina Nöcker, Weizhe Li, Peter Hommelhoff, Ofer Neufeld
Light-field-driven photocurrents represent a powerful tool for generating photocurrents without external bias in light-matter systems that lack inversion symmetry. While these photocurrents are used in electronic applications, such as current sources, switches, and photovoltaics, their presence can also be used to probe material properties in and out of equilibrium, such as topology. Here we advance this path of light-field-driven photocurrent spectroscopy by utilizing tailored laser fields for ultrafast photocurrent generation to study time-reversal symmetry (TRS) broken phases. We employ combinations of bichromatic linearly-polarized laser beams that individually respect mirror (spatial) and time-reversal symmetry, individually precluding photocurrents, but when combined can break symmetries and generate photocurrents. We show, both theoretically and experimentally, that unique choices of the relative polarization angle and two-color phase imposes a forbidden photocurrent selection rule in TRS-invariant systems, as the tailored light maintains TRS while breaking all other spatial symmetries. We then employ state-of-the-art ab-initio simulations to validate this physical mechanism, and, crucially, predict its breaking in materials with intrinsically-broken TRS, creating a background free signal for magnetism and Chern physics. Our work paves way for probing TRS-broken phases of matter in an ultrafast time-resolved manner, not requiring the application of external magnetic fields or even circularly-polarized electric fields.
Authors: Xingjian Lu, Shuzhe Shi
The Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy provides a time-reversal-symmetric framework for describing the nonequilibrium evolution of many-body systems. Despite the success of Boltzmann-based numerical approaches, systematically extending beyond this lowest-order truncation to the full nonlinear BBGKY hierarchy remains a major challenge. Moreover, even at the Boltzmann level, accurately treating the nonlinear collision term still presents significant difficulties. Here we propose the spectral BBGKY hierarchy, an analytically equivalent and numerically tractable reformulation of the conventional BBGKY hierarchy. The spectral formulation reduces the original 6n-dimensional phase-space problem to the evolution of spectral coefficients over the 3n-dimensional coordinate space. We also develop an analytic scheme for computing the collision integrals, which achieves high accuracy and removes the need for ensemble averaging over repeated stochastic evolutions from the same initial state. The scheme evaluates the full eight-fold integral exactly for massless particles, and reduces it to a three-fold one for massive particles. The validity of the spectral BBGKY hierarchy is verified through conservation law analysis, comparison with an analytical solution, convergence tests, and analysis of spectral coefficient leakage. At minimal truncation, the spectral BBGKY yields a spectral nonlinear Boltzmann equation that captures full dynamics with a computational cost comparable to that of linearized approaches. When extended to higher-order truncations, the spectral BBGKY hierarchy provides a flexible framework for studying multiparticle correlations. This framework advances our ability to investigate the early thermalization puzzle in relativistic heavy-ion collisions and to elucidate the applicability of hydrodynamics at remarkably early stages of quark-gluon plasma evolution.
Authors: Leonardo Ermann, Klaus M. Frahm, Dima L. Shepelyansky
We study properties of opinion formation on Wikipedia Ising Networks. Each Wikipedia article is represented as a node and links are formed by citations of one article to another generating a directed network of a given language edition with millions of nodes. Ising spins are placed at each node and their orientation up or down is determined by a majority vote of connected neighbors. At the initial stage there are only a few nodes from two groups with fixed competing opinions up and down while other nodes are assumed to have no initial opinion with no effect on the vote. The competition of two opinions is modeled by an asynchronous Monte Carlo process converging to a spin polarized steady-state phase. This phase remains stable with respect to small fluctuations induced by an effective temperature of the Monte Carlo process. The opinion polarization at the steady-state provides opinion (spin) preferences for each node. In the framework of this Ising Network Opinion Formation model we analyze the influence and competition between political leaders, world countries and social concepts. This approach is also generalized to the competition between three groups of different opinions described by three colors, for example Donald Trump, Vladimir Putin, Xi Jinping or USA, Russia, China within English, Russian and Chinese editions of Wikipedia of March 2025. We argue that this approach provides a generic description of opinion formation in various complex networks.
Authors: Taige Wang, Ya-Hui Zhang
Intertwining intrinsic topological order with gapless collective modes remains a central challenge in many-body physics. We show that a quantum-Hall trilayer at $\nu_{1}=\nu_{2}=\nu_{3}= \frac13$, tuned solely by the inter-layer spacing $d$, realizes this goal. Large-scale density-matrix renormalization group (DMRG) calculations and a Chern-Simons field theory analysis reveal an intermediate ``anyon-exciton condensate'' separating the familiar $\nu_{\mathrm{tot}}=1$ exciton condensate ($d \to 0$) from three decoupled Laughlin liquids ($d \to \infty$). In this phase, neutral bi-excitons condense while a $\nu=\frac23$ Laughlin topological order survives, yielding a Goldstone mode coexisting with fractionalized anyons. A Ginzburg-Landau analysis maps out the finite-temperature phase diagram. The anyon-exciton condensate can be experimentally verified through a vanishing double-counter-flow resistance and a fractional layer-resolved Hall resistivity $R_{xy}=\frac{5}{2} h/e^{2}$, both within reach of existing high-mobility trilayer devices.
Authors: Thomas Ayral
Near-term quantum processors are limited in terms of the number of qubits and gates they can afford. They nevertheless give unprecedented access to programmable quantum systems that can efficiently, although imperfectly, simulate quantum time evolutions. Dynamical mean field theory, on the other hand, maps strongly-correlated lattice models like the Hubbard model onto simpler, yet still many-body models called impurity models. Its computational bottleneck boils down to investigating the dynamics of the impurity upon addition or removal of one particle. This task is notoriously difficult for classical algorithms, which has warranted the development of specific classical algorithms called "impurity solvers" that work well in some regimes, but still struggle to reach some parameter regimes. In these lecture notes, we introduce the tools and methods of quantum computing that could be used to overcome the limitations of these classical impurity solvers, either in the long term -- with fully quantum algorithms, or in the short term -- with hybrid quantum-classical algorithms.
Authors: Ryohei Ikeda, Yuta Murakami, Daiki Sakai, Tatsuya Miyamoto, Toshimitsu Ito, Hiroshi Okamoto
Solids in an intense laser field show high-harmonic generation (HHG), which can provide information on carrier dynamics and band structures in weakly correlated systems. In strongly correlated systems, a laser field can induce a transition between the various electronic phases formed by the entanglement of charge, spin, and orbital degrees of freedom via carrier generation. The HHG accompanying this process should contain information on the nonequilibrium electronic-state dynamics along the oscillating field - an aspect that remains unresolved to date. Here, we show that an intense mid-infrared (MIR) pulse induces a Mott insulator-metal transition in a one-dimensional cuprate, Sr2CuO3, the evolution of which is reflected by the spectral features of HHs. When the electric-field amplitude exceeds 6 MV/cm, carriers are efficiently generated and each harmonic frequency decreases from odd multiples of the MIR frequency. Dynamical mean-field theory indicates that these redshifts originate from a series of electronic-structure reconstructions in each electric-field cycle during the melting of the Mott-insulator state, which modifies the radiation phase from carrier recombination cycle-by-cycle. This phenomenon is negligible in rigid-band systems. This experimental-theoretical study confirms that HH spectroscopy research can potentially unravel the sub-cycle dynamics of nonequilibrium phase transitions in correlated materials.
Authors: Isaac Vorreiter, Jonathan Y. Huang, Scott D. Liles, Joe Hillier, Ruoyu Li, Bart Raes, Stefan Kubicek, Julien Jussot, Sofie Beyne, Clement Godfrin, Sugandha Sharma, Danny Wan, Nard Dumoulin Stuyck, Will Gilbert, Chih Hwan Yang, Andrew S. Dzurak, Kristiaan De Greve, Alexander R. Hamilton
Silicon spin qubits in gate-defined quantum dots leverage established semiconductor infrastructure and offer a scalable path toward transformative quantum technologies. Holes spins in silicon offer compact all-electrical control, whilst retaining all the salient features of a quantum dot qubit architecture. However, silicon hole spin qubits are not as advanced as electrons, due to increased susceptibility to disorder and more complex spin physics. Here we demonstrate single-qubit gate fidelities up to 99.8% and a two-qubit gate quality factor of 240, indicating a physical fidelity limit of 99.7%. These results represent the highest performance reported in natural silicon to date, made possible by fast qubit control, exchange pulsing, and industrial-grade fabrication. Notably, we achieve these results in a near-identical device as used for highly reproducible, high-fidelity electron spin qubits. With isotopic purification and device-level optimisations in the future, our hole spin qubits are poised to unlock a new operation regime for quantum CMOS architectures.
Authors: T. Karabassov, I. V. Bobkova, A. M. Bobkov, A. S. Vasenko, A. A. Golubov
We address a previously unexplored type of dynamical proximity effect that occurs in s-wave topological superconductor/ferromagnetic insulator (TS/FI) heterostructures. It is predicted that magnons in the FI and the Nambu-Goldstone (NG) collective superconducting phase mode in the TS are coupled, forming composite magnon-NG excitations. The mechanism of this coupling is associated with the complete spin-momentum locking of electrons in the helical surface state of the TS. The strength of the magnon-NG coupling is strongly anisotropic with respect to the mutual orientation of the magnon wave vector and the equilibrium magnetization of the FI. This effect provides a mechanism for the interconversion of spin signals and the spinless signals carried by collective superconducting excitations, thereby giving new impetus to the development of superconducting spintronics.
Authors: Anyuan Gao, Naoto Nagaosa, Ni Ni, Su-Yang Xu
Quantum geometry, which describes the geometry of Bloch wavefunctions in solids, has become a cornerstone of modern quantum condensed matter physics. The quantum geometrical tensor encodes this geometry through two fundamental components: the quantum metric (real part) and the Berry curvature (imaginary part). While the Berry curvature gained prominence through its manifestation in the intrinsic anomalous Hall effect, recent advances have revealed equally significant effects arising from the quantum metric. This includes its signatures in nonlinear transport, superfluid density of flat-band superconductors, and nonlinear optical responses. These advances underscore how quantum geometry is reshaping our understanding of condensed matter systems, with far-reaching implications for future technologies. In this review, we survey recent progress in the field, focusing on both foundational concepts and emergent phenomena in transport and optics-with particular emphasis on the pivotal role of the quantum metric.
Authors: G. A. Bobkov, V. A. Bobkov, I. V. Bobkova, A. M. Bobkov, A. A. Golubov
In recent years, a number of studies have predicted the emergence of a nontrivial proximity effect in superconductor/antiferromagnet (S/AF) heterostructures. This effect is of considerable interest for the efficient integration of antiferromagnetic materials into the fields of superconducting spintronics and electronics. A key element of this proximity effect is the Neel triplet correlations, initially predicted for S/AF heterostructures with checkerboard G-type antiferromagnetic ordering. However, various forms of antiferromagnetic ordering exist, and an important open question concerns the generalization of these results to such cases. In this paper, we develop a theory of the proximity effect in S/AF heterostructures with arbitrary two-sublattice antiferromagnetic ordering, aiming to clarify which antiferromagnets are capable of inducing triplet correlations and what structure these correlations may exhibit. We show that, in S/AF heterostructures with collinear compensated antiferromagnets, the dominant superconducting triplet correlations are of the checkerboard Neel type, as originally predicted for G-type antiferromagnets. In contrast, layered Neel triplet correlations, although potentially generated by layered antiferromagnets, are significantly weaker. Consequently, in S/AF heterostructures with layered antiferromagnetic ordering, the proximity-induced triplet correlations may exhibit either a checkerboard Neel or a conventional ferromagnetic structure, depending on the specific antiferromagnet and its orientation relative to the S/AF interface.
Authors: Karma Tenzin, Berkay Kilic, Raghottam Sattigeri, Zhiren He, Chao Chen Ye, Marcio Costa, Marco Buongiorno Nardelli, Carmine Autieri, Jagoda Slawinska
Chiral crystals, due to the lack of inversion and mirror symmetries, exhibit unique spin responses to external fields, enabling physical effects rarely observed in high-symmetry systems. Here, we show that materials from the chiral dichalcogenide family TM$_3$X$_6$ (T = 3d, M = 4d/5d, X = S) exhibit persistent spin texture (PST) - unidirectional spin polarization of states across large regions of the reciprocal space - in their nonmagnetic metallic phase. Using the example of NiTa$_{3}$S$_{6}$ and NiNb$_{3}$S$_{6}$, we show that PSTs cover the full Fermi surface, a rare and desirable feature that enables efficient charge-to-spin conversion and suggests long spin lifetimes and coherent spin transport above magnetic ordering temperatures. At low temperatures, the materials that order antiferromagnetically become chiral altermagnets, where spin textures originating from spin-orbit coupling and altermagnetism combine in a way that sensitively depends on the orientation of the Neel vector. Using symmetry analysis and first-principles calculations, we classify magnetic ground states across the family, identify cases with weak ferromagnetism, and track the evolution of spin textures and charge-to-spin conversion across magnetic phases and different Neel vector orientations, revealing spin transport signatures that allow one to distinguish Neel vector directions. These findings establish TM$_3$X$_6$ as a tunable platform for efficient charge-to-spin conversion and spin transport, combining structural chirality, persistent spin textures, and altermagnetism.
Authors: Diego Fernández de la Pradilla, Esteban Moreno, Johannes Feist
Theoretical accounts of ultrastrongly coupled light-matter systems commonly assume that it arises from the interaction of an emitter with propagating photon modes supported by a structure, understanding photons as the excitations of the transverse electromagnetic field. This description discards the Coulomb interaction between the emitter and structure charges. Here, we show with a general argument based on electromagnetic constraints that the emitter-photon coupling strength is fundamentally limited. Accordingly, we conclude that the ultrastrong coupling regime cannot be reached with photons. Instead, it must originate from the Coulomb interactions between charges. A further corollary is that the so-called polarization self-energy term does not need to be included. We illustrate our claims by solving an analytical model of the paradigmatic case of an emitter next to a metallic nanosphere. These findings shed light on the fundamental processes underlying ultrastrong coupling, clarify the role of the polarization self-energy term and compel a reevaluation of previous literature.
Authors: Violet Williams, Jayakrishnan M. P. Nair, Yaroslav Tserkovnyak, Benedetta Flebus
The growing interest in quantum magnonics is driving the development of advanced techniques for generating, controlling, and detecting non-classical magnonic states. Here, we explore the potential of an ensemble of solid-state spin defects coupled to a shared magnetic bath as a source of such states. We establish a theoretical framework to characterize the quantum correlations among magnons emitted by the ensemble into the bath and investigate how these correlations depend on experimentally tunable parameters. Our findings show that the emitted magnons retain the quantum correlations inherent to the solid-state emitters, paving the way for the deterministic generation of quantum many-body magnonic states.
Authors: Zhenfeng Ouyang, Peng-Jie Guo, Rong-Qiang He, Zhong-Yi Lu
Altermagnetism, a newly discovered magnetic phase, has spurred growing research activity. Studies from a perspective of dynamical electronic correlation still remain scarce. Employing density functional theory plus dynamical mean-field theory (DFT+DMFT) that incorporates dynamical electronic correlation, we demonstrate that CaCrO$_3$ is a strongly correlated altermagnet. Our DFT+DMFT calculations successfully reproduce the correlated metallic behavior of CaCrO$_3$ and quantitatively capture the incoherent state observed experimentally. We also identify that the altermagnetic CaCrO$_3$ is a Hund's metal. The incoherent state is attributed to Hund's coupling, which gives rise to a non-Fermi liquid behavior. Moreover, we find that altermagnetism can induce flat bands, and these incipient flat bands are further promoted by the strong renormalization from Hundness, which further drives a heavy-fermion behavior. Hence, we establish CaCrO$_3$ as a strongly correlated altermagnet and propose that Hund's metals provide an ideal platform for investigating the interplay between electronic correlation and altermagnetism. Our work will promote the study of strongly correlated altermagnetism physics.
Authors: Henry Davenport, Johannes Knolle, Frank Schindler
In translationally invariant semiconductors that host exciton bound states, one can define an infinite number of possible exciton Berry connections. These correspond to the different ways in which a many-body exciton state, at fixed total momentum, can be decomposed into free electron and hole Bloch states that are entangled by an exciton envelope wave function. Inspired by the modern theory of polarization, we define an exciton projected position operator whose eigenvalues single out two unique choices of exciton Berry phase and associated Berry connection - one for electrons, and one for holes. We clarify the physical meaning of these exciton Berry phases and provide a discrete Wilson loop formulation that allows for their numerical calculation without a smooth gauge. As a corollary, we obtain a gauge-invariant expression for the exciton polarisation at a given total momentum, i.e. the mean separation of the electron and hole within the exciton wave function. In the presence of crystalline inversion symmetry, the electron and hole exciton Berry phases are quantized to the same value and we derive how this value can be expressed in terms of inversion eigenvalues of the many-body exciton state. We then consider crystalline $C_2 \mathcal{T}$ symmetry, for which no symmetry eigenvalues are available as it is anti-unitary, and confirm that the exciton Berry phase remains quantized and still diagnoses topologically distinct exciton bands. Our theory thereby generalizes the notion of shift excitons, whose exciton Wannier states are displaced from those of the non-interacting bands by a quantized amount, beyond symmetry indicators.
Authors: Anuradha Wijesinghe, Yongxi Ou, Anjali Rathore, Chandima Edirisinghe, Pradip Adhikari, An-Hsi Chen, Dustin Gilbert, Anthony Richardella, Nitin Samarth, Joon Sue Lee
Antimony (Sb), an element with strong spin-orbit coupling, is predicted to undergo a topological phase transition from a topological semimetal to a topological insulator as its dimensionality approaches the two-dimensional limit, driven by the quantum confinement effect. In this study, we investigate this transition in Sb thin films grown by molecular beam epitaxy, employing electrical transport measurements and angle-resolved photoemission spectroscopy (ARPES). Electrical transport measurements revealed signatures of a modified electronic band structure, including a Hall response with multiple carrier types, a decreasing carrier concentration, and a transition in the curvature of the longitudinal resistance from quadratic to linear with decreasing film thickness. Temperature-dependent magnetoresistance further showed weak antilocalization below 16 K, indicating strong spin-orbit coupling and suggesting the presence of non-trivial topological states. Analysis of the WAL characteristics revealed a single coherent conducting channel and a thickness-dependent change in the phase decoherence mechanism. Complementary ARPES measurements confirmed that reducing the film thickness lifts the conduction band at the M-point, consistent with the emergence of a band gap. These findings support theoretical predictions of a thickness-dependent band structure evolution driven by the quantum confinement effect, providing a foundation for further exploration of topological phase transitions in Sb as well as Bi1-xSbx. The realization of an elemental topological material with simplified stoichiometry and semiconductor compatibility presents a promising avenue for next-generation hybrid systems and applications in spintronics and quantum technologies.
Authors: Chang-An Li, Björn Trauzettel
We investigate the spectrum of Andreev bound states and supercurrent in a $p$-wave non-Hermitian Josephson junction (NHJJ) in one dimension. The studied NHJJ is composed of two topological $p$-wave superconductors connected by a non-Hermitian dissipative junction. Starting from the effective non-Hermitian Bogoliubov-de Gennes bulk Hamiltonian, we find that a pair of exceptional points emerge in the complex spectrum of Andreev quasi-bound states. The two exceptional points locate symmetrically with respect to phase difference $\phi=\pi$ at zero real energy. Their separation is tunable by the non-Hermitian dissipation strength. By analyzing the non-Hermitian scattering process at the junction, we explicitly demonstrate the loss of quasiparticles through the decay of scattering amplitude probabilities. Furthermore, we obtain the supercurrent directly by the inelastic Andreev reflection amplitudes, which provides a more intuitive interpretation of transport properties in NHJJs. The supercurrent varies continuously as a function of $\phi$ across the exceptional points. No enhancement of critical current is observed. We also generalize our analysis to mixed $s$-$p$ wave NHJJ.
Authors: Albert Suceava, Sankalpa Hazra, Jadupati Nag, John Hayden, Safdar Imam, Zhiwen Liu, Abishek Iyer, Mercouri Kanatzidis, Susan Trolier-McKinstry, Jon-Paul Maria, Venkatraman Gopalan
Nonlinear optical microscopy such as in the optical second-harmonic generation (SHG) modality has become a popular tool today for probing materials in the physical and biological sciences. While imaging and spectroscopy are widely used in the microscopy mode, nonlinear polarimetry, which can shed light on materials' symmetry and microstructure, is relatively underdeveloped. This is partly because quantitative analytical modeling of the optical SHG response for anisotropic crystals and films largely assumes low-numerical aperture (NA) focusing of light, where the plane-wave approximation is sufficient. Tight focusing provides unique benefits in revealing out-of-plane polarization responses, which cannot be detected by near-plane-wave illumination at normal incidence. Here, we outline a method for quantitatively analyzing SHG polarimetry measurements obtained under high-NA focusing within a microscope geometry. Experiments and simulations of a variety of standard samples, from single crystals to thin films, are in good agreement, including measured and simulated spatial SHG maps of ferroelectric domains. A solution to the inverse problem is demonstrated, where the spatial distribution of an SHG tensor with unknown tensor coefficient magnitudes is determined by experimentally measured polarimetry. The ability to extract the out-of-plane component of the nonlinear polarization in normal incidence is demonstrated, which can be valuable for high-resolution polarimetry of 2D materials, thin films, heterostructures, and uniaxial crystals with a strong out-of-plane response. Copyright 2025 Optica Publishing Group. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved. this https URL
Authors: Thomas J. Ugras, Daniel J. Gracias, Oriol Arteaga, Richard D. Robinson
Reciprocity, the principle that a system response is identical in the forward path compared to the backward path, is a fundamental concept across physics, from electrical circuits and optics to acoustics and heat conduction. Nonreciprocity arises when this symmetry is broken, enabling directional-dependent behavior. In photonics, nonreciprocity allows control over the propagation of electromagnetic waves, essential for isolators and circulators. But achieving optical nonreciprocity typically requires complex metamaterials, exotic media, or strong external fields. Because of this, researchers have historically overlooked the possibility that readily available materials could support nonreciprocal optical behavior, assuming that conventional systems lack the ability to produce nonreciprocal behavior. In this work, we challenge that assumption by revisiting the light-matter interactions of chiroptic and linearly anisotropic media. Through Stokes-Mueller formalism we derive a simple analytical expression that predicts a pathway to nonreciprocal absorption and emission of orthogonal linear polarizations. We test this idea experimentally using solution-processed films of CdS, CdSe, and CdTe magic-size clusters that possess commensurate circular dichroism (CD) and linear dichroism (LD)values and find that they can support this effect, engineering films that exhibit nonreciprocal absorption and emission of linearly polarized light. Based on the derived expressions and experiments, several design rules are presented. Our findings reveal that nonreciprocal linear dichroism and emission can be achieved in readily processable, macroscopically symmetric materials by harnessing chiral-linear optical interference. This work opens new opportunities for scalable, polarization-based photonic control for direction-dependent optical routing, optical logic, and polarization-multiplexed information encoding.
Authors: Sang-Eon Lee, Yue Li, Yeonkyu Lee, W. Kice Brown, PeiYu Cai, Jinyoung Yun, Chanyoung Lee, Alex Moon, Lingrui Mei, Jaeyong Kim, Yan Xin, Julie A. Borchers, Thomas W. Heitmann, Matthias Frontzek, William D. Ratcliff, Gregory T. McCandless, Julia Y. Chan, Elton J. G. Santos, Jeehoon Kim, Charudatta M. Phatak, Vadym Kulichenko, Luis Balicas
The layered compound Fe3GaTe2 is attracting attention due to its high Curie temperature, low dimensionality, and the presence of topological spin textures above room temperature, making Fe$_3$GaTe$_2$ a good candidate for applications in spintronics. Here, we show, through transmission electron microscopy (TEM) techniques, that Fe$_3$GaTe$_2$ single crystals break local inversion symmetry while maintaining global inversion symmetry according to X-ray diffraction. Coupled to the observation of Néel skyrmions via Lorentz-TEM, our structural analysis provides a convincing explanation for their presence in centrosymmetric materials. Magnetization measurements as a function of the temperature displays a sharp first-order thermodynamic phase-transition leading to a reduction in the magnetic moment. This implies that the ground state of Fe$_3$GaTe$_2$ is globally ferrimagnetic and not a glassy magnetic state composed of ferrimagnetic, and ferromagnetic domains as previously claimed. Neutron diffraction studies indicate that the ferromagnetic to ferrimagnetic transition upon reducing the external magnetic field is associated with a change in the magnetic configuration/coupling between Fe1 and Fe2 moments. We observe a clear correlation between the hysteresis observed in both the skyrmion density and the magnetization of Fe$_3$GaTe$_2$. This indicates that its topological spin textures are affected by the development of ferrimagnetism upon cooling. Observation, via magnetic force microscopy, of magnetic bubbles at the magnetic phase boundary suggests skyrmions stabilized by the competition among magnetic phases and distinct exchange interactions. Our study provides an explanation for the observation of Néel skyrmions in centrosymmetric systems, while exposing a correlation between the distinct magnetic phases of Fe$_3$GaTe$_2$ and topological spin textures.
Authors: Alexander P. Antonov, Hartmut Löwen
The traditional Mpemba effect refers to an anomalous cooling phenomenon when an initial hotter system cools down faster than an initial warm system. Such counterintuitive behavior has been confirmed and explored across phase transitions in condensed matter systems and also for colloidal particles exposed to a double-well potential. Here we predict a frictional Mpemba effect for a macroscopic body moving actively on a surface governed by Coulomb (dry) friction. For an initial high temperature, relaxation towards a cold state occurs much faster than that for an intermediate initial temperature, due to a large temperature overshooting in the latter case. This frictional Mpemba effect can be exploited to steer the motion of robots and granules.
Authors: Tomoki Hotta, Le Duc Anh, Takahiro Chiba, Yohei Kota, Masaaki Tanaka
Magnetoresistance typically exhibits even symmetry with respect to the magnetic field, owing to time reversal symmetry (TRS) as dictated by Onsager reciprocity relations. However, in certain systems where TRS is broken, magnetoresistance may acquire an odd component with respect to the magnetic field, referred to as odd parity magnetoresistance (OMR). To date, reported OMR values have been modest, usually restricted to a few tens of percent even under high magnetic fields. Here, we report the discovery of a giant OMR reaching up to 1,150% under a relatively low field of 1 T in a heterostructure composed of 3 nm thick alpha Sn and a ferromagnetic semiconductor, (In,Fe)Sb. Although alpha Sn in this thickness range is a trivial narrow gap semiconductor, analysis of Shubnikov de Haas oscillations combined with ab initio calculations reveals the emergence of tilted topological surface states, induced via magnetic proximity from the (In,Fe)Sb layer. The observed OMR behavior is well explained by a Boltzmann transport model assuming the presence of oppositely tilted Weyl cones in the alpha Sn band structure. Our findings not only shed new light on the physics of OMR but also suggest promising avenues for its application in electronic and spintronic devices, such as ultrasensitive magnetic sensors.
Authors: Rafael Gonzalez-Hernandez, Bernardo Uribe
We present models of topological insulating Hamiltonians exhibiting intrinsic altermagnetic features, protected by combined three-fold or four-fold rotational symmetries with time-reversal. We demonstrate that the spin Chern number serves as a robust topological invariant in two-dimensional systems, while for three-dimensional structures, the topological nature is characterized by the spin Chern numbers computed on the $k_z$=$0$ and $k_z$=$\pi$ planes. The resulting phases support symmetry-protected boundary modes, including corner, hinges and surface states, whose structure is determined by the magnetic symmetry and the local magnetic moments. Our findings bridge the fields of altermagnetism and topological quantum matter, and establish a theoretical framework for engineering spintronic topological systems without net magnetization.
Authors: D. A-León, D.A. Landínez Téllez, J. Roa-Rojas, Rafael Gonzalez-Hernandez
The investigation of topological materials has uncovered groundbreaking phases of matter with significant implications for quantum technologies. Here, we explore the antiferromagnetic topological insulator family V(Bi$_{1-x}$Sb$_{x}$)$_{2}$Te$_{4}$ ($x$=$0$, $0.5$, $1$), formed by introducing vanadium telluride (VTe) layers into the layered topological insulator (Bi$_{1-x}$Sb$_{x}$)$_{2}$Te$_{3}$. Our results reveal the tunability of the spin Hall conductivity (SHC) and its topological contribution, quantified by the recently introduced average Spin Chern Number (ASCN), via Sb concentration. The materials' strong topological insulating behavior is established through spin-orbit coupling-induced band inversions, nontrivial $\mathbb{Z}_2$ invariants, and the presence of topological surface states. These findings position V(Bi$_{1-x}$Sb$_{x}$)$_{2}$Te$_{4}$ as promising candidates for next-generation spintronic devices and advanced quantum applications.
Authors: S.V. Streltsov, D.M. Korotin
By combining symmetry analysis and direct density functional calculations including the spin-orbit coupling, we demonstrate that LaMn2Si2 is an M-type altermagnet. Our results predict a large anomalous Hall effect, with a non-zero xy component of -360 S/cm, accompanied by a pronounced magneto-optical response. Remarkably, electron doping of LaMn2Si2 is predicted to substantially enhance the Hall conductivity, with values reaching up to -650 S/cm. These results suggest that silicates with general formula RM2Si2 can be an interesting platform for studying both altermagnetism and anomalous Hall effect.
Authors: Sang-Eon Lee, Myung-Hwa Jung
This study explores the identification of sample inhomogeneity via magnetic quantum oscillations analysis in semimetal NbSb$_2$. By doping Bi and Cr, we obtained a homogeneous Bi-doped sample and an inhomogeneous Cr-doped sample, whose homogeneity was confirmed by comparing the magnetic quantum oscillation before and after grinding the samples. The magnetic quantum oscillations in the inhomogeneous sample exhibited a distinct phase shift and unusual field-dependent amplitude, believed to result from a non-uniform Fermi energy. The analysis of the magnetic quantum oscillations demonstrated that the homogeneous Bi-doped sample can be interpreted by the symmetric and Lorentzian effective Fermi energy distribution, while the inhomogeneous Cr-doped sample exhibited an asymmetric distribution, illustrating an unconventional violation of the Lifshitz-Kosevich formula. This research provides a novel method for identifying material inhomogeneity and mitigating potential misinterpretations of magnetic quantum oscillations' unusual phase, commonly seen as a nontrivial Berry phase indicator in topological materials studies.
Authors: Junhyeok Jeong, Kifu Kurokawa, Shiro Sakai, Tomotaka Nakayama, Kotaro Ando, Naoshi Ogane, Soonsang Huh, Matthew D. Watson, Timur K. Kim, Cephise Cacho, Chun Lin, Makoto Hashimoto, Donghui Lu, Takami Tohyama, Kazuyasu Tokiwa, Takeshi Kondo
In multilayered high-Tc cuprates with three or more CuO2 layers per unit cell, the inner CuO2 planes (IPs) are spatially separated from the dopant layers and thus remain cleaner than the outer planes (OPs). While both interlayer coupling and the presence of clean IPs have been proposed as key factors enhancing superconductivity, their individual roles have been difficult to disentangle, as IPs and OPs typically become superconducting simultaneously. Here we investigate five-layer (Cu,C)Ba2Ca4Cu5Oy (Cu1245) with Tc = 78 K and three-layer Ba2Ca2Cu3O6(F,O)2 (F0223) with Tc = 100 K using ARPES, and uncover an unprecedented situation, in which only the IPs become superconducting while the OPs remain metallic at low temperatures. Model calculations indicate that more than 95% of the OP wavefunction remains confined to OP itself, with minimal hybridization from the superconducting IPs. In particular, we experimentally realize an ideal configuration: a single superconducting CuO2 layer sandwiched between heavily overdoped metallic outer layers, which screen disorder originating from the dopant layers. Strikingly, this clean CuO2 layer exhibits the largest superconducting gap among all known cuprates and coherent Bogoliubov peaks extending beyond the antiferromagnetic zone boundary -- long regarded as the boundary beyond which coherence vanishes in heavily underdoped cuprates. Furthermore, a widely extended coherent flat band emerges at the Brillouin zone edge, overcoming the pseudogap damping effect. Our results introduce a new physical parameter, the degree of screening, to investigate the competition between superconductivity and the pseudogap, potentially shedding new light on its origin. The nearly disorder-free superconducting CuO2 layers offer a model platform for bridging the gap between disordered real materials and idealized theoretical models, which generally neglect disorder effects.
Authors: Koki Mizuno, Hirone Ishida, Manato Teranishi
Spin pumping with superconductors has been extensively studied, particularly in double-layer systems. In this study, we investigate spin pumping in a trilayer system comprising a ferromagnetic insulator (FMI), a superconductor (SC), and a normal metal (NM). We derive the AC and DC spin currents in the NM layer induced by spin motion in the FMI under circularly polarized microwave irradiation. If we treat the spin motion as classical, the AC spin current is expressed. On the other hand, if we treat the spin motion as quantum quasiparticles, the DC spin current is derived. After these derivations, while the computational cost of evaluating the spin current is extremely high, we mitigate this using the Quantics Tensor Cross Interpolation (QTCI) method. We present numerical results showing the dependence of the spin current on temperature, microwave frequency, and superconductor layer thickness. Notably, the temperature dependence of AC and DC spin currents exhibits a coherence peak. Furthermore, we have discovered a transition structure in the dependence of the spin current on the thickness of the superconductor layer, where the dependence changes after a particular frequency.
Authors: Soo-hyon Phark, Hong Thi Bui, We-hyo Seo, Yaowu Liu, Valeria Sheina, Curie Lee, Christoph Wolf, Andreas J. Heinrich, Roberto Robles, Nicolas Lorente
Single atomic adsorbates on ultrathin insulating films provide a promising route toward bottom-up quantum architectures based on atomically identical yet individually addressable spin qubits on solid surfaces. A key challenge in engineering quantum-coherent spin nanostructures lies in understanding and controlling the spin state of individual adsorbates. In this work, we investigate single titanium (Ti) atoms adsorbed on MgO/Ag(100) surfaces using a combined scanning tunneling microscopy and electron spin resonance. Our measurements reveal two distinct spin states, $S = 1/2$ and $S = 1$, depending on the local adsorption site and the thickness of the MgO film. Density functional theory calculations suggest a Ti$^+$ configuration for the Ti adsorbates with approximately 3 electrons in the 4$s$ and 3$d$ valence shells. Using a multi-orbital atomic multiplet calculations the site dependence of the spin can be rationalized as a charge redistribution between spin-polarizing and depolarizing orbitals. These findings underscore the potential of surface-supported single atoms as spin qubits with tunable spin and charge states, enabling atom-by-atom control in the realization of a versatile quantum platform on surfaces.
Authors: Xiaohua Wu, Junyang Chen, Mingqiang Gu, Yujun Zhang, Shanmin Wang, Yanan Dai, Qihang Liu, Yue Zhao, Mingyuan Huang
The detection and manipulation of the spin configurations in layered magnetic semiconductors hold significant interest for developing spintronic devices in two-dimensional limit. In this letter, we report a systematical study on the photoluminescence (PL) from the high energy excitons in few-layer CrSBr and its application on detecting the spin configurations. Besides the broad excitonic emission peak (Xl) at around 1.34 eV, we also observed another strong excitonic emission peak (Xh) at around 1.37 eV in hBN encapsulated 2L sample, which splits into two peaks in 3L and 4L samples. With help of the first principles calculations, we conclude that the Xh peak is associated with the transition between the top valence band and the second lowest conduction band, which is forbidden by the inversion symmetry in 1L CrSBr. Furthermore, the position and intensity of the Xh peak are strongly dependent on the interlayer magnetic order of the CrSBr samples, which provides an efficient way to probe their spin configurations. In addition, when the magnetic field is applied at the easy axis direction, we resolve an intermediate magnetic state besides the antiferromagnetic and ferromagnetic states in 3L and 4L samples. Our results reveal few-layer CrSBr as an ideal platform to study the interaction between the excitons and magnetism.
Authors: Luca Buiarelli, Turan Birol, Brian M. Andersen, Morten H. Christensen
The shandite structure hosts transition metals arranged in kagome layers stacked rhombohedrally, and interspersed with post-transition metal ions and chalcogens. The electronic states near the Fermi level are dominated by the transition metal $d$-orbitals and feature saddle points near several of the high-symmetry positions of the Brillouin zone, most notably the F and L points. Combining symmetry considerations with ab initio methods, we study the electronic and structural properties of these materials with an emphasis on the connection between electronic saddle points at specific momenta and structural instabilities at these momenta. While the parent compounds studied are all found to be structurally stable in the $R\bar{3}m$ space group under ambient conditions we show that, in specific compounds, moving the saddle point closer to the Fermi level using either hydrostatic pressure or doping, can induce a structural instability. The importance of the electronic degrees of freedom in driving this instability is supported by the dependence of the frequency of the soft phonon mode on the electronic smearing temperature, as is the case in charge density wave materials. Our first-principles calculations show that as the smearing temperature is increased, the compound becomes structurally stable again. Our findings survey the structural properties of a large family of shandite materials and shed light on the role played by saddle points in the electronic structure in driving structural instabilities in rhombohedrally stacked kagome-layered materials belonging to the $R\bar{3}m$ space group.
Authors: Gabriel Martínez-Carracedo, Amador García-Fuente, László Oroszlány, László Szunyogh, Jaime Ferrer
We investigate from first principles a variety of low-dimensional open quantum spin systems based on magnetic nanographene structures that contain spin-1/2 and spin-1 triangulenes and/or olympicenes. These graphene nanostructures behave as localized spins and can be effectively described by a quantum bilinear-biquadratic Heisenberg Hamiltonian, for which we will compute the energy spectrum and the quantum numbers associated with the low-energy eigenstates. We propose the experimental realization of antiferromagnetic alternating spin chains using these graphene nanostructures, which result in ferrimagnetic systems whose ground state spin and degeneracy depend on the length of the chain. We also identify a double degeneracy in the total spin quantum number $S$ in the first excited state for three-leg spin graphs (3-LSGs). This degeneracy depends on both the number of sites and the spin species that compose the 3-LSG. We identify the double degeneracy of the first excited state as a consequence of swapping transformation symmetry of the Hamiltonian.
Authors: R.M. Dubrovin, Z.V. Gareeva, A.V. Kimel, A.K. Zvezdin
Contrary to conventional wisdom that spin dynamics induced by current are exclusive to metallic magnets, we theoretically predict that such phenomena can also be realized in magnetic insulators, specifically in the magnetoelectric antiferromagnet $\mathrm{Cr}_{2}\mathrm{O}_{3}$. We reveal that the displacement current driven by the THz electric field is able to generate a N{é}el spin-orbit torque in this insulating system. By introducing an alternative electric dipole order parameter arising from the dipole moment at $\mathrm{Cr}^{3+}$ sites, we combine symmetry analysis with a Lagrangian approach and uncover that the displacement current couples to the antiferromagnetic spins and enables ultrafast control of antiferromagnetic order. The derived equations of motion show that this effect competes with the linear magnetoelectric response, offering a novel pathway for manipulating antiferromagnetic order in insulators. Our findings establish insulator antiferromagnets as a viable platform for electric field driven antiferromagnetic spintronics and provide general design principles for non-metallic spin-orbit torque materials.
Authors: Mauro Pulzone, Natalya S. Fedorova, Hugo Aramberri, Jorge Íñiguez-González
We show how to construct Landau-like free energy potentials using a machine-learning approach. For concreteness, we focus on perovskite oxide PbTiO$_{3}$. We work with a training set obtained from Monte Carlo simulations based on an atomistic ''second-principles'' potential for PbTiO$_{3}$. We rely exclusively on data that would be experimentally accessible -- i.e., temperature-dependent polarization and strain, both with and without external electric fields and stresses applied --, to explore scenarios where the training set could be obtained from laboratory measurements. We introduce a scheme that allows us to identify optimal polynomial models of the temperature-dependent free energy surface, mapped as a function of the homogeneous electric polarization and homogeneous strain. Our results for PbTiO$_{3}$ show that a very simple polynomial -- where only two parameters depend linearly on temperature -- is sufficient to yield a correct description of the material's behavior. Remarkably, the obtained models also capture the subtle couplings by which elastic strain controls key features of ferroelectricity in PbTiO$_{3}$ -- i.e., the symmetry of the polar phase and the discontinuous character of the transition --, despite the fact that no effort was made to include such information in the training set. We emphasize the distinctive aspects of our methodology (which relies on an original form of validation step) by comparing it with the usual machine-learning approach for model construction. Our results illustrate how physically motivated models can have remarkable predictive power, even if they are derived from a limited amount of data. We argue that such ''third-principles'' models can be the basis for predictive macroscopic or mesoscopic simulations of ferroelectrics and other materials undergoing non-reconstructive structural transitions.
Authors: Mirian Garcia Fernandez, Abhishek Nag, Stefano Agrestini, Sahil Tippireddy, Dirk Backes, Urs Staub, Taka-hisa Arima, Kejin Zhou
The electron in a solid can be considered a bound state of the three independent, fundamental degrees of freedom creating quasi-particles: spinons, carrying the electron spin; plasmons carrying the collective charge mode and orbitons carrying its orbital degree of freedom. These fundamental degrees of freedom could form ordering states in which dynamics or collective motions could occurr and manifest as low-energy excitations. The exotic properties that appear in the materials exhibiting these electronic orderings are associated with these low-energy excitations. Although the orbital order (OO) and its coupling to the spin system creates very interesting phenomena, the microscopic origin of OO has been much less explored than other electronic properties as it is very difficult to directly access experimental information from OO. Due to the recent improvement in energy resolution and flux, soft x-ray resonant inelastic scattering (RIXS) allows for a re-examination of orbital excitations in manganites. Here, we present a study of low energy excitations in half doped A-site ordered SmBaMn_{2}O_{6} through a combination of RIXS and soft x-ray resonant elastic scattering (REXS) measurements. The obtained experimental data confirm the OO at \mathbf{q} = (0.25, 0.25, 0) and find various low energy excitations below 200 meV. while several excitations can be assigned to be of magnetic and phononic origin, a group of excitations between 80 and 200 meV show a temperature dependence distinctively following that of the OO making them possible candidates for orbital excitations.
Authors: Itishree Pradhan, Hao Li, Alina Rupp, Yosuke Sato, Henri Vo Van Qui, Miuko Tanaka, Toshiya Ideue, Erwann Bocquillon, Masayuki Hashisaka
We report the development of a cryogenic powder filter that simultaneously offers high attenuation of radio-frequency (RF) signals in the gigahertz (GHz) range and minimized parasitic capacitance to ground. Conventional powder filters, which consist of a signal line passing through a metal powder-filled housing, attenuate high-frequency signals via the skin effect. However, these designs often suffer from significant parasitic capacitance between the signal line and the grounded chassis, which can compromise the performance of sensitive measurement setups by limiting their frequency bandwidth. In this work, we demonstrate that a multilayer powder filter design effectively achieves both high RF attenuation and reduced parasitic capacitance. This solution suppresses sample heating due to the unintentional intrusion of RF signals through the wiring, without degrading the performance of the measurement setup.
Authors: H. Acosta-Rivera, V. Rico, F.J. Ferrer, T.C. Rojas, R. Alvarez, N. Martin, A.R. Gonzalez-Elipe, A. Palmero
The formation of VO2 crystalline domains in amorphous substoichiometric nanocolumnar VOx thin films subjected to an oxidation process at temperatures below 300°C has been studied. It is obtained that values of [O]/[V] above 1.9 lead to the sole formation of V2O5 after oxidation, while values below 1.9 favor the formation of VO2, V3O7 and V2O5 crystalline domains for temperatures as low as 260°C. Moreover, it is found that the adsorption of oxygen and its incorporation into the film network produce a relevant volume expansion in a so-called swelling mechanism that makes pores shrink. Under some specific conditions, the low temperature oxidation does not only trigger the formation of VO2 domains but also a drastic reduction of oxygen-deficient amorphous VOx in the films, which clearly improves the overall transparency and thermochromic modulation capabilities. The changes in the optical and electrical properties of these films during the metal-insulator transition have been studied, finding the best performance when the stoichiometry of the film before oxidation is [O]/[V]=1.5 and the oxidation temperature 280°C. These conditions yield a relatively transparent coating that presents an optical modulation in the near-infrared range of nearly 50% and a drop of electrical resistivity of more than two orders of magnitude. A tentative model based on the volume increase experienced by film upon oxidation is proposed to link the structural/chemical features of the films and the formation of VO2 domains at such relatively low temperatures.
Authors: Jinxiong Jia, Longjun Xiang, Zhenhua Qiao, Jian Wang
The linear Edelstein effect is a cornerstone phenomenon in spintronics that describes the generation of spin magnetization in response to an applied electric field. Recent theoretical advances have reignited interest in its nonlinear counterpart, the nonlinear Edelstein effect, in which spin magnetization is induced by a second-order electric field. However, the intrinsic contribution to both effects is generally forbidden in systems preserving time-reversal symmetry ($\mathcal{T}$) or composite symmetries such as $\mathcal{T}\tau_{1/2}$, where $\tau_{1/2}$ denotes a half-lattice translation. In such systems, spin magnetization typically emerges either from extrinsic mechanisms but limited to metals due to their Fermi-surface property, or from dynamical electric fields with a terahertz driving frequency. Here, we propose a new mechanism for spin magnetization, arising from the interplay of magnetic and electric fields, termed the nonlinear magnetoelectric Edelstein effect. Remarkably, its intrinsic component, determined purely by the material's band structure, can appear even in $\mathcal{T}$-invariant materials, but lacking inversion symmetry ($\mathcal{P}$), including insulators. On the other hand, we illustrate that its extrinsic component can serve as a sensitive indicator of the Néel vector reversal in $\mathcal{P}\mathcal{T}$-symmetric antiferromagnetic materials, offering a novel route for antiferromagnetic order detection. To validate our theory, we perform explicit calculations using a two-band Dirac model and a tight-binding model on a honeycomb lattice, finding that both effects yield sizable spin magnetization. Our findings establish the nonlinear magnetoelectric Edelstein effect as a versatile platform for both exploring nonlinear spin physics and enabling symmetry-based detection of antiferromagnetic order.
Authors: Y. Solyaev, V. Dobryanskiy, Nguyen Long, Stanislav Chernyshikhin
In this paper, we present the results of single-track experiments conducted for different fractions of standard AlSi10Mg powder, which were sieved to achieve varying mean size of the particles. We observed strong differences in the melting behaviour of fractions at relatively low levels of input energy in laser powder bed fusion (LPBF) process. Namely, the remarkable particle size effect arises for the position of lack of fusion boundary, i.e. for the range of process parameters where the laser power becomes sufficient for complete through-thickness melting of the powder layer at given laser scanning speed. We established that this boundary corresponds to an approximately constant linear energy density at low levels of Peclet number (Pe < 2), while the constant enthalpy density defines this boundary at the higher levels (Pe > 2). Specifically, when the mean particle size ranges from 28 to 64 microns, the required linear energy density for stable track formation ranges from 50 to 167 J/m and the nominal enthalpy density ranges from 4.4 to 15 J/mm^3. Based on the scaling law analysis and numerical simulations, we show that observed phenomena can be attributed to the change of absorptivity of powder layer, which depends on particle size and packing density. Also, we show that the values of absorptivity identified based on the analysis of position of lack of fusion boundary (0.13-0.38 for powder size 64-28 microns) correlate well with those found from the analysis of melt pool width in the formed single-tracks.
Authors: Michail Lianeris, Davi Rodrigues, Andrea Meo, Dimitris Kechrakos, Anna Giordano, Mario Carpentieri, Giovanni Finocchio, Riccardo Tomasello
The increasing need for efficient thermal management in nanoelectronics requires innovative thermal sensing solutions, as conventional sensors often exhibit nonlinear responses, low sensitivity, and complex calibration. We predict a temperature dependence in the response of existing skyrmion based spintronic diodes and propose their use as nanoscale thermal sensors. These devices leverage magnetic skyrmions topologically protected spin textures known for their robustness, nanoscale dimensions, and low power dynamics. We demonstrate high thermal sensitivity with a linear temperature response over a wide range. This linearity, observed in both the amplitude and frequency of the skyrmion excitation, ensures redundancy that enables precise and reliable temperature measurement. In addition, the use of multilayer systems enhances the sensitivity and robustness of the device. These results provide a foundation for skyrmion-based caloritronic devices with promising applications in spintronic sensors, thermal management, nanoelectronics, and skyrmion-caloritronics.
Authors: Laurenz Beckemeyer, Markus Kraft, Mariel Kempa, Dirk Schuricht, Robin Steinigeweg
We discuss a quantum typicality approach to examine systems composed of two subsystems at different temperatures. While dynamical quantum typicality is usually used to simulate high-temperature dynamics, we also investigate low-temperature dynamics using the method. To test our method, we investigate the energy current between subsystems at different temperatures in various paradigmatic spin-1/2 chains, specifically the XX chain, the critical transverse-field Ising chain, and the XXZ chain. We compare our numerics to existing analytical results and find a convincing agreement for the energy current in the steady state for all considered models and temperatures.
Authors: Ganga S. Kumar, Sudipta Goswami, Shubhasree Chatterjee, Dilruba Hasina, Miral Verma, Devajyoti Mukherjee, Chandan Kumar Ghosh, Dipten Bhattacharya
We report a remarkable enhancement of specific negative capacitance in multidomain La-doped Pb(Zr$_{0.4}$Ti$_{0.6}$)O$_3$ (PLZT) ferroelectric capacitors when bias voltage pulse profile (amplitude and timescale) induces switching of the ferroelectric domains following intrinsic switching kinetics associated with minimum energy barrier. This is because of emergence of maximum domain wall density during ``switching" of the domains. Domain configuration changes from such an ``optimum" state if higher or lower bias voltage is applied at a much faster or slower rate. Phase-field simulation using time-dependent Ginzburg-Landau equation shows dependence of the domain wall density during switching on the bias voltage amplitude and its maximization at a specific bias voltage amplitude. The radius of curvature of the resulting polarization ($P$) versus voltage ($V$) hysteresis loop at the coercive voltage ($V_C$) also turns out to be depending on whether or not intrinsic switching kinetics is followed. All these results indicate a close correlation among the bias voltage pulse profile (amplitude and time scale), domain wall density during switching, shape of the resulting ferroelectric hysteresis loop, and the transient negative capacitance. It may have important ramifications both in the context of physics behind negative capacitance in a multidomain ferroelectric capacitor and devices being developed by exploiting its advantages.
Authors: Michael K. Steinbauer, Peter Flauger, Matthias Küß, Stephan Glamsch, Emeline D. S. Nysten, Matthias Weiß, Dieter Suess, Hubert J. Krenner, Manfred Albrecht, Claas Abert
Filtering surface acoustic wave (SAW) signals of specified frequencies depending on the strength of an external magnetic field in a magnetostrictive material has garnered significant interest due to its potential scientific and industrial applications. Here, we propose a device that achieves selective SAW attenuation by instead programming its internal magnetic state. To this end, we perform micromagnetic simulations for the magnetoelastic interaction of the Rayleigh SAW mode with spin waves (SWs) in exchange-decoupled Co/Ni islets on a piezoelectric LiTaO$_3$ substrate. Due to the islets exhibiting perpendicular magnetic anisotropy, the stray-field interaction between them leads to a shift in the SW dispersion depending on the magnetic alignment of neighboring islets. This significantly changes the efficiency of the magnetoelastic interaction at specified frequencies. We predict changes in SAW transmission of 28.9 dB/mm at 3.8 GHz depending on the state of the device. For the efficient simulation of the device, we extend a prior energy conservation argument based on analytical solutions of the SW to finite-difference numerical calculations, enabling the modeling of arbitrary magnetization patterns like the proposed islet-based design.
Authors: Miriam Rike Ebert, David Christian Ohnmacht, Wolfgang Belzig, Juan Carlos Cuevas
Multiterminal superconducting junctions have revitalized the investigation of the Josephson effect. One of the most interesting aspects of these hybrid systems is the occurrence of multi-Cooper pair tunneling processes that have no analog in two-terminal devices. Such correlated tunneling events are also intimately connected to the Andreev bound states (ABSs) supported by these structures. Josephson junctions with four superconducting terminals have attracted special attention because they are predicted to support ABSs with nontrivial topological properties. Here, we present a theoretical study of sextets, which are correlated tunneling processes involving three Cooper pairs and four different superconducting terminals. We investigate how sextets can be identified from the analysis of the current-phase relation, we show how sextets are connected to the hybridization of ABSs, and we discuss their existence in recent experiments on four-terminal devices realized in hybrid Al/InAs heterostructures.
Authors: Marco Bussoletti (1), Mirko Gallo (1), Amir Jafari (2), Gregory L. Eyink (2,3) ((1) Department of Mechanical and Aerospace Engineering, Sapienza University of Rome, (2) Department of Applied Mathematics and Statistics, The Johns Hopkins University, (3) Department of Physics, The Johns Hopkins University)
It is experimentally well-established that non-equilibrium long-range correlations of concentration fluctuations appear in free diffusion of a solute in a solvent, but it remains unknown how such correlations are established dynamically. We address this problem in a model of Donev, Fai \& Vanden-Eijnden (DFV), obtained from the high-Schmidt limit of the Landau-Lifschitz fluctuating hydrodynamic equations for a binary mixture. We consider an initial planar interface of the mean concentration field in an infinite space domain, idealizing prior experiments. Using methods borrowed from turbulence theory, we show both analytically and numerically that a quasi-steady regime with self-similar time decay of concentration correlations appears at long time. In addition to the expected ``giant concentration fluctuations'' with correlations $\propto r$ for $r\lesssim L(t)=(Dt)^{1/2},$ with diffusivity $D,$ a new regime with spatial decay $\propto 1/r$ appears for $r\gtrsim L(t).$ The quasi-steady regime arises from an initial stage of transient growth $\propto t,$ confirming the prediction of DFV for $r\gtrsim L(t)$ and discovering an analogous result for $r\lesssim L(t).$ Our results give new insight into the emergence of non-equilibrium long-range correlations and provide novel predictions that may be investigated experimentally.
Authors: Nicholas Tovazzi, Gorka Muñoz-Gil, Michele Caraglio
Through evolution, bacteria have developed the ability to perform chemotactic motion in order to find nourishment. By adopting a machine learning approach, we aim to understand how this behavior arises. We consider run-and-tumble agents able to tune the instantaneous probability of switching between the run and the tumble phase. When such agents are navigating in an environment characterized by a concentration field pointing towards a circular target, we investigate how a chemotactic strategy may be learned starting from unbiased run-and-tumble dynamics. We compare the learning performances of agents that sense only the instantaneous concentration with those of agents having a short-term memory that allows them to perform temporal comparisons. While both types of learning agents develop successful target-search policies, we demonstrate that those achieved by agents endowed with temporal comparison abilities are significantly more efficient, particularly when the initial distance from the target is large. Finally, we also show that when an additional length scale is imposed, for example by fixing the initial distance to the target, the learning agents can leverage this information to further improve their efficiency in locating the target.
Authors: Mathias Zambach, Miriam Varón, Thomas Veile, Bima N. Sanusi, Matti Knaapila, Anders M. Jørgensen, László Almásy, Christer Johansson, Ziwei Ouyang, M. Beleggia, Cathrine Frandsen
We here present printable and castable magnetic nanocomposites containing superparamagnetic 11$\pm$3 nm $\gamma$-Fe$_2$O$_3$ particles in an insulating poly-vinyl alcohol polymer matrix. The nanocomposites feature well-dispersed particles with volume fractions between 10 and 45 \%, as confirmed by small-angle neutron scattering. The magnetic volume susceptibility is as high as 17, together with negligible hysteresis at low frequency, and constant AC-response up to the high-kHz range. Measured hysteresis curves at 100-900 kHz with up to 110 mT induced $B$-fields in the nanocomposite show that power losses depend on $B$-field squared, and frequency to the power of 1-1.3. The only loss mechanism in the nanocomposite is hysteresis losses at $>$100 kHz frequencies, where the largest particles in the 11$\pm$3 nm distribution transition from the superparamagnetic to blocked regime. To mitigate the resulting hysteresis losses (up 10$^2$-10$^5$ kW/m$^3$) a more narrow particle size distribution could be used for future materials. The presented material is eddy current-free and easily integrated into micro-fabrication protocols, as we demonstrate by fabrication of 3-turn print circuit board based inductors with cast/manual printed nanocomposite inductor cores, on which induction has been measured up to 100 MHz.
Authors: P. Skokowski (1), M. Matczak (1), Ł. Frąckowiak (1), T. Bednarchuk (2), M. Kowacz (1), B. Anastaziak (1 and 3), K. Synoradzki (1) ((1) Institute of Molecular Physics, Polish Academy of Sciences, Poznań, Poland, (2) Institute of Low Temperatures and Structural Research, Polish Academy of Sciences, Wrocław, Poland, (3) NanoBioMedical Centre, Adam Mickiewicz University, Poznań, Poland)
We present the structural, magnetic, and magnetocaloric properties of amorphous thin films Tb-Co and Dy-Co with stoichiometry Tb$_{31}$Co$_{69}$ and Dy$_{31}$Co$_{69}$, deposited on naturally oxidized silicon Si (100) substrates. Samples with a thickness $d=50$ nm covered with a protective Au overlayer with a thickness $d_{\rm Au} =5 $ nm were produced using the pulsed laser deposition technique. The X-ray diffraction analysis indicated the presence of a crystallized Laves phase in the prepared materials. Magnetization measurements as a function of temperature revealed ferrimagnetic behavior in both samples. We estimated the compensation temperature $T_{\rm comp}$ of the amorphous phase for Tb$_{31}$Co$_{69}$ at 81.5 K and for Dy$_{31}$Co$_{69}$ at 88.5 K, while we found the Curie temperature $T_{\rm C,\ Laves}$ of the crystallized Laves phases at 204.5 K and at 117 K, respectively. We investigated the magnetocaloric effect in a wide temperature range, covering $T_{\rm comp}$ of amorphous phases and $T_{\rm C,\ Laves}$ of crystallized Laves phases. The analysis for the magnetic field change of $\Delta \mu_0H=5$ T showed values of the magnetic entropy change of $-\Delta S_{\rm M}=4.9$ mJ cm$^{-3}$ K$^{-1}$ at $T_{\rm comp}$ and $-\Delta S_{\rm M}=6.6$ mJ cm$^{-3}$ K$^{-1}$ at $T_{\rm C,\ Laves}$ for Tb$_{31}$Co$_{69}$, while for Dy$_{31}$Co$_{69}$, we determined the values of $-\Delta S_{\rm M}=35$ mJ cm$^{-3}$ K$^{-1}$ at $T_{\rm comp}$ and $-\Delta S_{\rm M}=28$ mJ cm$^{-3}$ K$^{-1}$ at $T_{\rm C,\ Laves}$.
Authors: Khushi Mahajan, Chamkor Singh
We consider pattern formation in a sheared dense mixture of cohesive and non-cohesive grains. Our findings show that cohesive grains, which would typically form distributed agglomerates, instead segregate into percolating stripes or layers when the cohesive grain concentration ($c_o$) and cohesion strength ($C$) increase -- in a way that the average agglomerate size and the average normal stress collapse onto a single curve when plotted against $c_oC$. Our central proposal is that the development of interfaces between cohesive and non-cohesive grains is akin to phase separation in binary molecular mixtures driven by an effective free energy, although we are dealing with a non-equilibrium system; we setup the segregation flux such that the effect of this free energy is activated only upon application of the external driving. By constructing the segregation flux proportional to the gradient of the variational derivative of the free energy, we closely reproduce the layering in the steady-state limit. We find a robust correspondence between the parameter $c_o C$ in the discrete simulations and the parameters in the free energy.
Authors: Michael L. Li, Dingyu Shen, Jesus A. del Alamo, Martin Z. Bazant
Three-terminal electrochemical ionic synapses (EIoS) have recently attracted interest for in-memory computing applications. These devices utilize electrochemical ion intercalation to modulate the ion concentration in the channel material. The electrical conductance, which is concentration dependent, can be read separately and mapped to a non-volatile memory state. To compete with other random access memory technologies, linear and symmetric conductance modulation is often sought after, properties typically thought to be limited by the slow ion diffusion timescale. A recent study by Onen et al.[1] examining protonic EIoS with a tungsten oxide (WO3) channel revealed that this limiting timescale seemed irrelevant, and linear conductance modulation was achieved over nanosecond timescales, much faster than the bulk ion diffusion. This contrasts with previous studies that have shown similar conductance modulation with pulse timescales of milliseconds to seconds. Understanding the phenomena behind these conductance modulation properties in EIoS systems remains a crucial question gating technological improvements to these devices. Here, we provide a theoretical explanation that demonstrates how linearity and symmetry arise from consistent control over the electrolyte-WO3 interface. Comparing these past works, changes in the WO3 channel crystallinity were identified, affecting material thermodynamics and revealing that the device achieving nanosecond pulse timescales underwent phase separation. Coupling of electric field polarizatino and increased electron conductivity in high-concentration filaments, the reaction environment at the gate electrode can be controlled, resulting in ideal conductance modulation within the diffusion-limited regime. This work highlights the potential for phase-separating systems to overcome the traditional diffusion barriers that limit EIoS performance.
Authors: Giulia Janzen, Euan D. Mackay, Rastko Sknepnek, D. A. Matoz-Fernandez
Curvature plays a central organizational role in active polymer dynamics. Using large-scale Langevin-dynamics simulations, we study active semiflexible filaments confined to smooth curved surfaces and map how curvature, bending rigidity, and activity interact. We find geodesic alignment, curvature lensing, and curvature-induced trapping. In particular, regions of negative Gaussian curvature localize filaments and hinder global surface exploration. These results show how surface geometry can be used to control the organization and transport of active matter on curved substrates
Authors: Robbe De Prins, Guy Van der Sande, Peter Bienstman, Thomas Van Vaerenbergh
Ising machines (IMs) are specialized devices designed to efficiently solve combinatorial optimization problems. Among such problems, Boolean Satisfiability (SAT) is particularly relevant in industrial applications. To solve SAT problems using IMs, it is crucial to incorporate higher-order interactions. However, in analog IMs, interactions of different orders scale unevenly with the continuous spin amplitudes, introducing imbalances that can significantly degrade performance. We present a numerical comparison of methods to mitigate these imbalances, evaluating time-to-solution and success rate on Uniform Random 3-SAT instances from the SATLIB benchmark set. Our results show that the most effective approach employs spin interactions that are proportional to the signs of spins, rather than their continuous amplitudes. This generalizes our previous work, which showed that such interactions best mitigate imbalances induced by external fields in quadratic analog IMs. In this work, its advantage becomes substantially more pronounced, as it naturally mitigates imbalances across all interaction orders. We further demonstrate that smooth approximations of this method make it compatible with analog hardware. Our findings underscore the central role of spin-sign-based interactions in enabling robust and scalable analog IM dynamics.
Authors: Dominick S. Scaletta, Ngoc Thanh Mai Tran, Marta Musso, Dean G. Jarrett, Heather M. Hill, Massimo Ortolano, David B. Newell, Albert F. Rigosi
This work introduces a pseudofractal analysis for optimizing high-resistance graphene-based quantized Hall array resistance standards (QHARS). The development of resistance standard device designs through star-mesh transformations is detailed, aimed at minimizing element count. Building on a recent mathematical framework, the approach presented herein refines QHARS device concepts by considering designs incorporating pseudofractals (which may be expressed as star-mesh transformations). To understand how future QHARS pseudofractal designs enable varying sizes of neighborhoods of available quantized resistance, Minkowski-Bouligand algorithms are used to analyze fractal dimensions of the device design topologies. Three distinct partial recursion cases are explored in addition to the original full recursion design, and expressions for their total element counts are derived. These partial recursions, assessed through their fractal dimensions, offer enhanced flexibility in achieving specific resistance values within a desired neighborhood compared to full recursion methods, albeit with an increased number of required elements. The formalisms presented are material-independent, making them broadly applicable to other quantum Hall systems and artifact standards.
Authors: I. Babich, I. Reznikov, I. Begichev, A. E. Kazantsev, S. Slizovskiy, D. Baranov, M. Siskins, Z. Zhan, P. A. Pantaleon, M. Trushin, J. Zhao, S. Grebenchuk, K. S. Novoselov, K. Watanabe, T. Taniguchi, V. I. Falko, A. Principi, A. I. Berdyugin
The electronic quality of graphene has improved significantly over the past two decades, revealing novel phenomena. However, even state-of-the-art devices exhibit substantial spatial charge fluctuations originating from charged defects inside the encapsulating crystals, limiting their performance. Here, we overcome this issue by assembling devices in which graphene is encapsulated by other graphene layers while remaining electronically decoupled from them via a large twist angle (~10-30°). Doping of the encapsulating graphene layer introduces strong Coulomb screening, maximized by the sub-nanometer distance between the layers, and reduces the inhomogeneity in the adjacent layer to just a few carriers per square micrometre. The enhanced quality manifests in Landau quantization emerging at magnetic fields as low as ~5 milli-Tesla and enables resolution of a small energy gap at the Dirac point. Our encapsulation approach can be extended to other two-dimensional systems, enabling further exploration of the electronic properties of ultrapure devices.
Authors: Dominick S. Scaletta, Ngoc Thanh Mai Tran, Marta Musso, Valery Ortiz Jimenez, Heather M. Hill, Dean G. Jarrett, Massimo Ortolano, Curt A. Richter, David B. Newell, Albert F. Rigosi
This work elaborates on how one may develop high-resistance quantized Hall array resistance standards (QHARS) by using star-mesh transformations for element count minimization. Refinements are made on a recently developed mathematical framework optimizing QHARS device designs based on full, symmetric recursion by reconciling approximate device values with exact effective quantized resistances found by simulation and measurement. Furthermore, this work explores the concept of fractal dimension, clarifying the benefits of both full and partial recursions in QHARS devices. Three distinct partial recursion cases are visited for a near-1 Gigaohm QHARS device. These partial recursions, analyzed in the context of their fractal dimensions, offer increased flexibility in accessing desired resistance values within a specific neighborhood compared to full recursion methods, though at the cost of the number of required devices.
Authors: Rasmus S. Nielsen, Axel G. Medaille, Arnau Torrens, Oriol Segura-Blanch, Seán R. Kavanagh, David O. Scanlon, Aron Walsh, Edgardo Saucedo, Marcel Placidi, Mirjana Dimitrievska
Selenium is experiencing renewed interest as a elemental semiconductor for a range of optoelectronic and energy applications due to its irresistibly simple composition and favorable wide bandgap. However, its high volatility and low radiative efficiency make it challenging to assess structural and optoelectronic quality, calling for advanced, non-destructive characterization methods. In this work, we employ a closed-space encapsulation strategy to prevent degradation during measurement and enable sensitive probing of vibrational and optoelectronic properties. Using temperature-dependent Raman and photoluminescence spectroscopy, we investigate grown-in stress, vibrational dynamics, and electron-phonon interactions in selenium thin films synthesized under nominally identical conditions across different laboratories. Our results reveal that short-range structural disorder is not intrinsic to the material, but highly sensitive to subtle processing variations, which strongly influence electron-phonon coupling and non-radiative recombination. We find that such structural disorder and grown-in stress likely promote the formation of extended defects, which act as dominant non-radiative recombination centers limiting carrier lifetime and open-circuit voltage in photovoltaic devices. These findings demonstrate that the optoelectronic quality of selenium thin films can be significantly improved through precise control of synthesis and post-deposition treatments, outlining a clear pathway toward optimizing selenium-based thin film technologies through targeted control of crystallization dynamics and microstructural disorder.
Authors: Qing Zhang, Karin M. Rabe, Xiaohui Liu
Could electrons stabilize ferroelectric polarization in unpolarized system? Basically, electron doping was thought to be contrary to polarization due to the well-known picture that the screening effect on Coulomb interaction diminishes ferroelectric polarization. However, in this paper, we propose a novel mechanism of stabilizing highly-polar supertetragonal BaSnO3 by electron doping. With moderate compressive strain applied, less than -5.5%, BaSnO3 exhibits stable nonpolarized normal tetragonal structure and an unstable supertetragonal state which is characterized with extremely large c/a ratio and giant polarization. We found that the band gap of the supertetragonal state is much smaller than the normal tetragonal state, with a difference around 1.2eV. Therefore, the energy of the doped electrons selectively favors the smaller gap supertetragonal state than the larger band gap normal tetragonal state, and the critical strain to stabilize the supertetragonal phase could be reduced by electron doping. This mechanism guarantees the controllable supertetragonal structures by electron doping and ensures the coexistence of giant polarization and conducting in high-mobility BaSnO3, and is promising to design high-mobility ferroelectrics conductor.
Authors: Leyla Majidi, Azadeh Faridi, Reza Asgari
Motivated by recent progress in employing two key classes of two-dimensional materials-topological insulators and transition-metal dichalcogenides (TMDCs)-as spin sources for generating spin-orbit torque (SOT), we investigate current-induced spin polarization and the resulting SOT in bilayers composed of a TMDC (WSe$_2$ or MoSe$_2$) and ferromagnetic chromium iodide (CrI$_3$), beyond the linear response regime. Using the steady-state Boltzmann equation, we find that intra-band transitions yield a strong field-like torque on the CrI$_3$ layer, while inter-band transitions give rise to a comparatively weaker damping-like torque in the WSe$_2$/CrI$_3$ system. Remarkably, the damping-like component is enhanced by up to three orders of magnitude in n-doped MoSe$_2$, reaching a strength comparable to the field-like torque, which itself is an order of magnitude larger than that in the WSe$_2$-based bilayer. Both torque components exhibit strong asymmetry between n-type and p-type doping in WSe$_2$ and MoSe$_2$ systems. Furthermore, we demonstrate that the twist angle plays a crucial role: depending on the TMDC and chemical potential, twisting can reverse the sign of the SOT and significantly modulate its magnitude. Finally, we show that a transverse gate electric field enables substantial tunability of the SOT, by nearly one order of magnitude, and induces a sign reversal at a twist angle of $10.16^{\circ}$.
Authors: Rishish Mishra, Harish Pothukuchi, Harinadha Gidituri, Juho Lintuvuori
Motivated by recent experiments of motile bacteria crossing liquid-liquid interfaces of isotropic- nematic coexistence (Cheon et al., Soft Matter 20: 7313-7320, 2024), we study the dynamics of prolate microswimmers traversing clean liquid-liquid interfaces. Using large-scale lattice Boltzmann simulations, we observe that neutrally wetting swimmers can be either trapped or cross the in- terface, depending on their initial angle, swimming speed and the interfacial tension between the two fluids. The simulation results are rationalized by considering a competition between interfacial (thermodynamic) and active (hydrodynamic) forces. The swimmers get trapped at the interface due to a thermodynamic trapping force, akin to Pickering effect, when the forces from interfacial tension dominate over the swimming forces. The trapping behavior can be captured by calculating a critical capillary number by balancing the interfacial and active energies. This prediction agrees remarkably well with the numerical simulations as well as the bacterial experiments of Cheon et al., (Soft Matter 20: 7313-7320, 2024). Finally, our results demonstrate that the torque resulting in a reorientation of the swimmers parallel to the interface have both hydro and thermodynamic components.
Authors: Pierre Lechifflart, Raisa-Ioana Biega, Linn Leppert
Three-dimensional metal halide double perovskites such as Cs$_2$AgBiBr$_6$ exhibit pronounced excitonic effects due to their anisotropic electronic structure and chemical localization effects. Their two-dimensional derivatives, formed by inserting organic spacer molecules between perovskite layers, were expected to follow well-established trends seen in Pb-based 2D perovskites, namely, increasing exciton binding energies with decreasing layer thickness due to enhanced quantum and dielectric confinement. However, recent experimental and computational studies have revealed anomalous behavior in Ag/Bi-based 2D perovskites, where this trend is reversed. Using ab initio many-body perturbation theory within the $GW$ and Bethe-Salpeter Equation frameworks, we resolve this puzzle by systematically comparing experimental structures with idealized models designed to isolate the effects of octahedral distortions, interlayer separation, and stacking. We find that structural distortions, driven by directional Ag d orbital bonding, govern the momentum-space origin and character of the exciton, and are the primary cause of the observed non-monotonic trends. Furthermore, we explore how interlayer distance and stacking influence band gaps and exciton binding energies, showing that, despite different chemistry, the underlying confinement physics mirrors that of Pb-based 2D perovskites. Our results establish design principles for tuning excitonic properties in this broader class of layered, lead-free materials.
Authors: Brindhu Malani S, Eugen Klein, Ronja Maria Piehler, Rostyslav Lesyuk, Christian Klinke
Quasi-2D metal halide perovskites have emerged as a promising material for photodetection due to excellent optoelectronic properties, simple synthesis, and robust stability. Albeit, developing high-performance photodetectors based on low-dimensional quasi-2D metal halide perovskite nanoparticles remains challenging due to quantum and dielectric confinement effects. Several approaches have been employed to improve efficiency, with plasmonic nanostructures being among the most effective ones. The resonant energy transfer and coupling between plasmons and excitons play a vital role in enhancing device performance. Here, we demonstrate enhanced photodetection of quasi-2D perovskite nanostripes resulting from the incorporation of octadecanethiol (ODT) functionalized Ag nanostructure arrays (ANA). Using colloidal lithography, ANA were fabricated. Reflectance spectroscopy and finite element method (FEM) simulations show that ANA supports localised surface plasmon resonance (LSPR) modes that spectrally coincide with the absorption and emission band of the perovskite. This spectral overlap enables interesting coupling interactions between the excitons and plasmons. The ODT-functionalized ANA photodetectors exhibit weak to intermediate coupling, resulting in a photocurrent enhancement factor of 838 %. They achieve photoresponsivities of up to 70.41 mA W^-1, detectivities of 1.48*10^11 Jones and external quantum efficiencies of 21.55 %, which are approximately 10 times higher than those of the reference photodetector. We present an approach to optimize the plasmon-exciton coupling and non-radiative energy transfer for developing high-performance plasmonic-perovskite hybrid photodetectors.
Authors: Marc Túnica, Francesca Chiodi, Michele Amato
Pushing dopant concentrations beyond the solubility limit in semiconductors -- a process known as hyperdoping -- has been demonstrated as an effective strategy for inducing superconductivity in cubic-diamond Si and SiGe materials. Additionally, previous studies have reported that several polytypes of Si may exhibit a type-I superconducting state under high pressure. In this work, we employ ground-state Density Functional Theory simulations to investigate the effects of both low and high B doping concentrations on the structural and thermodynamic properties of hexagonal-diamond SiGe alloys, with a systematic comparison to their cubic-diamond counterparts. Our results highlight three key findings: (i) structural analysis confirms that the lattice parameters of SiGeB alloys adhere to a ternary Vegard's law, consistent with observations in cubic-diamond SiGe alloys. However, at high doping concentrations, B incorporation can locally disrupt the hexagonal symmetry, particularly in the presence of B clustering; (ii) dopant formation energy calculations reveal that B is thermodynamically more stable in the hexagonal phase than in the cubic phase across all Ge concentrations, regardless of the doping level; (iii) mixing enthalpy calculations demonstrate that hyperdoped hexagonal-diamond SiGe alloys are thermodynamically stable across the full range of Ge compositions and that their tendency for hyperdoping is more favorable than that of cubic-diamond SiGe alloys. Taken together, these findings indicate that hyperdoping is experimentally viable in hexagonal-diamond SiGe alloys and, in light of previous evidence, position these materials as a promising platform for the exploration of superconductivity in group IV semiconductors.
Authors: Koustav Roy, Dipendu Halder, Koustabh Gogoi, B. Tanatar, Saurabh Basu
Periodically driven systems intertwined with non-Hermiticity opens a rich arena for topological phases that transcend conventional Hermitian limits. The physical significance of these phases hinges on obtaining the topological invariants that restore the bulk-boundary correspondence, a task well explored for static non-Hermitian (NH) systems, while it remains elusive for the driven scenario. Here, we address this problem by constructing a generalized Floquet non-Bloch framework that analytically captures the spectral and topological properties of time-periodic NH systems. Em- ploying a high-frequency Magnus expansion, we analytically derive an effective Floquet Hamiltonian and formulate the generalized Brillouin zone for a periodically driven quasi-one-dimensional system, namely, the Creutz ladder with a staggered complex potential. Our study demonstrates that the skin effect remains robust (despite the absence of non-reciprocal hopping) across a broad range of driving parameters, and is notably amplified in the low-frequency regime due to emergent longer- range couplings. We further employ a symmetric time frame approach that generates chiral-partner Hamiltonians, whose invariants, when appropriately combined, account for the full edge-state struc- ture. To substantiate the theoretical framework, we propose a topolectrical circuit (TEC) that serves as a viable experimental setting. Apart from capturing the skin modes, the proposed TEC design faithfully reproduces the presence of distinct Floquet edge states, as revealed through the voltage and impedance profiles, respectively. Thus, our work not only offers a theoretical framework for exploring NH-driven systems, but also provides an experimentally feasible TEC architecture for realizing these phenomena stated above in a laboratory.
Authors: Radha Balakrishnan, Rossen Dandoloff, Victor Atanasov, Avadh Saxena
We derive the Schrödinger equation for a particle confined to the surface of a normal and a binormal helical nanoribbon, obtain the quantum potentials induced by their respective curved surface geometries, and study the localized states of the particle for each ribbon. When the particle momentum satisfies a certain geometric condition, the particle localizes near the inner edge for a normal ribbon, and on the central helix for a binormal ribbon. This result suggests the presence of a pseudo-force that pushes the particle transversely along the width of the ribbon. We show that this phenomenon can be interpreted as a quantum analog of the Coriolis effect, which causes a transverse deflection of a classical particle moving in a rotating frame. We invoke Ehrenfest's theorem applicable to localized states and identify the quantized angular velocities of the rotating frames for the two ribbons. If the particle is an electron, its localization at a specific width gives rise to a Hall-like voltage difference across the ribbon's width. However, unlike in the Hall effect, its origin is not an applied magnetic field, but the ribbon's curved surface geometry. When a normal helical ribbon is mechanically flipped to a binormal configuration in a periodic fashion, it results in a periodic electron transport from the inner edge to the center, giving rise to a quantum AC voltage. This can be used for designing nanoscale electromechanical devices. Quantum transport on a helical nanoribbon can be controlled by tuning the bends and twists of its surface, suggesting diverse applications in biopolymers and nanotechnology.
Authors: Masafumi Fukuma, Yusuke Namekawa
The Worldvolume Hybrid Monte Carlo (WV-HMC) method [arXiv:2012.08468] is an efficient and low-cost algorithm for addressing the sign problem. It mitigates the sign problem while avoiding the ergodicity issues that are intrinsic to algorithms based on Lefschetz thimbles. In this study, we apply the WV-HMC method to the Hubbard model away from half filling, which is known to suffer from a severe sign problem. We compute the number density on lattices of spatial size $6 \times 6$ and $8 \times 8$ at inverse temperature $\beta = 6.4$ using $N_t = 20$ Trotter steps. Our results show that the WV-HMC method remains effective even in parameter regions where non-thimble Monte Carlo methods fail due to severe sign problems. In this work, we employ direct solvers for fermion matrix inversion, with a computational cost of $O(N^3)$, where $N$ is the number of degrees of freedom and proportional to the spacetime lattice volume. An alternative algorithm employing pseudofermions and iterative solvers, which reduces the cost to $O(N^2)$ at the expense of careful parameter tuning, will be discussed in a separate publication.
Authors: Kaan Alp Yay, W. Joe Meese, Elliot Kisiel, Matthew J. Krogstad, Anisha G. Singh, Rafael M. Fernandes, Zahir Islam, Ian R. Fisher
Electronic nematic order is a correlated phase of matter in which low-energy electronic states spontaneously break a discrete rotational symmetry of a crystal lattice. Bilinear coupling between the electronic nematic and strains of the same symmetry yields a single pseudoproper ferroelastic phase transition at which both the nematic and lattice strain onset concurrently. To minimize elastic energy, the crystal forms structural twin domains, each with a distinct orientation of the nematic director (i.e. each with a specific sign of the induced shear strain). While the effects of externally induced strains on these domains are well established, the intrinsic behavior of spontaneous strain fields within individual domains has been hitherto unexplored, largely due to the lack of appropriate experimental tools. Here, we report the discovery of spontaneous mesoscopic strain waves within individual nematic domains of an underdoped iron-based superconductor, observed using dark-field X-ray microscopy (DFXM). This technique combines high spatial and reciprocal-space resolution with full-field, bulk-sensitive imaging, enabling direct visualization of subdomain strain modulations emerging concurrently with the onset of nematic order. The elastic compatibility relations that govern inhomogeneous strains in continuous solids provide a natural mechanism for the emergent strain waves that we observe. Our findings reveal a broadly relevant form of strain self-organization and position DFXM as a powerful tool for probing the local interplay between lattice strain and electronic order.
Authors: W. Joe Meese, Rafael M. Fernandes
Electronic nematicity is widely observed in quantum materials with varying degrees of electronic correlation, manifesting through charge, spin, orbital, or superconducting degrees of freedom. A phenomenological model capable of describing this broad set of systems must also account for nemato-elasticity, by which nematic and elastic degrees of freedom become intertwined. However, being a tensor gauge field theory, elasticity must satisfy the compatibility relations which guarantee the integrability of lattice deformations. Here, we develop a formalism for nemato-elasticity that manifestly respects the elastic compatibility relations. We show that these constraints bifurcate the phase space of nematic fluctuations into two orthogonal sectors: one compatible and thus critical, the other incompatible and therefore gapped. The suppression of the latter leads to universal direction-selective nematic criticality in any crystal lattice. Moreover, the critical nematic modes are protected from pinning effects induced by microscopic defect strains, which necessarily induce both longitudinal and transverse correlated random fields. Finally, our results also reconcile seemingly contradictory nematic phenomena, such as the mean-field character of the nematic transition and the widespread presence of domain formation.
Authors: W. Joe Meese, Rafael M. Fernandes
The defining property of electronic nematicity -- the spontaneous breaking of rotational symmetry -- implies an unavoidable coupling between the nematic order parameter and elastic strain fields, known as nemato-elasticity. While both quantities are rank-2 tensors, the strain tensor is constrained through the Saint Venant compatibility relations. These three coupled second-order partial differential equations arise from the lattice displacement vector's role as a potential field, and they reflect the underlying gauge invariance of geometric deformations which are violated only in the presence of crystalline defects. In this work, we develop a theory of nemato-elasticity that incorporates elastic compatibility explicitly through a co-rotating helical basis. With our formalism, we show elasticity bestows tensor compatibility upon the nematic order parameter by suppressing incompatible nematic fluctuations. As a result, nemato-elasticity is markedly different from bare nematicity. In ideal media devoid of defects, we show the suppression of incompatible nematicity underlies direction-selective criticality, even in the absence of crystalline anisotropy. In systems with defects, meanwhile, we show that elastic pinning fields emanate from quenched defects, generating random longitudinal and transverse conjugate fields for the local nematic order parameter. The coexistence of direction-selective nematic criticality with pinning effects from random fields is explained within our theory from the transformation to the helical basis, implying that local experimental probes of nematicity will be influenced by a linear -- but nonlocal -- combination of long-ranged and short-ranged helical nematic modes. Because the compatibility relations are gauge constraints endowed in the isotropic medium, our results constitute universal features of nemato-elastic criticality present in all crystalline systems.
Authors: Umesh Kumar, Rafal Rechcinski, Tatiana de Picoli, Jukka Vayrynen, Satoshi Okamoto
Interfaces between topological insulators and superconductors are promising platforms for realizing Majorana zero modes (MZMs) via the superconducting proximity effect. We introduce a bilayer model consisting of the surface states of a three-dimensional topological insulator (3DTI) coupled to an $s$-wave superconductor and systematically study the role of interlayer tunneling strength ($t_\perp$). We find that increasing $t_\perp$ shifts the proximity-induced (PrI) gap minima away from the $\Gamma$-point, giving rise to momentum-selective interference patterns that manifest as spatial oscillations in the in-gap states. By introducing an antidot with a magnetic vortex in the SC layer, we investigate the nature of in-gap states including MZMs and Caroli-de Gennes-Matricon (CdGM) modes. With increasing hybridization strength, the energy separation between MZMs and CdGM states increases, enhancing the isolation of MZMs. Importantly, in the strong hybridization limit, the leading CdGM separation remains large inspite of the decrease in the PrI gap. Spin- and spatial-resolved wavefunction analysis reveals angular momentum asymmetries absent in conventional $s$-wave systems. A direct comparison with a standalone $s$-wave superconductor confirms the emergence of distinct $p$-wave-like features in the bilayer geometry. Our results provide experimentally relevant predictions for tuning the stability of MZMs and their differentiation from the CdGM modes in SC-3DTI heterostructures and offer a theoretical framework for probing unconventional superconductivity in engineered topological systems.
Authors: Alexander C. Tyner, Vladimir Juricic, Bitan Roy
The interplay of disorder and dimensionality governs the emergence and stability of electronic phases in quantum materials and quantum phase transitions among them. While three-dimensional (3D) dirty Fermi liquids and Weyl semimetals support robust metallic states, undergoing disorder-driven Anderson localization transitions at strong disorder and the later ones exhibiting additional semimetal-to-metal transition at moderate disorder, conventional two-dimensional (2D) non-interacting systems localize for arbitrarily weak disorder. Here, we show that 2D disordered projected branes, constructed by systematically integrating out degrees of freedom from a 3D cubic lattice via the Schur decomposition, faithfully reproduce the full quantum phase diagram of their 3D parent systems. Using large-scale exact diagonalization and kernel polynomial method, we numerically demonstrate that 2D projected branes host stable metallic and semimetallic phases. Remarkably, the critical exponents governing the semimetal-to-metal and metal-insulator transitions on such 2D projected branes are sufficiently close to those of their 3D counterparts. Our findings thus establish 2D projected branes as genuine quantum holographic images of their higher-dimensional disordered parent crystals, supporting stable semimetallic and metallic phases that are otherwise inaccessible in conventional 2D lattices. Finally, we point to experimentally accessible metamaterial platforms, most notably the photonic lattices with tunable refractive-index disorder, as promising systems to realize and probe these phenomena.
Authors: Archisman Panigrahi, Bitan Roy
Projected branes are constituted by only a small subset of sites of a higher-dimensional crystal, otherwise placed on a hyperplane oriented at an irrational or a rational slope therein, for which the effective Hamiltonian is constructed by systematically integrating out the sites of the parent lattice that fall outside such branes [Commun. Phys. 5, 230 (2022)]. Specifically, when such a brane is constructed from a square lattice, it gives rise to an aperiodic Fibonacci quasi-crystal or its rational approximant in one dimension. In this work, starting from square lattice-based models for topological crystalline insulators, protected by the discrete four-fold rotational ($C_4$) symmetry, we show that the resulting one-dimensional projected topological branes encode all the salient signatures of such phases in terms of robust endpoint zero-energy modes, quantized local topological markers, and mid-gap modes bound to dislocation lattice defects, despite such linear branes being devoid of the $C_4$ symmetry of the original lattice. Furthermore, we show that such branes can also feature all the hallmarks of two-dimensional strong and weak topological superconductors through Majorana zero-energy bound states residing near their endpoints and at the core of dislocation lattice defects, besides possessing suitable quantized local topological markers. Finally, we showcase a successful incarnation of a square lattice-based second-order topological insulator with the characteristic corner-localized zero modes in its geometric descendant one-dimensional quasi-crystalline or crystalline branes that feature a quantized localizer index and endpoint zero-energy modes only when one of its end points passes through a corner of the parent crystal. Possible designer quantum and meta material-based platforms to experimentally harness our theoretically proposed topological branes are discussed.
Authors: Bingjia Xiao, Tao Chen, Wenbin Zhang, Xin Qian, Puqing Jiang
Frequency-domain thermoreflectance (FDTR) is a widely used technique for characterizing thermal properties of multilayer thin films. However, extracting multiple parameters from FDTR measurements presents a nonlinear inverse problem due to its high dimensionality and multimodal, non-convex solution space. This study evaluates four popular global optimization algorithms: Genetic Algorithm (GA), Quantum Genetic Algorithm (QGA), Particle Swarm Optimization (PSO), and Fireworks Algorithm (FWA), for extracting parameters from FDTR measurements of a GaN/Si heterostructure. However, none achieve reliable convergence within 60 seconds. To improve convergence speed and accuracy, we propose an AI-driven hybrid optimization framework that combines each global algorithm with a Quasi-Newton local refinement method, resulting in four hybrid variants: HGA, HQGA, HPSO, and HFWA. Among these, HPSO outperforms all other methods, with 80% of trials reaching the target fitness value within 60 seconds, showing greater robustness and a lower risk of premature convergence. In contrast, only 30% of HGA and HQGA trials and 20% of HFWA trials achieve this threshold. We then evaluate the worst-case performance across 100 independent trials for each algorithm when the time is extended to 1000 seconds. Only HPSO, PSO, and HGA consistently reach the target accuracy, with HPSO converging five times faster than the others. HPSO provides a general-purpose solution for inverse problems in thermal metrology and can be readily extended to other model-fitting techniques.
Authors: Ya-Nan Lu, Dong Yuan, Yixuan Ma, Yan-Qing Liu, Si Jiang, Xiang-Qian Meng, Yi-Jie Xu, Xiu-Ying Chang, Chong Zu, Hong-Zheng Zhao, Dong-Ling Deng, Lu-Ming Duan, Pan-Yu Hou
Understanding and controlling non-equilibrium dynamics in quantum many-body systems is a fundamental challenge in modern physics, with profound implications for advancing quantum technologies. Typically, periodically driven systems in the absence of conservation laws thermalize to a featureless "infinite-temperature" state, erasing all memory of their initial conditions. However, this paradigm can break down through mechanisms such as integrability, many-body localization, quantum many-body scars, and Hilbert space fragmentation. Here, we report the experimental observation of dynamical freezing, a distinct mechanism of thermalization breakdown in driven systems, and demonstrate its application in quantum sensing using an ensemble of approximately $10^4$ interacting nitrogen-vacancy spins in diamond. By precisely controlling the driving frequency and detuning, we observe emergent long-lived spin magnetization and coherent oscillatory micromotions, persisting over timescales exceeding the interaction-limited coherence time ($T_2$) by more than an order of magnitude. Leveraging these unconventional dynamics, we develop a dynamical-freezing-enhanced ac magnetometry that extends optimal sensing times far beyond $T_2$, outperforming conventional dynamical decoupling magnetometry with a 4.3 dB sensitivity enhancement. Our results not only provide clear experimental observation of dynamical freezing -- a peculiar mechanism defying thermalization through emergent conservation laws -- but also establish a robust control method generally applicable to diverse physical platforms, with broad implications in quantum metrology and beyond.
Authors: Gabriele Calliari, Robert Ott, Hannes Pichler, Torsten V. Zache
The simulation of quantum field theories, both classical and quantum, requires regularization of infinitely many degrees of freedom. However, in the context of field digitization (FD) -- a truncation of the local fields to $N$ discrete values -- a comprehensive framework to obtain continuum results is currently missing. Here, we propose to analyze FD by interpreting the parameter $N$ as a coupling in the renormalization group (RG) sense. As a first example, we investigate the two-dimensional classical $N$-state clock model as a $\mathbb{Z}_N$ FD of the $U(1)$-symmetric $XY$-model. Using effective field theory, we employ the RG to derive generalized scaling hypotheses involving the FD parameter $N$, which allows us to relate data obtained for different $N$-regularized models in a procedure that we term $\textit{field digitization scaling}$ (FDS). Using numerical tensor-network calculations at finite bond dimension $\chi$, we further uncover an unconventional universal crossover around a low-temperature phase transition induced by finite $N$, demonstrating that FDS can be extended to describe the interplay of $\chi$ and $N$. Finally, we analytically prove that our calculations for the 2D classical-statistical $\mathbb{Z}_N$ clock model are directly related to the quantum physics in the ground state of a (2+1)D $\mathbb{Z}_N$ lattice gauge theory which serves as a FD of compact quantum electrodynamics. Our study thus paves the way for applications of FDS to quantum simulations of more complex models in higher spatial dimensions, where it could serve as a tool to analyze the continuum limit of digitized quantum field theories.
Authors: Heba A. Labib, Goksu Can Toga, J. K. Freericks, A. F. Kemper
Pump-probe spectroscopy is a powerful tool for probing response dynamics of quantum many-body systems in and out-of-equilibrium. Quantum computers have proved useful in simulating such experiments by exciting the system, evolving, and then measuring observables to first order, all in one setting. Here, we use this approach to investigate the mixed-field Ising model, where the longitudinal field plays the role of a confining potential that prohibits the spread of the excitations, spinons, or domain walls into space. We study the discrete bound states that arise from such a setting and their evolution under different quench dynamics by initially pumping the chain out of equilibrium and then probing various non-equal time correlation functions. Finally, we study false vacuum decay, where initially one expects unhindered propagation of the ground state, or true vacuum, bubbles into the lattice, but instead sees the emergence of Bloch oscillations that are directly the reason for the long-lived oscillations in this finite-size model. Our work sets the stage for simulating systems out-of-equilibrium on classical and quantum computers using pump-probe experiments without needing ancillary qubits.
Authors: Dmitry S. Ageev, Vladimir A. Bykov
In this paper, we study excited states in Anti-de Sitter (AdS) space prepared by local operator insertions of a massive scalar field, corresponding to operator quenches for free fields in AdS. Using the AdS/CFT correspondence, we compute the time evolution of boundary observables in the dual states. We then introduce a hard wall in AdS Poincare coordinates to impose an infrared cutoff, creating a confining deformation of the dual conformal field theory, and analyze the dynamics of excited states in this confining background. By comparing the evolution of boundary two-point correlation functions in the deformed theory to the statistics of Gaussian random matrix ensembles, we show that for sufficiently heavy operators the fluctuations approach quite close those of the Gaussian Unitary Ensemble (GUE). Finally, we extend our analysis to the compact BTZ black hole and its hard wall deformation, finding qualitatively similar behavior.
Authors: Agnese Marcato, Aleksandra Pachalieva, Ryley G. Hill, Kai Gao, Xiaoyu Wang, Esteban Rougier, Zhou Lei, Vinamra Agrawal, Janel Chua, Qinjun Kang, Jeffrey D. Hyman, Abigail Hunter, Nathan DeBardeleben, Earl Lawrence, Hari Viswanathan, Daniel O'Malley, Javier E. Santos
Accurately predicting when and how materials fail is critical to designing safe, reliable structures, mechanical systems, and engineered components that operate under stress. Yet, fracture behavior remains difficult to model across the diversity of materials, geometries, and loading conditions in real-world applications. While machine learning (ML) methods show promise, most models are trained on narrow datasets, lack robustness, and struggle to generalize. Meanwhile, physics-based simulators offer high-fidelity predictions but are fragmented across specialized methods and require substantial high-performance computing resources to explore the input space. To address these limitations, we present a data-driven foundation model for fracture prediction, a transformer-based architecture that operates across simulators, a wide range of materials (including plastic-bonded explosives, steel, aluminum, shale, and tungsten), and diverse loading conditions. The model supports both structured and unstructured meshes, combining them with large language model embeddings of textual input decks specifying material properties, boundary conditions, and solver settings. This multimodal input design enables flexible adaptation across simulation scenarios without changes to the model architecture. The trained model can be fine-tuned with minimal data on diverse downstream tasks, including time-to-failure estimation, modeling fracture evolution, and adapting to combined finite-discrete element method simulations. It also generalizes to unseen materials such as titanium and concrete, requiring as few as a single sample, dramatically reducing data needs compared to standard ML. Our results show that fracture prediction can be unified under a single model architecture, offering a scalable, extensible alternative to simulator-specific workflows.
Authors: Pushkar Mohile (1), Paul M. Goldbart (1) ((1) Stony Brook University, U.S.A.)
Proximity measurements probe whether pairs of particles are close to one another. We consider the impact of post-selected random proximity measurements on a quantum fluid of many distinguishable particles. We show that such measurements induce random spatial localization of a fraction of the particles, and yet preserve homogeneity macroscopically. Eventually, all particles localize, with a distribution of localization lengths that saturates at a scale controlled by the typical measurement rate. The steady-state distribution of these lengths is governed by a familiar scaling form.
Authors: Abdiel de Jesús Espinosa-Champo, Gerardo G. Naumis
Holey graphene (HG) is a novel two-dimensional (2D) material that has attracted considerable attention due to its remarkable electrical, thermal, and mechanical properties. The recent discovery of flat bands in HG has garnered significant interest. In this work, we systematically investigate the tunable plasmonic modes and optical conductivity of HG at or near the flat band condition by changing the holes radii and periodic configuration. It is found that HG presents nearly flat plasmonic bands in configurations with larger hole radii. Hyperbolic plasmons are found due to the breaking of the graphene's bipartite sublattice symmetry induced by the holes. Such an effect is also confirmed by looking at the optical conductivity, that also presents a marked anisotropy. The material's marked optical anisotropy leads to hyperbolic plasmons, making it a promising platform for nanophotonic applications.
Authors: Megan Powell, Euan Parry, Conor McGeough, Alexander Zotov, Alessandro Rossi
Silicon carbide is a wide-bandgap semiconductor with an emerging CMOS technology platform and it is widely deployed in high power and harsh environment electronics. This material is also attracting interest for quantum technologies through its crystal defects, which can act as spin-based qubits or single-photon sources. In this work, we assess the cryogenic performance of commercial power MOSFETs to evaluate their suitability for CMOS-compatible quantum electronics. We perform a statistical study of threshold voltage and subthreshold swing from 300 K down to 650 mK, focusing on reproducibility and variability. Our results show significant performance degradation at low temperatures, including large gate hysteresis, threshold voltage shifts, and subthreshold swing deterioration. These effects suggest instability in electrostatic control, likely due to carrier freeze-out and high interface trap density, which may pose challenges for the reliable use of this transistor technology towards the realisation of quantum devices or cryo-CMOS electronics.
Authors: Arjun Sharma, Donald L. Koch
The extensional rheology of dilute suspensions of spheres in viscoelastic or polymeric liquids is studied computationally. At low polymer concentration (c) and Deborah number (De), a wake of highly stretched polymers forms downstream of the particles due to larger local velocity gradients than the imposed flow, indicated by a positive deviation in local De. This increases the suspension's extensional viscosity with time and De for De less than 0.5. When De exceeds 0.5 (the coil-stretch transition), the fully stretched polymers from the far field collapse in regions with lower local velocity gradients around the particle's stagnation points, reducing suspension viscosity relative to the polymer-only liquid. The interaction between local flow and polymers intensifies with increasing c. Highly stretched polymers impede local flow, reducing local De, while it increases in regions with collapsed polymers. Initially, increasing c aligns local De and polymer stretch with far-field values, diminishing particle-polymer interaction effects. However, beyond a certain c, a new mechanism emerges. At low c, fluid three particle radii upstream exhibits increased local De, stretching polymers beyond their undisturbed state. As c increases, this deviation becomes negative, collapsing polymers and resulting in increasingly negative stress from particle-polymer interactions at large De and time. At high c, this negative interaction stress scales as c squared, surpassing the linear increase in polymer stress, making dilute sphere suspensions more effective at reducing the viscosity of viscoelastic liquids at larger De and c.
Authors: Diogo J. L. Rodrigues
The canonical-ensemble description of reactive quantum gas mixtures is reformulated by incorporating a single global particle-number-conservation constraint over the combined spectra of inter-converting species. This constraint replaces the conventional equality of chemical potentials. Fermi-Dirac or Bose-Einstein correlations naturally emerge across one-particle energy eigenstates of species sharing identical spin-statistics, which in ergodic single-systems manifest as intrinsic features of the equilibrium state. By embedding all microstates linked by conversion pathways, the framework incorporates concentration fluctuations in the statistical description. The formalism offers fresh insights into quantum chemical equilibrium in reactive mixtures with composition fluctuations and smoothly reduces to the classical ideal gas limit via an extended partition function that generalizes classical chemical-equilibrium treatments.
Authors: Simone Artini, Gabriele Lo Monaco, Alberto Imparato, Mauro Paternostro, Sandro Donadi
We rigorously analyze the non-equilibrium thermodynamic behavior of various formulations of quantum Brownian motion (QBM) using the framework of stochastic thermodynamics. While the widely used Caldeira-Leggett master equation exhibits desirable thermodynamic features, such as the fulfilment of a detailed balance, it fails to ensure complete positivity. In contrast, several completely positive and trace-preserving (CPTP) extensions turn out to be thermodynamically controversial. We show that such extensions introduce anomalous phase-space structures that violate detailed balance at the steady state, leading to non-vanishing entropy production and effective non-equilibrium current of unclear physical origins. Our results highlight a fundamental tension between quantum consistency and thermodynamic equilibration in open quantum systems.
Authors: Georgios Konstantinou
We present a reformulation of quantum adiabatic theory in terms of an emergent electromagnetic framework, emphasizing the physical consequences of geometric structures in parameter space. Contrary to conventional approaches, we demonstrate that a Berry electric field naturally arises in systems with dynamic Hamiltonian, when the full time-dependent wavefunction is used to define the gauge potentials. This surprising result bridges the gap between static and dynamical formulations and leads to a deeper understanding of how gauge structures manifest in quantum systems. Building on this, we construct Berry Maxwell equations by analogy with classical electrodynamics, defining Berry electric and magnetic fields as derivatives of scalar and vector potentials obtained from the full quantum state. We verify these equations explicitly and derive field-theoretic identities such as generalized continuity and vorticity relations. This field-based formulation reveals the topological charges, monopole structures, and gauge currents that underlie parameter space, and clarifies how Berry curvature corrections enter dynamical quantities like expectation values and particle velocities. Our results establish a new regime of emergent electromagnetism in parameter space, unifying time-independent and time-dependent geometric phases within a covariant formalism. The implications extend to quantum transport, polarization, and topological classification of phases, providing a robust and generalizable framework for quantum systems driven by adiabatic or nonadiabatic evolution.
Authors: Arvind Murugan, David Zwicker, Charlotta Lorenz, Eric R. Dufresne
To maintain homeostasis, living cells process information with networks of interacting molecules. Traditional models for cellular information processing have focused on networks of chemical reactions between molecules. Here, we describe how networks of physical interactions could contribute to the processing of information inside cells. In particular, we focus on the impact of biomolecular condensation, a structural phase transition found in cells. Biomolecular condensation has recently been implicated in diverse cellular processes. Some of these are essentially computational, including classification and control tasks. We place these findings in the broader context of physical computing, an emerging framework for describing how the native dynamics of nonlinear physical systems can be leveraged to perform complex computations. The synthesis of these ideas raises questions about expressivity (the range of problems that cellular phase transitions might be able to solve) and learning (how these systems could adapt and evolve to solve different problems). This emerging area of research presents diverse opportunities across molecular biophysics, soft matter, and physical computing.
Authors: Keiichi Shigechi
We study the Fuss--Catalan algebras, which are generalizations of the Temperley--Lieb algebra and act on generalized Dyck paths, through non-crossing partitions. First, the Temperley--Lieb algebra is defined on non-crossing partitions, and a bijection between a Dyck path and a non-crossing partition is shown to be compatible with the Temperley--Lieb algebra on Dyck paths, or equivalently chord diagrams. We show that the Kreweras endomorphism on non-crossing partitions is equivalent to the rotation of chord diagrams under the bijection. Secondly, by considering an increasing $r$-chain in the graded lattice of non-crossing partitions, we define the Fuss--Catalan algebras on increasing $r$-chains. Through a bijection between an increasing $r$-chain and a generalized Dyck path, one naturally obtains the Fuss--Catalan algebra on generalized Dyck paths. As generalizations of the Fuss--Catalan algebra, we introduce the one- and two-boundary Fuss--Catalan algebras. Increasing $r$-chains of symmetric non-crossing partitions give symmetric generalized Dyck paths by the bijection, and the boundary Fuss--Catalan algebras naturally act on them. We show that these representations are compatible with the diagrammatic representations of the algebras by use of generalized chord diagrams. Thirdly, we discuss the integrability of the Fuss--Catalan algebras. For the Fuss--Catalan algebras with boundaries, we obtain a new solution of the reflection equation in the case of $r=2$.
Authors: K.V. Nikolaev, L.I. Goray, P.S. Savchenkov, A.V. Rogachev, A.A. Chouprik, T.N. Berezovskaya, D.V. Mokhov, S.A. Garakhin, N.I. Chkhalo, A.D. Buravleuv, S.N. Yakunin
This study explores the use of synchrotron measurements as a nanometrology tool for blazed gratings. In grazing incidence geometry, one can measure both the conical diffraction and the diffuse scattering on the grating simultaneously in a single scattering pattern. The sensitivity of scattering patterns to the structure of the blazed gratings is evaluated. The diffraction component of the pattern is shown to be sensitive to the average groove profile of the gratings. Meanwhile, the diffuse scattering depends on the roughness morphology of the reflective surface of blazed gratings. These findings are supported by numerical simulations. The simulations were performed using several rigorous solvers for the Helmholtz equations, and with a perturbation theory. The analysis relies on synchrotron data, as well as data from atomic force microscopy and scanning electron microscopy. The aim of this article is to draw the attention of the optical community to the synchrotron measurements as a nanometrology tool for the modern optical elements.
Authors: Enrico Cinti, Sebastian De Haro, Mark Golden, Umut Gürsoy, Henk T.C. Stoof
This paper introduces the physics and philosophy of strange metals, which are characterized by unusual electrical and thermal properties that deviate from conventional metallic behaviour. The anomalous strange-metal behaviour discussed here appears in the normal state of a copper-oxide high-temperature superconductor, and it cannot be described using standard condensed-matter physics. Currently, it can only be described through a holographic dual, viz.~a four-dimensional black hole in anti-de Sitter spacetime. This paper first introduces the theory of, and specific experiments carried out on, strange metals. Then it discusses a number of philosophical questions that strange metals open up regarding the experimental evidence for holography and its realist interpretation. Strange metals invert the explanatory arrows, in that usual holographic arguments are seen as giving explanations of the bulk quantum-gravity theory from the boundary. By contrast, the aim here is, by using holography, to explain the experimentally discovered and anomalous properties of strange metals.
Authors: Arjun Sharma, Ritabrata Thakur, Sharath Jose, Rama Govindarajan
A wide range of natural and engineered fluid flows exhibit spatial or temporal viscosity variations, spanning scales from microbial locomotion to planetary mantle convection. These variations introduce qualitatively new physical mechanisms absent in constant-viscosity flows. This review surveys such phenomena across scales. In low Reynolds number (Stokes) flows, viscosity gradients couple translation and rotation, enabling novel particle responses to uniform forcing-- mechanisms that microorganisms may exploit. In shear flows, viscosity variation alters base flow profiles and breaks symmetries, modifying stability and transition dynamics. At high Reynolds numbers, stratification fundamentally changes the singular perturbation structure governing energy production, enhancing or suppressing canonical instabilities and introducing new ones. Viscosity variation also affects nonnormal growth and nonlinear interactions that drive transition to turbulence. While laminar and fully developed turbulence have been extensively studied, transitional processes remain poorly understood in variable-viscosity flows. In turbulent regimes, viscosity variation impacts jets, wall-bounded flows, and mixing layers. At geophysical scales, incorporating eddy viscosity stratification in climate models may improve predictions, while in Earth's mantle, viscosity contrasts drive large-scale convection and geological evolution. Particle-laden flows, common across contexts, can generate effective viscosity stratification through inhomogeneous loading. Throughout, we highlight cases where viscosity variation alters flow behavior qualitatively, and point to open questions. This review aims to guide graduate students and researchers toward tractable, cross-disciplinary problems.
Authors: Nuno Crokidakis, Lucas Sigaud
In social contexts where individuals consume varying amounts, such as shared meals or bar gatherings, splitting the total bill equally often yields surprisingly fair outcomes. In this work, we develop a statistical physics framework to explain this emergent fairness by modeling individual consumption as stochastic variables drawn from a realistic distribution, specifically the gamma distribution. Introducing a Boltzmann-like weighting factor, we derive exact analytical expressions for the partition function, average consumption, variance, and entropy under economic or social penalization constraints. Numerical simulations, performed using the Marsaglia-Tsang algorithm, confirm the analytical results with high precision. Drawing a direct parallel between individual consumption and ideal gas particle energy in the canonical ensemble, we show how the law of large numbers, mutual compensation, and the effective ordering induced by penalization combine to make equal cost-sharing statistically robust and predictable. These findings reveal that what appears to be an informal social convention is, in fact, grounded in the same fundamental principles that govern the collective behavior of particles in thermodynamic systems, highlighting the interdisciplinary power of statistical physics.
Authors: Fernando Martínez-García, Álvaro Rubio-García, Samuel Fernández-Lorenzo, Juan José García-Ripoll, Diego Porras
We introduce SA-FDR, a novel algorithm for $\ell_0$-norm feature selection that considers this task as a combinatorial optimisation problem and solves it by using simulated annealing to perform a global search over the space of feature subsets. The optimisation is guided by the Fisher discriminant ratio, which we use as a computationally efficient proxy for model quality in classification tasks. Our experiments, conducted on datasets with up to hundreds of thousands of samples and hundreds of features, demonstrate that SA-FDR consistently selects more compact feature subsets while achieving a high predictive accuracy. This ability to recover informative yet minimal sets of features stems from its capacity to capture inter-feature dependencies often missed by greedy optimisation approaches. As a result, SA-FDR provides a flexible and effective solution for designing interpretable models in high-dimensional settings, particularly when model sparsity, interpretability, and performance are crucial.
Authors: Hayun Park, Hunpyo Lee
We developed a graph-based block-diagonalization (GBBD) method for the full configuration interaction Hamiltonian of molecular systems to efficiently calculate the exact eigenvalues of low-energy states. In this approach, the non-zero matrix elements of the Hamiltonian are represented as edges on a graph, which naturally decomposes into disconnected clusters. Each cluster corresponds to an independent block in the block-diagonalized form of the Hamiltonian. The eigenvalues in the low-energy sector were obtained by solving the eigenvalue problem for each block matrix and by solving a modified Hamiltonian subject to orthonormality constraints with respect to previously computed lower-energy eigenstates. We applied the GBBD method to linear hydrogen H chains ranging from H$_2$ to H$_{12}$. The results showed excellent agreement with exact ones, confirming both the accuracy and efficiency of the proposed method. Finally, we discussed several physical properties with respect to the number of H$_2$ molecules.
Authors: Sayan Bhowmik, Andrew J. Medford, Phanish Suryanarayana
We present an accurate and efficient framework for real-space Hubbard-corrected density functional theory. In particular, we obtain expressions for the energy, atomic forces, and stress tensor suitable for real-space finite-difference discretization, and develop a large-scale parallel implementation. We verify the accuracy of the formalism through comparisons with established planewave results. We demonstrate that the implementation is highly efficient and scalable, outperforming established planewave codes by more than an order of magnitude in minimum time to solution, with increasing advantages as the system size and/or number of processors is increased. We apply this framework to examine the impact of exchange-correlation inconsistency in local atomic orbital generation and introduce a scheme for optimizing the Hubbard parameter based on hybrid functionals, both while studying TiO$_2$ polymorphs.
Authors: Sana Boughdachi, Benedikt Heizenreder, Ananya Sitaram, Erik Dierikx, Yan Xie, Sander Klemann, Paul Klop, Jeroen Koelemeij, Rafał Wilk, Florian Schreck, Andreas Brodschelm
We demonstrate a quasi-continuous sub-$\mu$K strontium source achieved without the use of a high-finesse cavity-locked laser. Our frequency reference is based on a dispersion-optimized, fiber-based frequency comb that enables sub-kHz linewidths. The long-term stability of the comb is defined by an external RF reference: either a 10 MHz RF signal from the Dutch Metrology Institute (VSL), or a tunable RF source whose long-term stability is maintained by monitoring and stabilizing the position of a narrow-line magneto-optical trap (MOT). The comb-stabilized system is benchmarked against a conventional cavity-locked laser and achieves comparable performance in broadband and single-frequency MOTs using the narrow $^1$S$_0$ $\rightarrow$ $^3$P$_1$ laser cooling transition. We generate high-flux, sub-$\mu$K samples of all three bosonic strontium isotopes and demonstrate quasi-continuous outcoupling from the MOT. These results highlight the system's suitability for compact, robust, and field-deployable continuous cold atom devices.
Authors: F. Romeo, J. Settino
We show that global properties of an unknown quantum network, such as the average degree, hub density, and the number of closed paths of fixed length, can be inferred from strictly local quantum measurements. In particular, we demonstrate that a malicious agent with access to only a small subset of nodes can initialize quantum states locally and, through repeated short-time measurements, extract sensitive structural information about the entire network. The intrusion strategy is inspired by extreme learning and quantum reservoir computing and combines short-time quantum evolution with a non-iterative linear readout with trainable weights. These results suggest new strategies for intrusion detection and structural diagnostics in future quantum Internet infrastructures.
Authors: Kazuki Doi, Tadashi Takayanagi
We consider the evolution of entanglement entropy in a two-dimensional conformal field theory with a holographic dual. Specifically, we are interested in a class of excited states produced by a combination of pure-state (local operator) and mixed-state local quenches. We employ a method that allows us to determine the full time evolution analytically. While a single insertion of a local operator gives rise to a logarithmic time profile of entanglement entropy relative to the vacuum, we find that this growth is heavily suppressed in the presence of a mixed-state quench, reducing it to a time-independent constant bump. The degree of suppression depends on the relative position of the quenches as well as the ratio of regularization parameters associated with the quenches. This work sheds light on the interesting properties of gravitational scattering involving black holes.
Authors: Aditya Banerjee
Given that any subsystem of a closed out-of-equilibrium quantum system is an open quantum system, its dynamics (reduced from the full system's unitary evolution) can be either Markovian (memory-less) or non-Markovian, with the latter necessarily impeding the process of relaxation and thermalization. Seemingly independently, such non-ergodic dynamics occurs when an initial state has spectral weight on the so-called quantum scar states, which are non-thermalizing states embedded deep in the spectrum of otherwise thermal states. In this article, we present numerical evidence that the presence of quantum scars is a microscopic ingredient that enables and enhances non-Markovianity of the dynamics of subsystems. We exemplify this with the PXP model and its deformations which either enhance or erase the signatures of scarred dynamics when quenched from a simple product state that is known to have significant overlaps with the scarred subspace in the spectrum. By probing information backflows with the dynamical behaviour of the distances between temporally-separated states of small subsystems, systematic signatures of subsystem non-Markovianity in these models are presented, and it is seen that scarring-enhancing (erasing) deformations also exhibit enhanced (diminished) subsystem non-Markovianity. This sheds new light on the dynamical memories associated with quantum scarring, and opens interesting new questions at the interface of quantum scarring and an open quantum systems approach to investigating far-from-equilibrium and non-thermalizing isolated quantum many-body systems.
Authors: Hiroyasu Tajima, Koji Yamaguchi, Ryuji Takagi, Yui Kuramochi
Quantum technologies offer exceptional -- sometimes almost magical -- speed and performance, yet every quantum process costs physical resources. Designing next-generation quantum devices, therefore, depends on solving the following question: which resources, and in what amount, are required to implement a desired quantum process? Casting the problem in the language of quantum resource theories, we prove a universal cost-irreversibility tradeoff: the lower the irreversibility of a quantum process, the greater the required resource cost for its realization. The trade-off law holds for a broad range of resources -- energy, magic, asymmetry, coherence, athermality, and others -- yielding lower bounds on resource cost of any quantum channel. Its broad scope positions this result as a foundation for deriving the following key results: (1) we show a universal relation between the energetic cost and the irreversibility for arbitrary channels, encompassing the energy-error tradeoff for any measurement or unitary gate; (2) we extend the energy-error tradeoff to free energy and work costs; (3) we extend the Wigner-Araki-Yanase theorem, which is the universal limitation on measurements under conservation laws, to a wide class of resource theories: the probability of failure in distinguishing resourceful states via a measurement is inversely proportional to its resource cost; (4) we prove that infinitely many resource-non-increasing operations in fact require an infinite implementation cost. These findings reveal a universal relationship between quantumness and irreversibility, providing a first step toward a general theory that explains when -- and how -- quantumness can suppress irreversibility.
Authors: Harshit Kumar Sandhu, Saurav Dutta, Rajesh Chaunsali
Nonreciprocal wave propagation allows for directional energy transport. In this work, we systematically investigate wave dynamics in an elastic lattice that combines nonreciprocal stiffness with viscous damping. After establishing how conventional damping counteracts the system's gain, we introduce a non-dissipative form of nonreciprocal damping in the form of gyroscopic damping. We find that the coexistence of nonreciprocal stiffness and nonreciprocal damping results in a decoupled control mechanism. The nonreciprocal stiffness is shown to govern the temporal amplification rate, while the nonreciprocal damper independently tunes the wave's group velocity and oscillation frequency. This decoupling gives rise to phenomena such as the enhancement of net amplification for slower-propagating waves and boundary-induced wave mixing. These findings provide a theoretical framework for designing active metamaterials with more versatile control over their wave propagation characteristics.
Authors: Dian Jing, Pablo Sala, Liang Jiang, Ruben Verresen
Topological order (TO) provides a natural platform for storing and manipulating quantum information. However, its stability to noise has only been systematically understood for Abelian TOs. In this work, we exploit the non-deterministic fusion of non-Abelian anyons to inform active error correction and design decoders where the fusion products, instead of flag qubits, herald the noise. This intrinsic heralding enhances thresholds over those of Abelian counterparts when noise is dominated by a single non-Abelian anyon type. Furthermore, we present an approach for determining the optimal threshold for non-Abelian TOs with perfect anyon syndromes for any noise model, formulated as a statistical mechanics model using Bayesian inference. We numerically illustrate these results for $D_4 \cong \mathbb Z_4 \rtimes \mathbb Z_2$ TO. In particular, for non-Abelian charge noise and perfect syndrome measurement, we find an optimal threshold $p_c=0.218(1)$, whereas an intrinsically heralded minimal-weight perfect-matching (MWPM) decoder already gives $p_c=0.20842(2)$, outperforming standard MWPM with $p_c = 0.15860(1)$. Our work highlights how non-Abelian properties can enhance stability, rather than reduce it, and discusses potential generalizations for achieving fault tolerance.
Authors: Gerald Curran III, Luke J. Weaver, Zachary Rex, Ivan Biaggio
Decoherence effects for entangled triplet pairs in organic molecular crystals are analyzed for the case when excitons can hop between inequivalent lattice sites. The fluorescence quantum beats caused by quantum interference upon triplet-triplet recombination into an emissive singlet state are predicted as a function of hopping time and magnetic field based on a Monte Carlo analysis. Depending on exciton hopping rates, it is possible to have complete global decoherence and suppression of fluorescence quantum beats in the limit of zero magnetic field, and to have quantum beats that decay at different rates depending on magnetic field strength.
Authors: Amruthesh Thirumalaiswamy, Clary Rodríguez-Cruz, Robert A. Riggleman, John C. Crocker
Foams and dense emulsions display complex mechanical behavior, including intermittent rearrangement dynamics, power-law rheology, and slow recovery after perturbation. These effects have long been considered evidence for glassy physics in these and other materials having similar mechanics, such as the cytoskeleton. Here we study such anomalous mechanics in a simulated wet foam driven by ripening and find behavior that has a different physical origin than that in glasses. Rather, the dynamics is due to a balance of forces from the system's self-similar potential energy landscape and viscous stress. At the lowest viscosities, bubbles move intermittently, with the system shifting abruptly between shallow potential energy minima. For higher viscosities, in contrast, the bubbles move continuously and the system follows a tortuous, fractal path through high-dimensional configuration space, at higher mean energy than the lower viscosity case. The long-time dynamics and power-law rheology are the direct consequence of the potential energy landscape's self-similar geometry. Lastly, we find that the slow recovery of perturbed foams is due to the foam being kinetically rather than energetically trapped in high-energy portions of the energy landscape. Overall, viscous ripening foams follow a biased energy minimization pathway that explores regions of the energy landscape that are qualitatively different (flatter and smoother) than those corresponding to well-annealed glasses.
Authors: Tobias Zier, Eeuwe S. Zijlstra, Martin E. Garcia, David A. Strubbe
An intense femtosecond-laser excitation of a solid induces highly nonthermal conditions. In materials like silicon, laser-induced bond-softening leads to a highly incoherent ionic motion and eventually nonthermal melting. But is this outcome an inevitable consequence, or can it be controlled? Here, we performed ab initio molecular dynamics simulations of crystalline silicon after timed multiple femtosecond-laser pulse excitations with fluence above the nonthermal melting threshold. Our results demonstrate an excitation mechanism that pauses nonthermal melting and creates a metastable state instead, with an electronic structure similar to the ground state. This mechanism can be generalized to other materials, potentially enabling structural and/or electronic transitions to metastable phases in the high-excitation regime. In addition, our approach could be used to switch off nonthermal contributions in experiments, allowing reliable electron-phonon coupling constants to be obtained more easily.
Authors: Yuyang Dong, Yuto Kinoshita, Masayuki Ochi, Ryu Nakachi, Ryuji Higashinaka, Satoru Hayami, Yuxuan Wan, Yosuke Arai, Soonsang Huh, Makoto Hashimoto, Donghui Lu, Masashi Tokunaga, Yuji Aoki, Tatsuma D. Matsuda, Takeshi Kondo
Skyrmions in noncentrosymmetric materials are believed to occur due to the Dzyaloshinskii-Moriya interaction. By contrast, the skyrmion formation mechanism in centrosymmetric materials remains elusive. Here, we reveal the intrinsic electronic structure of the centrosymmetric GdRu2Si2 by selectively measuring magnetic domains using angle-resolved photoemission spectroscopy (ARPES). We found robust Fermi surface (FS) nesting, consistent with the magnetic modulation q-vector detected by the previous resonant x-ray scattering measurements. The pseudogap opens at the nested FS portions, which vary for different magnetic domains. The anomalous pseudogap disconnects the FS to generate Fermi arcs with twofold symmetry. These results indicate that the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction plays a decisive role in generating the screw spin modulation responsible for the skyrmion formation in GdRu2Si2. Furthermore, we demonstrate the flexible nature of magnetism in GdRu2Si2 by manipulating magnetic domains with magnetic field and temperature cyclings, providing potential future applications for data storage and processing devices.
Authors: Shuyang Wang, Jay D. Sau
The chiral anomaly is one of the robust quantum effects in relativistic field theories with a chiral symmetry where charges in chiral sectors appear to be separately conserved. The chiral anomaly, which is often associated with a renormalization-invariant topological term, is a violation of this conservation law due to quantum effects. Such anomalies manifest in Weyl materials as an electromagnetic field-induced transfer of charge between Fermi pockets. However, the emergent nature of the conservation of chiral charge leads to manifestations of the chiral anomaly response that depend on the details of the system such as the strength of interactions. In this paper, we apply an approach where the chiral symmetry in solid materials is replaced by the combination of charge $U(1)$ gauge and spatial translation symmetry. The chiral anomaly in this case is replaced by a mixed anomaly between the two symmetries and the chiral charge can be defined as being proportional to the total momentum. We show that the chiral anomaly associated with this chiral charge is unrenormalized by interactions in contrast to other chiral charges in $(1+1)D$ whose renormalization is regularization dependent. In $(3+1)$D Weyl systems, this chiral anomaly is equivalent to the charge transferred between Fermi surfaces which can be measured through changes in Fermi-surface-enclosed volume. We propose a pump-probe technique to measure this.
Authors: Riccardo Riolo, Andrea Tomadin, Giacomo Mazza, Reza Asgari, Allan H. MacDonald, Marco Polini
The question of whether or not passive sub-wavelength cavities can alter the properties of quantum materials is currently attracting a great deal of attention. In this Article we show that the Fermi liquid parameters of a two-dimensional metal are modified by cavity polariton modes, and that these changes can be monitored by measuring a paradigmatic magneto-transport phenomenon, Shubnikov-de Haas oscillations in a weak perpendicular magnetic field. This effect is intrinsic, and totally unrelated to disorder. As an illustrative example, we carry out explicit calculations of the quasiparticle velocity of graphene in a planar van der Waals cavity formed by natural hyperbolic crystals and metal gates. The largest effects of the cavity occur when the phonon polariton modes of the former match energetically the graphene plasmon. For typical graphene carrier densities this occurs in the Terahertz spectral range.
Authors: Yannick Deller, Martin Gärttner, Tobias Haas, Markus K. Oberthaler, Moritz Reh, Helmut Strobel
The scaling of local quantum entropies is of utmost interest for characterizing quantum fields, many-body systems, and gravity. Despite their importance, theoretically and experimentally accessing quantum entropies is challenging as they are nonlinear functionals of the underlying quantum state. Here, we show that suitably chosen classical entropies capture many features of their quantum analogs for an experimentally relevant setting. We describe the post-quench dynamics of a multi-well spin-1 Bose-Einstein condensate from an initial product state via measurement distributions of spin observables and estimate the corresponding entropies using the asymptotically unbiased $k$-nearest neighbor method. We observe the dynamical build-up of quantum correlations signaled by an area law, as well as local thermalization revealed by a transition to a volume law, both in regimes characterized by non-Gaussian distributions. We emphasize that all relevant features can be observed at small sample numbers without reconstructing the underlying state or measurement distributions, rendering our method directly applicable to a large variety of models and experimental platforms.
Authors: Hannes Braun, Michael M. Scherer, Laura Classen
Interaction-induced charge orders with electronic origin occur as states of spontaneously broken symmetry in several materials platforms. An electronic mechanism for charge order requires an attractive component in the effective charge vertex. We put forward such a mechanism for the formation of unconventional charge density waves in a metal. These states result from the condensation of particle-hole pairs with finite wave vector and non-zero angular momentum and correspond to bond or loop current order on a lattice. The mechanism we describe can be viewed as Kohn Luttinger analysis in the particle-hole channel with finite transferred momentum. It incorporates one-loop spin and pairing correctionsn, which are then used as an input for a summation in the charge channel triggering an instability. We extend our analysis to a spin-fluctuation approach, where the effective charge interaction is dressed by the particle-hole ladder with exchanged momentum. We argue that this mechanism works for weakly-interacting metals with nested Fermi surface and a large number of fermion flavors. We apply the Kohn-Luttinger-like approach to square- and triangular-lattice Hubbard models with SU($N_f$) flavour symmetry and show that it leads to different types of $p$-wave charge density waves. We also study effects beyond weak coupling at and away from Van Hove filling in terms of a phenomenological model with additional exchange interaction. In the vicinity of Van Hove filling, we obtain $d$-wave charge density waves with wave vectors determined by nesting as leading instabilities. In addition, we find another charge density wave with wave vector $K/4$ on the triangular lattice on both sides of Van Hove filling. We demonstrate that this $K/4$ instability can win the competition against pairing for $N_f=4$ via an unbiased functional renormalisation group calculation.
Authors: A. Astillero, J. J. Ruiz-Lorenzo
We study the critical dynamics of the three-dimensional Heisenberg model with random cubic anisotropy in the out-of-equilibrium and equilibrium regimes. Analytical approaches based on field theory predict that the universality class of this model is that of the three-dimensional site-diluted Ising model. We have been able to estimate the dynamic critical exponent by working in the equilibrium regime and by computing the integrated autocorrelation times obtaining $z=2.50(5)$ (without taking into account scaling corrections) and $z=2.29(11)$ (by fixing the scaling corrections to that predicted by field theory). In the out-of-equilibrium regime we have focused in the study of the dynamic correlation length which has allowed us to compute the dynamic critical exponent obtaining $z=2.38(2)$, which is compatible with the equilibrium ones. Finally, both estimates are also compatible with the most accurate prediction $z=2.35(2)$, from numerical simulations of the 3D site-diluted Ising model, in agreement with the predictions based on field theory.
Authors: Michael A. Sauer, Souvik Mondal, Brandon Neff, Sthitadhi Maiti, Matthias Heyden
Protein function does not solely depend on structure but often relies on dynamical transitions between distinct conformations. Despite this fact, our ability to characterize or predict protein dynamics is substantially less developed compared to state-of-the-art protein structure prediction. Molecular simulations provide unique opportunities to study protein dynamics, but the timescales associated with conformational changes generate substantial challenges. Enhanced sampling algorithms with collective variables can greatly reduce the computational cost of sampling slow processes. However, defining collective variables suitable to enhance sampling of protein conformational transitions is non-trivial. Low-frequency vibrations have long been considered as promising candidates for collective variable but their identification so far relied on assumptions inherently invalid at low frequencies. We recently introduced an analysis of molecular vibrations that does not rely on such approximations and remains accurate at low frequencies. Here, we modified this approach to efficiently isolate low-frequency vibrations in proteins and applied it to a set of five proteins of varying complexity. We demonstrate that our approach is not only highly reproducible but results in collective variables that consistently enhance sampling of protein conformational transitions and associated free energy surfaces on timescales compatible with high throughput applications. This enables the efficient generation of protein conformational ensembles, which will be key for future prediction algorithms aiming beyond static protein structures.
Authors: David X. Horvath, Benjamin Doyon, Paola Ruggiero
The statistics of fluctuations on large regions of space encodes universal properties of many-body systems. At equilibrium, it is described by thermodynamics. However, away from equilibrium such as after quantum quenches, the fundamental principles are more nebulous. In particular, although exact results have been conjectured in integrable models, a correct understanding of the physics is largely missing. In this letter, we explain these principles, taking the example of the number of particles lying on a large interval in one-dimensional interacting systems. These are based on simple hydrodynamic arguments from the theory of ballistically transported fluctuations, and in particular the Euler-scale transport of long-range correlations. Using these principles, we obtain the full counting statistics (FCS) in terms of thermodynamic and hydrodynamic quantities, whose validity depends on the structure of hydrodynamic modes and on the fluctuations in the initial state. In fermionic-statistics interacting integrable models with a continuum of hydrodynamic modes, such as the Lieb-Liniger model for cold atomic gases, the formula reproduces previous conjectures, but is in fact not exact: it gives the correct cumulants up to, including, order 5, while long-range correlations modify higher cumulants. In integrable and non-integrable models with two or less hydrodynamic modes, the formula is expected to give all cumulants.
Authors: Henok Weldeyesus, Pedro M.T. Vianez, Omid Sharifi Sedeh, Wooi Kiat Tan, Yiqing Jin, María Moreno, Christian P. Scheller, Jonathan P. Griffiths, Ian Farrer, David A. Ritchie, Dominik M. Zumbühl, Christopher J.B. Ford, Oleksandr Tsyplyatyev
Luttinger liquids occupy a special place in physics as the most understood case of essentially quantum many-body systems. The experimental mission of measuring its main prediction, power laws in observable quantities, has already produced a body of exponents in different semiconductor and metallic structures. Here, we combine tunneling spectroscopy with density-dependent transport measurements in the same quantum wires over more than two orders of magnitude in temperature to very low electron temperatures down to $\sim$40 mK. This reveals that, when the second 1D subband becomes populated, the temperature dependence splits into two ranges with different exponents in the power-law dependence of the conductance, both dominated by the finite-size effect of the end-tunneling process. This result demonstrates the importance of measuring the Luttinger parameters as well as the number of modes independently through spectroscopy in addition to the transport exponent in the characterization of Luttinger liquids. This opens a new pathway to unambiguous interpretation of the exponents observed in quantum wires.
Authors: Yicheng Tang, Pradip Kattel, J.H. Pixley, Natan Andrei
We demonstrate that a boundary defect in the single spin-$\frac{1}{2}$ quantum $XX$ chain exhibits two-channel Kondo physics. Due to the presence of the defect, the edge spin fractionalizes into two Majorana fermions, out of which one decouples, and one is overscreened by the free fermion in bulk, leading to non-trivial boundary behavior characteristic of the two-channel Kondo model. When the ratio of boundary to bulk coupling exceeds a critical value of $\sqrt{2}$, a massive boundary-bound mode is exponentially localized near the impurity site for strong impurity coupling. This leads to unusual behavior in physical quantities, such as the $g$-function not being monotonic. We compute the $g-$function of the impurity from both thermodynamic and entanglement entropy calculations and show that it takes a non-integer value of $\sqrt{2}$ just as in the two-channel Kondo problem.
Authors: Anthony N. Zulli, Brendan C. Mulkerin, Meera M. Parish, Jesper Levinsen
We investigate the behavior of the Efimov effect -- a universal quantum few-body phenomenon -- in the presence of an external driving field. Specifically, we consider up to three bosonic atoms, such as $^{133}$Cs, interacting with a light atom, such as $^{6}$Li, where the latter has two internal spin states $\{\uparrow, \downarrow\}$ that are Rabi coupled. Assuming that only the spin-$\uparrow$ light atom interacts with the bosons, we find that the Rabi drive transposes the entire Efimov spectrum such that the Efimov trimers and tetramers are centered around the Rabi-shifted two-body scattering resonance. Crucially, we show that the Rabi drive preserves the trimers' discrete scaling symmetry, while universally shifting the Efimov three-body parameter, leading to a log-periodic modulation in the spectrum as the Rabi drive is varied. Our results suggest that Efimov physics can be conveniently explored using an applied driving field, opening up the prospect of an externally tunable three-body parameter.
Authors: Barak Budnick, Preben Forer, Pierpaolo Vivo, Sabrina Aufiero, Silvia Bartolucci, Fabio Caccioli
Using the replica method, we compute the statistics of the top eigenpair of diluted covariance matrices of the form $\mathbf{J} = \mathbf{X}^T \mathbf{X}$, where $\mathbf{X}$ is a $N\times M$ sparse data matrix, in the limit of large $N,M$ with fixed ratio and a bounded number of nonzero entries. We allow for random non-zero weights, provided they lead to an isolated largest eigenvalue. By formulating the problem as the optimisation of a quadratic Hamiltonian constrained to the $N$-sphere at low temperatures, we derive a set of recursive distributional equations for auxiliary probability density functions, which can be efficiently solved using a population dynamics algorithm. The average largest eigenvalue is identified with a Lagrange parameter that governs the convergence of the algorithm, and the resulting stable populations are then used to evaluate the density of the top eigenvector's components. We find excellent agreement between our analytical results and numerical results obtained from direct diagonalisation.
Authors: Christopher E. A. Barker, Charles Parton-Barr, Christopher H. Marrows, Olga Kazakova, Craig Barton
Skyrmions have been proposed as new information carriers in racetrack memory devices. To realise such devices, a small size; high speed of propagation; and minimal skyrmion Hall angle are required. Synthetic antiferromagnets (SAFs) present the ideal materials system to realise these aims. In this work, we use micromagnetic simulations to propose a new method for manipulating them using exclusively global magnetic fields. An out-of-plane microwave field induces oscillations in the skyrmions radius which in turn emits spin waves. When a static in-plane field is added, this breaks the symmetry of the skyrmions and causes asymmetric spin wave emission. This in turn drives motion of the skyrmions, with the fastest velocities observed at the frequency of the intrinsic out-of-phase breathing mode of the pair of skyrmions. This behaviour is investigated over a range of experimentally realistic antiferromagnetic interlayer exchange coupling strengths, and the results compared to previous works studying similar motion driven with an oscillating electric field. Through this the true effect of varying the exchange coupling strength is determined, and greater insight is gained into the mechanism of skyrmion motion. These results will help to inform the design of future novel computing architectures based on the dynamics of skyrmions in synthetic antiferromagnets.
Authors: R.M. Dubrovin, A.V. Kimel, A.K. Zvezdin
Although magnetoelectric effects in metals are usually neglected, assuming that applied electric fields are screened by free charge carriers, the skin depth, defining the penetration depth of the fields, is non-zero and for THz electric fields typically reaches 400 nm. Hence, if the thickness of an antiferromagnetic film is of the order of tens of nm, electric field induced effects cannot be neglected. Here, we theoretically study the THz electric field induced spin dynamics in the metallic antiferromagnet $\mathrm{Mn}_{2}\mathrm{Au}$, whose spin arrangements allow it to exhibit a linear magnetoelectric effect. We show that the THz magnetoelectric torque in metallic antiferromagnets is proportional to the time derivative of the polarization induced by the THz electric field. Our simulations reveal that the magnetoelectric driven spin dynamics is indeed not negligible, and for a fair explanation of previously published experimental results in $\mathrm{Mn}_{2}\mathrm{Au}$ competition between THz magnetoelectric and Néel spin-orbit torques must be taken into account. Thus, it is shown that even in metallic antiferromagnets the THz magnetoelectric effect on spins can be strong and thus cannot be neglected.
Authors: Carlo Andrea Rozzi, Annamaria Lisotti, Guido Goldoni, Valentina De Renzi
Shape-memory alloys exhibit a solid-to-solid phase transition that involves a temperature-driven rearrangement of their crystal structure and is responsible for their remarkable properties and numerous technological applications. Here, we propose a simple experiment that analyzes the sound emitted by a Ni$_{40}$Ti$_{50}$Cu$_{10}$ bar at different temperatures as it undergoes a transition between its austenite and martensite phases. We show that the phase transition, which occurs slightly above room temperature, can be qualitatively detected by the ear and quantitatively described using a very simple experimental setup and sound analysis tools. Such a sound-based investigation provides an unusual and engaging way to experimentally introduce solid-to-solid phase transitions, that is suitable for undergraduate courses.
Authors: Shoummo Ahsan Khandoker, Estelle M. Inack, Mohamed Hibat-Allah
Understanding the principles of protein folding is a cornerstone of computational biology, with implications for drug design, bioengineering, and the understanding of fundamental biological processes. Lattice protein folding models offer a simplified yet powerful framework for studying the complexities of protein folding, enabling the exploration of energetically optimal folds under constrained conditions. However, finding these optimal folds is a computationally challenging combinatorial optimization problem. In this work, we introduce a novel upper-bound training scheme that employs masking to identify the lowest-energy folds in two-dimensional Hydrophobic-Polar (HP) lattice protein folding. By leveraging Dilated Recurrent Neural Networks (RNNs) integrated with an annealing process driven by temperature-like fluctuations, our method accurately predicts optimal folds for benchmark systems of up to 60 beads. Our approach also effectively masks invalid folds from being sampled without compromising the autoregressive sampling properties of RNNs. This scheme is generalizable to three spatial dimensions and can be extended to lattice protein models with larger alphabets. Our findings emphasize the potential of advanced machine learning techniques in tackling complex protein folding problems and a broader class of constrained combinatorial optimization challenges.
Authors: Nagamalleswara Rao Alluri, Longfei Song, Stephanie Girod, Barnik Mandal, Juliette Cardoletti, Vid Bobnar, Torsten Granzow, Veronika Kovacova, Adrian-Marie Philippe, Emmanuel Defay, Sebastjan Glinsek
K$_{0.5}$Na$_{0.5}$NbO$_3$ is among the most promising lead-free piezoelectrics. While its sputtered films match the performance of the champion piezoelectric Pb(Zr,Ti)O$_3$, reproducible processing of high-quality and time-stable solution-processed K$_{0.5}$Na$_{0.5}$NbO$_3$ films remains challenging. Here, we report 1 $\mu$m-thick Mn-doped K$_{0.5}$Na$_{0.5}$NbO$_3$ films prepared through a chemical solution deposition process, which have perfectly dense microstructure and uniform composition across their thickness. The films exhibit a high transverse piezoelectric coefficient ($e_{31,f} = -15.4$ C/m$^2$), high dielectric permittivity ($\varepsilon_r \approx 920$), low dielectric losses ($\tan\delta = 0.05$) and can withstand electric fields up to at least 1 MV/cm. The functional properties show excellent stability over time, and the synthesis process is reproducible. Furthermore, a surface acoustic haptic device is demonstrated by using K$_{0.5}$Na$_{0.5}$NbO$_3$ thin-film actuators. The results demonstrate the high potential of Mn-doped K$_{0.5}$Na$_{0.5}$NbO$_3$ films to become a replacement for lead-based Pb(Zr,Ti)O$_3$ films in piezoelectric applications.
Authors: Ming-Hua Chang, Steffen Backes, Donghui Lu, Nicolas Gauthier, Makoto Hashimoto, Guan-Yu Chen, Hai-Hu Wen, Sung-Kwan Mo, Zhi-Xun Shen, Roser Valenti, Heike Pfau
Understanding how renormalized quasiparticles emerge in strongly correlated electron materials provides a challenge for both experiment and theory. It has been predicted that distinctive spin and orbital screening mechanisms drive this process in multiorbital materials with strong Coulomb and Hund's interactions. Here, we provide the experimental evidence of both mechanisms from angle-resolved photoemission spectroscopy on RbFe$_2$As$_2$. We observe that the emergence of low-energy Fe 3$d_{xy}$ quasiparticles below 90K is tied to spin screening. A second process changes the spectral weight at high energies up to room temperature. Supported by theoretical calculations we attribute it to orbital screening of Fe 3d atomic excitations. These two cascading screening processes drive the temperature evolution from a bad metal to a correlated Fermi liquid.
Authors: Josef Willsher, Johannes Knolle
Quantum spin liquids (QSLs) are long-range entangled phases of frustrated magnets exhibiting fractionalized spin excitations. In two dimensions, there is limited analytical understanding of their excitation spectra beyond parton mean-field theories, which fail to capture many features of the finite frequency dynamical response from recent experimental and numerical works. We use a self-consistent random phase approximation (RPA) for the $J_1$-$J_2$ Heiseneberg model on the triangular lattice to describe the strong spinon-spinon interactions of the U(1) Dirac QSL. We obtain quantitative results for the dynamical spin structure factor and phase diagram compatible with comprehensive numerical efforts. We extend the method to chiral QSLs, and discuss its broad range of applicability to other models and for describing inelastic neutron scattering experiments.
Authors: Zhiren He, Prathap Kumar Jharapla, Nicolas Leconte, Jeil Jung, Guru Khalsa
In this theoretical work, we propose an all-optical method for fast, precise manipulation of two-dimensional multilayers by transferring orbital angular momentum from phase-structured light (e.g. vortex beams) to a 2D material flake. We model the light-matter interaction, analyze the twist dynamics, and develop a phase diagram for optical twists by mapping the system onto an impulsively forced nonlinear pendulum. Our findings reveal rich dynamical responses spanning single- and multi-pulse twist angle control to (quasi)stable dynamical trajectories, and suggest a pathway for all-optical measurement of the twist potential energy. Aided by classical potential estimates for the interlayer energy and numerical simulation, we demonstrate the feasibility of this approach with hexagonal boron nitride bilayers and extend the results to dichalcogenides with first-principles calculations. These results can be generalized to other 2D multilayers, paving the way for scalable and customizable moiré electronics and photonics.
Authors: Jihang Zhu, Yang-Zhi Chou, Yi Huang, Sankar Das Sarma
We theoretically predict the in-plane magnetic field-induced orbital Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting states in twisted WSe$_2$ homobilayers (tWSe$_2$), focusing on its dependence on layer polarization and Fermi surface geometry. For unpolarized layers, finite-momentum pairing emerges only at low temperatures and above a critical field $B_{c1,\parallel}$. When layer symmetry is broken, finite-momentum pairing is stabilized at any nonzero field, with a critical temperature higher than that of the zero-momentum state. Notably, we identify a phase transition, which separates two distinct FFLO phases, when there are two separate Fermi pockets residing in the two moiré mini-valleys associated with opposite layers. We further discuss the effects of twist angles and applied field directions. Our findings establish tWSe$_2$ as a promising platform for realizing and manipulating FFLO states via twist angle, displacement field, and filling factor.
Authors: Eudomar Henríquez-Guerra, Alberto M. Ruiz, Marta Galbiati, Alvaro Cortes-Flores, Daniel Brown, Esteban Zamora-Amo, Lisa Almonte, Andrei Shumilin, Juan Salvador-Sánchez, Ana Pérez-Rodríguez, Iñaki Orue, Andrés Cantarero, Andres Castellanos-Gomez, Federico Mompeán, Mar Garcia-Hernandez, Efrén Navarro-Moratalla, Enrique Díez, Mario Amado, José J. Baldoví, M. Reyes Calvo
Tailoring magnetoresistance and magnetic anisotropy in van der Waals magnetic materials is essential for advancing their integration into technological applications. In this regard, strain engineering has emerged as a powerful and versatile strategy to control magnetism at the two-dimensional (2D) limit. Here, we demonstrate that compressive biaxial strain significantly enhances the magnetoresistance and magnetic anisotropy of few-layer CrSBr flakes. Strain is efficiently transferred to the flakes from the thermal compression of a polymeric substrate upon cooling, as confirmed by temperature-dependent Raman spectroscopy. This strain induces a remarkable increase in the magnetoresistance ratio and in the saturation fields required to align the magnetization of CrSBr along each of its three crystalographic directions, reaching a twofold enhancement along the magnetic easy axis. This enhancement is accompanied by a subtle reduction of the Néel temperature by ~10K. Our experimental results are fully supported by first-principles calculations, which link the observed effects to a strain-driven modification in interlayer exchange coupling and magnetic anisotropy energy. These findings establish strain engineering as a key tool for fine-tuning magnetotransport properties in 2D magnetic semiconductors, paving the way for implementation in spintronics and information storage devices.
Authors: Munkhtuguldur Altangerel, Quentin Barthélemy, Étienne Lefrançois, Jordan Baglo, Manel Mezidi, Gaël Grissonnanche, Ashvini Vallipuram, Emma Campillo, Anne Forget, Dorothée Colson, Ruixing Liang, D. A. Bonn, W. N. Hardy, Cyril Proust, Louis Taillefer
The thermal Hall conductivity of the trilayer cuprate HgBa$_2$Ca$_2$Cu$_3$O$_{8+\delta}$ (Hg1223) - the superconductor with the highest critical temperature $T_c$ at ambient pressure - was measured at temperatures down to 2 K for three dopings in the underdoped regime ($p$ = 0.09, 0.10, 0.11). By combining a previously introduced simple model and prior theoretical results, we derive a formula for the inverse mean free path, $1 / \ell$, which allows us to estimate the mean free path of $d$-wave quasiparticles in Hg1223 below $T_c$. We find that $1 / \ell$ grows as $T^3$, in agreement with the theoretical expectation for a clean $d$-wave superconductor. Measurements were also conducted on the single layer mercury-based cuprate HgBa$_2$CuO$_{6+\delta}$ (Hg1201), revealing that the mean free path in this compound is roughly half that of its three-layered counterpart at the same doping ($p$ = 0.10). This observation can be attributed to the protective role of the outer planes in Hg1223, which results in a more pristine inner plane. We also report data in an ultraclean crystal of YBa$_2$Cu$_3$O$_y$ (YBCO) with full oxygen content $p$ = 0.18, believed to be the cleanest of any cuprate, and find that $\ell$ is not longer than in Hg1223.
Authors: Edison P. Carlisle, George Yumnam, Stuart Calder, Bianca Haberl, Jia-Xin Xiong, Michael A. McGuire, Alex Zunger, Raphaël P. Hermann, Benjamin A. Frandsen
The hexagonal antiferromagnet MnTe has attracted enormous interest as a prototypical example of a spin-compensated magnet in which the combination of crystal and spin symmetries lifts the spin degeneracy of the electron bands without the need for spin-orbit coupling, a phenomenon called non-relativistic spin splitting (NRSS). Subgroups of NRSS are determined by the specific spin-interconverting symmetry that connects the two opposite-spin sublattices. In MnTe, this symmetry is rotation, leading to the subgroup with spin splitting away from the Brillouin zone center, often called altermagnetism. MnTe also has the largest spontaneous magnetovolume effect of any known antiferromagnet, implying strong coupling between the magnetic moment and volume. This magnetostructural coupling offers a potential knob for tuning the spin-splitting properties of MnTe. Here, we use neutron diffraction with $\textit{in situ}$ applied pressure to determine the effects of pressure on the magnetic properties of MnTe and further explore this magnetostructural coupling. We find that applying pressure significantly increases the Néel temperature but decreases the ordered magnetic moment. We explain this as a consequence of strengthened magnetic exchange interactions under pressure, resulting in higher $T_\mathrm{N}$, with a simultaneous reduction of the local moment of individual Mn atoms, described here via density functional theory. This reflects the increased orbital hybridization and electron delocalization with pressure. These results show that the magnetic properties of MnTe can be controlled by pressure, opening the door to improved properties for spintronic applications through tuning via physical or chemical pressure.
Authors: Georg Diez, Nele Dethloff, Gerhard Stock
Dimensionality reduction represents a crucial step in extracting meaningful insights from Molecular Dynamics (MD) simulations. Conventional approaches, including linear methods such as principal component analysis as well as various autoencoder architectures, typically operate under the assumption of independent and identically distributed data, disregarding the sequential nature of MD simulations. Here, we introduce a physics-informed representation learning framework that leverages Gaussian Processes combined with variational autoencoders to exploit the temporal dependencies inherent in MD data. Time-dependent kernel functions--such as the Matérn kernel--directly impose the temporal correlation structure of the input coordinates onto a low-dimensional space, preserving Markovianity in the reduced representation while faithfully capturing the essential dynamics. Using a three-dimensional toy model, we demonstrate that this approach can successfully identify and separate dynamically distinct states that are geometrically indistinguishable due to hidden degrees of freedom. Applying the framework to a $50\,\mu$s-long MD trajectory of T4 lysozyme, we uncover dynamically distinct conformational substates that previous analyses failed to resolve, revealing functional relationships that become apparent only when temporal correlations are taken into account. This time-aware perspective provides a promising framework for understanding complex biomolecular systems, in which conventional collective variables fail to capture the full dynamical picture.
Authors: Adam J. Czarnecki, Nikola L. Kolev, Patrick See, Nick Sullivan, Wyatt A. Behn, Neil J. Curson, Taylor J.Z. Stock, Peter Grütter
As silicon-based devices continue to shrink to the nanoscale, traps at the Si-SiO$_2$ interface pose increasing challenges to device performance. These traps reduce channel carrier mobility and shift threshold voltages in integrated circuits, and introduce charge noise in quantum systems, reducing their coherence times. Knowledge of the precise location of such traps aids in understanding their influence on device performance. In this work, we demonstrate that frequency-modulated atomic force microscopy (fm-AFM) allows the detection of individual traps. We use this to study how sample preparation, specifically the introduction of a buried hydrogen termination layer, and post-processing annealing in forming gas (N$_2$+H$_2$), affects the density of donor-like traps in Si(100)-SiO$_2$ systems. We spatially map and quantify traps in both conventionally prepared ("pristine") silicon samples and those processed under ultra-high vacuum for hydrogen resist lithography (HRL). We confirm previous studies demonstrating hydrogen passivation of traps and find that hydrogen termination further reduces the donor-like trap density. We also observe a significant reduction in two-level donor-like traps in the hydrogen-terminated samples compared to pristine silicon samples. These findings suggest that HRL-prepared silicon may offer advantages for high-performance nanoscale and atomic-scale devices due to reduced trap densities.
Authors: Mohd Tahseen, Vivekanand Dabade
This paper investigates the conditions necessary for the elimination of transition layers at interfaces involving compound domains, extending the classical framework of cofactor conditions. Although cofactor conditions enable stress-free phase boundaries between Type I/II domains and austenite, their applicability to compound domains has remained limited. Here, we present a comprehensive theoretical framework to characterize all compatible interfaces, highlighting the fundamental importance of the commutation property among martensitic variants. By establishing necessary and sufficient algebraic conditions, referred to as extreme compatibility conditions, we demonstrate the simultaneous elimination of transition layers at phase interfaces for both Type I/II and compound laminates, across all volume fractions of the martensitic variants. We also investigate the possibility of achieving supercompatibility in non-conventional twins, recently observed in the NiMnGa system. The focus of our work is on cubic-to-orthorhombic and cubic-to-monoclinic~II phase transformations, for which the extreme compatibility conditions are explicitly derived and systematically analyzed. The theory predicts novel zero-elastic-energy microstructures, including an increased number of triple clusters, spearhead-shaped martensitic nuclei, stress-free inclusions of austenite within martensite, and distinctive four-fold martensitic clusters. This significantly expands the possible modes of forming stress-free interfaces between phases and reveals new energy-minimizing microstructures that can facilitate the nucleation of martensite within austenite and vice versa. These configurations highlight significant enhancements in transformation reversibility and material durability, guiding the rational design of next-generation shape memory alloys with optimized functional properties.
Authors: Mikhail Pekker, Mikhail N. Shneider
In this paper, the tunneling mechanism of cavitation in liquid helium for 3He and 4He is considered on the basis of the Schrödinger-like equation. It is assumed that the pairwise interactions of helium atoms are determined by the Lennard-Jones potential. The kinetics of nucleation and the mechanism that limits the growth of cavitation bubbles in liquid helium are considered, taking into account their growth in a negative pressure field.
Authors: V. Moshnyaga, Ch. Jooss, P. E. Blöchl, V. Bruchmann-Bamberg, A. Dehning, L. Allen-Rump, C. Hausmann, M. Krüger, A. Rathnakaran, S. Rajpurohit, D. Steil, C. Flathmann, J. Hoffmann, M. Seibt, C. Volkert
Energy conversion in materials can be considered as a sequence of elementary steps initiated by a primary excitation. While these steps are quite well understood in classical semiconductors in terms of quasiparticle (QP) excitations and interactions, their understanding in strongly correlated materials is still elusive. Here, we review the progress which has been achieved over recent years by studies of manganite perovskite oxides as a model system for materials with strong correlations. They show a subtle interplay of different types of correlations, i.e., electron-phonon, electron-electron and spin-spin, resulting in rich physical phenomena due to competition between different ground states accompanied by temperature- and field-induced phase transitions. They strongly impact various types of energy conversion and transport processes including friction at surfaces, thermal transport, time-, energy- and power-dependent optical excitations as well as photovoltaic energy conversion. The underlying microscopic processes can be broken down to the behavior of the low-energy thermal and high-energy optical excitations, their interactions, transport and conversion which are theoretically analyzed by using models of interacting and tunable QPs: Their nature and interactions can change during excitation, transport and phase transitions, thus modifying electronic structure. At sufficiently high stimulation, QP excitations can even induce or actuate phase transitions. As a result, we obtained a comprehensive understanding of energy conversion steps going far beyond single QP pictures and rigid band approximations well-known for conventional semiconductors.
Authors: Davide Breoni, Emanuele Locatelli, Luca Tubiana
We use numerical simulations to study tangentially active flexible ring polymers with different knot topologies. Simple, unknotted active rings display a transition from an extended phase to a collapsed one upon increasing the degree of polymerization. We find that topology has a significant effect on the polymer size at which the collapse takes place, with twist knots collapsing earlier than torus knots. Increasing knot complexity further accentuates this difference, as the collapse point of torus knots grows linearly with the minimum crossing number of the knot while that of twist knots shrinks, eventually canceling the actively stretched regime altogether. This behavior is a consequence of the ordered configuration of torus knots in their stretched active state, featuring an effective alignment for non-neighboring bonds which increases with the minimal crossing number. Twist knots do not feature ordered configurations or bond alignment, increasing the likelihood of collisions, leading to collapse. These results show that topology yields a degree of control on the properties of active ring polymers, and can be used to tune them. At the same time, they suggest that activity might introduce a bias for torus knots, as complex twist knots cannot be formed in extended active polymers.
Authors: Sudeepta Mukherjee, Hemant Kumar, B.S. Murty, Satyam Suwas, Surendra Kumar Makineni
The microstructural stability and mechanical properties of superalloys at high temperatures are significantly influenced by the composition and nature of the solutes they contain. Most of the alloys with high solvus temperature have higher gamma prime coarsening resistance, while the larger lattice misfit is attributed to higher gamma prime coarsening rate. In this work, we explore the influence of Co on the microstructure evolution, thermophysical/mechanical properties and gamma prime precipitate coarsening kinetics in a Ti-rich Ni-Co-Cr-Al-Ti based alloy. More specifically, we focus on the effect of partitioning of Co into the gamma matrix on the redistribution of other solutes across the interface. We observe a significant increase in the coarsening resistance and a twofold increase in the activation energy with the increase in the Co composition from 10at.%Co to 30at.%Co, even though the gamma prime solvus reduces by 75C. As otherwise, a higher solvus, usually, indicates better microstructural stability at high temperatures. We employed a combined experimental and theoretical approach by atom probe tomography (APT) and CALPHAD simulations to probe the critical role of Co partitioning to gamma matrix on the solute transport in the gamma matrix and flux across the gamma/gamma prime interfaces, which is found to control the overall gamma prime coarsening behavior in the alloy. The observed behavior was rationlised by the proposition of a simplistic unified coarsening rate expression that successfully decouples thermodynamic and kinetic contributions. Additionally, we also observe that the gamma prime volume fraction dominates over the gamma prime precipitate size on the 0.2% yield strength (YS) of the alloys.
Authors: Shengpu Huang, Zheng Qin, Fangyang Zhan, Dong-Hui Xu, Da-Shuai, Rui Wang
Recent studies have drawn growing attention on non-relativistic odd-parity magnetism in the wake of altermagnets. Nevertheless, odd-parity spin splitting is often believed to appear in non-collinear magnetic configurations. Here, using symmetry arguments and effective model analysis, we show that Floquet engineering offers a universal strategy for achieving odd-parity magnetism in two-dimensional (2D) collinear antiferromagnets under irradiation of periodic driving light fields such as circularly polarized light, elliptically polarized light, and bicircular light. A comprehensive classification of potential candidates for collinear monolayer or bilayer antiferromagnets is established. Strikingly, the light-induced odd-parity spin splitting can be flexibly controlled by adjusting the crystalline symmetry or the polarization state of incident light, enabling the reversal or conversion of spin-splitting. By combining first-principles calculations and Floquet theorem, we present illustrative examples of 2D collinear antiferromagnetic (AFM) materials to verify the light-induced odd-parity magnetism. Our work not only offers a powerful approach for uniquely achieving odd-parity spin-splitting with high tunability, but also expands the potential of Floquet engineering in designing unconventional compensated magnetism.
Authors: Z.Z. Alisultanov, A. Kudlis
We study multilayer topological insulators with random interlayer tunneling, known as off-diagonal disorder. Within the Burkov-Balents model a single Hermitian defect creates a bound state whose energy crosses the middle of the gap in the trivial phase but never in the topological phase; a non-Hermitian defect splits this level yet preserves the same crossing rule, so the effect serves as a local marker of topology. However, the key distinction persists: the bound state crosses zero in the trivial phase but not in the topological phase. Two complementary diagrammatic approaches give matching densities of states for the normal, topological, Weyl and anomalous quantum Hall regimes. Off diagonal disorder inserts bulk states into the gap and can close it: the Weyl phase remains robust under strong disorder, whereas the anomalous quantum Hall phase survives only for weak fluctuations, and the added bulk states shrink the Hall plateau, clarifying experimental deviations. Finally, we analyze edge modes. Uniform disorder shortens their localization length slightly, while Gaussian and Lorentzian disorder enlarge it and in the Gaussian case can even delocalize the edges. Although chirality is maintained, the enhanced overlap permits tunneling between opposite edges and pulls the longitudinal conductance away from its quantized value.
Authors: Pietro Maria Forcella, Cesare Tresca, Antonio Sanna, Gianni Profeta
Mercury chalcogenides is a class of materials that exhibit diverse structural phases under pressure, hosting exotic physical properties, including topological phases and chiral phonons. In particular, recent experimental results on HgS reports a new superconducting phase at 21 GPa, whose origin is unknown. In this letter we theoretically investigate the pressure-induced structural phase transition in HgS and the emergence of superconductivity in the rock salt phase. Remarkably, we discover that the rock salt phase hosts a two-gap superconducting phase originating from distinct Fermi surfaces. The unusually high critical temperature of 11 K emerges naturally within this multiband scenario, highlighting the role of interband coupling beyond isotropic approximation. These results place HgS among the few systems where multiband superconductivity is observed.
Authors: G. Niccoli, V. Terras
In this paper we continue our derivation of the correlation functions of open quantum spin 1/2 chains with unparallel magnetic fields on the edges; this time for the more involved case of the XXZ spin 1/2 chains. We develop our study in the framework of the quantum Separation of Variables (SoV), which gives us both the complete spectrum characterization and simple scalar product formulae for separate states, including transfer matrix eigenstates. Here, we leave the boundary magnetic field in the first site of the chain completely arbitrary, and we fix the boundary field in the last site $N$ of the chain to be a specific value along the $z$-direction. This is a natural first choice for the unparallel boundary magnetic fields. We prove that under these special boundary conditions, on the one side, we have a simple enough complete spectrum description in terms of homogeneous Baxter like $TQ$-equation. On the other side, we prove a simple enough description of the action of a basis of local operators on transfer matrix eigenstates as linear combinations of separate states. Thanks to these results, we achieve our main goal to derive correlation functions for a set of local operators both for the finite and half-infinite chains, with multiple integral formulae in this last case.
Authors: G. Niccoli, V. Terras
This paper is a continuation of [1], in which a set of matrix elements of local operators was computed for the XXZ spin-1/2 open chain with a particular case of unparallel boundary fields. Here, we extend these results to the more general case in which both fields are non-longitudinal and related by one constraint, allowing for a partial description of the spectrum by usual Bethe equations. More precisely, the complete spectrum and eigenstates can be characterized within the Separation of Variables (SoV) framework. One uses here the fact that, under the constraint, a part of this SoV spectrum can be described via solutions of a usual, homogeneous, TQ-equation, with corresponding transfer matrix eigenstates coinciding with generalized Bethe states. We explain how to generically compute the action of a basis of local operators on such kind of states, and this under the most general boundary condition on the last site of the chain. As a result, we can compute the matrix elements of some of these basis elements in any eigenstate described by the homogenous TQ-equation. Assuming, following a conjecture of Nepomechie and Ravanini, that the ground state itself can be described in this framework, we obtain multiple integral representations for these matrix elements in the half-infinite chain limit, generalizing those previously obtained in the case of longitudinal boundary fields and in the case of the special boundary conditions considered in [1].
Authors: Pavel P. Popov, Valentin Kasper, Maciej Lewenstein, Erez Zohar, Paolo Stornati, Philipp Hauke
Gauge-field configurations with nontrivial topology have profound consequences for the physics of Abelian and non-Abelian gauge theories. Over time, arguments have been gathering for the existence of gauge-field configurations with fractional topological charge, called fractons. Ground-state properties of gauge theories can drastically change in presence of fractons in the path integral. However, understanding the origin of such fractons is usually restricted to semiclassical argumentation. Here, we show that fractons persist in strongly correlated many-body systems, using the multiflavor Schwinger model of quantum electrodynamics as a paradigm example. Through detailed numerical tensor-network analysis, we find strong fracton signatures even in highly discretized lattice models, at sizes that are implementable on already existing quantum-simulation devices. Our work sheds light on how the nontrivial topology of gauge theories persists in challenging nonperturbative regimes, and it shows a path forward to probing it in tabletop experiments.
Authors: Zetian Mao, Chuan-Shen Hu, Jiawen Li, Chen Liang, Diptesh Das, Masato Sumita, Kelin Xia, Koji Tsuda
Message passing neural networks have demonstrated significant efficacy in predicting molecular interactions. Introducing equivariant vectorial representations augments expressivity by capturing geometric data symmetries, thereby improving model accuracy. However, two-body bond vectors in opposition may cancel each other out during message passing, leading to the loss of directional information on their shared node. In this study, we develop Equivariant N-body Interaction Networks (ENINet) that explicitly integrates l = 1 equivariant many-body interactions to enhance directional symmetric information in the message passing scheme. We provided a mathematical analysis demonstrating the necessity of incorporating many-body equivariant interactions and generalized the formulation to $N$-body interactions. Experiments indicate that integrating many-body equivariant representations enhances prediction accuracy across diverse scalar and tensorial quantum chemical properties.
Authors: Gian Marcello Andolina, Vittoria Stanzione, Vittorio Giovannetti, Marco Polini
Finding a quantum battery model that displays a genuine quantum advantage, while being prone to experimental fabrication, is an extremely challenging task. In this Letter we propose a deceptively simple quantum battery model that displays a genuine quantum advantage, saturating the quantum speed limit. It consists of two harmonic oscillators (the charger and the battery), coupled during the non-equilibrium charging dynamics by a non-linear interaction. We first present the model, then certify the genuine quantum advantage, and finally briefly discuss how the battery can be fabricated through the use of superconducting circuits.
Authors: Shunta Takahashi
Anyon condensation in wormhole geometries is investigated in the Virasoro TQFT (VTQFT) formulation, a proposed reformulation of 3d AdS quantum gravity. We first review some elementary techniques of VTQFT and summarize a gauging scheme for non-invertible symmetries referred to as anyon condensation. We then exhibit that anyon condensation is applicable to VTQFT even though the category of Wilson lines associated with it is not strictly a modular tensor category (MTC) due to the continuously infinite label $p\in\mathbb{R}_+$. More specifically, it is shown that the partition function of the wormhole factorizes upon condensing the so-called diagonal condensable anyon $\mathcal{A}=\int_{0}^{\infty}dp\,L_p\boxtimes\overline{L}_p$ in VTQFT. The resulting $2$d boundary theory is Liouville CFT by symmetry TFT construction, and to our knowledge, this is among the very few explicit computational examples of gauging \textit{continuous non-invertible} symmetries in the literature.
Authors: Corentin Bertrand, Pauline Besserve, Michel Ferrero, Thomas Ayral
Noise is often regarded as a limitation of quantum computers. In this work, we show that in the dynamical mean field theory (DMFT) approach to strongly-correlated systems, it can actually be harnessed to our advantage. Indeed, DMFT maps a lattice model onto an impurity model, namely a finite system coupled to a dissipative bath. While standard approaches require a large number of high-quality qubits in a unitary context, we propose a circuit that harvests amplitude damping to reproduce the dynamics of this model with a blend of noisy and noiseless qubits. We find compelling advantages with this approach: a substantial reduction in the number of qubits, the ability to reach longer time dynamics, and no need for ground state search and preparation. This method would naturally fit in a partial quantum error correction framework.
Authors: Peng Li, Yaxin Guo, Yaoxu Yan, Bingzhu Zheng, Wenchao Zhang, Jingai Mu, Fu Liu, Yanpeng Zhang, Feng Yun, Rongqian Wu, Yi Lyu, Renren Deng, Feng Li
Determining the local symmetry of luminescent centers in crystals is critical for understanding and controlling their optical transitions, yet current methods are limited by stringent experimental requirements and ambiguous symmetry assignments. Here, we develop a robust computational electromagnetics framework that directly connect the local symmetry and chirality of rare-earth-doped single crystals to the polarization states of their emitted light. This framework is experimentally validated through the precise determination of point and space group symmetries using high-resolution, polarization-resolved micro-photoluminescence ({\mu}-PL) spectra. Unlike conventional approaches that usually rely on analyzing multiple transitions at cryogenic temperatures, our technique operates at room temperature, requires only a single optical transition, and enables accurate orientation of symmetry axes. This enables deterministic polarization control of nano-emitters by tailoring symmetry groups and selecting appropriate transition dipoles, eliminating the need for bulky or complex photonic structures. Additionally, we demonstrate the function of bio-sensing, via determining single particle orientations in complex cellular environments using minimal polarization measurements. These results pave the way for advances in energy transfer systems, ultra-bright rare-earth nanocrystals, nanophotonic materials, and real-time single-particle tracking in biological contexts.
Authors: Surajit Bera, Marco Schirò
We study the non-stabilizerness or quantum magic of the Sachdev-Ye-Kitaev ($\rm SYK$) model, a prototype example of maximally chaotic quantum matter. We show that the Majorana spectrum of its ground state, encoding the spreading of the state in the Majorana basis, displays a Gaussian distribution as expected for chaotic quantum many-body systems. We compare our results with the case of the $\rm SYK_2$ model, describing non-chaotic random free fermions, and show that the Majorana spectrum is qualitatively different in the two cases, featuring an exponential Laplace distribution for the $\rm SYK_2$ model rather than a Gaussian. From the spectrum we extract the Stabilizer Renyi Entropy (SRE) and show that for both models it displays a linear scaling with system size, with a prefactor that is larger for the SYK model, which has therefore higher magic. Finally, we discuss the spreading of quantun magic under unitary dynamics, as described by the evolution of the Majorana spectrum and the Stabilizer Renyi Entropy starting from a stabilizer state. We show that the SRE for the $\rm SYK_2$ model equilibrates rapidly, but that in the steady-state the interacting chaotic SYK model has more magic than the simple $\rm SYK_2$. Our results suggest that the Majorana spectrum is qualitatively distinct in chaotic and non-chaotic many-body systems.
Authors: Barbara Jasser, Jovan Odavic, Alioscia Hamma
The Sachdev-Ye-Kitaev (SYK) model is of paramount importance for the understanding of both strange metals and a microscopic theory of two-dimensional gravity. We study the interplay between Stabilizer Rényi Entropy (SRE) and entanglement entropy in both the ground state and highly excited states of the SYK4+SYK2 model interpolating the highly chaotic four-body interactions model with the integrable two-body interactions one. The interplay between these quantities is assessed also through universal statistics of the entanglement spectrum and its anti-flatness. We find that SYK4 is indeed characterized by a complex pattern of both entanglement and non-stabilizer resources while SYK2 is non-universal and not complex. We discuss the fragility and robustness of these features depending on the interpolation parameter.
Authors: Donghee Lee, Hye-Sung Lee, Jaeok Yi
Theoretical understanding of deep learning remains elusive despite its empirical success. In this study, we propose a novel "synaptic field theory" that describes the training dynamics of synaptic weights and biases in the continuum limit. Unlike previous approaches, our framework treats synaptic weights and biases as fields and interprets their indices as spatial coordinates, with the training data acting as external sources. This perspective offers new insights into the fundamental mechanisms of deep learning and suggests a pathway for leveraging well-established field-theoretic techniques to study neural network training.
Authors: Takanori Ishii, Daichi Takeda
We develop, in the AdS/CFT correspondence, a method to compute correlation functions when the CFT is governed by the Lindblad equation for open quantum systems, via the AdS theory. Using a simple example in AdS$_3$/CFT$_2$, we demonstrate that the predictions of the AdS theory based on our method match the direct computations in the dual CFT. We also briefly discuss the relaxation problem and the holographic entropy in this example.
Authors: Huatian Hu, Zhiwei Hu, Christophe Galland, Wen Chen
Dual-band plasmonic nanoantennas, exhibiting two widely separated user-defined resonances, are fundamental building blocks for the investigation and optimization of plasmon-enhanced optical phenomena, including photoluminescence, Raman scattering, and various nonlinear effects such as harmonic generation or sum-frequency generation, parametric down-conversion, etc. The nanoparticle-on-slit (NPoS) or nanoparticle-in-groove (NPiG) is a recently proposed dual-band antenna with independently tunable resonances at mid-infrared and visible wavelengths. It was used to enhance the corresponding sum- and difference-frequency generation processes from optimally located molecules by an estimated $10^{13}$-fold. However, the theoretical understanding of such structures and their eigenmodes remains poor, hindering further optimization and limiting broader applications. Here, we explore a diverse range of nanocavity-like quasi-normal modes (QNMs) supported by NPoS structures, examining the contributions of both their near-field (i.e., giant photonic density of states) and far-field (i.e., spatial radiation patterns) characteristics to frequency upconversion. We identify methods for independently tuning the visible and mid-infrared resonances while conserving a good mode overlap in the near field, which is essential for efficient nonlinear processes. Moreover, through mode analysis, we unveil an experimentally unexplored fundamental resonance with greater field enhancement and much-improved mode overlap with the mid-infrared field, which could, in principle, further boost the mid-infrared upconversion efficiency by 5-fold compared to existing results. This work helps to rationalize and optimize the enhancement of nonlinear effects across a wide spectral range using a flexible and experimentally attractive nanoplasmonic platform.
Authors: Steven Samuels, William Campbell, Michael E. Tobar, Maxim Goryachev
A low-noise cryogenic microwave spectroscopy experiment was performed on a high-purity lithium fluoride (LiF) crystal. The spectroscopy data revealed avoided level crossing interactions in whispering gallery modes, indicative of electron spin resonance (ESR) coupling with paramagnetic impurities. Analysis of the interaction spectra identified distinct spin systems corresponding to $(S = 3/2, I = 7/2)$, $(S = 1, I = 7/2)$, and $(S = 3/2, I = 0)$. The number of hyperfine splittings observed, together with the natural abundance of ions possessing the appropriate nuclear spin values, suggest that V$^{2+}$ and V$^{3+}$ impurities, exhibiting orthorhombic distortion, are the most likely sources of the narrow interaction features. This interpretation is supported by earlier ESR studies and established manufacturing records for LiF crystal growth. Additionally, a separate set of broader interaction points is consistent with an orthorhombic model involving a $(S = 3/2, I = 0)$ spin system, although the specific impurity responsible for this interaction remains unidentified.
Authors: Corentin Delacour, M Mahmudul Hasan Sajeeb, Joao P. Hespanha, Kerem Y. Camsari
Sampling Boltzmann probability distributions plays a key role in machine learning and optimization, motivating the design of hardware accelerators such as Ising machines. While the Ising model can in principle encode arbitrary optimization problems, practical implementations are often hindered by soft constraints that either slow down mixing when too strong, or fail to enforce feasibility when too weak. We introduce a two-dimensional extension of the powerful parallel tempering algorithm (PT) that addresses this challenge by adding a second dimension of replicas interpolating the penalty strengths. This scheme ensures constraint satisfaction in the final replicas, analogous to low-energy states at low temperature. The resulting two-dimensional parallel tempering algorithm (2D-PT) improves mixing in heavily constrained replicas and eliminates the need to explicitly tune the penalty strength. In a representative example of graph sparsification with copy constraints, 2D-PT achieves near-ideal mixing, with Kullback-Leibler divergence decaying as O(1/t). When applied to sparsified Wishart instances, 2D-PT yields orders of magnitude speedup over conventional PT with the same number of replicas. The method applies broadly to constrained Ising problems and can be deployed on existing Ising machines.
Authors: Shunsuke A. Sato, Hannes Hübener, Umberto De Giovannini, Angel Rubio
We introduce a new theoretical framework -- the polarized Houston basis -- to model nonequilibrium dynamics in driven open quantum systems, formulated for use within the quantum master equation. This basis extends conventional Houston states by incorporating field-induced polarization effects, enabling a more accurate description of excitation dynamics under external driving. Using a one-dimensional dimer-chain model, we examine band population dynamics through projections onto polarized Houston states, original Houston states, and naive Bloch states. We find that the polarized Houston basis significantly suppresses spurious Bloch-state excitations and virtual transitions present in standard Houston approaches, allowing for a cleaner extraction of real excitations. When implemented in the relaxation time approximation of the quantum master equation, this formalism also yields a substantial reduction of unphysical DC currents in insulating systems. Our results highlight the polarized Houston basis as a powerful tool for simulating nonequilibrium phenomena in light-driven open quantum materials.
Authors: Rui Zhu, Yulan Chen, Katharina Tholen, Zhiguo He, Thomas Pähtz
Maxey & Riley's (Phys. Fluids, vol. 26, 1983, 883) analytical solution for the flow around a small sphere at low particle Reynolds number tells us that the fluid-particle interaction force decomposes into a contribution from the local flow disturbance caused by the particle's boundary -- consisting of the drag, Faxen, virtual-mass, and history forces -- and another contribution from the stress of the background flow, termed generalized-buoyancy force. There is also a consensus that, for general disperse two-phase flow, the interfacial force density, resulting from averaging the fluid's and particles' equations of motion, decomposes in a likewise manner. However, there has been a long-standing controversy about the physical closure separating the generalized-buoyancy from the interfacial force density, especially whether or not pseudo-stresses, such as the Reynolds stress, should be attributed to the background flow. Furthermore, most existing propositions for this closure involve small-particle approximations. Here, we show that all existing buoyancy closures are mathematically inconsistent with at least one of three simple thought experiments designed to determine the roles of pseudo-stresses and small-particle approximations. We then derive the unique closure consistent with these thought experiments. It fully incorporates all pseudo-stresses, requires no approximation, and is supported by particle-resolved numerical simulations. Remarkably, it exhibits a low-pass filter property, attenuating buoyancy at short wavelengths, that prevents it from causing Hadamard instabilities, constituting a first-principle-based solution to the long-standing ill-posedness problem of two-fluid models. When employing the derived closure, even very simplistic two-fluid models are hyperbolic.
Authors: Nico Kirchner, Roderich Moessner, Frank Pollmann, Adam Gammon-Smith
Two-dimensional many-body quantum systems can exhibit topological order and support collective excitations with anyonic statistics different from the usual fermionic or bosonic ones. With the emergence of these exotic point-like particles, it is natural to ask what phases can arise in interacting many-anyon systems. To study this topic, we consider the particular case of Fibonacci anyons subject to an anyonic tight-binding model with nearest-neighbor repulsion on a two-leg ladder. Focusing on the case of half-filling, for low interaction strengths an ''anyonic'' metal is found, whereas for strong repulsion, the anyons form an insulating charge-density wave. Within the latter regime, we introduce an effective one-dimensional model up to sixth order in perturbation theory arising from anyonic superexchange processes. We numerically identify four distinct phases of the effective model, which we characterize using matrix product state methods. These include both the ferro- and antiferromagnetic golden chain, a $\mathbb{Z}_2$ phase, and an incommensurate phase.
Authors: Wojciech J. Jankowski, Robert-Jan Slager, Giandomenico Palumbo
We show that momentum-space tensor monopoles corresponding to nontrivial vector bundle generalizations, known as bundle gerbes, can be realized in bands of three-dimensional topological matter with nontrivial Hopf invariants. We provide a universal construction of tensor Berry connections in these topological phases, demonstrating how obstructions therein lead to $\mathbb{Z}$-quantized bulk magnetoelectric and nonlinear optical phenomena. We then pinpoint that these quantum effects are supported by intraband and interband torsion leading to nontrivial Dixmier-Douady classes in most known Hopf phases and in more general topological insulators realizing gerbe invariants falling beyond the tenfold classification of topological phases of matter. We furthermore provide an interacting generalization upon introducing many-body gerbe invariants by employing twisted boundary conditions. This opens an avenue to study gerbe invariants realized through higher-dimensional charge fractionalizations that can be electromagnetically probed.
Authors: Kyle Monkman, Joan Weng, Niclas Heinsdorf, Alberto Nocera, Marcel Franz
Superconductors are famously capable of supporting persistent electrical currents, that is, currents that flow without any measurable decay as long as the material is kept in the superconducting state. We introduce here a class of materials -- superconducting altermagnets -- that can both generate and carry persistent {\em spin} currents. This includes spin-polarized electrical supercurrent as well as pure spin supercurrent that facilitates spin transport in the absence of any charge transport. A key to this remarkable property is the realization that the leading superconducting instability of altermagnetic metals consists of two independent condensates formed of spin-up and spin-down electrons. In the non-relativistic limit the two condensates are decoupled and can thus naturally support persistent currents with any spin polarization, including pure spin supercurrents realized in the charge counterflow regime. We describe a novel ``spin-current dynamo effect'' that can be used to generate pure spin supercurrent in such systems by driving a charge current along certain crystallographic directions. Away from the non-relativistic limit, when spin-orbit interactions and magnetic disorder are present, we find that the spin current generically develops spatial oscillations but, importantly, no dissipation or decay. This is in stark contrast to spin currents in normal diffusive metals which tend to decay on relatively short lengthscales. We illustrate the above properties by performing model calculations relevant to two distinct classes of altermagnets and various device geometries.
Authors: Megan F. Biggs, Sin-hang (Enoch)Ho, Aldair Alejandro, Matthew Lutz, Clayton D. Moss, Jeremy A. Johnson
Time reversal symmetry breaking motion of chiral phonon-polaritons in LiNbO3 is probed via the ultrafast Faraday effect. By combining a pair of perpendicularly polarized THz pulses with the right relative delay, we create a chiral THz driving field to excite chiral phonon-polaritons. The chiral atomic motion combines with the inverse Faraday effect from the circularly polarized THz pump to induce a magnetic moment field in the nonmagnetic material, LiNbO3. We attempt to quantify the strength of the magnetic field with Faraday rotation probe measurements. The direction of the Faraday signal flips when the input THz pulse is changed from left- to right-circular polarization, and we estimate a strong induced magnetic field strength of ~11 Tesla based on the Faraday rotation.
Authors: Weijie Li, Evgeny Redekop, Christiano Wang Beach, Canxun Zhang, Xiaowei Zhang, Xiaoyu Liu, Will Holtzmann, Chaowei Hu, Eric Anderson, Heonjoon Park, Takashi Taniguchi, Kenji Watanabe, Jiun-haw Chu, Liang Fu, Ting Cao, Di Xiao, Andrea F. Young, Xiaodong Xu
Twisted bilayer MoTe$_2$ (tMoTe$_2$) has emerged as a robust platform for exploring correlated topological phases, notably supporting fractional Chern insulator (FCI) states at zero magnetic field across a wide range of twist angles. The evolution of magnetism and topology with twist angle remains an open question. Here, we systematically map the magnetic phase diagram of tMoTe$_2$ using local optical spectroscopy and scanning nanoSQUID-on-tip (nSOT) magnetometry. We identify spontaneous ferromagnetism at moiré filling factors $\nu = -1$ and $-3$ over a twist angle range from 2.1$^\circ$ to 3.7$^\circ$, revealing a universal, twist-angle-insensitive ferromagnetic phase. At 2.1$^\circ$, we further observe robust ferromagnetism at $\nu = -5$, absent in the devices with larger twist angle -- a signature of the flattening of higher bands in this twist angle range. Temperature-dependent measurements reveal a contrasting twist-angle dependence of the Curie temperatures between $\nu = -1$ and $\nu = -3$, indicating distinct interplay between exchange interaction and bandwidth for the two Chern bands. Despite spontaneous time-reversal symmetry breaking, we find no evidence of a topological gap at $\nu = -3$; however, fragile correlated topological phases could be obscured by the device disorder evident in our spatially resolved measurements. Our results establish a global framework for understanding and controlling magnetic order in tMoTe$_2$ and highlight its potential for accessing correlated topological phases in higher energy Chern band.
Authors: Zesen Fu, Mengli Hu, Aolin Li, Haiming Duan, Junwei Liu, Fangping Ouyang
We present a theoretical and first-principles study of a two-dimensional altermagnet exhibiting spin-valley locking and strain-tunable topological phases. By constructing a minimal tight-binding model constrained by altermagnetic symmetry, we show that biaxial strain can drive a transition from a trivial insulator to a type-II quantum spin Hall (QSH) phase. Furthermore, we derive an analytical strain-induced perturbation theory that identifies two critical curves, dividing the phase space into four regions corresponding to a trivial insulator, a type-II QSH phase, and two quantum anomalous Hall phases with opposite Chern numbers. Remarkably, the Chern number can be reversed purely by changing the strain direction --without modifying magnetization or applying magnetic fields. The model reveals a universal phase diagram for materials with the same symmetry and valley structure. First-principles calculations on monolayer CrO confirm the predicted topological transitions, establishing strain engineering as an effective route for topological control in two-dimensional altermagnetic materials.
Authors: Ji Soo Lim, Carmine Autieri, Merit Spring, Martin Kamp, Amar Fakhredine, Pavel Potapov, Daniel Wolf, Sergii Pylypenko, Axel Lubk, Johannes Schultz, Nicolas Perez, Börge Mehlhorn, Louis Veyrat, Mario Cuoco, Fadi Choueikan, Philippe Ohresser, Bernd Büchner, Giorgio Sangiovanni, Ralph Claessen, Michael Sing
Magnetic materials with strong spin-orbit coupling (SOC) are essential for the advancement of spin-orbitronic devices, as they enable efficient spin-charge conversion, complex magnetic structures, spin-valley physics, topological phases and other exotic phenomena. 5d transition-metal oxides such as SrIrO3 feature large SOC, but usually show paramagnetic behavior due to broad bands and a low density of states at the Fermi level, accompanied by a relatively low Coulomb repulsion. Here, we unveil ferromagnetism in 5d SrIrO3 thin films grown on SrTiO3 (111). Through substrate-induced structural engineering, a zigzag stacking of three-unit-cell thick layers along the [111] direction is achieved, stabilizing a ferromagnetic state at the interfaces. Magnetotransport measurements reveal an anomalous Hall effect below ~30 K and hysteresis in the Hall conductivity below 7 K, indicating ferromagnetic ordering. X-ray magnetic circular dichroism further supports these results. Theoretical analysis suggests that the structural engineering of the IrO6 octahedral network enhances the density of states at the Fermi level and thus stabilizes Stoner ferromagnetism. This work highlights the potential of structurally engineered 5d oxides for spin-orbitronic devices, where efficient control of SOC-induced magnetic phases by electric currents can lead to lower energy consumption and improved performance in next-generation device technologies.
Authors: Bo Li, Ding-Fu Shao, Alexey A. Kovalev
In antiferromagnetic spintronics, accessing the spin degree of freedom is essential for generating spin currents and manipulating magnetic order, which generally requires lifting spin degeneracy. This is typically achieved through relativistic spin-orbit coupling or non-relativistic spin splitting in altermagnets. Here, we propose an alternative approach: a dynamical spin splitting induced by an optical field in antiferromagnets. By coupling the driven system to a thermal bath, we demonstrate the emergence of steady-state pure spin currents, as well as linear-response longitudinal and transverse spin currents. Crucially, thermal bath engineering allows the generation of a net spin accumulation without relying on spin-orbit coupling. Our results provide a broadly applicable and experimentally tunable route to control spins in antiferromagnets, offering new opportunities for spin generation and manipulation in antiferromagnetic spintronics.
Authors: Alexander V. Milovanov, Alexander Iomin
We study the spreading dynamics of an initially localized wave packet in 1D nonlinear Schrödinger lattices with random potential. It is shown that adding small dielectric coupling to surrounding random medium results in asymptotic localization of the nonlinear field. The nonlinear localization length depends on dielectric loss of the medium at low temperatures and the value of nonlinearity parameter. The model predicts a possibility of self-induced localization when the ``medium" to which the wave field is dielectrically coupled is the nonlinear wave itself.
Authors: Alexander C. Jenkins, Hiranya V. Peiris, Andrew Pontzen
The decay of metastable 'false vacuum' states via bubble nucleation plays a crucial role in many cosmological scenarios. Cold-atom analog experiments will soon provide the first empirical probes of this process, with potentially far-reaching implications for early-Universe cosmology and high-energy physics. However, an inevitable difference between these analog systems and the early Universe is that the former have a boundary. We show, using a combination of Euclidean calculations and real-time lattice simulations, that these boundaries generically cause rapid bubble nucleation on the edge of the experiment, obscuring the bulk nucleation that is relevant for cosmology. We demonstrate that implementing a high-density 'trench' region at the boundary completely eliminates this problem, and recovers the desired cosmological behavior. Our findings are relevant for ongoing efforts to probe vacuum decay in the laboratory, providing a practical solution to a key experimental obstacle.
Authors: Yi-Ting Tu, David M. Long, Dominic V. Else
't Hooft anomalies of global symmetries play a fundamental role in quantum many-body systems and quantum field theory (QFT). In this paper, we make a systematic analysis of lattice anomalies - the analog of 't Hooft anomalies in lattice systems - for which we give a precise definition. Crucially, a lattice anomaly is not a feature of a specific Hamiltonian, but rather is a topological invariant of the symmetry action. The controlled setting of lattice systems allows for a systematic and rigorous treatment of lattice anomalies, shorn of the technical challenges of QFT. We find that lattice anomalies reproduce the expected properties of QFT anomalies in many ways, but also have crucial differences. In particular, lattice anomalies and QFT anomalies are not, contrary to a common expectation, in one-to-one correspondence, and there can be non-trivial anomalies on the lattice that are infrared (IR) trivial: they admit symmetric trivial gapped ground states, and map to trivial QFT anomalies at low energies. Nevertheless, we show that lattice anomalies (including IR-trivial ones) have a number of interesting consequences in their own right, including connections to commuting projector models, phases of many-body localized (MBL) systems, and quantum cellular automata (QCA). We make substantial progress on the classification of lattice anomalies and develop several theoretical tools to characterize their consequences on symmetric Hamiltonians. Our work places symmetries of quantum many-body lattice systems into a unified theoretical framework and may also suggest new perspectives on symmetries in QFT.
Authors: Muhammad Akram, Aayush Vijayvargia, Hae-Young Kee, Onur Erten
Spin-orbital generalizations of Kitaev model, such as Yao-Lee model, have attracted recent attention due to their enhanced stability of spin liquid phases against perturbations. Motivated by microscopic calculations for the realization of Yao-Lee model showing additional interactions, we study the phase diagram of the Yao-Lee model with added Kitaev and Heisenberg terms. While the plaquette operator is conserved even in the presence of added perturbations, the model becomes no longer exactly solvable. Using perturbation and Majorana mean-field theory, we find magnetic order can arise in the spin sector while the orbital sector remains a liquid for dominant Kitaev interactions, whereas both sectors form liquid phases when Yao-Lee interactions dominate. Additional Heisenberg exchange can enhance or suppress the magnetic order, revealing a rich coexistence of magnetic and topological phases.
Authors: Thomas H. Swift, Alberto Gomez-Saiz, Virginia N. Ciriano-Tejel, David F. Wise, Grayson M. Noah, John J. L. Morton, M. Fernando Gonzalez-Zalba, Mark A. I. Johnson
State-of-the-art quantum processors have recently grown to reach 100s of physical qubits. As the number of qubits continues to grow, new challenges associated with scaling arise, such as device variability reduction and integration with cryogenic electronics for I/O management. Spin qubits in silicon quantum dots provide a platform where these problems may be mitigated, having demonstrated high control and readout fidelities and compatibility with large-scale manufacturing techniques of the semiconductor industry. Here, we demonstrate the monolithic integration of 384 p-type quantum dots, each embedded in a silicon transistor, with on-chip digital and analog electronics, all operating at deep cryogenic temperatures. The chip is fabricated using 22-nm fully-depleted silicon-on-insulator (FDSOI) CMOS technology. We extract key quantum dot parameters by fast readout and automated machine learning routines to determine the link between device dimensions and quantum dot yield, variability, and charge noise figures. Overall, our results demonstrate a path to monolithic integration of quantum and classical electronics at scale.
Authors: Yang Zhou, Ali Eltareb, Gustavo E. Lopez, Nicolas Giovambattista
As a liquid approaches the glass state, its dynamics slows down rapidly, by a few orders of magnitude in a very small temperature range. In the case of light elements and small molecules containing hydrogen (e.g., water), such a process can be affected by nuclear quantum effects (due to quantum fluctuations/atoms delocalization). In this work, we apply the potential energy landscape (PEL) formalism and path-integral computer simulations to study the low-temperature behavior of a Lennard-Jones binary mixture (LJBM) that obeys quantum mechanics. We show that, as for the case of classical liquids, (i) a configurational entropy $S_{IS}$ can be defined, and (ii) the Adam-Gibbs equation, which relates the diffusion coefficient of a liquid and its $S_{IS}$, holds for the studied quantum LJBM. Overall, our work shows that one theoretical approach, the PEL formalism, can be used to describe low-temperature liquids close to their glass transition, independently of whether the system obeys classical or quantum mechanics.
Authors: Takuya Kobayashi, Kent Andrew Sakurai, Shinji Michimura, Hiromi Taniguchi
We report the structural, electrical, and magnetic properties of the organic conductor $\kappa$-(BEST)$_2$Cu$_2$(CN)$_3$ (BEST: bis(ethylenediseleno)tetrathiafulvalene; abbreviated as $\kappa$-BEST-CN), which is isostructural with the quantum spin liquid candidate $\kappa$-(ET)$_2$Cu$_2$(CN)$_3$ (ET: bis(ethylenedithio)tetrathiafulvalene; abbreviated as $\kappa$-ET-CN). Resistivity measurements demonstrate that $\kappa$-BEST-CN exhibits semiconducting behavior, governed by the same conducting mechanism as $\kappa$-ET-CN. Under a pressure of ~0.1 GPa, $\kappa$-BEST-CN undergoes a superconducting transition with an onset temperature of ~4 K. From the comparison of the critical pressures of superconductivity between $\kappa$-ET-CN and $\kappa$-BEST-CN, $\kappa$-BEST-CN can be regarded as a chemically pressurized analogue of $\kappa$-ET-CN. Therefore, $\kappa$-BEST-CN, in which only the effective pressure changes without altering the anion structure, is considered a valuable reference material for elucidating the enigmatic properties observed in $\kappa$-ET-CN. Furthermore, the spin susceptibility of $\kappa$-BEST-CN is slightly larger than that of $\kappa$-ET-CN and shows weaker temperature dependence, which cannot be explained by the localized spin model. This behavior clarifies the anomalous magnetic properties of a system with frustration near the Mott transition, serving to stimulate future theoretical research.
Authors: Jyesta M. Adhidewata, Joel E. Moore
The excitations of fractional quantum Hall effect (FQHE) states have been largely inaccessible to experimental probes until recently. New electron scanning tunneling microscopy (STM) results from Hu this http URL. (2023) show promise in detecting and identifying these excited states via the local density of states (LDOS) spectrum. On a torus, there exists a mapping to a 1D lattice Hamiltonian with center-of-mass or dipole moment conservation. In this work, we apply perturbation theory starting from the thin cylinder limit ($L_x \rightarrow \infty, L_y
Authors: Dibyendu Samanta, Sudeep Kumar Ghosh
The superconducting diode effect (SDE), characterized by a directional asymmetry in the critical supercurrents, typically requires external magnetic fields to break time-reversal symmetry -- posing challenges for scalability and device integration. Here, we demonstrate a field-free realization of the SDE in a helical Shiba chain proximitized by a d-wave altermagnet. Using a self-consistent Bogoliubov-de Gennes approach, we uncover a topological Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state that hosts tunable Majorana zero modes at the chain ends. This state is stabilized by the interplay between the exchange coupling of magnetic adatoms and the induced altermagnetic spin splitting. Crucially, the same FFLO phase supports strong nonreciprocal supercurrents, achieving diode efficiencies exceeding 45% without applied magnetic fields. The d-wave altermagnet plays a dual role: it intrinsically breaks time-reversal symmetry, enabling topological superconductivity, and introduces inversion symmetry breaking via momentum-dependent spin-splitting, driving the field-free SDE in a junction-free setting. The supercurrent-controlled finite Cooper pair momentum of the FFLO state modulates both the topological gap and the diode response. Our results establish the Shiba chain-altermagnet heterostructure as a promising platform for realizing topological superconducting devices with efficient, intrinsic superconducting diode functionality -- offering a scalable pathway towards dissipationless quantum technologies.
Authors: Yi-Hong Chen, Si-Yuan Chen, Xin-Chi Zhou, Xiong-Jun Liu
Fractional topological phases, such as the fractional quantum Hall state, usually rely on strong interactions to generate ground state degeneracy with gap protection and fractionalized topological response. Here, we propose a fractional topological phase without interaction in $(1+1)$-dimension, which is driven by the Stark localization on top of topological flat bands, different from the conventional mechanism of the strongly correlated fractional topological phases. A linear potential gradient applied to the flat bands drives the Stark localization, under which the Stark localized states may hybridize and leads to a new gap in the real space, dubbed the real space energy gap (RSEG). Unlike the integer topological band insulator obtained in the weak linear potential regime without closing the original bulk gap, the fractional topological Stark insulating phase is resulted from the RSEG when the linear potential gradient exceeds a critical value. We develop a theoretical formalism to characterize the fractional topological Stark insulator, and further show that the many-body state under topological pumping returns to the initial state only after multiple $2\pi$ periods of evolution, giving the fractional charge pumping, similar to that in fractional quantum Hall state. Finally, we propose how to realize the fractional topological Stark insulator in real experiment.
Authors: Armen Harutyunyan
Magneto-transport properties of a two-dimensional electron gas in a chain of planar quantum rings are investigated under the Rashba spin-orbit interaction and a transverse homogeneous magnetic field. A modulation potential function models the ring-chain periodicity along one direction and the confinement in the perpendicular one. The electron energy minibands collapse into discrete levels with high degeneracy at specific magnetic field values. The Rashba effect significantly influences the system's properties. Calculations reveal a transition from diamagnetic to paramagnetic behavior in the spin-difference orbital magnetization at high Rashba coupling strengths. This is consistent with the reversal of the spin-difference persistent current observed at the same Rashba values. Total and spin-difference magnetizations exhibit oscillations linked to miniband nodes. The longitudinal magnetoconductance component shows oscillations resembling Shubnikov-De Haas behavior, while the transverse component displays a ladder-like profile reminiscent of the quantum Hall effect. However, both phenomena are more closely associated with the periodic collapse of minibands, leading to strong density-of-states oscillations, rather than with the mechanisms behind the quantum Hall effect. This highlights the rich physics of quantum topological phases in nanostructures with non-trivial geometry. At high Rashba coupling, this behavior degrades. Spin magnetization shows pronounced oscillations, indicating complex interplay between the Zeeman and Rashba effects on spin polarization. These results offer insights into experimentally relevant electronic and spin characteristics attainable in modulated semiconductor structures, contributing to the development of advanced 2D-based materials for magneto-transport and spintronics applications.
Authors: Zhejunyu Jin, Zhaozhuo Zeng, Jie Liu, Tianci Gong, Ying Su, Kai Chang, Peng Yan
Nonrelativistic magnon chiral splitting in altermagnets has garnered significant recent attention. In this work, we demonstrate that nonlinear three-wave mixing -- where magnons split or coalesce -- extends this phenomenon into unprecedented relativistic regimes. Employing a bilayer antiferromagnet with Dzyaloshinskii-Moriya interactions, we identify three distinct classes of chiral splitting, each dictated by specific symmetries, such as $C_4T$, $\sigma_v T$, or their combination. This reveals a novel bosonic mechanism for symmetry-protected chiral splitting, capitalizing on the unique ability of magnons to violate particle-number conservation, a feature absent in low-energy fermionic systems. Our findings pave the way for engineering altermagnetic splitting, with potential applications in advanced magnonic devices and deeper insights into magnon dynamics in complex magnetic systems.
Authors: Zijun Huang, Tong Li, Longfu Li, Rui Chen, Zaichen Xiang, Shuangyue Wang, Jingjun Qin, Yucheng Li, Lingyong Zeng, Dinghua Bao, Huixia Luo
Searching for new superconductors, especially unconventional superconductors, has been studied extensively for decades but remains one of the major outstanding challenges in condensed matter physics. Medium/high-entropy alloys (MEAs-HEAs) are new fertile soils of unconventional superconductors and generate widespread interest and questions on the existence of superconductivity in highly disordered materials. Here, we report on the effect of Ni-doped on the crystal structure and superconductivity properties of strongly coupled TiHfNbTa MEA. XRD results indicate that the maximum solid solution of (Ti1/4Hf1/4Nb1/4Ta1/4)1-xNix is about 7.7%. Resistivity, magnetic susceptibility, and specific heat measurements demonstrated that (Ti1/4Hf1/4Nb1/4Ta1/4)1-xNix HEAs are all bulk type-II superconductors and follow the trend of the increase of Tc with the increase of Ni-doped contents. The specific heat jump of all (Ti1/4Hf1/4Nb1/4Ta1/4)1-xNix are much larger than the BCS value of 1.43, suggesting all these HEAs are strongly coupled superconductors. Additionally, large Kadawaki-Woods ratio values suggest that there is a strong electron correlation effect in this system. The (Ti1/4Hf1/4Nb1/4Ta1/4)1-xNix HEA system is a new ideal material platform for the study of strong correlation behavior and strongly coupled superconductivity, which provides an insight into the physics of high-temperature superconductors or other unconventional superconductors.
Authors: Antonio Picano, Matthieu Vanhoecke, Marco Schirò
We study the dissipative dynamics of correlated fermions evolving in presence of a local dephasing bath. To this extent we consider the infinite coordination limit of the corresponding Lindblad master equation, provided by Dynamical Mean-Field Theory for open quantum systems. We solve the resulting quantum impurity problem, describing an Anderson impurity coupled to a local dephasing, using weak-coupling perturbation theory in interaction and dephasing. We show that the dissipative dynamics describes heating towards infinite temperature, with a relaxation rate that depends strongly on interaction. The resulting steady-state spectral functions are however non-trivial and show an interplay between coherent quasiparticle peak and local dephasing. We then discuss how thermalization towards infinite temperature emerges within DMFT, by solving the impurity problem throughout its self-consistency. We show that thermalization under open quantum system dynamics is qualitatively different from the closed system case. In particular, the thermalization front found in the unitary is strongly modified, a signature of the irreversibility of the open system dynamics.
Authors: Guozhu Song, Xiangliang Zheng, Xiaodong Yao, Xuefeng Zhou, Chao Gu, Qinghua Zhang, Jian Chen, Chenglu Huang, Tiancheng Yang, Leiming Fang, Ping Miao, Lingxiang Bao, Wen Yin, Xiaohui Yu, Jinlong Zhu, Wei Bao, Yusheng Zhao, Erjia Guo, Shanmin Wang
Perovskite-type ternary nitrides with predicted exciting ferroelectricity and many other outstanding properties hold great promise to be an emerging class of advanced ferroelectrics for manufacturing diverse technologically important devices. However, such nitride ferroelectrics have not yet been experimentally identified, mainly due to the challenging sample synthesis by traditional methods at ambient pressure. Here we report the successful high-pressure synthesis of a high-quality ferroelectric nitride perovskite of CeTaN3-{\delta} with nitrogen deficiency, adopting an orthorhombic Pmn21 polar structure. This material is electrically insulating and exhibits switchable and robust electric polarization for producing ferroelectricity. Furthermore, a number of other extraordinary properties are also revealed in this nitride such as excellent mechanical properties and chemical inertness, which would make it practically useful for many device-relevant applications and fundamentally important for the study of condensed-matter physics.
Authors: Lisa M. Rütten, Eva Liebhaber, Gael Reecht, Kai Rossnagel, Katharina J. Franke
Magnetic adatom chains on superconductors provide a platform to explore correlated spin states and emergent quantum phases. Using low-temperature scanning tunneling spectroscopy, we study the distance-dependent interaction between Fe atoms on 2H-NbSe$_2$. While single atoms exhibit four Yu-Shiba-Rusinov states and partially occupied $d$ levels consistent with a $S=2$ spin state, the spin is quenched when two Fe atoms reside in nearest neighbor lattice sites, where the $d$ levels of the atoms hybridize. The non-magnetic dimer configuration is stable in that dimerization persists in chains with weak interactions among the dimers. Thus, the spin-state quenching has important implications also for Fe chains. While even-numbered chains are stable and non-magnetic, odd-numbered chains host a single magnetic atom at one of the chain's ends, with its position being switchable by voltage pulses. Our findings emphasize the role of interatomic coupling in shaping quantum ground states and suggest that engineering alternating hopping amplitudes analogous to the Su-Schrieffer-Heeger model may offer a pathway to realizing topological systems.
Authors: R Eid (LCF), S Tiengo (LCF), M Lévy (LCF), T Bourdel (LCF)
Rabi-coupled spinor Bose-Einstein condensates, with competing intra-and interspecies interactions, enable independent control of two-and three-body interactions. We show that coupling can also drive the system into a strongly nonlinear regime of saturating interaction. More precisely, the equation of state interpolates between low-and high-density regimes described by two different two-body scattering lengths. Interestingly, the transition can be determined by the strength of the coupling. We experimentally demonstrate this saturation phenomenon by measurements of the interaction energy of a Bose-Einstein condensate as a function of the detuning and of the strength of the Rabi coupling in spin mixtures of potassium 39.
Authors: Pietro Maria Forcella, Cesare Tresca, Antonio Sanna, Gianni Profeta
Mercury chalcogenides are a class of materials that exhibit diverse structural phases under pressure, leading to a range of exotic physical properties, including topological phases and chiral phonons. In particular, the phase diagram of mercury sulfide (HgS) remains difficult to characterize, with significant uncertainty surrounding the transition pressure between phases. Based on recent experimental results, we employ Density Functional Theory and Superconducting Density Functional Theory to investigate the pressure-induced structural phase transition in HgS and its interplay with the emergence of superconductivity as the crystal transitions from the cinnabar phase (space group P3$_1$21) to the rock salt phase (space group Fm$\bar{3}$m). Remarkably, the rocksalt phase hosts a multigap superconducting state driven by distinct Fermi surface sheets, with two dominant gaps; the unusually high critical temperature of $\sim$11 K emerges naturally within this multiband scenario, highlighting the role of interband coupling beyond isotropic models. These results place HgS among the few systems where multiband superconducting gap structures emerge under pressure.
Authors: Naratip Nunchot, Youichi Yanase
We study a dirty two-dimensional superconductor with Rashba spin-orbit coupling and in-plane Zeeman fields described by the nonlinear sigma model that includes short-range electron-electron interactions from the Coulomb and Cooper channels. The renormalized Ginzburg-Landau theory, which includes the weak localization effects at the one-loop level, is constructed by using the Keldysh functional formalism. It is shown that the tricritical point appears in the phase diagram. The superconducting diode quality factor increases divergently as the system approaches the tricritical point. Near the superconducting phase transition lines, the absolute value of the diode quality factor decreases due to the cooperation of localization and interactions. The normal conductivity of the resistive state, in which the superconducting state is destroyed by the critical current, is calculated, and localization behaviors are demonstrated.
Authors: Md Mushfiqul Islam, Nishat N. Labiba, Lawrence O. Hall, David S. Simmons
Synthetic sequence-controlled polymers promise to transform polymer science by combining the chemical versatility of synthetic polymers with the precise sequence-mediated functionality of biological proteins. However, design of these materials has proven extraordinarily challenging, because they lack the massive datasets of closely related evolved molecules that accelerate design of proteins. Here we report on a new Artifical Intelligence strategy to dramatically reduce the amount of data necessary to accelerate these materials' design. We focus on data connecting the repeat-unit-sequence of a \emph{compatibilizer} molecule to its ability to reduce the interfacial tension between distinct polymer domains. The optimal sequence of these molecules, which are essential for applications such as mixed-waste polymer recycling, depends strongly on variables such as concentration and chemical details of the polymer. With current methods, this would demand an entirely distinct dataset to enable design at each condition. Here we show that a deep neural network trained on low-fidelity data for sequence/interfacial tension relations at one set of conditions can be rapidly tuned to make higher-fidelity predictions at a distinct set of conditions, requiring far less data that would ordinarily be needed. This priming-and-tuning approach should allow a single low-fidelity parent dataset to dramatically accelerate prediction and design in an entire constellation of related systems. In the long run, it may also provide an approach to bootstrapping quantitative atomistic design with AI insights from fast, coarse simulations.
Authors: De-Zhang Li, Xin Wang
Partition function zeros are powerful tools in understanding critical behavior. In this paper we present new results of the Fisher zeros of two-dimensional Ising models, in the framework of free-fermion eight-vertex model. First we succeed in finding special boundary conditions for the free-fermion model, under which the partition function of a finite lattice can be expressed in a double product form. Using appropriate mappings, these boundary conditions are transformed into the corresponding versions of the square, triangular and honeycomb lattice Ising models. Each Ising model is studied in the cases of a zero field and of an imaginary field $i(\pi/2)k_BT$. For the square lattice model we rediscover the famous Brascamp-Kunz (B-K) boundary conditions. For the triangular and honeycomb lattice models we obtain the B-K type boundary conditions, and the Fisher zeros are conveniently solved from the product form of partition function. The advantage of B-K type boundary conditions is that the Fisher zeros of any finite lattice exactly lie on certain loci, and the accumulation points of zeros can be easily determined in the thermodynamic limit. Our finding and method would be very helpful in studying the partition function zeros of vertex and Ising models.
Authors: Hoshu Hiyane, Thomás Fogarty, Jose Carlos Pelayo, Thomas Busch
We show that strongly correlated impurities confined in an optical lattice can form localized, molecule-like dimer states in the presence of a Bose-Einstein condensate (BEC). By systematically studying the effect of the lattice potential on this mixture, we reveal the two roles of the condensate in assisting the formation of dimerized impurities: mediating the attractive interaction among impurities and rescaling the lattice potential of impurities. At strong coupling between the impurities and the condensate, the two mechanisms cooperate to induce a structural transition, resulting in the rearrangement of dimers. We also show that the nonequilibrium dynamics of these states can be interpreted as a dimerized soliton train.
Authors: C. Koliofoti, M. A. Javed, R.-P. Riwar
The task of finding a consistent relationship between a quantum Hamiltonian and a classical Lagrangian is of utmost importance for basic, but ubiquitous techniques like canonical quantization and path integrals. Nonconvex kinetic energies (which appear, e.g., in Wilczek and Shapere's classical time crystal, or nonlinear capacitors) pose a fundamental problem: the Legendre transformation is ill-defined, and the more general Legendre-Fenchel transformation removes nonconvexity essentially by definition. Arguing that such anomalous theories follow from suitable low-energy approximations of well-defined, harmonic theories, we show that seemingly inconsistent Hamiltonian and Lagrangian descriptions can both be valid, depending on the coupling strength to a dissipative environment. Essentially there occurs a dissipative phase transition from a non-convex Hamiltonian to a convex Lagrangian regime, involving exceptional points in imaginary time. This resolves apparent inconsistencies and provide computationally efficient methods to treat anomalous, nonconvex kinetic energies.
Authors: Daniil Domaretskiy, Zefei Wu, Van Huy Nguyen, Ned Hayward, Ian Babich, Xiao Li, Ekaterina Nguyen, Julien Barrier, Kornelia Indykiewicz, Wendong Wang, Roman V. Gorbachev, Na Xin, Kenji Watanabe, Takashi Taniguchi, Lee Hague, Vladimir I. Fal'ko, Irina V. Grigorieva, Leonid A. Ponomarenko, Alexey I. Berdyugin, Andre K. Geim
The electronic quality of two-dimensional systems is crucial when exploring quantum transport phenomena. In semiconductor heterostructures, decades of optimization have yielded record-quality two-dimensional gases with transport and quantum mobilities reaching close to 10$^8$ and 10$^6$ cm$^2$/Vs, respectively. Although the quality of graphene devices has also been improving, it remains comparatively lower. Here we report a transformative improvement in the electronic quality of graphene by employing graphite gates placed in its immediate proximity, at 1 nm separation. The resulting screening reduces charge inhomogeneity by two orders of magnitude, bringing it down to a few 10$^7$ cm$^-2$ and limiting potential fluctuations to less than 1 meV. Quantum mobilities reach 10$^7$ cm$^2$/Vs, surpassing those in the highest-quality semiconductor heterostructures by an order of magnitude, and the transport mobilities match their record. This quality enables Shubnikov-de Haas oscillations in fields as low as 1 mT and quantum Hall plateaus below 5 mT. Although proximity screening predictably suppresses electron-electron interactions, fractional quantum Hall states remain observable with their energy gaps reduced only by a factor of 3-5 compared to unscreened devices, demonstrating that many-body phenomena at spatial scales shorter than 10 nm remain robust. Our results offer a reliable route to improving electronic quality in graphene and other two-dimensional systems, which should facilitate the exploration of new physics previously obscured by disorder.
Authors: Yanyan Yang, Weiwei Lin
Current-induced magnetization switching, a fundamental phenomenon related to spin-transport of electrons, enables non-voltaic and fast information write, facilitating applications in low-power memory and logic devices. However, magnetization switching by spin-orbit torques is usually attributed to current flowing in the nonmagnetic metal layer of multilayers or in magnetic alloys with heavy elements. Here, we report perpendicular magnetization switching induced by current flowing in an elemental ferromagnet nickel single layer. This prototype structure demonstrates that current-induced magnetization switching is a general phenomenon of magnet. The results suggest that the current induces an effective transverse magnetic field with an out-of-plane component leading to the magnetization switching, different to the conventional spin-orbit torques. Our work opens the new insight and reveals the intrinsic mechanism of current-induced torques.
Authors: Shalika R. Bhandari, R. Tamang, Keshav Shrestha, Samy Brahimi, Samir Lounis, D. P. Rai
We have investigated the pressure-dependent electronic structure, phonon stability, and anomalous Hall response of the recently discovered altermagnet FeSb2 from density functional theory (DFT) and Wannier function analysis. From density functional perturbation theory (DFPT) calculations, we have found that FeSb2 remains dynamically stable up to 10 GPa, evidenced by positive phonon frequencies. Our spin-polarised band structure shows that the node of band crossing between spin-up and spin-down bands around the Fermi energy exactly lies at the Gamma and A-symmetry points. The Fermi crossing is mostly exhibited by band-24, band-25 and band-26. The non-relativistic spin-splitting (NRSS) along M'-Gamma-M and A-Z-A' symmetry is attributed to the broken time-reversal (PT ) symmetry. There are significant changes in the band profile under applied pressure, as one can see the shifting of the node of band-24 and band-26 towards the lower energy side. The NRSS exhibited by band-24 along M'-Gamma-M symmetry is notably small. Although the strength of NRSS of band-26 along A-Z-A' symmetry is significant but reduces under applied pressure. The anomalous Hall conductivity (AHC) values are prominent in -1 to 1 eV range. A sharp peaked and positive AHC values at ambient pressure, becomes spectrally broadened and negative at 10 GPa due to pressure-induced band crossings and redistribution of Berry curvature near the Fermi level. We have observed that the values of spin hall conductivity (SHC) are around 2-2.5 times lower as compared to AHC and prominent in between -1.0 eV to 1.0 eV. Our results establish FeSb2 as a tunable altermagnetic candidate where pressure can modulate both topological transport and dynamic stability, offering opportunities for strain-engineered Hall responses in compensated magnetic systems.
Authors: Ron Q. Nguyen, Hai-Tian Wu, Erin Morissette, Naiyuan J. Zhang, Peiyu Qin, Kenji Watanabe, Takashi Taniguchi, Aaron W. Hui, Dima E. Feldman, J. I. A. Li
Superconductivity and the quantum Hall effect are conventionally viewed as mutually exclusive: the former is suppressed by magnetic fields, while the latter relies on them. Here, we report the surprising coexistence of these two phenomena in rhombohedral hexalayer graphene. In this system, a superconducting phase is not destroyed -- but instead stabilized -- by an out-of-plane magnetic field. Strikingly, this superconducting state coexists and competes with a sequence of quantum Hall states that appear at both integer and half-integer Landau level fillings. Both the superconducting and quantum Hall states exhibit sharply defined thermal transitions or crossovers, with nearly identical onset temperatures -- pointing to a shared underlying mechanism. Taken together, our observations uncover an unprecedented interplay between superconducting and topological phases, challenging conventional paradigms and opening a new frontier in condensed matter physics.
Authors: Niharika Tamuli, Saumen Acharjee
We investigate the spin-polarized ballistic transport in a three-terminal Zigzag graphene nanoribbon (ZGNR) device using a tight binding model, non-equilibrium Green function formalism within the Landauer-Büttiker framework. We study the transmission spectrum, density of states, I-V characteristics, spin-resolved conductance and spin current by varying ribbon geometries and an out-of-plane Zeeman field. In absence of magnetization, transport is dominated by subband quantization and resonant edge states, with pronounced dependence on ribbon width and length while the introduction of a Zeeman field offers spin-selective transport and inducing half-metallic behavior, particularly in narrower ribbons, highlighting the interplay between quantum confinement, edge-localized states and spin-dependent interactions. Moreover, we found Fabry-Pérot-like interference in conductance spectrum and bias-driven mode activation with strong spin filtering effects. The spin current is found to be tunable via magnetic field and gate voltage. Also, it remains stable under thermal fluctuations, demonstrating suitability for room-temperature operation. Finally, the energy and width dependence of the Fano factor reveals distinct quantum interference features and spin-polarized transport signatures. These findings indicate the potential of the three-terminal ZGNR based device for scalable and gate-controllable spintronic applications.
Authors: Ibrahim Al-Azki, Valentina Baccetti
Complex systems exhibit macroscopic behaviors that emerge from the coordinated interactions of their individual components. Understanding the microscopic origins of these emergent properties remains challenging, particularly in systems beyond canonical examples, due to the absence of a generalized framework for identifying the governing degrees of freedom. The multiscale complexity formalism aims to address this challenge by employing information-theoretic indices of structure to identify the scales at which collective behaviors emerge. In this paper, we evaluate the complexity profile index as a tool for identifying such scales by applying it to two-dimensional ferromagnetic Ising systems. We demonstrate that these systems exhibit multiscale behavior in the critical region, and the emergence of macroscopic magnetization in the ordered phase corresponds to a non-monotonic behavior of the complexity profile at large scales. Additionally, we show that the pairwise complexity exhibits a maximum in the disordered phase that remains bounded in the thermodynamic limit.
Authors: Victor Azumah, Venkatasubramanian Viswanathan
Electrochemical ammonia synthesis via lithium-mediated nitrogen dissociation has demonstrated exceptional Faradaic efficiency at ambient conditions, but its viability is limited by a high energy cost of ~9.12 eV per NH3 via lithium electrodeposition. Here, we establish the thermodynamic limits for dissociative nitrogen reduction using elemental metals by decomposing the process into three steps: metal deposition, nitridation, and protonation. We derive energetic constraints that any viable mediator must satisfy and show that highly reducing metals impose significant energetic penalties. To reduce this cost, we explore solvent tuning and bimetallic alloy strategies that shift deposition potentials without compromising nitridation spontaneity. Our results offer design principles for lowering the energy input of dissociative nitrogen reduction while maintaining its selectivity advantage over associative routes.
Authors: Changdon Shin, Sunghyun Yoon, Yongchul G. Chung
Cyclic swing adsorption processes, such as pressure vacuum swing adsorption (PVSA), have emerged as a promising technology for upgrading biogas by separating carbon dioxide (CO2) from methane (CH4). The rational design of adsorbent materials with tailored properties is important for deployment of high-performance PVSA technology. Metal-organic frameworks (MOFs), particularly the CALF-20 isoreticular series, have attracted interest due to their high CO2 selectivity, thermal and water stability. In this study, we report a multiscale assessment of CALF-20 and its isoreticular five derivatives by integrating molecular simulations and PVSA cycle optimization. Structural parameters such as pore volume, pore size, and isosteric adsorption enthalpy were first calculated, followed by atomistic grand canonical Monte Carlo (GCMC) simulations. Process-level performances of the six materials were evaluated and optimized using the Thompson Sampling Efficient Multi-objective Optimization (TSEMO) algorithm. From the process-level optimization, we found that FumCALF-20 is the only material that can reach CH4 purity > 0.90 while maintaining high recovery. Other materials either lacked sufficient CO2 capacity or showed inefficient CH4 desorption at low pressures. This study underscores the value of process-level optimization in MOF evaluation and screening for energy-efficient biogas upgrading.
Authors: Vitaly V. Chaban
Polyurethane (PU) and its numerous fine-tuned derivatives are widely employed as CO2 scavengers thanks to (1) physisorption and (2) functionalization of the PU backbone with other CO2 sorbents. In the present work, it has been unraveled why PU cannot exhibit CO2 chemisorption, despite possessing the nitrogen docking sites and exhibiting strong electrostatic sorbent-sorbate interactions. Furthermore, a few types of spatial separation of the active sorption sites have been proposed to unleash the chemisorption functionality of PU. By comparing various structural modifications of PU by using the in-silico methodology, we have identified that CO2 chemisorption by PU takes place in the case of implementing methyl and ethyl fragments between the oxygen and nitrogen atoms of PU. Herewith, the introduction of the ethyl moiety even makes CO2 chemisorption energetically favorable relative to physisorption. The reported specific progress on materials design represents an obvious practical value for chemical engineers developing inexpensive CO2 scavengers.
Authors: Javed Akhtar, Jogeswar Chhatria, Sooraj Kunnikuruvan, Satyesh K. Yadav, Tarak K. Patra
Developing efficient and universal polymer crosslinking strategies is pivotal for advanced material design, especially for challenging matrixes like polyethylene, polypropylene, and polystyrene. Traditional crosslinkers such as divinylbenzene (DVB) often requires high-temperature radical initiators and are limited by poor compatibility with saturated hydrocarbon matrices. In contrast, bis-diazirine (BD) crosslinkers offer a promising alternative by harnessing thermally or photochemically generated carbene intermediates for highly selective C-H bond insertions. Here, we employ density functional theory (DFT)-based electronic structure calculations to elucidate the molecular mechanisms and energetics of BD-mediated crosslinking across PE, PP, and PS. We demonstrate that BD enables efficient covalent linkage through low free energy barriers , facilitating crosslinking at moderate temperatures without catalysts and with minimal sensitivity to polymer chain length. Moreover, BD exhibits selective reactivity towards the tertiary and secondary C-H bonds in PP and PS, respectively. Comparative analysis shows that BD dramatically outperforms DVB, especially in saturated polymers, enabling reaction times that are orders of magnitude faster. Our findings provide atomistic insights into BD crosslinker reactivity and establish a mechanistic foundation for next-generation, universal C-H activation-based crosslinking technologies.
Authors: Boris Gurevich, Weihua Xie, Mohsen Yarmohammadi, Michael H. Kolodrubetz
We investigate the coupling of two spatially separated qubits via topologically protected edge states in a two-dimensional Hofstadter lattice. In this hybrid platform, the qubits are coupled to distinct edge sites of the lattice, enabling long-range interactions mediated by topological edge modes. We solve the full system Hamiltonian and analyze the resulting eigenstate structure to uncover the conditions under which coherent qubit interactions emerge. Our analysis reveals that the effective coupling is highly sensitive to the qubit placement, energy detuning, and the topological character of the edge spectrum. We obtain an analytical solution that goes beyond the perturbative regime, capturing the full interplay between the qubits and edge modes. These results provide a foundation for exploring information transport and many-body effects in engineered quantum systems where interactions are mediated by topological edge modes.
Authors: Djamil Lakhdar-Hamina, Xingxin Liu, Richard Barney, Sarah H. Miller, Alaina M. Green, Norbert M. Linke, Victor Galitski
We implement a quantum generalization of a neural network on trapped-ion and IBM superconducting quantum computers to classify MNIST images, a common benchmark in computer vision. The network feedforward involves qubit rotations whose angles depend on the results of measurements in the previous layer. The network is trained via simulation, but inference is performed experimentally on quantum hardware. The classical-to-quantum correspondence is controlled by an interpolation parameter, $a$, which is zero in the classical limit. Increasing $a$ introduces quantum uncertainty into the measurements, which is shown to improve network performance at moderate values of the interpolation parameter. We then focus on particular images that fail to be classified by a classical neural network but are detected correctly in the quantum network. For such borderline cases, we observe strong deviations from the simulated behavior. We attribute this to physical noise, which causes the output to fluctuate between nearby minima of the classification energy landscape. Such strong sensitivity to physical noise is absent for clear images. We further benchmark physical noise by inserting additional single-qubit and two-qubit gate pairs into the neural network circuits. Our work provides a springboard toward more complex quantum neural networks on current devices: while the approach is rooted in standard classical machine learning, scaling up such networks may prove classically non-simulable and could offer a route to near-term quantum advantage.
Authors: Moha Naeimi, Tim Völzer, Regina Lange, Kevin Oldenburg, Stefan Lochbrunner, Ingo Barke, Sylvia Speller
Among the organic semiconductors, rubrene stands out in terms of hole mobility, luminescence yield and exciton migration distance. A novel type of rubrene microcrystal is prepared in the orthorhombic phase, exhibiting zone-sectored tabular domains with distinct photoluminescence (PL) characteristics. These sectors exhibit distinct PL spectra and time-evolution, arising from differences in the in-plane orientation of the orthorhombic unit cell relative to the crystal surface. A combination of polarised optical microscopy, fluorescence lifetime imaging microscopy (FLIM), and atomic force microscopy (AFM) is used to characterise the samples in terms of crystal orientation, fluorescence lifetime, and photoluminescence spectra. Spatially resolved PL spectroscopy reveals that the redshifted 650 nm emission band has polarisation along the transition dipole moment and is associated with high photon absorption due to the alignment of excitation polarisation and transition dipole moment and selectively localized within specific sectors of the crystal. The detected photon originates from direct emission of a geminate coherent triplet pair, or from its fusion. This band exhibits pure mono-exponential dynamics with 3.7 ns lifetime. The triplet fusion behaviour in the succeeding time regimes can be treated in the framework of power law scaling and random walk. The emission kinetics are modelled using rate equations describing geminate and non-geminate exciton fusion processes, enabling a quantitative interpretation of the spatially resolved PL kinetics. These findings introduce a material-based strategy, opening novel routes for photonic applications and light harvesting.
Authors: Beatrice Donelli, Gabriele De Chiara, Francesco Scazza, Stefano Gherardini
We introduce a nonequilibrium phenomenon reminiscent of Anderson's orthogonality catastrophe (OC) that arises in the transient dynamics following an interaction quench between a quantum system and a localized defect. Even if the system comprises only a single particle, the overlap between the asymptotic and initial superposition states vanishes with a power law scaling with the number of energy eigenstates entering the initial state and with an exponent that depends on the interaction strength. The presence of quantum coherence in the initial state is reflected onto the discrete counterpart of an infinite discontinuity in the system spectral function, a hallmark of Anderson's OC, as well as in the quasiprobability distribution of work due to the quench transformation. The positivity loss of the work distribution is directly linked with a reduction of the minimal time imposed by quantum mechanics for the state to orthogonalize. We propose an experimental test of coherence-enhanced orthogonalization dynamics based on Ramsey interferometry of a trapped cold-atom system.
Authors: Angel Paredes, Jose Guerra-Carmenate, Humberto Michinel
We analyze quantum droplets formed in a two-dimensional symmetric mixture of Bose-Einstein condensed atoms. For sufficiently large atom numbers, these droplets exhibit a flat-top density profile with sharp boundaries governed by surface tension. Within the bulk of the droplet, traveling matter waves - localized density dips - can propagate at constant velocity while maintaining their shape. Using numerical simulations and qualitative analysis, we investigate the rich phenomenology that arises when such excitations reach the boundary of a finite droplet. We show that they can emit a small outgoing droplet, excite internal modes of the host soliton, or, in the case of vortex-antivortex pairs, split into individual vortices propagating backward near the edge. Furthermore, we demonstrate that traveling waves can be dynamically generated near the boundary through the collision of distinct droplets, and we discuss their trajectories and interactions.
Authors: Alessandro Chiarini, Rahul K. Singh, Marco E. Rosti
Polymeric turbulence, flows of fluids with dilute polymer additives at high Reynolds numbers, exhibits striking deviations from the Kolmogorovean behaviour of Newtonian turbulence. Recent experiments as well as simulations have uncovered a robust self-similar energy spectrum scaling as $k^{-2.3}$, in sharp contrast to the $k^{-5/3}$ scaling of Newtonian flows. The origin of this novel scaling, however, has remained unresolved. In this work, we uncover the underlying physical mechanism responsible for this emergent behaviour. Using fundamental governing equations aided by scaling arguments, we show that the fluid energy cascade is depleted by the polymers at a constant rate across a wide range of scales. This constant depletion rate acts as a second invariant, alongside the total energy flux, thereby setting the scaling properties of the spectrum. Our results reveal that polymeric turbulence is governed by two simultaneous invariants, unlike the single-invariant structure of Newtonian turbulence, and suggest new strategies for turbulence control through suitably engineered and targeted polymer design.
Authors: Ilnaz I. Fairushin, Anatolii V. Mokshin
In this paper, the theoretical model of weak decaying collective excitations characteristic of many-particle systems with long-range interaction potentials is developed using the example of one-component strongly coupled Yukawa plasmas. The proposed model is based on the self-consistent relaxation theory of collective dynamics and covers spatial scales from extended hydrodynamics to scales related to the mean interparticle distance. The theoretical model reproduces the dynamic structure factor spectra and the corresponding dispersion characteristics in agreement with molecular dynamics simulation data without using any fitting parameters. In the limit of small wave numbers, the correspondence of the proposed theoretical model with the damped harmonic oscillator model is established. The simple analytical expression for the sound attenuation coefficient of strongly coupled Yukawa plasmas is obtained.
Authors: Mustapha Driouech, Michele Guerrini, Caterina Cocchi
Optical limiting (OL), a crucial mechanism for protecting human eyes and sensitive sensors from intense radiation, relies on understanding the optical nonlinearities acting on the systems. Assessing and disentangling the effects at play is crucial to predict and control the nonlinear optical response in real materials. In this ab initio study based on real-time time-dependent density-functional theory, we investigate non-perturbatively the absorption spectra of a set of thiophene oligomers, the building blocks of technologically relevant organic semiconductors, excited by broadband radiation of increasing intensity. Under strong electric fields, the absorption cross section grows significantly below the onset of linear excitations, exhibiting saturation typical of OL. By exciting the oligothiophenes with a train of pulses targeting the first and second excited states of each moiety and analyzing the resulting population dynamics, we reveal excited-state absorption (ESA) in the near-infrared to visible region. Our results indicate ESA as the driving mechanism for OL in oligothiophene molecules, thereby providing important insight to design novel compounds with optimized nonlinear optical characteristics.
Authors: Rui Zhu, Yulan Chen, Katharina Tholen, Zhiguo He, Thomas Pähtz
Maxey \& Riley's (\textit{Phys. Fluids}, vol.~26, 1983, 883) analytical solution for the flow around a small sphere at low particle Reynolds number tells us that the fluid-particle interaction force decomposes into a contribution from the local flow disturbance caused by the particle's boundary -- consisting of the drag, Faxen, virtual-mass, and history forces -- and another contribution from the stress of the background flow, termed generalized-buoyancy force. There is also a consensus that, for general disperse two-phase flow, the interfacial force density, resulting from averaging the fluid's and particles' equations of motion, decomposes in a likewise manner. However, there has been a long-standing controversy about the physical closure separating the generalized-buoyancy from the interfacial force density, especially whether or not pseudo-stresses, such as the Reynolds stress, should be attributed to the background flow. Furthermore, most existing propositions for this closure involve small-particle approximations. Here, we show that all existing buoyancy closures are mathematically inconsistent with at least one of three simple thought experiments designed to determine the roles of pseudo-stresses and small-particle approximations. We then derive the unique closure consistent with these thought experiments. It fully incorporates all pseudo-stresses, requires no approximation, and is supported by particle-resolved numerical simulations. Remarkably, it exhibits a low-pass filter property, attenuating buoyancy at short wavelengths, that prevents it from causing Hadamard instabilities, constituting a first-principle-based solution to the long-standing ill-posedness problem of two-fluid models. When employing the derived closure, even the simplest two-fluid model, the dissipation-free one-pressure model, is hyperbolic.
Authors: Marius Willner, Marco Trenti, Dirk Lebiedz
Tree tensor networks (TTNs) are widely used in low-rank approximation and quantum many-body simulation. In this work, we present a formal analysis of the differential geometry underlying TTNs. Building on this foundation, we develop efficient first- and second-order optimization algorithms that exploit the intrinsic quotient structure of TTNs. Additionally, we devise a backpropagation algorithm for training TTNs in a kernel learning setting. We validate our methods through numerical experiments on a representative machine learning task.
Authors: Simon Daubner, Alexander E. Cohen, Benjamin Dörich, Samuel J. Cooper
Materials science inherently spans disciplines: experimentalists use advanced microscopy to uncover micro- and nanoscale structure, while theorists and computational scientists develop models that link processing, structure, and properties. Bridging these domains is essential for inverse material design where you start from desired performance and work backwards to optimal microstructures and manufacturing routes. Integrating high-resolution imaging with predictive simulations and data-driven optimization accelerates discovery and deepens understanding of process-structure-property relationships. The differentiable physics framework evoxels is based on a fully Pythonic, unified voxel-based approach that integrates segmented 3D microscopy data, physical simulations, inverse modeling, and machine learning.
Authors: Cheng Giuseppe Chen, Chenyu Tang, Alberto Megías, Radu A. Talmazan, Sergio Contreras Arredondo, Benoît Roux, Christophe Chipot
The discovery of transition pathways to unravel distinct reaction mechanisms and, in general, rare events that occur in molecular systems is still a challenge. Recent advances have focused on analyzing the transition path ensemble using the committor probability, widely regarded as the most informative one-dimensional reaction coordinate. Consistency between transition pathways and the committor function is essential for accurate mechanistic insight. In this work, we propose an iterative framework to infer the committor and, subsequently, to identify the most relevant transition pathways. Starting from an initial guess for the transition path, we generate biased sampling from which we train a neural network to approximate the committor probability. From this learned committor, we extract dominant transition channels as discretized strings lying on isocommittor surfaces. These pathways are then used to enhance sampling and iteratively refine both the committor and the transition paths until convergence. The resulting committor enables accurate estimation of the reaction rate constant. We demonstrate the effectiveness of our approach on benchmark systems, including a two-dimensional model potential, peptide conformational transitions, and a Diels--Alder reaction.
Authors: Jona Nagerl, Natalia G. Berloff
Networks of phase oscillators can serve as dense associative memories if they incorporate higher-order coupling beyond the classical Kuramoto model's pairwise interactions. Here we introduce a generalized Kuramoto model with combined second-harmonic (pairwise) and fourth-harmonic (quartic) coupling, inspired by dense Hopfield memory theory. Using mean-field theory and its dynamical approximation, we obtain a phase diagram for dense associative memory model that exhibits a tricritical point at which the continuous onset of memory retrieval is supplanted by a discontinuous, hysteretic transition. In the quartic-dominated regime, the system supports bistable phase-locked states corresponding to stored memory patterns, with a sizable energy barrier between memory and incoherent states. We analytically determine this bistable region and show that the escape time from a memory state (due to noise) grows exponentially with network size, indicating robust storage. Extending the theory to finite memory load, we show that higher-order couplings achieve superlinear scaling of memory capacity with system size, far exceeding the limit of pairwise-only oscillators. Large-scale simulations of the oscillator network confirm our theoretical predictions, demonstrating rapid pattern retrieval and robust storage of many phase patterns. These results bridge the Kuramoto synchronization with modern Hopfield memories, pointing toward experimental realization of high-capacity, analog associative memory in oscillator systems.
Authors: Alisa Knizel, Leonid Petrov
We investigate the asymptotic behavior of the q-Racah probability measure on lozenge tilings of a hexagon whose side lengths scale linearly with a large parameter $L$, while the parameters $q\in(0,1)$ and $\kappa\in \mathbf{i}\mathbb{R}$ remain fixed. This regime differs fundamentally from the traditional case $q\sim e^{-c/L}\to1$, in which random tilings are locally governed by two-dimensional translation-invariant ergodic Gibbs measures. In the fixed-q regime we uncover a new macroscopic phase, the waterfall (previously only observed experimentally), where the two-dimensional Gibbs structure collapses into a one-dimensional random stepped interface that we call a barcode. We prove a law of large numbers and exponential concentration, showing that the random tilings converge to a deterministic waterfall profile. We further conjecture an explicit correlation kernel of the one-dimensional barcode process arising in the limit. Remarkably, the limit is invariant under shifts by $2\mathbb{Z}$ but not by $\mathbb{Z}$, exhibiting an emergent period-two structure absent from the original weights. Our conjectures are supported by extensive numerical evidence and perfect sampling simulations. The kernel is built from a family of functions orthogonal in both spaces $\ell^{2}(\mathbb{Z})$ and $\ell^{2}(\mathbb{Z}+\frac12)$, that may be of independent interest. Our proofs adapt the spectral projection method of Borodin-Gorin-Rains (https://arxiv.org/abs/0905.0679) to the regime with fixed~q. The resulting asymptotic analysis is substantially more involved, and leads to non-self-adjoint operators. We overcome these challenges in the exponential concentration result by a separate argument based on sharp bounds for the ratios of probabilities under the q-Racah orthogonal polynomial ensemble.
Authors: Haoran Wang, Alessandro Principi
Non-abelian anyonic excitations of quantum spin liquids have potential for application to topological quantum computation, but designing logical operations requires developing protocols to faithfully create, move, and read-out such quasiparticles. In this paper, we present a protocol that manipulates the $Z_2$ fluxes (``visons''), and their bound Majorana zero mode, of the Kitaev model. This is achieved by adiabatically switching-off and -on interaction terms in the Hamiltonian, and applying a local magnetic field. We test our protocol by exchanging two Majorana zero modes, analysing the errors it produces. We find that the error rate of our protocol can be suppressed exponentially by increasing the adiabatic turn-on time and the size of the system. However, realistic implementations must consider the trade off between different error sources.
Authors: Feng Liu, Alessandro Principi
Pair spin-orbit interaction can emerge in strongly-interacting systems characterized by a large spin-orbit coupling. Here we study the role of this interaction in stabilizing ordered and unconventional superconducting phases. We find that, if the system avoids superconductivity, the order realized is a combination of charge-density and spin-vorticity waves. The latter is reminiscent of a loop-current state, albeit in the spin, rather in the charge, channel. If the system becomes superconducting, the order parameter assumes the form of a paired density wave, i.e. pairing occurs at finite momentum. Intriguingly, one of the possible pairings acquires a form analogous to Amperean superconductivity. However, the order parameter here is always a blend of paired density wave and Amperean pairing, rather than being purely one or the other.
Authors: T. I. Weinberger, Z. Wu, A. J. Hickey, D. E. Graf, G. Li, P. Wang, R. Zhou, A. Cabala, J. Pu, V. Sechovsky, M. Valiska, G. G. Lonzarich, F. M. Grosche, A. G. Eaton
The phase landscape of UTe$_2$ features a remarkable diversity of superconducting phases under applied pressure and magnetic field. Recent quantum oscillation studies at ambient pressure have revealed the quasi-2D Fermi surface of this material. However, the pressure-dependence of the Fermi surface remains an open question. Here we track the evolution of the UTe$_2$ Fermi surface as a function of pressure up to 19.5 kbar by measuring quantum interference oscillations. We find that in sufficient magnetic field to suppress both superconductivity at low pressures and incommensurate antiferromagnetism at higher pressures, the quasi-2D Fermi surface found at ambient pressure smoothly connects to that at 19.5 kbar, with no signs of a reconstruction over this pressure interval. We observe a smooth increase in oscillatory frequency with increasing pressure, indicating that the warping of the cylindrical Fermi sheets continuously increases with pressure. By computing a tight-binding model, we show that this enhanced warping indicates increased $f$-orbital contribution at the Fermi level - up to and beyond the critical pressure at which superconductivity is truncated. These findings highlight the value of high-pressure quantum interference measurements as a new probe of the electronic structure in heavy fermion materials.
Authors: Christopher L. Baldwin
We rigorously prove that in nearly arbitrary quantum spin chains with power-law-distributed random fields, namely such that the probability of a field exceeding $h$ scales as $h^{-\alpha}$, it is impossible for any operator evolving in the Heisenberg picture to spread with dynamical exponent less than $1/\alpha$. In particular, ballistic growth is impossible for $\alpha < 1$, diffusive growth is impossible for $\alpha < 1/2$, and any finite dynamical exponent becomes impossible for sufficiently small $\alpha$. This result thus establishes a wide family of models in which the disorder provably prevents conventional transport. We express the result as a tightening of Lieb-Robinson bounds due to random fields -- the proof modifies the standard derivation such that strong fields appear as effective weak interactions, and then makes use of analogous recent results for random-bond spin chains.
Authors: Yukino Terui, Yuka Inoue, Yohei Hamakawa, Kosuke Tatsumura, Kazue Kudo
Collaborative filtering generates recommendations by exploiting user-item similarities based on rating data, which often contains numerous unrated items. To predict scores for unrated items, matrix factorization techniques such as nonnegative matrix factorization (NMF) are often employed. Nonnegative/binary matrix factorization (NBMF), which is an extension of NMF, approximates a nonnegative matrix as the product of nonnegative and binary matrices. While previous studies have applied NBMF primarily to dense data such as images, this paper proposes a modified NBMF algorithm tailored for collaborative filtering with sparse data. In the modified method, unrated entries in the rating matrix are masked, enhancing prediction accuracy. Furthermore, utilizing a low-latency Ising machine in NBMF is advantageous in terms of the computation time, making the proposed method beneficial.
Authors: Hao Zhang, Alex Kamenev
Finding an exact ground state of a three-dimensional (3D) Ising spin glass is proven to be an NP-hard problem (i.e., at least as hard as any problem in the nondeterministic polynomial-time (NP) class). Given validity of the exponential time hypothesis, its computational complexity was proven to be no less than $2^{N^{2/3}}$, where $N$ is the total number of spins. Here, we report results of extensive experimentation with D-Wave 3D annealer with $N\le 5627$. We found exact ground states (in a probabilistic sense) for typical realizations of 3D spin glasses with the efficiency, which scales as $2^{N/ \beta}$ with $\beta\approx 10^3$. Based on statistical analysis of low-energy states, we argue that with an improvement of annealing protocols and device noise reduction, $\beta$ can be increased even further. This suggests that, for $N<\beta^3$, annealing devices provide most efficient way to find an exact ground state.
Authors: Michael Meixner, Marcel Krämer, Nils Wentzell, Pietro M. Bonetti, Sabine Andergassen, Alessandro Toschi, Thomas Schäfer
The destruction of metallicity due to the mutual Coulomb interaction of quasiparticles gives rise to fascinating phenomena of solid state physics such as the Mott metal-insulator transition and the pseudogap. A key observable characterizing their occurrences is the single-particle spectral function, determined by the fermionic self-energy. In this paper we investigate in detail how real space fluctuations are responsible for a self-energy that drives the Mott-Hubbard metal-insulator transition. To this aim we first introduce a real space fluctuation diagnostics approach to the Hedin equation, which connects the fermion-boson coupling vertex $\lambda$ to the self-energy $\Sigma$. Second, by using cellular dynamical mean-field theory calculations for $\lambda$ we identify the leading physical processes responsible for the destruction of metallicity across the transition.
Authors: Yuxuan Mu, Di Wang, Xiangang Wan
It is widely accepted that spin-orbit coupling (SOC) generally locks spin and spatial degrees of freedom, as a result, the spin, despite being an axial vector, is fixed and cannot rotate independently, and the magnetic system should be described by magnetic space groups (MSGs). While as a new type of group, spin space groups (SSGs) have been introduced to approximately describe the symmetry of magnetic systems with negligible SOC, and received significant attention recently. In this work, we prove that in two cases of coplanar spin configurations, there are spin-only operations that strictly hold even with considerable Dzyaloshinskii-Moriya interaction (DMI), and the symmetry of their spin models could be described by the spin-coplanar SSG. In addition, we also find that for spin-collinear cases, regardless the strength of DMI, the magnon systems within the framework of linear spin wave theory (LSWT) also preserve the decoupled spin and spatial rotations, but the symmetry does not belong to the conventional definitions of collinear spin groups. We discuss the potential realization of these novel symmetries in rod, layer, and three-dimensional (3D) space groups. Our work extends the applicability of SSGs to magnetic materials with heavy elements, and reveals that the coexistence of DMI and SSG symmetries provides new opportunity for exploring novel magnon transport phenomena, and potential material realization had also been discussed.
Authors: Koyena Bose, Ajit C. Balram
The Moore-Read Pfaffian (Pf) state exhibits two distinct neutral excitation modes, the bosonic magnetoroton mode, and the neutral fermion mode. These two modes have been conjectured to be supersymmetric (SUSY) partners in the long-wavelength limit. Previous studies on these neutral excitations of the Pf state have shown evidence in favor of SUSY in the vicinity of the second Landau level (SLL) Coulomb interaction. Inspired by that, using the framework of parton theory, we test the SUSY conjecture for a state that lies in the same universality class as the particle-hole conjugate of the Pf, namely the anti-Pf (aPf) state, by constructing explicit wave functions for its magnetoroton and neutral fermion excitations and evaluating them for very large system sizes. As with the previous studies on the Pf state, we find that the long-wavelength gaps of the neutral modes of the parton state belonging to the same topological class as the aPf are close to each other for the SLL Coulomb interaction. Furthermore, using the parton wave functions, we compute the dispersion of various neutral collective excitations, including the magnetoroton, neutral fermion, and parton-excitons, for several notable non-Abelian and Abelian states. Finally, we propose a parton-exciton ansatz for the gapped neutral excitation of the composite fermion Fermi liquid at quarter filling and compute its dispersion for the Coulomb interaction in the lowest Landau level.
Authors: Börge Göbel, Lennart Schimpf, Ingrid Mertig
Chirality-induced spin selectivity (CISS), a phenomenon wherein chiral structures selectively determine the spin polarization of electron currents flowing through the material, has garnered significant attention due to its potential applications in areas such as spintronics, enantioseparation, and catalysis. The underlying physical effect is the Edelstein effect that converts charge to angular momentum. Besides a spin contribution there exists a contribution based on the orbital angular momentum but the precise mechanism for its generation remains yet to be understood. Here, we introduce the minimal model for explaining the phenomenon based on the orbital Edelstein effect. We consider non-local inter-site contributions to the current-induced orbital angular momentum and reveal the underlying mechanism by analytically calculating the Edelstein susceptibilities in a tight-binding and Boltzmann approach. While the orbital angular momentum is directly generated by the chirality of the crystal, the spin contribution of each spin-split band pair relies on spin-orbit coupling. Using tellurium as an example, we show that the orbital contribution surpasses the spin contribution by orders of magnitude.
Authors: Mariia Radova, Wojciech G. Stark, Connor S. Allen, Reinhard J. Maurer, Albert P. Bartók
Machine-learned interatomic potentials are revolutionising atomistic materials simulations by providing accurate and scalable predictions within the scope covered by the training data. However, generation of an accurate and robust training data set remains a challenge, often requiring thousands of first-principles calculations to achieve high accuracy. Foundation models have started to emerge with the ambition to create universally applicable potentials across a wide range of materials. While foundation models can be robust and transferable, they do not yet achieve the accuracy required to predict reaction barriers, phase transitions, and material stability. This work demonstrates that foundation model potentials can reach chemical accuracy when fine-tuned using transfer learning with partially frozen weights and biases. For two challenging datasets on reactive chemistry at surfaces and stability and elastic properties of tertiary alloys, we show that frozen transfer learning with 10-20% of the data (hundreds of datapoints) achieves similar accuracies to models trained from scratch (on thousands of datapoints). Moreover, we show that an equally accurate, but significantly more efficient surrogate model can be built using the transfer learned potential as the ground truth. In combination, we present a simulation workflow for machine learning potentials that improves data efficiency and computational efficiency.
Authors: Carlos Arauz-Moreno, Keyvan Piroird, Elise Lorenceau
In this study, we present an experimental work on bubble nucleation and growth using a model system comprised of viscoelastic polyvinyl butyral confined in a Hele-Shaw cell geometry that is decompressed at elevated temperatures. The appearance and growth of bubbles are connected to the temperature-induced shift in chemical equilibrium experienced simultaneously by two gases present in the bulk. The latter becomes simultaneously oversaturated with water vapor and slightly undersaturated in air. Our bubbles grow with various shapes and sizes depending on the initial morphology of the nucleus or the presence of neighboring bubbles. For large nuclei, bubbles grow anisotropically because of contact line pinning. The likelihood of nucleation is related to the amount of water dissolved in the bulk and the imposed temperature. Counter-intuitively, the number of nuclei whence a bubble can grow is inversely correlated with said temperature. In an analogy with champagne, we show that nucleation can either be natural, at trapped fibers or dust particles, or artificial, at crenels we purposefully made in the glass surface. Our results indicate that the growth rate of bubbles can be impacted by the nucleation mechanism.
Authors: Patrick Tscheppe, Marcel Klett, Henri Menke, Sabine Andergassen, Niklas Enderlein, Philipp Hansmann, Thomas Schäfer
We formulate a quantum embedding algorithm in real-space for the simultaneous theoretical treatment of nonlocal electronic correlations and disorder, the coherent cellular dynamical mean-field theory (C-CDMFT). This algorithm combines the molecular coherent potential approximation with the cellular dynamical mean-field theory. After a pedagogical review of quantum embedding theories for disordered and interacting electron systems, and a detailed discussion of its work flow, we present first results from C-CDMFT for the half-filled two-dimensional Anderson-Hubbard model on a square lattice: (i) the analysis of its Mott metal-insulator transition as a function of disorder strength, and (ii) the impact of different types of disorder on its magnetic phase diagram. For the latter, by means of a ``disorder diagnostics'', we are able to precisely identify the contributions of different disorder configurations to the system's magnetic response.
Authors: Jonathan House, Rashad Bakhshizada, Skirmantas Janušonis, Ralf Metzler, Thomas Vojta
Fractional Brownian motion is a Gaussian stochastic process with long-range correlations in time; it has been shown to be a useful model of anomalous diffusion. Here, we investigate the effects of mutual interactions in an ensemble of particles undergoing fractional Brownian motion. Specifically, we introduce a mean-density interaction in which each particle in the ensemble is coupled to the gradient of the total, time-integrated density produced by the entire ensemble. We report the results of extensive computer simulations for the mean-squared displacements and the probability densities of particles undergoing one-dimensional fractional Brownian motion with such a mean-density interaction. We find two qualitatively different regimes, depending on the anomalous diffusion exponent $\alpha$ characterizing the fractional Gaussian noise. The motion is governed by the interactions for $\alpha < 4/3$ whereas it is dominated by the fractional Gaussian noise for $\alpha > 4/3$. We develop a scaling theory explaining our findings. We also discuss generalizations to higher space dimensions and nonlinear interactions, the relation of our process to the ``true'' or myopic self-avoiding walk, as well as applications to the growth of strongly stochastic axons (e.g., serotonergic fibers) in vertebrate brains.
Authors: Chakradhar Sahoo, Yann in 't Veld, Alfred J. H. Jones, Zhihao Jiang, Greta Lupi, Paulina E. Majchrzak, Kimberly Hsieh, Kenji Watanabe, Takashi Taniguchi, Philip Hofmann, Jill A. Miwa, Yong P. Chen, Malte Rösner, Søren Ulstrup
The electronic band gap of a two-dimensional semiconductor within a device architecture is sensitive to variations in screening properties of adjacent materials in the device and to gate-controlled doping. Here, we employ micro-focused angle resolved photoemission spectroscopy to separate band gap renormalization effects stemming from environmental screening and electron-doping during \textit{in situ} gating of a single-layer WS$_{2}$ device. The WS$_{2}$ is supported on hBN and contains a section that is exposed to vacuum and another section that is encapsulated by a graphene contact. We directly observe the doping-induced semiconductor-metal transition and band gap renormalization in the two sections of WS$_2$. Surprisingly, a larger band gap renormalization is observed in the vacuum-exposed section than in the graphene-encapsulated - and thus ostensibly better screened - section of the WS$_2$. Using $GW$ calculations, we determine that intrinsic screening due to stronger doping in vacuum exposed WS$_2$ exceeds the external environmental screening in graphene-encapsulated WS$_2$.
Authors: Shaohua Guan
Despite significant advances in stochastic thermodynamics, a universal and rigorous ensemble framework for nonequilibrium steady states remains lacking. Here, we provide a concise framework for generalized ensemble theory through a matrix-based approach. By introducing an observation matrix, we show that any discrete probability distribution can be formulated as a generalized Boltzmann distribution, with observables and their conjugate variables serving as basis vectors and coordinates in a vector space. Within this framework, we identify the minimal sufficient statistics required to infer the Boltzmann distribution. The nonequilibrium thermodynamic relations and fluctuation-dissipation relations naturally emerge from this framework. Our findings provide a new approach to developing generalized ensemble theory for nonequilibrium steady-state systems.
Authors: Pratyasha Tripathy, Hetvi Jadav, Himanshu Pandey
Sorbent materials, such as graphene-based systems coated with Cr, are being investigated as potential hydrogen storage materials. Graphene, a 2D material with a high surface-to-volume ratio, has been employed. A comparison is conducted between graphene systems with single vacancy defects and those without defects, using Cr adsorption. To verify the effectiveness of hydrogen storage, ab initio calculations are carried out both with and without Van der Waals interactions. The system's binding energy is calculated to assess efficiency. According to the Department of Energy in the United States, the ideal range for binding energy for reversible hydrogen storage is between 0.2 and 0.6 eV. To anticipate the stability of the efficient materials at room temperature, this work exploits the molecular dynamics computations to depict their thermal stability spectrum.
Authors: Stephen E. Gant, Antonios M. Alvertis, Christopher J. N. Coveney, Jonah B. Haber, Marina R. Filip, Jeffrey B. Neaton
Monoclinic bismuth vanadate (m-BiVO$_4$) is a promising indirect band gap semiconductor for photoelectrochemical water splitting, yet the characteristics of its low-lying photoexcitations, or excitons, remain poorly understood. Here, we use an ab initio Bethe-Salpeter equation approach that incorporates phonon screening to compute the nature and lifetimes of the low-lying excitons of m-BiVO$_4$. Our calculations indicate that at 0 K, the lowest-lying exciton energy exceeds the indirect band gap, enabling spontaneous dissociation into free carriers via phonon emission within picoseconds. At 300 K, both phonon emission and absorption effects reduce this timescale to only a few femtoseconds. Phonon screening also greatly reduces the binding energy of the lowest-lying exciton, leading to an optical absorption spectrum that better reproduces experimental measurements. Overall, our findings establish the general conditions under which phonon emission-driven exciton dissociation can occur in indirect gap semiconductors, and they emphasize the critical role phonon screening can play in predictive calculations of photophysical properties of complex materials.
Authors: Gabe Schumm, Shiwei Zhang, Anders W. Sandvik
Implementing an improved method for analytic continuation and working with imaginary-time correlation functions computed using quantum Monte Carlo simulations, we resolve the single-particle dispersion relation and the density of states (DOS) of the two-dimensional Hubbard model at half-filling. At intermediate interactions of $U/t = 4,6$, we find quadratic dispersion around the gap minimum at wave-vectors $\mathbf{k} = (\pm \pi/2, \pm \pi/2)$ (the $\Sigma$ points). We find saddle points at $\mathbf{k} = (\pm \pi,0),(0,\pm \pi)$ (the X points) where the dispersion is approximately quartic, leading to a sharp DOS maximum above the almost flat ledge arising from the states close to $\Sigma$. The fraction of quasiparticle states within the ledge is $n_{\rm ledge} \approx 0.15$. Upon doping away from half-filling, within the rigid-band approximation, these results support Fermi pockets around the $\Sigma$ points, with states around the X points becoming filled only at doping fractions $x \ge n_{\rm ledge}$. The high density of states away from the $\Sigma$ gap edge may be an important clue for a finite minimum doping level for superconductivity and other instabilities of doped Mott insulators.
Authors: Ivan Yahniuk, Dmitriy A. Kozlov, Mariya D. Moldavskaya, Leonid E. Golub, Vasily V. Bel'kov, Ivan A. Dmitriev, Sergey S. Krishtopenko, Frederic Teppe, Yurii Ivonyak, Artem Bercha, Grzegorz Cywiński, Wojciech Knap, Sergey D. Ganichev
Positive terahertz photoconductivity is observed at room temperature in CdHgTe thin films with different Cd contents. We show that electron gas heating caused by Drude-like absorption results in positive photoconductivity because of the interband activation mechanism specific for undoped narrow-gap semiconductors and semimetals. Applying intense terahertz radiation, we observed that the photoconductivity saturates at high intensities, which was found to be caused by absorption bleaching. Both the magnitude of the photoconductivity and the saturation intensity are shown to exhibit an exponential dependence on the hydrostatic pressure. We show that this is a consequence of the fact that both phenomena are controlled by the ratio of energy and momentum relaxation times.
Authors: Tianjiao Lei, Esther Hessong, Brandon Fields, Raphael Pierre Thiraux, Daniel S. Gianola, Timothy J. Rupert
Although nanocrystalline alloys regularly exhibit high strengths, their use in structural applications often face challenges due to sample size limitations, unstable microstructures, and the limited ability to plastically deform. The incorporation of amorphous grain boundary complexions has been proposed to address these issues, by simultaneously stabilizing nanocrystalline grain structures for scale-up processing and improving alloy toughness. In the present study, the mechanical behavior of bulk nanocrystalline Al-Mg-Y is examined with macroscale compression testing, probing a length scale that is relevant to real-world structural applications. Bulk samples were fabricated via a simple powder metallurgy approach, with different pressing temperatures and times employed for consolidation in order to investigate microstructural and property evolution. All of the specimens contained primary face-centered cubic Al and secondary Al4C3 and Al3Y phases, with the Al3Y particles exhibiting two populations of small equiaxed and larger elongated particles. Appreciable plasticity was measured along with high ultimate stresses over 800 MPa due to the presence of amorphous grain boundary complexions. Microstructural characterization of fracture surfaces revealed that the area fraction of dimpled regions increased with longer hot-pressing time. Most importantly, the elongated Al3Y particles formed regular cellular patterns with increasing hot-pressing time, delaying shear localization and significantly enhancing plasticity. The hierarchy present in the microstructure of the Al-Mg-Y alloy, from amorphous grain boundary complexions to secondary phases, gives rise to excellent bulk mechanical properties, which are attractive for structural applications.
Authors: Andrej Vilfan, Bogdan Cichocki, Jeffrey C. Everts
We study the hydrodynamic drag force exerted on a sphere in a static anisotropic porous medium. This problem is analysed using the Brinkman-Debye-Bueche equations with an axisymmetric shielding (or permeability) tensor. Using the exact Green's functions for this model fluid within a single-layer boundary element formulation, we numerically compute the friction tensor for a translating sphere subjected to stick boundary conditions. Furthermore, we derive approximate analytical expressions for small anisotropy using the Lorentz reciprocal theorem. By benchmarking this result against the numerical solutions, we find that a linear approximation is valid in a broad parameter regime. Our results are important for studying self-diffusion in general anisotropic porous media, but can also be applied to small tracers in nematic fluids composed of disk- or rod-like crowders.
Authors: Vo Tien Phong, Cyprian Lewandowski
Recently, fractional quantum anomalous Hall effects have been discovered in two-dimensional moiré materials when a topologically nontrivial band with Chern number $\mathcal{C}=1$ is partially doped. Remarkably, superlattice Bloch bands can carry higher Chern numbers that defy the Landau-level paradigm and may even host exotic fractionalized states with non-Abelian quasiparticles. Inspired by this exciting possibility, we propose twisted \textit{rhombohedral} trilayer-bilayer graphene at $\theta \sim 1.2^\circ$ as a field-tunable quantum anomalous Chern insulator that features spectrally-isolated, kinetically-quenched, and topologically-nontrivial bands with $\mathcal{C} = 2,3$ favorable for fractional phases once fractionally doped, as characterized by their quantum geometry. Based on extensive self-consistent mean-field calculations, we show that these phases are stabilized by Coulomb interactions and are robust against variations in dielectric environment, tight-binding hopping parameters, and lattice relaxation.
Authors: T. Chouinard, D. M. Broun
We present a microwave-frequency method for measuring polar Kerr effect and spontaneous time-reversal symmetry breaking (TRSB) in unconventional superconductors. While this experiment is motivated by work performed in the near infrared using zero-loop-area Sagnac interferometers, the microwave implementation is quite different, and is based on the doubly degenerate modes of a TE$_{111}$ cavity resonator, which act as polarization states analogous to those of light. The resonator system has $in$-$situ$ actuators that allow quadrupolar distortions of the resonator shape to be controllably tuned, as these compete with the much smaller perturbations that arise from TRSB. The most reliable way to the detect the TRSB signal is by interrogating the two-mode resonator system with circularly polarized microwaves, in which case the presence of TRSB shows up unambiguously as a difference between the forward and reverse transmission response of the resonator - i.e., as a breaking of reciprocity. We illustrate and characterize a coupler system that generates and detects circularly polarized microwaves, and then show how these are integrated with the TE$_{111}$ resonator, resulting in a dilution refrigerator implementation with a base temperature of 20 mK. We show test data on yttrium-iron-garnet (YIG) ferrite and the van der Waals ferromagnet CrGeTe$_3$ as an illustration of how the system operates, then present data showing system performance under realistic conditions at millikelvin temperatures.
Authors: Brendan Lucas, Google Gemini 2.5 Pro Preview 05-06
Useful chemical processes often involve a desired steady state probability distribution, equilibrium or not, from which product is extracted. Given many different ways to attain the same steady state, which candidate "loses" the least in terms of time and energy? A scalar thermodynamic information criterion (TIC), inspired by AIC, assigns lower values to chemical processes with less estimated "loss" to generate the same desired steady state. As an element of thermodynamic machine learning, TIC naturally extends statistical objective optimization into the realm of chemical physics.
Authors: Satadeep Bhattacharjee, Seung-Cheol Lee
The recently proposed physics-based framework by Huo and Johnson~\cite{huo2024capturing} models the attention mechanism of Large Language Models (LLMs) as an interacting two-body spin system, offering a first-principles explanation for phenomena like repetition and bias. Building on this hypothesis, we extract the complete Query-Key weight matrices from a production-grade GPT-2 model and derive the corresponding effective Hamiltonian for every attention head. From these Hamiltonians, we obtain analytic phase boundaries and logit gap criteria that predict which token should dominate the next-token distribution for a given context. A systematic evaluation on 144 heads across 20 factual-recall prompts reveals a strong negative correlation between the theoretical logit gaps and the model's empirical token rankings ($r\approx-0.70$, $p<10^{-3}$).Targeted ablations further show that suppressing the heads most aligned with the spin-bath predictions induces the anticipated shifts in output probabilities, confirming a causal link rather than a coincidental association. Taken together, our findings provide the first strong empirical evidence for the spin-bath analogy in a production-grade model. In this work, we utilize the context-field lens, which provides physics-grounded interpretability and motivates the development of novel generative models bridging theoretical condensed matter physics and artificial intelligence.
Authors: Filippo Antola, Sebastiano Battisti, Alessandro Braggio, Francesco Giazotto, Giorgio De Simoni
In this study, we examined the supercurrent diode effect (SDE) in mesoscopic superconducting weak links formed by asymmetric Dayem bridges. These planar metallic constrictions, which naturally exhibit Josephsonlike behavior, offer a fundamental platform for investigating nonreciprocal transport phenomena in a regime where the bridge width aligns with the superconducting coherence length. The foundational concept is inspired by the Tesla valve, a classical fluidic device that achieves flow rectification through interference and turbulence between fluid streams enabled by geometric asymmetry. Analogously, we demonstrate that spatial asymmetry within superconducting structures can result in rectification due to the polarity-dependent interaction between transport and screening currents. By implementing controlled geometric defects at the junction between the constriction and superconducting leads, we induce current crowding and disrupt spatial inversion symmetry, thus facilitating directional switching behavior. Experimental results indicate a linear-in-field rectification regime at low magnetic fields, driven by the interaction between transport and screening currents, which is succeeded by complex vortex dynamics within the superconducting banks at elevated fields. Time-dependent Ginzburg-Landau simulations replicate significant features of the experimental observations and substantiate the influence of both screening currents and rearrangements of Abrikosov vortices. A comparative study across various geometries highlights the crucial role of defect shape and spatial confinement in determining the rectification efficiency, revealing a minimum threshold in bridge width below which crowding-induced SDE is significantly reduced. Our findings advocate for mesoscopic Dayem bridges as a flexible platform for designing and controlling superconducting diode functionalities.
Authors: Z. C. Tu
We introduce a minimal model consisting of a two-body system with stochastically broken reciprocity (i.e., random violation of Newton's third law) and then investigate its statistical behaviors, including fluctuations of velocity and position, time evolution of probability distribution functions, energy gain, and entropy production. The effective temperature of this two-body system immersed in a thermal bath is also derived. Furthermore, we heuristically present an extremely minimal model where the relative motion adheres to the same rules as in classical mechanics, while the effect of stochastically broken reciprocity only manifests in the fluctuating motion of the center of mass.
Authors: Tingting Liu, Shuhong Li, Yunlong Liu, Shuchao Qin, Yang Liu, Wenjun Wang, Minghui Qin
The nonreciprocal propagation of spin waves (SWs) offers opportunities for developing novel functional magnonic logic devices, where controllability is crucial for magnetic signal processing. Domain walls act as natural waveguides due to their magnetic configuration, offering a platform for the in-depth investigation of nonreciprocal SW propagation and its manipulation. In this work, we theoretically and numerically investigate the tunable spin-wave nonreciprocity in ferrimagnetic domain-wall channels under the influence of an external field. It is revealed that the Dzyaloshinskii-Moriya interaction exerts dual control over both nonreciprocal spin-wave propagation and spin-splitting phenomena. Moreover, SW nonreciprocity is magnetically tunable, with its sign reversibly switched by inverting the applied field direction, while preserving the host spin configuration. The orientation of the magnetic field can selectively stabilize or destabilize the domain wall structure, offering precise control over spin-wave nonreciprocity. Ultimately, we demonstrate a controllable SW transmission scheme via external magnetic field modulation, providing critical insights for the design of future magnonic devices.
Authors: Paul C Bressloff
We use macroscopic fluctuation theory (MFT) to analyse current fluctuations in a non-interacting Brownian gas with one or more partially absorbing targets within a bounded domain $\Omega \subset \R^d$. We proceed by coarse-graining a generalised Dean-Kawasaki equation with Robin boundary conditions at the target surfaces. The exterior surface $\partial \Omega$ is maintained at a constant density $\owp$. We first derive MFT equations for the optimal noise-induced path for a single target under a saddle-point approximation of the associated path integral action. We then obtain the Gaussian distribution characterising small current fluctuations by linearising the MFT equations about the corresponding deterministic or noise-averaged system and solving the resulting stationary equations. The Robin boundary conditions are handled using the spectrum of a Dirichlet-to-Neumann operator defined on the target surface. We illustrate the theory by considering the finite interval and a circular annulus. In both cases we determine how the variance of the current depends on the rate of absorption $\kappa$. Finally, we extend our analysis to multiple partially absorbing targets. First, we obtain the general result that, in the case of partially absorbing targets ($0<\kappa<\infty$), the covariance matrix for current fluctuations supports cross correlations even in the absence of particle interactions. (These cross-correlations vanish in the totally absorbing limit $\kappa\rightarrow \infty$.) We then explicitly calculate the covariance matrix for circular targets in a 2D domain by assuming that the targets are much smaller than the characteristic size $L$ of the domain $\Omega$ and applying methods from singular perturbation theory.
Authors: Francesco Lorenzi, Luca Salasnich
We investigate the on-shell approximation in the context of s-wave scattering for ultracold two-body collisions. Our analysis systematically covers spatial dimensions D=1,2,3 , with the aim of identifying the regimes in which the approximation remains valid when applied to commonly used model interaction potentials. Specifically, we focus on the square well and delta shell potentials, both of which admit analytical solutions for the s-wave scattering problem in all dimensions considered. By employing the exact analytical expressions for the s-wave scattering phase shift, we perform a direct comparison between the exact on-shell matrix element of the interaction potential and their corresponding approximations across a range of collision momenta. Particular attention is given to the low-energy regime. Our findings indicate that, although the on-shell approximation generally improves with increasing momentum, its accuracy also improves for weaker potentials. Remarkably, in the limit of weak interactions, we demonstrate that the on-shell approximation becomes exact at leading order. In this regime, the approximation offers a controlled means of deriving the low-momentum expansion of the potential and may serve as a useful tool in constructing effective interactions for quantum field theories.
Authors: Miguel Alvarado, Alfredo Levy Yetati, Ramón Aguado, Rubén Seoane Souto
We propose using Andreev bound states (ABS) as spectroscopic probes to characterize Majorana zero modes (MZMs) in quantum-dot based minimal Kitaev chains. Specifically, we show that tunneling conductance measurements with a superconducting probe hosting an ABS reveal four subgap peaks whose voltage positions and relative heights enable extraction of the MZM energy splitting and Bogoliubov-de Gennes coherence factors. This provides direct access to zero-splitting regimes and to the local Majorana polarization - a measure of the Majorana character. The method is compatible with existing experimental architectures and remains robust in extended chains.
Authors: Rodrigo A. Dourado, Jeroen Danon, Martin Leijnse, Rubén Seoane Souto
The coherence factors of quasiparticles in a superconductor determine their properties, including transport and susceptibility to electric fields. In this work, we propose a way to infer the local coherence factors using local transport to normal leads. Our method is based on measuring the local current through a lead as the coupling to a second one is varied: the shape of the current is determined by the ratio between the local coherence factors, becoming independent of the coupling to the second lead in the presence of local electron-hole symmetry, {\it i.e.} coherence factors $|u|=|v|$. We apply our method to minimal Kitaev chains: arrays of quantum dots coupled via narrow superconducting segments. These chains feature Majorana-like quasiparticles (zero-energy states with $|u|=|v|$) at discrete points in parameter space. We demonstrate that the local current allows us to estimate the local Majorana polarization (MP) -- a measurement of the local Majorana properties of the state. We derive an analytical expression for the MP in terms of local currents and benchmark it against numerical calculations for 2- and 3-sites chains that include a finite Zeeman field and electron-electron interactions. These results provide a way to quantitatively assess the quality of Majorana states in short Kitaev chains.
Authors: Lodovico Scarpa, Abdulla Alhajri, Vlatko Vedral, Fabio Anza
Predicting the stationary behavior of observables in isolated many-body quantum systems is a central challenge in quantum statistical mechanics. While one can often use the Gibbs ensemble, which is simple to compute, there are many scenarios where this is not possible and one must instead use another ensemble, such as the diagonal, microcanonical or generalized Gibbs ensembles. However, these all require detailed information about the energy or other conserved quantities to be constructed. Here we propose a general and computationally easy approach to determine the stationary probability distribution of observables with few outcomes. Interpreting coarse measurements at equilibrium as noisy communication channels, we provide general analytical arguments in favor of the applicability of a maximum entropy principle for this class of observables. We show that the resulting theory accurately predicts stationary probability distributions without detailed microscopic information like the energy eigenstates. Extensive numerical experiments on 7 non-weakly interacting spin-1/2 Hamiltonians demonstrate the broad applicability and robustness of this framework in both quantum integrable and chaotic models.
Authors: Xiaohan Bie, Manoj Arthanari, Evelin Barbosa de Melo, Baihua Ren, Juancheng Li, Stephen Yue, Salim Brahimi, Jun Song
This study employs deep learning techniques to segment scanning electron microscope images, enabling a quantitative analysis of carbide precipitates in lower bainite and tempered martensite steels with comparable strength. Following segmentation, carbides are investigated, and their volume percentage, size distribution, and orientations are probed within the image dataset. Our findings reveal that lower bainite and tempered martensite exhibit comparable volume percentages of carbides, albeit with a more uniform distribution of carbides in tempered martensite. Carbides in lower bainite demonstrate a tendency for better alignment than those in tempered martensite, aligning with the observations of other researchers. However, both microstructures display a scattered carbide orientation, devoid of any discernible pattern. Comparative analysis of aspect ratios and sizes of carbides in lower bainite and tempered martensite unveils striking similarities. The deep learning model achieves an impressive pixelwise accuracy of 98.0% in classifying carbide/iron matrix at the individual pixel level. The semantic segmentation derived from deep learning extends its applicability to the analysis of secondary phases in various materials, offering a time-efficient, versatile AI-powered workflow for quantitative microstructure analysis.
Authors: Hannah J. Manetsch, Gyohei Nomura, Elie Bataille, Kon H. Leung, Xudong Lv, Manuel Endres
Optical tweezer arrays have transformed atomic and molecular physics, now forming the backbone for a range of leading experiments in quantum computing, simulation, and metrology. Typical experiments trap tens to hundreds of atomic qubits, and recently systems with around one thousand atoms were realized without defining qubits or demonstrating coherent control. However, scaling to thousands of atomic qubits with long coherence times, low-loss, and high-fidelity imaging is an outstanding challenge and critical for progress in quantum science, particularly towards quantum error correction. Here, we experimentally realize an array of optical tweezers trapping over 6,100 neutral atoms in around 12,000 sites, simultaneously surpassing state-of-the-art performance for several metrics that underpin the success of the platform. Specifically, while scaling to such a large number of atoms, we demonstrate a coherence time of 12.6(1) seconds, a record for hyperfine qubits in an optical tweezer array. We show room-temperature trapping lifetimes of 23 minutes, enabling record-high imaging survival of 99.98952(1)% with an imaging fidelity of over 99.99%. We present a plan for zone-based quantum computing and demonstrate necessary coherence-preserving qubit transport and pick-up/drop-off operations on large spatial scales, characterized through interleaved randomized benchmarking. Our results, along with recent developments, indicate that universal quantum computing and quantum error correction with thousands to tens of thousands of physical qubits could be a near-term prospect.
Authors: S.E. Skipetrov, I.M. Sokolov
A solid transparent medium with randomly positioned, immobile impurity atoms is a promising candidate for observation of Anderson localization of light in three dimensions. It can have low losses and allows for mitigation of the detrimental effect of longitudinal optical fields by an external magnetic field, but it has its own issues: thermal oscillations of atoms around their equilibrium positions and inhomogeneous broadening of atomic spectral lines due to random local electric fields. Our calculations suggest that these complications should not impede observation of Anderson localization of light in such materials provided that sufficiently high number densities of impurities can be reached. The thermal oscillations hardly affect light propagation whereas the inhomogeneous broadening can be compensated for by increasing the number density of impurities.
Authors: Robin Y. Wen, Gilles Parez, Liuke Lyu, William Witczak-Krempa, Achim Kempf
We show that, in finite dimensions, around any $m$-partite product state $\rho_{\rm prod}=\rho_1\otimes...\otimes\rho_m$, there exists an ellipsoid of separable states centered around $\rho_{\rm prod}$. This separable ellipsoid contains the separable ball proposed in previous works, and the volume of the ellipsoid is typically exponentially larger than that of the ball, due to the hierarchy of eigenvalues in typical states. We further generalize this ellipsoidal criterion to a trace formula that yields separable region around all separable states, and further study biseparability. Our criteria not only help numerical procedures to rigorously detect separability, but they also lead to a nested hierarchy of SLOCC-stable subsets that cover the separable set. We apply the procedure for separability detection to 3-qubit X states, genuinely entangled 4-qubit states mixed with noise, and the 1d transverse field Ising model at finite temperature to illustrate the power of our procedure for understanding entanglement in physical systems.
Authors: Yanyan Bu, Zexin Yang
We consider the chiral phase transition relevant for QCD matter at finite temperature but with vanishing baryon density. Presumably, the chiral phase transition is of second order for two-flavor QCD in the chiral limit. Near the transition temperature, we apply the Schwinger-Keldysh formalism and construct a low-energy effective field theory for the system, in which fluctuations and dissipations are systematically captured. The dynamical variables involve the chiral charge densities and order parameter (chiral condensate). Via the holographic Schwinger-Keldysh technique, the effective action is further confirmed within a modified AdS/QCD model. With higher-order terms suitably neglected, the stochastic equations derived from the effective field theory resemble those of model F in the Hohenberg-Halperin classification. Within the effective field theory, we briefly discuss the spontaneous breaking of chiral symmetry and Goldstone modes.
Authors: Yudong Wei, Zhongshu Hu, Yajing Guo, Zhentian Qian, Shengjie Jin, Xuzong Chen, Xiong-jun Liu
Radio-frequency (RF) control is a key technique in cold atom experiments. We present a compact and efficient RF circuit based on a capacitive transformer network, where a low-frequency coil operating up to 30MHz serves as both an intrinsic inductor and a power-sharing element. The design enables high current delivery and flexible impedance matching across a wide frequency range. We integrate both broadband and narrowband RF networks into a unified configuration that overcomes the geometric constraints imposed by the metallic chamber. In evaporative cooling, the broadband network allows a reduction of the applied RF input power from 14.7dBW to -3.5dBW, owing to its non-zero coil current even at ultra-low frequencies. This feature enables the Bose-Fermi mixture to be cooled below 10{\mu}K. In a Landau-Zener protocol, the coil driven by the narrowband network transfers 80% of rubidium atoms from |F = 2,mF = 2> to |2,-2> in 1 millisecond, achieving a Rabi frequency of approximately 9 kHz at an input power of 0.1dBW.
Authors: Apolinario Miguel Tan, Franco Pellegrini, Stefano de Gironcoli
We study the convergence of a linear atomic cluster expansion (ACE) potential with respect to its basis functions, in terms of the effective two-body interactions of elemental Carbon and Silicon systems. We build ACE potentials with descriptor sets truncated at body-orders $K=2$ to $K=5$ trained on a diverse Carbon dataset and on Silicon dimers to pentamers. The potentials trained on diverse structures with standard ACE bases are not able to recover the correct dimer curves much less produce stable curves or solutions. While employing ACE bases removed of self-interactions still does not generalize to the DFT-expected results, properly tailored datasets and basis sets are able to show signs of convergence and stability in the curves and expansions, suggesting a method to build potentials with interpretable bases with respect to the cluster expansion.
Authors: T. Koide, F. Nicacio
We present a systematic procedure to derive a quantum master equation for thermal relaxation in real scalar field theory, expanding on the method proposed in [Koide and Nicacio, Phys. Lett. A494, 129277 (2024)]. We begin by introducing a generalized model for a classical scalar field interacting with a Brownian thermostat, consistent with stochastic thermodynamics. Applying canonical quantization to this model, we derive the corresponding quantum master equation, that is applicable to any form of the scalar field Hamiltonian. While its evolution is generally non-CPTP (Completely Positive and Trace-Preserving), it can be adjusted to describe a CPTP evolution, such as those found in the GKSL (Gorini-Kossakowski-Sudarshan-Lindblad) equation by appropriately tuning the parameters of the model. In this framework, we define heat, work, and entropy in a way that satisfies the first and second laws of quantum thermodynamics. This suggests that the quantum-classical correspondence extends beyond closed systems governed by unitary time evolution to open systems as well. We further investigate the relation between the second law in quantum thermodynamics and relative entropy, providing insights into the study of quantum fluctuations through information-theoretical techniques in quantum field theory.
Authors: Riccardo Borsato, Miguel García Fernández
Using a Drinfeld twist of Jordanian type, we construct a deformation of the non-compact and $\mathfrak{sl}_2$-invariant $XXX_{-1/2}$ spin-chain. Before the deformation, the seed model can be understood as a sector of the $\mathfrak{psu}(2,2|4)$-invariant spin-chain encoding the spectral problem of $\mathcal{N}=4$ super Yang-Mills at one loop in the planar limit. The deformation gives rise to interesting features because, while being integrable, the Hamiltonian is non-hermitian and non-diagonalisable, so that it only admits a Jordan decomposition. Moreover, the eigenvalues of the deformed Hamiltonian coincide with those of the original undeformed spin-chain. We use explicit examples as well as the techniques of the coordinate and of the algebraic Bethe ansatz to discuss the construction of the (generalised) eigenvectors of the deformed model. We also show that the deformed spin-chain is equivalent to an undeformed one with twisted boundary conditions, and that it may be derived from a scaling limit of the non-compact $U_q(\mathfrak{sl}_2)$-invariant $XXZ_{-1/2} $ spin-chain.
Authors: Pierre-François Loos, Martial Boggio-Pasqua, Aymeric Blondel, Filippo Lipparini, Denis Jacquemin
We report theoretical best estimates of vertical transition energies (VTEs) for a large number of excited states and molecules: the \textsc{quest} database. This database includes 1489 \emph{aug}-cc-pVTZ VTEs (731 singlets, 233 doublets, 461 triplets, and 64 quartets) for both valence and Rydberg transitions occurring in molecules containing from 1 to 16 non-hydrogen atoms. \textsc{Quest} also includes a significant list of VTEs for states characterized by a partial or genuine double-excitation character, known to be particularly challenging for many computational methods. The vast majority of the reported values are deemed chemically-accurate, that is, are within $\pm0.05$ eV of the FCI/\emph{aug}-cc-pVTZ estimate. This allows for a balanced assessment of the performance of popular excited-state methodologies. We report the results of such benchmarks for various single- and multi-reference wavefunction approaches, and provide extensive supporting information allowing testing of other models. All corresponding data associated with the \textsc{quest} database, along with analysis tools, can be found in the associated \textsc{GitHub} repository at the following URL: this https URL.
Authors: Byungmin Kang, Patrick A. Lee
We propose cyclotron resonance as an optical probe for emergent fractionalized excitations in $\mathrm{U}(1)$ quantum spin liquids, focusing on kagome antiferromagnets. In contrast to conventional systems, where cyclotron resonance directly couples to charged carriers, spinons in spin liquids are charge-neutral and interact only through an emergent gauge field. We identify two key mechanisms by which an external physical electromagnetic field induces emergent electric and magnetic fields, enabling indirect coupling to spinons. Using these mechanisms, we compute the absorption rate of the cyclotron resonance response for Dirac spinons forming Landau levels. Our analysis shows that, although the absorption per layer is small, the absence of a skin-depth limitation in insulating spin liquids allows for cumulative absorption comparable to graphene in realistic sample sizes for the recently discovered spin-liquid candidate material YCu${}_3$(OH)${}_6$Br${}_2$[Br${}_{1-y}$(OH)${}_y$]. Our findings shows that cyclotron resonance is a viable experimental probe of spinon Landau quantization and emergent gauge fields, providing powerful positive experimental signatures of quantum spin liquids.
Authors: W. Makhlouf, B. Senjean, E. Fromager
Localized orbital-based quantum embedding, as originally formulated in the context of density matrix embedding theory (DMET), is revisited from the perspective of lattice density functional theory (DFT). An in-principle exact (in the sense of full configuration interaction) formulation of the theory, where the occupations of the localized orbitals play the role of the density, is derived for any (model or ab initio) electronic Hamiltonian. From this general formalism we deduce an exact relation between the local Hartree-exchange-correlation (Hxc) potential of the full-size Kohn-Sham (KS) lattice-like system and the embedding chemical potential that is adjusted on each embedded fragment, individually, such that both KS and embedding cluster systems reproduce the exact same local density. When well-identified density-functional approximations (that find their justification in the strongly correlated regime) are applied, a practical self-consistent local potential functional embedding theory (LPFET), where the local Hxc potential becomes the basic variable, naturally emerges from the theory. LPFET differs from previous density embedding approaches by its fragment-dependent embedding chemical potential expression, which is a simple functional of the Hxc potential. Numerical calculations on prototypical systems show the ability of such an ansatz to ease convergence and improve substantially the description of density profiles (localized orbital occupations in this context) in strongly correlated systems.
Authors: Nasaru Khan, Yuliia Shemerliuk, Sebastian Selter, Bernd Büchner, Saicharan Aswartham, Pradeep Kumar
The Zhang-Rice (ZR) singlet is an intriguing quantum state offering potential to realize a spin-orbit-entangled bosonic quasiparticle, which gives rise to the Zhang-Rice exciton. Its formation is attributed to the correlation between a localized d-orbital of a transition metal and the p-orbitals of the neighbouring ligands. The layered two-dimensional (2D) antiferromagnetic Ni2P2S6 system provide an excellent platform to probe the ZR exciton dynamics along with the role of exciton-phonon coupling. Here, we present a comprehensive study of ZR exciton and coupling with the phonons in bulk and few-layered single crystals of Ni2P2S6 using temperature, polarization and power-dependent photoluminescence (PL) spectroscopy. At cryogenic temperatures, the PL spectra reveal distinct phonon sidebands spaced by an energy difference of nearly 117 cm-1, indicative of exciton-phonon hybridization. Polarization-resolved measurements demonstrate a strong optical anisotropy, with a linear polarization degree of ~ 40 % at 4 K. Excitation power variation highlights linear scaling of PL intensity in the low-power regime, followed by spectral deformation at higher powers attributed to the phonon-assisted recombination and exciton saturation effects. ZR exciton and phonon side bands survival temperature decreases with decreasing flake thickness suggesting their tunability. The emergence and suppression of phonon sidebands with temperature and flake thickness emphasize dimensional sensitivity and coherence limits of excitonic states. Our findings position Ni2P2S6 as a promising candidate for tunable and anisotropic optoelectronic applications, while offering insight into quasiparticle interactions in 2D magnetic systems.
Authors: Yu. A. Pusep, M. A. T. Patricio, G. M. Jacobsen, M. D. Teodoro, G. M. Gusev, A. K. Bakarov
A radical restructuring of the optical response of highly excited electron-hole plasma formed in a mesoscopic GaAs/AlGaAs channel in a quantizing magnetic field when an electric current flows in the channel has been discovered. In the absence of current, the emission spectra are caused by transitions between Landau levels formed in the conduction band and in the valence band of heavy holes. A critical electric current leads to a drastic change in the emission spectra with a predominant contribution from light holes. It is shown that the current causes local accumulation of light holes due to Coulomb drag, which leads to strong electron-hole coupling and, as a consequence, the formation of excitons and trions.
Authors: Daiki Ootsuki, Akitoshi Nakano, Urara Maruoka, Takumi Hasegawa, Masashi Arita, Miho Kitamura, Koji Horiba, Teppei Yoshida, Ichiro Terasaki
We report the electronic structure of the thermoelectric semimetal Ta$_2$PdSe$_6$ with a large thermoelectric power factor and giant Peltier conductivity by means of angle-resolved photoemission spectroscopy (ARPES). The ARPES spectra reveal the coexistence of a sharp hole band with a light electron mass and a broad electron band with a relatively heavy electron mass, which originate from different quasi-one-dimensional (Q1D) chains in Ta$_2$PdSe$_6$. Moreover, the electron band around the Brillouin-zone (BZ) boundary shows a replica structure with respect to the energy originating from plasmonic polarons due to electron-plasmon interactions. The different scattering effects and interactions in each atomic chain lead to asymmetric transport lifetimes of carriers: a large Seebeck coefficient can be realized even in a semimetal. Our findings pave the way for exploring the thermoelectric materials in previously overlooked semimetals and provide a new platform for low-temperature thermoelectric physics, which has been challenging with semiconductors.
Authors: S. D. Nabi, M. Zhu, K. Yu. Povarov, D. G. Mazzone, J. Lass, Y. Wu, Z. Yan, S. Gvasaliya, A. Zheludev
We report thermodynamic, neutron diffraction, and inelastic neutron scattering measurements on Cs$_2$RuO$_4$, a member of the celebrated family of frustrated magnets Cs$_2$MX$_4$ (M = Cu, Co, X = Br, Cl). Unlike the previously studied members, it is based on $4d$ transition metal ions with $S=1$. Mapping out the $H-T$ magnetic phase diagram reveals an unusual continuous spin-flop-like phase transition associated with a quantum critical point within the antiferromagnetically ordered phase. A quantitative analysis of the complex magnetic excitation spectrum measured in zero field allows us to derive a model magnetic Hamiltonian for this compound. Its main feature is a frustration of magnetic anisotropy on a level that is much higher than in any of the previously studied species. This frustration naturally explains the peculiar phase transition observed.
Authors: M. Yu. Kagan, M. M. Korovushkin, V. A. Mitskan, K. I. Kugel, A. L. Rakhmanov, A. V. Rozhkov, A. O. Sboychakov
It has been shown that the Kohn--Luttinger superconductivity mechanism interplaying with other types of ordering can be implemented in systems with a hexagonal lattice. A number of unusual properties of such systems in the normal phase have also been considered. Our previous results on Kohn--Luttinger superconductivity with $p$-, $d$-, and $f$-wave pairing in monolayer and AB bilayer graphene, obtained disregarding the effect of substrate potential and impurities, have been presented in the first part. Then, the interplay of the superconducting Kohn--Luttinger state with the spin density wave state in actual AB, AA, and twisted bilayer graphene has been discussed in detail. In the last parts, a number of anomalous properties in the normal phase and the appearance of nematic superconductivity alongside with the spin density wave in the twisted bilayer graphene have been presented.
Authors: Yoshihiko Ihara, Ramender Kumar, Kota Miyakoshi, Migaku Oda, Kenji Ishida
In copper oxides (cuprates) with single CuO$_2$ layer such as La$_{2-x}$Ba(Sr)$_x$CuO$_4$, antiferromagnetism coexists with superconductivity at small doping levels $x$, where chemical disorders are significant. Here, we report that superconductivity occurs in a uniform and fully ordered N${é}$el state in a single-layer cuprate La$_2$CuO$_{4+\delta}$ with a small amount of excess oxygen $(\delta = 0.015)$ as demonstrated by the $^{139}$La nuclear quadrupole resonance measurement. A uniform oxygen distribution in the crystal is crucial for achieving microscopic phase coexistence and overcoming the miscibility gap associated with the staging instability; self-organized periodic oxygen arrangement driven by mobile oxygen atoms. This finding prompts the reconsideration of superconductivity in cuprates, highlighting that it can emerge in a robust N${é}$el state that retains sizable magnetic moments and hosts only a small carrier density.
Authors: Bindu, Amandeep Singh, Amir Hen, Lukas Drago Cavar, Sebastian Maria Ulrich Schultheis, Shira Yochelis, Yossi Paltiel, Andrew F. May, Angela Wittmann, Mathias Klaui, Dmitry Budker, Hadar Steinberg, Nir Bar-Gill
Recently discovered 2D van der Waals magnetic materials, and specifically Iron-Germanium-Telluride ($\rm Fe_{5}GeTe_{2}$), have attracted significant attention both from a fundamental perspective and for potential applications. Key open questions concern their domain structure and magnetic phase transition temperature as a function of sample thickness and external field, as well as implications for integration into devices such as magnetic memories and logic. Here we address key questions using a nitrogen-vacancy center based quantum magnetic microscope, enabling direct imaging of the magnetization of $\rm Fe_{5}GeTe_{2}$ at sub-micron spatial resolution as a function of temperature, magnetic field, and thickness. We employ spatially resolved measures, including magnetization variance and cross-correlation, and find a significant spread in transition temperature yet with no clear dependence on thickness down to 15 nm. We also identify previously unknown stripe features in the optical as well as magnetic images, which we attribute to modulations of the constituting elements during crystal synthesis and subsequent oxidation. Our results suggest that the magnetic anisotropy in this material does not play a crucial role in their magnetic properties, leading to a magnetic phase transition of $\rm Fe_{5}GeTe_{2}$ which is largely thickness-independent down to 15 nm. Our findings could be significant in designing future spintronic devices, magnetic memories and logic with 2D van der Waals magnetic materials.
Authors: Nadia Benlakhouy, El Mustapha Feddi, Abdelouahed El Fatimy
In twisted bilayer graphene (TBLG), chiral tunneling can be tuned by parameters such as the twist angle, barrier height, and Fermi energy. This differs from the tunneling behavior observed in monolayer and Bernal bilayer graphene, where electrons either pass completely through or are fully blocked due to the Klein paradox. Here we investigate the effect of a perpendicular interlayer bias on electron tunneling through electrostatic barriers in TBLG. Using a dual-gated model, which controls the carrier density and interlayer potential difference independently, we compute the transmission and reflection probabilities of electrons at different angles and energies for representative twist angles of $\theta = 1.8^{\circ}$, $3.89^{\circ}$, and $9.43^{\circ}$. We find that a moderate bias suppresses normal-incidence transmission by opening a band gap in the low-energy spectrum. Our results show this leads to near-total reflection at low energy, with transmission starting to increase just above the gap due to twist-dependent conducting channels. The applied bias breaks the system's effective inversion symmetry, resulting in pronounced direction-dependent and valley-specific asymmetries in the angular distribution of transmitted electrons. We show that electrons incident at different angles show notable variations in transmission under bias. Furthermore, interlayer bias modulates Fabry--Pérot--like resonances in the TBLG barrier, shifting the energies of transmission peaks and altering their intensity.
Authors: Nadir Samos Sáenz de Buruaga, Silvia N. Santalla, Germán Sierra, Javier Rodríguez-Laguna
We introduce the concept of entanglement halos, a set of strongly entangled distant sites within the ground state of a quantum many-body system. Such halos emerge in star-like systems with exponentially decaying couplings, as we show using both free-fermions and the spin-1/2 antiferromagnetic Heisenberg model. Depending on the central connectivity, entanglement halos may exhibit trivial and non trivial symmetry-protected topological features. Our findings highlight how geometry and connectivity can generate complex entanglement structures with rich physical content, which can be experimentally accessible via state-of-the-art technologies.
Authors: Sabera M. Borno, Robin Khisa, Israt H. Zarin, Md Hasan Mahmud, Nicholas D. Brubaker, Ryan C. Hayward, Nabila Tanjeem
Understanding the collective actuation of microscopic structures driven by external fields can lead to the development of next-generation autonomous machines. With this goal in mind, we investigated light-induced collective motion of thermocapillary microswimmers at the air-water interface. We found that Marangoni forces, which lead to long-ranged repulsive interparticle interactions, can cause microswimmers to synchronize their circular motion in a collective chase mode that resembles predator-prey behavior often observed in nature. We examined different degrees of confinement in small systems containing 2-6 particles of different individual swimming velocities and shapes. Thanks to the strong repulsive interactions between particles, a sustained chasing mode was observed for particle packing fractions above a critical value of 0.25. At lower packing fractions, swimmers transition between chasing, bouncing, and intermittent pausing, likely due to time-varying activity levels. Additionally, we report that a new synchronized mode can be introduced by incorporating chirality in particle shapes, where the microswimmers collectively reverse the direction of their circular motion periodically. Our results point to a simple but powerful mechanism of obtaining collective synchronization in synthetic confined systems where particles are designed with different shapes and activity levels.
Authors: Junsong Sun, Huaiming Guo, Bohm-Jung Yang
We study the geometric contribution to the superfluidity in quasicrystals in which the conventional momentum-space quantum geometric tensor cannot be defined due to the lack of translational invariance. Based on the correspondence between the momentum and magnetic flux, we introduce the flux-space quantum metric in finite-size closed systems and reveal its contribution to the superfluid weight in quasicrystalline superconductors. As a toy model, we study the attractive Hubbard model on the Fibonacci quasiperiodic stub lattices that host flat energy spectra even in the presence of quasiperiodic hoppings. In the weak-coupling limit, we establish the relation between superfluid weight and the flux-space quantum metric in quasicrystal superconductors with flat energy spectra. Moreover, by analyzing the spread of Wannier functions, we propose a general fluctuation mechanism that explains how quasiperiodicity modulates the integrated flux-space quantum metric. Our theory provides a general way to examine the effect of the quantum geometry in systems lacking translational symmetry.
Authors: Xinyan Li, Kenna Ashen, Chuqiao Shi, Nannan Mao, Saagar Kolachina, Kaiwen Yang, Tianyi Zhang, Sajid Husain, Ramamoorthy Ramesh, Jing Kong, Xiaofeng Qian, Yimo Han
Two-dimensional van der Waals (vdW) materials hold the potential for ultra-scaled ferroelectric (FE) devices due to their silicon compatibility and robust polarization down to atomic scale. However, the inherently weak vdW interactions enable facile sliding between layers, introducing complexities beyond those encountered in conventional ferroelectric materials and presenting significant challenges in uncovering intricate switching pathways. Here, we combine atomic-resolution imaging under in-situ electrical biasing conditions with first-principles calculations to unravel the atomic-scale switching mechanisms in SnSe, a vdW group-IV monochalcogenide. Our results uncover the coexistence of a consecutive 90 degrees switching pathway and a direct 180 degrees switching pathway from antiferroelectric (AFE) to FE order in this vdW system. Atomic-scale investigations and strain analysis reveal that the switching processes simultaneously induce interlayer sliding and compressive strain, while the lattice remains coherent despite the presence of multidomain structures. These findings elucidate vdW ferroelectric switching dynamics at atomic scale and lay the foundation for the rational design of 2D ferroelectric nanodevices.
Authors: Song-Bo Zhang, Lun-Hui Hu
Non-relativistic spin-splitting in unconventional antiferromagnets has garnered much attention for its promising spintronic applications and open fundamental questions. Here, we uncover a unique even-parity spin texture in chiral non-collinear antiferromagnets, exemplified using a kagome lattice. We consider two distinct types of electrons in the system: one with Schrödinger-like dispersion and the other exhibiting Dirac-like behavior. Remarkably, we show that, for both electron types, this spin texture induces an exotic coexistence of opposite-spin singlet and equal-spin triplet Cooper pairs with finite momentum when proximity-coupled to conventional superconductors. The triplet pairing arises from the intrinsic spin rotation of the antiferromagnet and does not require net magnetization or spin-orbit coupling. Moreover, we identify an unprecedented and tunable phase difference between singlet and triplet pairings, controllable through junction orientation. This mixed pairing state can be experimentally probed via damped oscillations in order parameters and 0-$\pi$ transitions in Josephson junctions. Additionally, we analyze the effect of out-of-plane spin canting, elucidating its role in generating spin-polarized supercurrents, and discuss Mn$_3$Ga and Mn$_3$Ge to test our predictions.
Authors: Soumyaranjan Dash, Anish Koley, Sanjeev Kumar
We study the model for spin-1/2 J1-J2 Heisenberg antiferromagnets on a square lattice in the presence of spin vacancies. In order to overcome the methodological challenges associated with analyzing models with magnetic frustration and inhomogeneities, we introduce a new semi-classical approach in which singlet dimers are treated as effective classical degrees of freedom. The energetic and entropic aspects of the dimer formation are included via a classical Monte Carlo scheme that allows for the dynamical conversion of spin pairs into dimers and vice versa. We show that our semi-classical approach recovers the qualitative physics of the J1-J2 model in the absence of vacancies. The vacancies lead to a broadening of the spin-liquid regime between the Néel and the stripe antiferromagnetic phases. This suggests a possible new route to discover spin-liquid ground states by tuning the J2/J1 ratio in doped square lattice antiferromagnets.
Authors: Miguel Alvarado, Alfredo Levy Yetati, Ramón Aguado, Rubén Seoane Souto
We propose using Andreev bound states (ABS) as spectroscopic probes to characterize Majorana zero modes (MZMs) in quantum-dot based minimal Kitaev chains. Specifically, we show that tunneling conductance measurements with a superconducting probe hosting an ABS reveal four subgap peaks whose voltage positions and relative heights enable extraction of the MZM energy splitting and Bogoliubov-de Gennes coherence factors. This provides direct access to zero-splitting regimes and to the local Majorana polarization - a measure of the Majorana character. The method is compatible with existing experimental architectures and remains robust in extended chains.
Authors: M. Belogolovskii, I. P. Nevirkovets
Here, we report experimental evidence suggesting the emergence of robust, possibly chiral, edge states in artificially engineered multilayers composed of alternating nanometer-thick layers of nonmagnetic aluminum (Al) and ferromagnetic nickel (Ni). Using phase-sensitive Josephson interferometry, we observed distinct SQUID-like oscillations (instead of the conventional Fraunhofer patterns) in the maximum supercurrent versus in-plane probing magnetic field patterns, which can be associated with one-dimensional current-carrying modes localized at the sample boundaries. These results were obtained for multilayers consisting of up to ten Al/Ni bilayers sandwiched between superconducting Nb electrodes to form Josephson junctions. The spatially confined flow of supercurrent suggests the possible presence of chiral Andreev edge states reminiscent of those found in higher-order topological insulators, despite the absence of strong spin-orbit coupling or intrinsic topological band structure. The discovery of edge-localized charge transport in structures made of materials without intrinsic topological order challenges the prevailing understanding of topological phenomena and highlights the possibility of developing topological metamaterials as a tunable platform for exploring nontrivial edge physics.
Authors: Camille Godinot, Emmanuel Rigal, Frédéric Bernard, Philippe Emonot, Pierre-Eric Frayssines, Luc Védie, Marc Bernacki
Controlling the microstructure of a diffusion welded interface is a critical point to ensure optimum mechanical properties and the homogeneity of the joint. Beyond the intimate contact formation between bonded parts studied in the literature, this article focuses on the grain boundary crossing of the interface during this process and its measurement. Following this perspective, a Level-Set method has been used for full-field microstructure simulations in 2D with various interface parameters. Two crossing measurement models have been formulated, tested and discussed over the simulations.
Authors: Yupeng Wang, Jiaqi An, Chunhui Ye, Xiangqi Wang, Di Mai, Hongze Zhao, Yang Zhang, Chiyu Peng, Kenji Watanabe, Takashi Taniguchi, Xiaoyu Sun, Rucheng Dai, Zhongping Wang, Wei Qin, Zhenhua Qiao, Zengming Zhang
Moiré superlattices enable engineering of correlated quantum states through tunable periodic potentials, where twist angle controls periodicity but dynamic potential strength modulation remains challenging. Here, we develop a high-pressure quantum transport technique for van der Waals heterostructures, achieving the ultimate pressure limit (~9 GPa) in encapsulated moiré devices. In aligned graphene/h-BN, we demonstrate that pressure induces a substantial enhancement of the moiré potential strength, evidenced by the suppression of the first valence bandwidth and the near-doubling of the primary band gap. Moreover, we report the first observation of a tertiary gap emerging above 6.4 GPa, verifying theoretical predictions. Our results establish hydrostatic pressure as a universal parameter to reshape moiré band structures. By enabling quantum transport studies at previously inaccessible pressure regimes, this Letter expands the accessible parameter space for exploring correlated phases in moiré systems.
Authors: L. Martinelli, S. Rüdiger, I. Bialo, J. Oppliger, F. Igoa Saldana, M. v. Zimmermann, E. Weschke, R. Arpaia, J. Chang
Solid matter is classified through symmetry of ordering phenomena. Experimentally, this approach is straightforward, except when distinct orderings occur with identical or almost identical symmetry breaking. Here we show that the cuprate system Y$_{1-x}$Pr$_x$Ba$_2$Cu$_3$O$_{6+y}$ hosts two distinct orderings with almost identical translational symmetry breaking. Only when applying site-sensitive resonant elastic x-ray scattering (REXS), charge ordering can be conclusively differentiated from a super-lattice structure. These two orderings occur with almost the same in-plane symmetry but manifest at different atomic sites and display different temperature dependence. Differentiating these orders provides an important clue to the anomalous behavior of PrBa$_2$Cu$_3$O$_7$ within the 123-series of high-temperature superconductors. We conclude that the symmetry breaking at the Pr-site is unfavorable for superconducting pairing.
Authors: Shmuel Gurvitz, Dmitri Sokolovski
We present a transparent and analytically tractable approach to the problem of time-dependent electron transport through tunneling barriers. Using the Single-Electron Approach, we study a model system composed of a time-dependent tunneling barrier coupled to two reservoirs of finite bandwidth. Avoiding Floquet expansions, we derive simple expressions for the time-dependent tunneling current in both adiabatic and non-adiabatic regimes. Our formulation, based on the tunneling Hamiltonian framework, relates barrier modulation to measurable phase shifts in the steady-state current, offering a physically intuitive definition of the tunneling (or traversal) time. Remarkably, in the Markovian limit (wide-band reservoirs), we recover the well-known result of vanishing tunneling time. In contrast, for finite-bandwidth leads, we predict a finite time delay given by the inverse bandwidth. Our findings provide a robust foundation for understanding tunneling dynamics in non-Markovian environments and may serve as a benchmark for experimental investigations involving tunable band structures.
Authors: Youshen Wu, Xin Guan, Shengli Zhang, Lei Zhang
We introduce an exactly solvable lattice model that reveals a universal finite-size scaling law for configurational entropy driven purely by geometry. Using exact enumeration via Burnside's lemma, we compute the entropy for diverse 1D, 2D, and 3D lattices, finding that the deviation from the thermodynamic limit $s_{\infty} = \ln (z)$ scales as $\Delta s_{N} \sim N^{-1/d}$, with lattice-dependent higher-order corrections. This scaling, observed across structures from chains to FCC and diamond lattices, offers a minimal framework to quantify geometric influences on entropy. The model captures the order of magnitude of experimental residual entropies (e.g., $S_{\mathrm{molar}} = R \ln 12 \approx 20.7 \, \mathrm{J/mol \cdot K}$) and provides a reference for understanding entropy-driven order in colloids, clusters, and solids.
Authors: Miguel Sánchez Sánchez, Tobias Stauber
We benchmark the recently proposed projection method [Phys. Rev. B 111, 205133 (2025)] for magic-angle twisted bilayer graphene (MATBG) across various symmetry-breaking phases at charge neutrality. The flat-band projected solutions agree well with the full tight-binding, with band structures and total energies differing by only a few meV. The projection to the flat bands is justified, owing to the increased gap to the remote bands in the normal state. Moreover, we employ a novel set of order parameters that allow us to visualize the wave functions locally in real space and quantify the breaking of various symmetries in the correlated phases. These order parameters are suitable to characterize MATBG and generic honeycomb systems.
Authors: Wen-Xin Jiang, Zhen-Hao Gong, Yuantao Chen, Zhigang Gui, Li Huang
Valley polarization and altermagnetism are two emerging fundamental phenomena in condensed matter physics, offering unprecedented opportunites for information encoding and processing in novel energy-efficient devices. By coupling valley and spin degrees of freedom with ferroic orders such as ferroelectricity, nonvolatile memory functionalities can be achieved. Here, we propose a way to realize ferroelectric-valley (FE-valley) and FE-altermagnetic coupling in a bilayer antiferromagnetic (AFM) honeycomb lattices based on an effective four-band spin-full $k\cdot p$ model. Our proposal is validated in bilayer MnPTe$_3$ through first-principles calculations. A spontaneous out-of-plane electric polarization occurs in AB- (BA-) stacking configuration, which is reversibly switchable via interlayer sliding. Remarkably, polarization reversal simultaneously inverts both layer-resolved valley polarization and altermagnetic spin splitting. This dual control enables tunable layer-spin-locked anomalous valley Hall effects and an unprecedented magnetoelectric response in 2D antiferromagnets. Our work establishes a general paradigm for electrically programmable valleytronic and spintronic functionalities of 2D AFM materials.
Authors: Mohsen Yarmohammadi
We study a dimerized spin-1/2 chain, such as CuGeO$_3$, hosting triplon excitations coupled to optical phonons under weak terahertz laser driving. Both phonons and triplons weakly lose energy into the surrounding baths, forming a non-equilibrium steady state. In the strong phonon-triplon coupling regime, phonons near the two-triplon continuum hybridize strongly with triplons. Using mean-field Lindblad dynamics, we show that this strong hybridization induces sharp first-order phase transitions -- either single or simultaneous double -- in the emission spectrum, mainly due to dissipation-induced nonlinearities. Using mean-field Floquet analysis of harmonic modes in both sectors, we analytically confirm the existence of these phase transitions. Furthermore, we map the complete steady-state phase diagram by varying key control parameters and provide experimentally relevant parameters for observing these transitions in laser-driven CuGeO$_3$.
Authors: Yating Sha, Kai Liu, Chenxin Jiang, Dan Ye, Shuhan Liu, Zhongxun Guo, Jingjing Gao, Ming Tian, Neng Wan, Kenji Watanabe, Takashi Taniguchi, Bingbing Tong, Guangtong Liu, Li Lu, Yuanbo Zhang, Zhiwen Shi, Zixiang Hu, Guorui Chen
The fractional quantum Hall effect (FQHE), particularly at half-filling of Landau levels, provides a unique window into topological phases hosting non-Abelian excitations. However, experimental platforms simultaneously offering large energy gaps, delicate tunability, and robust non-Abelian signatures remain scarce. Here, we report the observation of a cascade of even-denominator FQH states at filling factors ${\nu}$ = ${-5/2}$, ${-7/2}$, ${-9/2}$, ${-11/2}$, and ${-13/2}$, alongside numerous odd-denominator states in mixed-stacked pentalayer graphene, a previously unexplored system characterized by intertwined quadratic and cubic band dispersions. These even-denominator states, representing the highest filling half-filled states reported so far in the zeroth Landau level (ZLL), emerge from two distinct intra-ZLL and exhibit unprecedented displacement field tunability driven by LL crossings in the hybridized multiband structure. At half fillings, continuous quasiparticle phase transitions between paired FQH states, magnetic Bloch states, and composite Fermi liquids are clearly identified upon tuning external fields. Numerical calculations, revealing characteristic sixfold ground-state degeneracy and chiral graviton spectral analysis, suggest the observed even-denominator FQH states belong to the non-Abelian Moore-Read type. These results establish mixed-stacked multilayer graphene as a rich and versatile crystalline platform for exploring tunable correlated topological phases.
Authors: Rodrigo A. Dourado, Jeroen Danon, Martin Leijnse, Rubén Seoane Souto
The coherence factors of quasiparticles in a superconductor determine their properties, including transport and susceptibility to electric fields. In this work, we propose a way to infer the local coherence factors using local transport to normal leads. Our method is based on measuring the local current through a lead as the coupling to a second one is varied: the shape of the current is determined by the ratio between the local coherence factors, becoming independent of the coupling to the second lead in the presence of local electron-hole symmetry, {\it i.e.} coherence factors $|u|=|v|$. We apply our method to minimal Kitaev chains: arrays of quantum dots coupled via narrow superconducting segments. These chains feature Majorana-like quasiparticles (zero-energy states with $|u|=|v|$) at discrete points in parameter space. We demonstrate that the local current allows us to estimate the local Majorana polarization (MP)--a measurement of the local Majorana properties of the state. We derive an analytical expression for the MP in terms of local currents and benchmark it against numerical calculations for 2- and 3-sites chains that include a finite Zeeman field and electron-electron interactions. These results provide a way to quantitatively assess the quality of Majorana states in short Kitaev chains.
Authors: Shengpu Huang, Zheng Qin, Fangyang Zhan, Dong-Hui Xu, Da-Shuai, Rui Wang
Recent studies have drawn growing attention on non-relativistic odd-parity magnetism in the wake of altermagnets. Nevertheless, odd-parity spin splitting is often believed to appear in non-collinear magnetic configurations. Here, using symmetry arguments and effective model analysis, we show that Floquet engineering offers a universal strategy for achieving odd-parity magnetism in two-dimensional (2D) collinear antiferromagnets under irradiation of periodic driving light fields such as circularly polarized light, elliptically polarized light, and bicircular light. A comprehensive classification of potential candidates for collinear monolayer or bilayer antiferromagnets is established. Strikingly, the light-induced odd-parity spin splitting can be flexibly controlled by adjusting the crystalline symmetry or the polarization state of incident light, enabling the reversal or conversion of spin-splitting. By combining first-principles calculations and Floquet theorem, we present illustrative examples of 2D collinear antiferromagnetic (AFM) materials to verify the light-induced odd-parity magnetism. Our work not only offers a powerful approach for uniquely achieving odd-parity spin-splitting with high tunability, but also expands the potential of Floquet engineering in designing unconventional compensated magnetism.
Authors: Z.Z. Alisultanov, A. Kudlis
We study multilayer topological insulators with random interlayer tunnelling, known as off-diagonal disorder. Within the Burkov-Balents model a single Hermitian defect creates a bound state whose energy crosses the middle of the gap in the trivial phase but never in the topological phase; a non-Hermitian defect splits this level yet preserves the same crossing rule, so the effect serves as a local marker of topology. However, the key distinction persists: the bound state crosses zero in the trivial phase but not in the topological phase. Two complementary diagrammatic approaches give matching densities of states for the normal, topological, Weyl and anomalous quantum Hall regimes. Off diagonal disorder inserts bulk states into the gap and can close it: the Weyl phase remains robust under strong disorder, whereas the anomalous quantum Hall phase survives only for weak fluctuations, and the added bulk states shrink the Hall plateau, clarifying experimental deviations. Finally, we analyse edge modes. Uniform disorder shortens their localization length slightly, while Gaussian and Lorentzian disorder enlarge it and in the Gaussian case can even delocalize the edges. Although chirality is maintained, the enhanced overlap permits tunnelling between opposite edges and pulls the longitudinal conductance away from its quantized value.
Authors: Hideki Matsuoka, Amaki Moriyama, Tomohiro Hori, Yoshinori Tokura, Yoshihiro Iwasa, Shu Seki, Masayuki Suda, Naoya Kanazawa
Chiral molecular systems offer unique pathways to control spin and magnetism beyond conventional symmetry operations. Here, we demonstrate that chiral ionic liquids enable electric-field modulation of two-dimensional (2D) ferromagnetism in FeSi(111) thin films via electric double-layer transistor (EDLT) gating. FeSi hosts chemically-stable, surface-confined ferromagnetism without bulk moments, making the interfacial spins highly responsive to chiral-ion adsorption. Using both achiral and chiral ionic liquids, we systematically compare electrochemical and electrostatic gating effects. While both gating modes modulate magnetic properties such as anomalous Hall conductivity and coercive field, only chiral ionic gating biases the ratio of up- and down-magnetized domains in a handedness-dependent manner, evidencing chirality-induced symmetry breaking. This work establishes chiral ion gating as a novel strategy for controlling magnetic order and opens new directions for chiral spintronics.
Authors: Łukasz Wolański, Dawid Ciszewski, Piotr Szkudlarek, José Lorenzana, Wojciech Grochala
We use density functional theory calculations to study simple but diverse stoichiometries within the novel chemical capacitor (CC) setup. We look at main effects occurring in this device, extremes of the physicochemical properties, and we study limits of applicability of this nano-object. In the cases studied, CC permits achieving charge transfer of up to 1.74 e per atom. Tuning of the charge transfer may be achieved via judicious choice of chemical constituents of the CC as well as use of a ferroelectric material as a separator layer. Different classes of chemical systems may be doped, including metallic and nonmetallic elements, and chemical compounds, in certain cases leading to the appearance of superconductivity.
Authors: Rajesh Swami, Daloo Ram, Anusree C.V, V. Kanchana, Z. Hossain
We report a comprehensive investigation of CeGaSi single crystals, including magnetic, thermodynamic, electronic, and magnetotransport properties. The powder x-ray diffraction refinement revealed that CeGaSi crystallizes in LaPtSi-type tetragonal structure with space group I41md. The electrical resistivity data show a metallic nature with a sharp drop occurring around T_m = 11 K, revealing a magnetic phase transition, which is confirmed by magnetic susceptibility and heat capacity data. The magnetic susceptibility, magnetization, and heat capacity data are analyzed through the crystalline electric field based on point charge model, suggesting that the six degenerate ground states of Ce3+ (J = 5/2) ion split into three doublets with an overall splitting energy = 288 K. The maximum negative magnetoresistance in CeGaSi for both B\parallel c and B\parallel ab field-direction is observed near T_m, it is attributed to the suppression of spin-disorder scattering by the magnetic field. The Hall resistivity data for B \parallel c and B\parallel ab show anomalous Hall signal. Our scaling analysis suggests that anomalous Hall effect in CeGaSi is dominated by the skew scattering mechanism. In addition, first-principles calculations identify CeGaSi as a nodal-line metal.
Authors: YeongKyu Lee, Changbong Hyeon
Circadian rhythms in living organisms are temporal orders emerging from biochemical circuits driven out of equilibrium. Here, we study how the rhythmicity of a biochemical clock is shaped using the KaiABC system. A phase diagram constructed as a function of KaiC and KaiA concentrations reveals a sharply bounded limit-cycle region, which naturally explains arrhythmia upon protein over-expression. Beyond the Hopf bifurcation, intrinsic noise enables regular oscillation via coherence resonance. Within the limit-cycle region, greater rhythmic precision incurs a higher energetic cost, following the thermodynamic uncertainty relation. The cost-minimizing period of the KaiABC clock ($\sim$21-hr) is close enough to entrain to 24-hr cycle of environment. Our study substantiates universal physical constraints on the robustness, precision, and efficiency of noisy biological clocks.
Authors: Milo Vescovo, Philippe Ben-Abdallah, Riccardo Messina
The spatially resolved near-field radiative heat transfer between a nanoscale probe and a substrate is studied in the fluctuational electrodynamics framework within the dipolar approximation. It is shown that the introduction of a thin polar film atop a non-dispersive substrate can lead to both an enhancement and a lateral focusing of the heat exchange. The influence of the probe--substrate separation, film thickness and substrate permittivity is analyzed, revealing that the effect originates from near-field interactions governed by the interplay between film-induced modifications of electromagnetic mode dispersion and the distance-dependent coupling strength. The results highlight a viable route toward the active control of local radiative heat transfer at the nanoscale.
Authors: Daniel Werner, Matthieu Vanhoecke, Marco Schirò, Enrico Arrigoni
We study the interplay between strong correlations and Markovian dephasing, resulting from monitoring the charge or spin degrees of freedom of a quantum dot described by a dissipative Anderson impurity model. Using the Auxiliary master equation approach we compute the steady-state spectral function and occupation of the dot and discuss the role of dephasing on Kondo physics. Furthermore, we consider a two-lead setup which allows to compute the steady-state current and conductance. We show that the Kondo steady-state is robust to moderate charge dephasing but not to spin dephasing, which we interpret in terms of dephasing-induced heating of low-energy excitations. Finally, we show universal scaling collapse of the non-linear conductance with a dephasing-dependent Kondo scale.