Authors: Oscar Custance, Manuel González Lastre, Kyungmin Kim, Estefanía Fernandez-Villanueva, Pablo Pou, Masayuki Abe, Hossein Sepehri-Amin, Shigeki Kawai, M. Verónica Ganduglia-Pirovano, Rubén Pérez
Water interactions with oxygen-deficient cerium dioxide (CeO$_2$) surfaces are central to hydrogen production and catalytic redox reactions, but the atomic-scale details of how defects influence adsorption and reactivity remain elusive. Here, we unveil how water adsorbs on partially reduced CeO$_{2-x}$(111) using atomic force microscopy (AFM) with chemically sensitive, oxygen-terminated probes, combined with first-principles calculations. Our AFM imaging reveals water molecules as sharp, asymmetric boomerang-like features radically departing from the symmetric triangular motifs previously attributed to molecular water. Strikingly, these features localize near subsurface defects. While the experiments are carried out at cryogenic temperature, water was dosed at room temperature, capturing configurations relevant to initial adsorption events in catalytic processes. Density functional theory identifies Ce$^{3+}$ sites adjacent to subsurface vacancies as the thermodynamically favored adsorption sites, where defect-induced symmetry breaking governs water orientation. Force spectroscopy and simulations further distinguish Ce$^{3+}$ from Ce$^{4+}$ centers through their unique interaction signatures. By resolving how subsurface defects control water adsorption at the atomic scale, this work demonstrates the power of chemically selective AFM for probing site-specific reactivity in oxide catalysts, laying the groundwork for direct investigations of complex systems such as single-atom catalysts, metal-support interfaces, and defect-engineered oxides.
Authors: Lucila Peralta Gavensky, Nathan Goldman, Gonzalo Usaj
Quantized bulk response functions are hallmark signatures of topological phases, but their manifestation in periodically driven (Floquet) systems is not yet fully established. Here, we show that two-dimensional anomalous Floquet systems exhibit a quantized bulk response encoded in a Chern-Simons axion (CSA) coupling angle, reflecting a topological magnetoelectric effect analogous to that in three-dimensional insulators. The periodic drive introduces an emergent "photon" dimension, allowing the system to be viewed as a three-dimensional Sambe lattice. Within this framework, cross-correlated responses such as photon-space polarization and magnetization density, emerge as physical signatures of the CSA coupling. The CSA angle, constructed from the non-Abelian Berry connection of Floquet states, admits a natural interpretation in terms of the geometry of hybrid Wannier states. These results provide a unified framework linking Floquet band topology to quantized bulk observables.
Authors: Roger Brunner, Titus Neupert, Glenn Wagner
We study a spinful, time-reversal symmetric lowest Landau level model for a flatband quantum spin Hall system at total filling fraction $\nu_\mathrm{T}=2/3$. Such models are relevant, e.g. for spin-valley locked moiré transition metal dichalcogenides. The opposite Chern number of the two spins hinders the formation of a quantum Hall ferromagnet, instead favouring other phases. We study the phase diagram in dependence on different short-range Haldane pseudopotentials $V_m$ and uncover several phases: A fractional topological insulator, a phase separated state, a spin-polarized fractional quantum Hall state, and the partially particle-hole transformed Halperin (111) state. The effect of the pseudopotentials $V_m$ depends on the parity of $m$, the relative angular momentum.
Authors: Jiamin Wen, Kaustuv Manna, Dung Vu, Subhadeep Bej, Yu Pan, Claudia Felser, Brian Skinner, Joseph P. Heremans
Thermoelectrics (TEs) are solid-state devices that can realize heat-electricity conversion. Transverse TEs require materials with a large Nernst effect, which typically requires a strong applied magnetic field. However, topological materials with magnetic order offer an alternative pathway for achieving large Nernst via the anomalous Hall effect and the accompanying anomalous Nernst effect (ANE) that arise from band topology. Here, we show that YbMnBi2 with a low Hall density and a chemical potential near the Weyl points has, to the best of our knowledge, the highest ANE-dominated Nernst thermopower of any magnetic material, with $S_{yx}$ around 110 $\mu$V/K ($T$ = 254 K, 5 T < $|\mu_0 H|$ < 9 T applied along the spin canting direction), due to the synergism between classical contributions from filled electron bands, large Hall conductivity of topological origin, and large resistivity anisotropy. An appreciable thermal Hall angle of $0.02 < (\nabla_y T)/(\nabla_x T) < 0.06$ was observed (40 K < $T$ < 310 K, $\mu_0 H$ = 9 T).
Authors: J. Xiao, A. Inbar, J. Birkbeck, N. Gershon, Y. Zamir, T. Taniguchi, K. Watanabe, E. Berg, S. Ilani
Electron interactions in quantum materials fundamentally shape their energy bands and, with them, the material's most intriguing quantum phases. Magic angle twisted bilayer graphene (MATBG) has emerged as a model system, where flat bands give rise to a variety of such phases, yet the precise nature of these bands has remained elusive due to the lack of high-resolution momentum space probes. Here, we use the quantum twisting microscope (QTM) to directly image the interacting energy bands of MATBG with unprecedented momentum and energy resolution. Away from the magic angle, the observed bands closely follow the single-particle theory. At the magic angle, however, we observe bands that are completely transformed by interactions, exhibiting light and heavy electronic character at different parts of momentum space. Upon doping, the interplay between these light and heavy components gives rise to a variety of striking phenomena, including interaction-induced bandwidth renormalization, Mott-like cascades of the heavy particles, and Dirac revivals of the light particles. We also uncover a persistent low-energy excitation tied to the heavy sector, suggesting a new unaccounted degree of freedom. These results resolve the long-standing puzzle in MATBG - the dual nature of its electrons - by showing that it originates from electrons at different momenta within the same topological heavy fermion-like flat bands. More broadly, our results establish the QTM as a powerful tool for high-resolution spectroscopic studies of quantum materials previously inaccessible to conventional techniques.
Authors: Abdelaali Boudjemaa
We theoretically investigate the non-equilibrium dynamics of homogeneous ultracold Bose gases of microwave-shielded polar molecules following a sudden quench of the scattering length at zero temperature. We calculate in particular the quantum depletion, the anomalous density, the condensate fluctuations, and the pair correlation function using both the time-dependent Bogoliubov approach and the self-consistent time-dependent Hartree-Fock-Bogoliubov approximation. During their time evolution, these quantities exhibit slow or fast oscillations depending on the strength of the shielding interactions. We find that at long time scales the molecular condensate is characterized by nonequilibrium steady-state momentum distribution functions, with depletion, anomalous density and correlations that deviate from their corresponding equilibrium values. We demonstrate that the pair correlations expand diffusively at short times while they spread ballistically at long times.
Authors: Yuchang Cai, Rui-Xing Zhang
Determining the symmetry of Cooper pairs remains a central challenge in the study of unconventional superconductors, particularly for chiral states that spontaneously break time-reversal symmetry. Here we demonstrate that point-like impurities in chiral superconductors generate in-gap bound states with a distinctive asymmetry: the local density of states at the impurity site vanishes at one bound-state energy, but not at its particle-hole conjugate. We prove this behavior analytically in generic two-dimensional, single-band chiral superconductors, showing it arises from a fundamental interplay between pairing chirality and crystalline rotation symmetry. Our numerical simulations confirm that this diagnostic feature persists in multiband systems and for spatially extended impurities. Our results establish a symmetry-enforced real-space diagnostic for chiral superconductivity at the atomic scale.
Authors: S. Carin Gavin, Hsun-Jen Chuang, Anushka Dasgupta, Moumita Kar, Kathleen M. McCreary, Sung-Joon Lee, M. Iqbal Bakti Utama, Xiangzhi Li, George C. Schatz, Tobin J. Marks, Mark C. Hersam, Berend T. Jonker, Nathaniel P. Stern
Two-dimensional (2D) transition metal dichalcogenides (TMDs) are attractive nanomaterials for quantum information applications due to single photon emission (SPE) from atomic defects, primarily tungsten diselenide (WSe2) monolayers. Defect and strain engineering techniques have been developed to yield high purity, deterministically positioned SPE in WSe2. However, a major challenge in application of these techniques is the low temperature required to observe defect-bound TMD exciton emission, typically limiting SPE to T<30 K. SPE at higher temperatures either loses purity or requires integration into complex devices such as optical cavities. Here, 2D heterostructure engineering and molecular functionalization are combined to achieve high purity (>90%) SPE in strained WSe2 persisting to over T=90 K. Covalent diazonium functionalization of graphite in a layered WSe2/graphite heterostructure maintains high purity up to T=90 K and single-photon source integrity up to T=115 K. This method preserves the best qualities of SPE from WSe2 while increasing working temperature to more than three times the typical range. This work demonstrates the versatility of surface functionalization and heterostructure design to synergistically improve the properties of quantum emission and offers new insights into the phenomenon of SPE from 2D materials.
Authors: Shama, Jordan T. McCourt, Merve Baksi, Gleb Finkelstein, Divine Kumah
Oxygen-scavenging at oxide heterointerfaces has emerged as a powerful route for stabilizing metastable phases that exhibit interesting phenomena, including high-mobility two-dimensional electron gases and high T$_{c}$ superconductivity. We investigate structural and chemical interactions at the heterointerface formed between Eu metal and the charged-ordered insulator, BaBiO$_3$, which leads to emergent superconductivity at 6 K. A combination of X-ray diffraction and electron microscopy measurements shows that oxygen scavenging by the Eu adlayer leads to the formation of EuO$_x$ and the superconducting intermetallic BaBi$_3$. The superconducting state is quasi-two-dimensional, as evidenced by the angle-dependent magnetotransport measurements and current-voltage characteristics. An in-plane upper critical field B$_{c2}$ significantly exceeding the Pauli paramagnetic limit is observed, possibly reflecting features of Ising superconductivity. The strong spin-orbit coupling at the Bi sites may pave the way for the realization of high-T$_{c}$ topological superconductivity.
Authors: Yuanji Xu, Huiyuan Zhang, Maoyuan Feng, Fuyang Tian
Altermagnetism has recently emerged as a distinct and fundamental class of magnetic order. Exploring its interplay with quantum phenomena such as unconventional superconductivity, density-wave instabilities, and many-body effects represents a compelling frontier. In this work, we theoretically confirm the presence of high-temperature metallic altermagnetism in KV$_2$Se$_2$O. We demonstrate that the anomalous metal-insulator-metal transition arises from a Lifshitz transition associated with Fermi surface reconstruction. The previously reported spin-density wave gap is found to lie below the Fermi level in our study and is now recognized to be attributed to the V-shaped density of states, originating from orbital-selective and sublattice-resolved half-metal-like behavior on a specific V atom. Furthermore, we identify the instability from the nesting of spin-momentum-locked two-dimensional Fermi surfaces, which induces the SDW state. These findings position KV$_2$Se$_2$O as a promising platform for investigating the interplay among altermagnetism, unconventional superconductivity, and density-wave order.
Authors: Lan Bo, Songli Dai, Xichao Zhang, Masahito Mochizuki, Xiaohong Xu, Zean Tian, Yan Zhou
Two-dimensional van der Waals materials offer a versatile platform for manipulating atomic-scale topological spin textures. In this study, using first-principles and micromagnetic calculations, we demonstrate a reversible transition between magnetic skyrmions and bimerons in a MoTeI/In_2Se_3 multiferroic heterostructure. The physical origin lies in the reorientation of the easy axis of magnetic anisotropy, triggered by the reversal of ferroelectric polarization. We show that the transition operates effectively under both static and dynamic conditions, exhibiting remarkable stability and flexibility. Notably, this transition can be achieved entirely through electric control, without requiring any external magnetic field. Furthermore, we propose a binary encoding scheme based on the skyrmion-bimeron transition, presenting a promising path toward energy-efficient spintronic applications.
Authors: Pengwei Zhao, Ryuichi Shindou
Phase transitions governed by topological defects constitute a cornerstone of modern physics. Two-dimensional (2D) Anderson transitions in chiral symmetry classes are driven by the proliferation of vortex-antivortex pairs -- a mechanism analogous to the Berezinskii-Kosterlitz-Thouless (BKT) transition in the 2D XY model. In this work, we extend this paradigm to three-dimensional (3D) chiral symmetry classes, where vortex loops emerge as the key topological defects governing the Anderson transition. By deriving the dual representation of the 3D nonlinear sigma model for the chiral unitary class, we develop a mean-field theory of its Anderson transition and elucidate the role of 1D weak band topology in the Anderson transition. Strikingly, our dual representation of the 3D NLSM in the chiral symmetry class uncovers its connection to the magnetostatics of 3D type-II superconductors. The metal-to-quasilocalized and quasilocalized-to-insulating transitions in 3D chiral symmetry class share a unified theoretical framework with the normal-to-mixed and mixed-to-superconducting transitions in 3D type-II superconductors under an external magnetic field, respectively.
Authors: Ramsamoj Kewat, Nirmal Ganguli
In this study, we investigate the spin texture of the hourglass fermions band network in BiInO$_3$ using density functional theory (DFT) and symmetry analysis. Hourglass fermions are of interest in spintronics due to their unique and robust band structure, as well as their potential applications in novel electronic devices. BiInO$_3$ exhibits non-symmorphic crystal symmetries, such as glide reflection and glide rotational symmetry, influencing its electronic properties. Through symmetry analysis, we explore the band crossings and spin textures along specific high-symmetry paths in the Brillouin zone. Our results reveal a fascinating hourglass-shaped band dispersion and spin polarisation governed by symmetry operations and spin-orbit interaction. We analyse the spin-splitting mechanisms, including Dresselhaus and Rashba spin-orbit interactions, and suggest potential applications for spin-based devices. This study sheds light on the role of symmetry in crystals for fascinating spin properties of hourglass fermions in non-symmorphic materials, offering insights for future developments in spintronics.
Authors: Joseane Santos Almeida, Sergio González Casal, Hassan Al Sabea, Valentin Barth, Gautam Mitra, Vincent Delmas, David Guérin, Olivier Galangau, Tiark Tiwary, Thierry Roisnel, Vincent Dorcet, Lucie Norel, Colin Van Dyck, Elke Scheer, Dominique Vuillaume, Jérôme Cornil, Stéphane Rigaut, Karine Costuas
The electronic and thermoelectric properties of molecular junctions formed from iron and ruthenium metal-acetylide were studied using complementary experimental techniques and quantum chemical simulations. We performed physical characterizations of single-molecule and self-assembled monolayer junctions of the same molecules that allowed meaningful comparisons between the Ru and Fe adducts. In the case of the Fe-containing junctions, two distinct oxidation states are present. These junctions exhibit one of the highest Seebeck coefficients (S ca. 130 {\mu}V/K) reported to date for similar systems paired with broad electric conductance distribution and limited thermal conductance. As a result, the experimental thermoelectric figure of merit ZT for Fe-containing junctions reaches up to 0.4 for junctions with relatively high conductance. This is one of the highest ZT values reported for molecular systems at room temperature.
Authors: Swarup K. Sarkar, Sh. Mardonov, E. Ya. Sherman, Pankaj K. Mishra
We theoretically investigate the ground state and dynamics of a Rabi-coupled pseudospin-1/2 Bose-Einstein condensate, where only one spin component is subjected to an external potential. We show that in the quasiperiodic potential the Rabi coupling induces localization between the components as it is raised above the threshold value. Interestingly, the localization is mutually induced by both components for the quasiperiodic confinement, whereas for a harmonic trap the localization is induced in the potential-free component by interaction with that confined in the potential. Further, we explore the condensate dynamics by implementing a periodic driving of the Rabi frequency, where various frequency-dependent delocalization patterns, such as double (triple)-minima, tree-(parquet)-like, and frozen distributions with a correlated propagation of different spin populations are observed in the condensate density. These features pave the way to control the condensate mass and spin density patterns, both in the stationary and dynamical realizations.
Authors: Markus Greiner, Olaf Mandel, Tilman Esslinger, Theodor W Hänsch, Immanuel Bloch
For a system at a temperature of absolute zero, all thermal fluctuations are frozen out, while quantum fluctuations prevail. These microscopic quantum fluctuations can induce a macroscopic phase transition in the ground state of a many-body system when the relative strength of two competing energy terms is varied across a critical value. Here we observe such a quantum phase transition in a Bose-Einstein condensate with repulsive interactions, held in a three-dimensional optical lattice potential. As the potential depth of the lattice is increased, a transition is observed from a superfluid to a Mott insulator phase. In the superfluid phase, each atom is spread out over the entire lattice, with long-range phase coherence. But in the insulating phase, exact numbers of atoms are localized at individual lattice sites, with no phase coherence across the lattice; this phase is characterized by a gap in the excitation spectrum. We can induce reversible changes between the two ground states of the system.
Authors: Hongxia Xue, Hsun-Chi Chan, Zuzhang Lin, Dalin Boriçi, Shaobo Zhou, Yanan Wang, Kenji Watanabe, Takashi Taniguchi, Cristiano Ciuti, Wang Yao, Dong-Keun Ki, Shuang Zhang
Recent studies on cavity-coupled two-dimensional electron gas demonstrate that vacuum-field engineering can tailor electronic transport properties of materials. By achieving ultra-strong coupling between a terahertz resonator and mesoscopic graphene, we demonstrate that cavity vacuum fields can alter the effective degeneracies of Landau levels, resulting in a nonlinear Landau fan diagram for massless Dirac fermions while preserving quantum-Hall quantization. Specifically, by leveraging graphene's gate-tunability, we observe that quantum-Hall features, minimum longitudinal and quantized Hall conductance for a given filling factor, occur at carrier densities reduced by more than 20 percent compared to systems without cavity. Theoretical analysis attributes this effect to the virtual cavity photon mediated transitions between the non-equidistant Landau levels in graphene, significantly reducing their effective degeneracy. This study paves the way for investigating cavity quantum electrodynamics in highly tunable, atomically thin two-dimensional crystals.
Authors: Sankar Das Sarma, Katharina Laubscher, Haining Pan, Jay D. Sau, Tudor D. Stanescu
One of the most important physical effects in condensed matter physics is the Rashba spin-orbit coupling (RSOC), introduced in seminal works by Emmanuel Rashba. In this article, we discuss, describe, and review (providing critical perspectives on) the crucial role of RSOC in the currently active research area of topological quantum computation. Most, if not all, of the current experimental topological quantum computing platforms use the idea of Majorana zero modes as the qubit ingredient because of their non-Abelian anyonic property of having an intrinsic quantum degeneracy, which enables nonlocal encoding protected by a topological energy gap. It turns out that RSOC is a crucial ingredient in producing a low-dimensional topological superconductor in the laboratory, and such topological superconductors naturally have isolated localized midgap Majorana zero modes. In addition, increasing the RSOC strength enhances the topological gap, thus enhancing the topological immunity of the qubits to decoherence. Thus, Rashba's classic work on SOC may lead not only to the realization of localized non-Abelian anyons, but also fault tolerant quantum computation.
Authors: Stewart Koppell, Otavio D. A. R. Bittencourt, Dip Joti Paul, Junwu Huang, Masha Baryakhtar, Karl K. Berggren
Light dark matter candidates such as axions and dark photons generically couple to electromagnetism, yielding dark-matter-to-photon conversion as a key search strategy. In addition to resonant conversion in cavities and circuits, light dark matter bosons efficiently convert to photons on material interfaces, with a broadband power proportional to the total area of these interfaces. In this work, we make use of interface conversion to develop a new experimental dark matter detector design: the disordered dielectric detector. We show that a volume filled with dielectric powder is an efficient, robust, and broadband target for axion-to-photon or dark-photon-to-photon conversion. We perform semi-analytical and numerical studies in small-volume 2D and 3D disordered systems to compute the conversion power as a function of dark matter mass. We also discuss the power gathered onto a sensitive photodetector in terms of the bulk properties of the disordered material, making it possible to characterize the predicted dark-matter-to-photon conversion rate across a wide range of wavelengths. Finally, we propose DPHaSE: the Dielectric Powder Haloscope SNSPD Experiment which is composed of a disordered dielectric target, a veto system, and a photon collection chamber to maximize the coupling between the powder target and a low noise superconducting nanowire single photon detector (SNSPD). The projected reach, in the 10 meV-eV mass range, is sensitive to QCD axion-photon couplings and exceeds current constraints on dark photon dark matter by up to 5 orders of magnitude.
Authors: Toshali Mitra, Sukrut Mondkar, Ayan Mukhopadhyay, Alexander Soloviev
Semi-holography provides a formulation of dynamics in gauge theories involving both weakly self-interacting (perturbative) and strongly self-interacting (non-perturbative) degrees of freedom. These two subsectors interact via their effective metrics and sources, while the full local energy-momentum tensor is conserved in the physical background metric. In the large $N$ limit, the subsectors have their individual entropy currents, and so the full system can reach a pseudo-equilibrium state in which each subsector has a different physical temperature. We first complete the proof that the global thermal equilibrium state, where both subsectors have the \textit{same} physical temperature, can be defined in consistency with the principles of thermodynamics and statistical mechanics. Particularly, we show that the global equilibrium state is the unique state with maximum entropy in the microcanonical ensemble. Furthermore, we show that in the large $N$ limit, a \textit{typical} non-equilibrium state of the full isolated system relaxes to the global equilibrium state when the average energy density is large compared to the scale set by the inter-system coupling. We discuss quantum statistical perspectives.
Authors: Alan C. Duriez, Andreia Saguia, Marcelo S. Sarandy
The characterization of quantum phase transitions is a fundamental task for the understanding of quantum phases of matter, with a number of potential applications in quantum technologies. In this work, we use digital quantum simulation as a resource to theoretically and experimentally study quantum phase transitions. More specifically, we implement the variational quantum eigensolver (VQE) algorithm to the one-dimensional spin-$1/2$ transverse-field Ising chain in the presence of boundary magnetic fields. Such fields can induce a rich phase diagram, including a first-order line and also a continuous wetting transition, which is a quantum version of the classical wetting surface phenomenon. We present results for noiseless simulations of the associated quantum circuits as well as hardware results taken from a superconducting quantum processor. For different regions of the phase diagram, the quantum algorithm allows us to predict the critical value of the magnetic fields responsible for either the first or second-order transitions occuring in the system.
Authors: Shuang Liang, Hassan Alnatah, Qi Yao, Jonathan Beaumariage, Ken West, Kirk Baldwin, Loren N. Pfeiffer, Natalia G. Berloff, David W. Snoke
Lattice arrays have been shown to have great value as simulators for complicated mathematical problems. In all physical lattices so far, coupling is only between nearest neighbors or nearest plus next-nearest neighbors; the geometry of the lattice controls the couplings of the sites. Realizing independently tunable, long-range interactions between distant condensates is a prerequisite for scalable analogue spin machines but has so far been restricted to short-range geometric coupling. In this work we show that it is possible using two-dimensional lattices of polariton condensates to use the third dimension to arbitrarily select two sites to couple coherently. Light emitted in the vertical direction from a condensate at one site can be imaged and sent back into the system to impinge on a different condensate at an arbitrary distance. We demonstrate this for the case of two condensates, in which we first ensure that they have no coupling within the plane of the lattice, and then use external imaging to phase lock the two together. Phase-resolved interferometry confirms clearly visible interference fringes and deterministic phase locking even when direct, planar coupling is suppressed. Analytical modeling reveals complementary mechanisms underpinning the robust coherence. Because the mirror adds no cameras, modulators, or electronic processing, the condensate pair operates as a pure, high-bandwidth analog element. Extension to dense graphs via segmented micro-mirror arrays is therefore ultimately limited only by the field of view and numerical aperture of the imaging optics. Our scheme thus paves the way to reconfigurable, energy-efficient polaritonic hardware for optimization, classification, clustering, and other neuromorphic tasks at the speed of light.
Authors: Yan V Fyodorov
We suggest a method of analyzing the joint probability density (JPD) ${\cal P}_N(z,{\bf v})$ of an eigenvalue $z$ and the associated right eigenvector ${\bf v}$ (normalized with ${\bf v}^*{\bf v}=1$) of non-Hermitian random matrices of a given size $N\times N$. The method, which represents an alternative to Girko Hermitization approach, is essentially based on the Kac-Rice counting formula applied to the associated characteristic polynomial combined with a certain integral identity for the Dirac delta function of such a polynomial. To illustrate utility of the general method we apply it to consider two particular cases: (i) one-parameter family of matrices interpolating between complex Ginibre and real Ginibre ensembles and (ii) a complex Ginibre matrix additively perturbed by a fixed matrix. In particular, in the former case we discuss the formation of an excess of eigenvalues in the vicinity of the real axis on approaching the real Ginibre limit, which eventually gives rise to the existence of a new scaling regime of "weak non-reality" as $N\to \infty$. In the second case we provide new insights into eigenvalue and eigenvector distribution for a general rank one perturbation of complex Ginibre matrices of finite size $N$, and in the structure of an outlier as $N\gg 1$. Finally we discuss a possible generalization of the proposed method which is expected to be suitable for analysis of JPD involving both left- and right eigenvectors.
Authors: Moritz Eder, Faith J. Lewis, Johanna I. Hütner, Panukorn Sombut, Maosheng Hao, David Rath, Jan Balajka, Margareta Wagner, Matthias Meier, Cesare Franchini, Ulrike Diebold, Michael Schmid, Florian Libisch, Jiří Pavelec, Gareth S. Parkinson
Gem-dicarbonyls of transition metals supported on metal (oxide) surfaces are common intermediates in heterogeneous catalysis. While infrared (IR) spectroscopy is a standard tool for detecting these species on applied catalysts, the ill-defined crystallographic environment of species observed on powder catalysts renders data interpretation challenging. In this work, we apply a multi-technique surface science approach to investigate rhodium gem-dicarbonyls on a single-crystalline rutile TiO$_2$(110) surface. We combine spectroscopy, scanning probe microscopy, and Density Functional Theory (DFT) to determine their location and coordination on the surface. IR spectroscopy shows the successful creation of gem-dicarbonyls on a titania single crystal by exposing deposited Rh atoms to CO gas, followed by annealing to 200-250 K. Low-temperature scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM) data reveal that these complexes are mostly aligned along the [001] crystallographic direction, corroborating theoretical predictions. Notably, x-ray photoelectron spectroscopy (XPS) data reveal multiple rhodium species on the surface, even when the IR spectra show only the signature of rhodium gem-dicarbonyls. As such, our results highlight the complex behavior of carbonyls on metal oxide surfaces, and demonstrate the necessity of multi-technique approaches for the adequate characterization of single-atom catalysts.
Authors: Taylor Baird, Rodolphe Vuilleumier, Sara Bonella
Lattice vibrations within crystalline solids, or phonons, provide information on a variety of important material characteristics, from thermal qualities to optical properties and phase transition behaviour. When the material contains light ions, or is subjected to sufficiently low temperatures and/or high pressures, anharmonic and nuclear quantum effects (NQEs) may significantly alter its phonon characteristics. Unfortunately, accurate inclusion of these two effects within numerical simulations typically incurs a substantial computational cost. In this work, we present a novel approach which promises to mitigate this problem. The scheme leverages the recently introduced quantum correlators approach for the extraction of anharmonic phonon frequencies from molecular dynamics data. To account for NQEs without excessive increase of the computational cost, we include nuclear quantum effects via the quantum thermal bath (QTB) method. This is the first full exploration of the use of QTB for the calculation of phonon dispersion relations. We demonstrate the noteworthy efficiency and accuracy of the scheme, and analyze its upsides and drawbacks by first considering 1-dimensional systems, and then the physically interesting case of solid neon.
Authors: Serge Galam
I address the challenge of extracting reliable insights from large datasets using a simplified model that illustrates how hierarchical classification can distort outcomes. The model consists of discrete pixels labeled red, blue, or white. Red and blue indicate distinct properties, and white represents unclassified or ambiguous data. A macro-color is assigned only if one color holds a strict majority among the pixels. Otherwise, the aggregate is labeled white, reflecting uncertainty. This setup mimics a percolation threshold at fifty percent. Assuming direct access of the various proportions of colors is infeasible from the data, I implement a hierarchical coarse-graining procedure. Elements (first pixels, then aggregates) are recursively grouped and reclassified via local majority rules, producing ultimately a single super-aggregate whose color represents the inferred macro-property of the collection of pixels as a whole. Analytical results, supported by simulations, show that the process introduces additional white aggregates beyond white pixels, which could be initially present. These arise from groups lacking a clear majority, requiring arbitrary symmetry-breaking decisions to attribute a color to them. While each local resolution may appear minor and inconsequential, their repetitions introduce a growing systematic bias. Even with complete data, unavoidable asymmetries in local rules are shown to skew outcomes. This study highlights a critical limitation of recursive data reduction. Insight extraction is shaped not only by data quality, but by how local ambiguity is handled. That results in built-in biases. Thus, the related flaws are not due to the data, but due to structural choices made during local aggregations. Though based on a simple model, the findings expose the high likelihood of inherent flaws in widely used hierarchical classification techniques.
Authors: Jerome Lloyd, Dmitry A. Abanin
Preparation of quantum thermal states of many-body systems is a key computational challenge for quantum processors, with applications in physics, chemistry, and classical optimization. We provide a simple and efficient algorithm for thermal state preparation, combining engineered bath resetting and modulated system-bath coupling to derive a quantum channel approximately satisfying quantum detailed balance relations. We show that the fixed point $\hat\sigma$ of the channel approximates the Gibbs state as $\|\hat\sigma -\hat\sigma_\beta\|\sim \theta^2$, where $\theta$ is the system-bath coupling and $\hat\sigma_\beta \propto e^{-\beta \hat H_S}$. We provide extensive numerics, for the example of the 2D Quantum Ising model, confirming that the protocol successfully prepares the thermal state throughout the finite-temperature phase diagram, including near the quantum phase transition. Our algorithm provides a path to efficient quantum simulation of quantum-correlated states at finite temperature with current and near-term quantum processors.
Authors: Luke D. Smith, Farhan T. Chowdhury, Jonas Glatthard, Daniel R. Kattnig
Magnetosensitive spin-correlated radical-pairs (SCRPs) offer a promising platform for noise-robust quantum metrology. However, unavoidable interradical interactions, such as electron-electron dipolar and exchange couplings, alongside deleterious perturbations resulting from intrinsic radical motion, typically degrade their potential as magnetometers. In contrast to this, we show how structured molecular motion modulating interradical interactions in a live chemical sensor in cryptochrome can, in fact, increase sensitivity and, more so, push precision in estimating magnetic field directions closer to the quantum Cramér-Rao bound, suggesting near-optimal metrological performance. Remarkably, this approach to optimality is amplified under environmental noise and persists with increasing complexity of the spin system, suggesting that perturbations inherent to such natural systems have enabled them to operate closer to the quantum limit to more effectively extract information from the weak geomagnetic field. This insight opens the possibility of channeling the underlying physical principles of motion-induced modulation of electron spin-spin interactions towards devising efficient handles over emerging molecular quantum information technologies.
Authors: Sergio E. Aguilar-Gutierrez
Can there be multiple bulk theories for the same boundary theory? We answer this affirmatively in the double-scaled SYK (DSSYK) model using the tools of constrained systems. We find different symmetry sectors generated by specific constraints within the chord Hilbert space of the DSSYK with matter. Each sector corresponds to a different bulk description. These include chord parity symmetry, corresponding to End-Of-The-World (ETW) branes and Euclidean wormholes in sine dilaton gravity; and relative time-translations in a doubled DSSYK model (as a single DSSYK with an infinitely heavy chord) used in de Sitter holography. We derive the partition functions and thermal correlation functions in the ETW brane and Euclidean wormhole systems from the boundary theory. We deduce the holographic dictionary by matching geodesic lengths in the bulk with the spread complexity of the parity-gauged DSSYK. The Euclidean wormholes of fixed size are perturbatively stable, and their baby universe Hilbert space is non-trivial only when matter is added. We conclude studying the constraints in the path integral of the doubled DSSYK. We derive the gauge invariant operator algebra of one of the DSSYKs dressed to the other one and discuss its holographic interpretation.
Authors: Pete Rigas
We extend previous results providing an exact formula for the variance of a linear statistic for the Jellium model, a one-dimensional model of Statistical mechanics obtained from the $k \longrightarrow 0^{+}$ limit of the Dyson log-gas. For such a computation of the covariance, in comparison to previous work for computations of the log-gas covariance, we obtain a formula between two linear statistics, given arbitrary functions $f$ and $g$ over the real line, that is dependent upon an asymptotic approximation of the Jellium probability distribution function from large $N$ deviations, and from an effective saddle-point action.
Authors: Miftah Hadi Syahputra Anfa, Sabri Elatresh, Hocine Bahlouli, Michael Vogl
Motivated by recent studies on topologically non-trivial moiré bands in twisted bilayer transition metal dichalcogenides (TMDs), we study MoTe$_2$ bilayer systems subject to pressure, which is applied perpendicular to the material surface. We start our investigation by first considering an untwisted bilayer system with an arbitrary relative shift between layers; a symmetry analysis for this case permits us to obtain a simplified effective low-energy Hamiltonian valid near the important $\mathbf{K}$ valley region of the Brillouin zone. Ab initio density functional theory (DFT) was then employed to obtain relaxed geometric structures for pressures within the range of 0.0 - 3.5 GPa and corresponding band structures. The DFT data were then fitted to the low-energy Hamiltonian to obtain a pressure-dependent Hamiltonian. We then apply our model to a twisted system by treating the twist as a position-dependent shift between layers - here, we assume rigid layers, which is a crucial simplification. In summary, this approach allowed us to obtain the explicit analytical expressions for a Hamiltonian that describes a twisted MoTe\textsubscript{2} bilayer under pressure. Our Hamiltonian then permitted us to study the impact of pressure on the band topology of the twisted system. As a result, we identified many pressure-induced topological phase transitions as indicated by changes in valley Chern numbers. Moreover, we found that pressure could be employed to flatten bands in some of the cases we considered.
Authors: Katharina Laubscher, Jay D. Sau
We study signatures of Majorana zero modes (MZMs) bound to Josephson vortices in superconductor-three-dimensional topological insulator-superconductor (S-TI-S) Josephson junctions placed in a perpendicular magnetic field. First, using semiclassical analytical as well as numerical techniques, we calculate the spatially resolved supercurrent density carried by the low-energy Caroli-de Gennes-Matricon (CdGM) states in the junction. Motivated by a recent experiment [Yue et al., Phys. Rev. B 109, 094511 (2024)], we discuss if and how the presence of vortex MZMs is reflected in supercurrent measurements, showing that Fraunhofer signatures alone are not suitable to reliably detect vortex MZMs. Next, we propose two ways in which we believe supercurrent measurements could be complemented to further verify that the junction does indeed host MZMs. Explicitly, we discuss how additional Majorana signatures could be obtained by (1) mapping out the local density of states in the junction via scanning tunneling microscopy techniques, and (2) microwave spectroscopy of the spectrum of low-energy CdGM states in the junction.
Authors: Paul Raux, Christophe Goupil, Gatien Verley
We derive the nonequilibrium conductance matrix for open stationary Chemical Reaction Networks (CRNs) described by a deterministic mass action kinetic equation. As an illustration, we determine the nonequilibrium conductance matrix of a CRN made of two pseudo-linear sub-networks, called chemical modules, in two different ways: First by computing the nonequilibrium conductances of the modules that are then serially connected. Second by computing the nonequilibrium conductance of the CRN directly. The two approaches coincide, as expected from our theory of thermodynamic circuits.
Authors: Fabrizio Canfora, Pablo Pais
A novel Bogomol'nyi-Prasad-Sommerfield (BPS) bound for the Gross-Pitaevskii equations in two spatial dimensions is presented. The energy can be bounded from below in terms of the combination of two boundary terms, one related to the vorticity (but ``dressed'' by the condensate profile) and the second to the ``skewness'' of the configurations. The bound is saturated by configurations that satisfy a system of two first-order partial differential equations. When such a BPS system is satisfied, the Gross-Pitaevskii equations are also satisfied. The analytic solutions of this BPS system in the present manuscript represent configurations with fractional vorticity living in an annulus. Using these techniques, we present the first analytic examples of this kind. The hydrodynamical interpretation of the BPS system is discussed, and the implications of these results are outlined.
Authors: Venkata D. Pamulaparthy, Rosemary J. Harris
We introduce a reinforcement learning method for a class of non-Markov systems; our approach extends the actor-critic framework given by Rose et al. [New J. Phys. 23 013013 (2021)] for obtaining scaled cumulant generating functions characterizing the fluctuations. The actor-critic is implemented using neural networks; a particular innovation in our method is the use of an additional neural policy for processing memory variables. We demonstrate results for current fluctuations in various memory-dependent models with special focus on semi-Markov systems where the dynamics is controlled by nonexponential interevent waiting time distributions.
Authors: Benjamin D. Woods
The exchange interaction $J$ offers a powerful tool for quantum computation based on semiconductor spin qubits. However, the exchange interaction in two-electron systems in the absence of a magnetic field is usually constrained to be non-negative $J \geq 0$, which inhibits the construction of various dynamically corrected exchange-based gates. In this work, we show that negative exchange $J < 0$ can be realized in two-electron Si quantum dot arrays in the absence of a magnetic field due to the presence of the valley degree of freedom. Here, valley phase differences between dots produce a non-trivial $\mathbb{Z}_2$ gauge field in the low-energy effective theory, which in turn can lead to a negative exchange interaction. In addition, we show that this $\mathbb{Z}_2$ gauge field can break Nagaoka ferromagnetism and be engineered by altering the occupancy of the dot array. Therefore, our work uncovers new tools for exchange-based quantum computing and a novel setting for studying quantum magnetism.
Authors: Koustav Roy, Gourab Paul, Debika Debnath, Kuntal Bhattacharyya, Saurabh Basu
We study nonreciprocal signatures of Josephson current (JC) in a quantum dot (QD)-based Josephson junction (JJ) that comprises of two periodically driven Kitaev chains (KCs) coupled with an intervening QD. The simultaneous breaking of the inversion symmetry ($\mathcal{IS}$) and the time-reversal symmetry ($\mathcal{TRS}$), indispensable for the Josephson diode effect (JDE), is achieved solely via the two Floquet drives that differ by a finite phase, which eventually results in a nonreciprocal current, and hence yields a finite JDE. It may be noted that the Floquet Majorana modes generated at both the far ends of the KCs (away from the QD) and adjacent to the QD junctions mediate the JC owing to a finite superconducting (SC) phase difference in the two KCs. We calculate the time-averaged JC and inspect the tunability of the current-phase relation (CPR) to ascertain the diode characteristics. The asymmetric Floquet drive also manifests an anomalous JC signature in our KC-QD-KC JJ. Furthermore, additional control over the QD energy level can be achieved via an external gate voltage that renders flexibility for the Josephson diode (JD) to act as an SC switching device. Tuning different system parameters, such as the chemical potential of the KCs, Floquet frequency, the relative phase mismatch of the drives, and the gate voltage, our model shows the highest possible rectification to be around $70\%$. Summarizing, our study provides an alternative scenario, replacing the traditional usage of an external magnetic field and spin-orbit coupling effects in a JD via asymmetrically driven Kitaev leads that entail Majorana-mediated transport.
Authors: Jesse Liebman, Svetlana Torunova, John A. Schlueter, Elena Zhilyaeva, Natalia Drichko
The BEDT-TTF (BEDT-TTF = bis(ethylenedithio)tetrathiafuvalene) based Mott insulators of the form $\kappa$-(BEDT-TTF)$_2$Hg(SCN)$_2$X (X=Br,Cl) host a correlated electron system on a triangular lattice of (BEDT-TTF)$^{+1}_2$ dimers. Each dimer lattice site carries one hole and one S=1/2 spin which interacts antiferromagnetically. Anionic substitution has been shown to tune across a charge order transition, where unequal share of the hole between the molecules of a dimer site results in electronic ferroelectricity. We demonstrate successful tuning across the charge order transition via uniaxial strain. We use Raman scattering spectroscopy to study the local charge state and collective dipole fulctuations. We induce charge order at 33 K in the quantum dipole liquid material $\kappa$-(BEDT-TTF)$_2$Hg(SCN)$_2$Br through application of tensile strain of 0.4% along the c-axis. We suppress charge order down to 10 K in $\kappa$-(BEDT-TTF)$_2$Hg(SCN)$_2$Cl by applying a tensile strain of 1.6% along the b-axis. We identify the softening of collective dipole fluctuations through the charge order transition, consistent with electronic ferroelectricity. We demonstrate tuning in both directions across a second-order ferroelectric phase transition via uniaxial strain.
Authors: Charles Emmett Maher, Katherine A. Newhall
Advancements in materials design and manufacturing have allowed for the production of ordered and disordered metamaterials with diverse and novel properties. Hyperuniform two-phase heterogeneous materials, which anomalously suppress density fluctuations on large length scales compared to typical disordered systems, and network materials are two classes of metamaterial that have desirable physical properties. Recent focus has been placed on the design of disordered hyperuniform network metamaterials that inherit the desirable properties of both of these metamaterial classes. In this work, we focus on determining the extent to which network structures derived from the spatial tessellations of hyperuniform point patterns inherit the hyperuniformity of the progenitor point patterns. In particular, we examine the Delaunay, Voronoi, Delaunay-Centroidal, and Gabriel tessellations of nonhyperuniform and hyperuniform point patterns in two- and three-dimensional Euclidean space. We use the spectral density to characterize the density fluctuations of two-phase media created by thickening the edges of these tessellations in two dimensions and introduce a novel variance-based metric to characterize the network structures directly in two and three dimensions. We find that, while none of the tessellations completely inherit the hyperuniformity of the progenitor point pattern, the degree to which the hyperuniformity is inherited is sensitive to the tessellation scheme and the short- and long-range translational disorder in the point pattern, but not to the choice of beam shape when mapping the networks into two-phase media.
Authors: Rob den Teuling, Ritesh Das, Artem V. Bondarenko, Elena V. Tartakovskaya, Gerrit E. W. Bauer, Yaroslav M. Blanter
We investigate the dipolar-exchange spin wave spectrum in thin ferromagnetic bilayers with inplane magnetization, incorporating interlayer exchange coupling and intra- and interlayer dipolar interactions. In the continuum approximation we analyze the nonreciprocity of propagating magnetic stray fields emitted by spin waves as a function of the relative orientation of the layer magnetizations that are observable by magnetometry of synthetic antiferromagnets or weakly coupled type-A van der Waals antiferromagnetic bilayers as a function of an applied magnetic field.
Authors: Takayuki Ishitobi
We investigate both the nonmagnetic and magnetic ordered phases of CeCoSi using Landau theory. Our analysis predicts three successive phase transitions at zero magnetic field. A quadrupole order parameter that emerges below $T_0=12$ K acts as a weak symmetry-breaking field on the antiferromagnetic ordering below $T_{\rm N}=9.4$ K, leading to two-stage magnetic transitions. In the higher-temperature antiferromagnetic phase within the range $T_{\rm s2}=8~{\rm K}
Authors: Alberto Martinez-Serra, Gionni Marchetti, Francesco D'Amico, Ivana Fenoglio, Barbara Rossi, Marco P. Monopoli, Giancarlo Franzese
When nanoparticles (NPs) are introduced into a biological solution, layers of biomolecules form on their surface, creating a corona. Understanding how the structure of the protein evolves into the corona is essential for evaluating the safety and toxicity of nanotechnology. However, the influence of NP properties on protein conformation is not well understood. In this study, we propose a new method that addresses this issue by analyzing multi-component spectral data using Machine Learning (ML). We apply the method to fibrinogen, a crucial protein in human blood plasma, at physiological concentrations while interacting with hydrophobic carbon or hydrophilic silicon dioxide NPs, revealing striking differences in the temperature dependence of the protein structure between the two cases. Our unsupervised ML method a) does not suffer from the challenges associated with the curse of dimensionality, and b) simultaneously handles spectral data from various sources. The method offers a quantitative analysis of protein structural changes upon adsorption and enhances the understanding of the correlation between protein structure and NP interactions, which could support the development of nanomedical tools to treat various conditions.
Authors: Leo Hahn
Run-and-tumble particles (RTPs) have emerged as a paradigmatic example for studying nonequilibrium phenomena in statistical mechanics. The invariant measure of a wide class of RTPs subjected to a potential possesses a density that is continuous at high tumble rates but exhibits divergences at low ones. This key feature, known as shape transition, constitutes a qualitative indicator of the relative closeness (continuous density) or strong deviation (diverging density) from the equilibrium setting. Furthermore, the points at which the density diverges correspond to the configurations where the system spends most of its time in the low tumble rate regime. Building on and extending existing results concerning the regularity of the invariant measure of one-dimensional piecewise-deterministic Markov processes (PDMPs), we show how to characterize the shape transition even in situations where the invariant measure cannot be computed explicitly. Our analysis confirms shape transition as a robust, general feature of RTPs subjected to a potential. We also refine the regularity theory for the invariant measure of one-dimensional PDMPs.
Authors: Michiya Chazono, Youichi Yanase
Finite-momentum superconductivity has become an important research topic in condensed matter physics. In particular, the orbital Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, which is stabi lized in atomically thin films by the orbital effect of an external magnetic field, has been getting attention as a fascinating finite-momentum superconducting state recently. We study the phase diagram of the trilayer Ising superconductor NbSe$_2$ in the in-plane magnetic field, taking into ac count the orbital effect, the paramagnetic effect, and the spin-orbit coupling. The finite-momentum gap structure in the high-field region is shown by a large-scale numerical calculation based on the Bogoliubov-de Gennes equation. We find an exotic superconducting phase, a layer-selective FFLO phase, in which finite-momentum Cooper pairs coexist with zero-momentum Cooper pairs, separated from the orbital FFLO phase.
Authors: Simon Svab, Rafael S. Eggli, Taras Patlatiuk, Miguel J. Carballido, Pierre Chevalier Kwon, Dominique A. Trüssel, Ang Li, Erik P.A.M. Bakkers, Andreas V. Kuhlmann, Dominik M. Zumbühl
Pauli Spin Blockade (PSB) is a key paradigm in semiconductor nanostructures and gives access to the spin physics. We report the direct observation of PSB with gate-dispersive reflectometry on double quantum dots with source-drain bias. The reservoir charge transitions are strongly modulated, turning on and off when entering and leaving the blockaded region, consistent with a simple model. Seen with holes in Ge and Si, the effects are enhanced with larger bias voltage and suppressed by magnetic field. This work lays the foundation for fast probing of spin physics and minimally invasive spin readout.
Authors: E. Altuntas, R. G. Lena, S. Flannigan, A. J. Daley, I. B. Spielman
Much of our knowledge of quantum systems is encapsulated in the expectation value of Hermitian operators, experimentally obtained by averaging projective measurements. However, dynamical properties are often described by products of operators evaluated at different times; such observables cannot be measured by individual projective measurements, which occur at a single time. For example, the dynamical structure factor describes the propagation of density excitations, such as phonons, and is derived from the spatial density operator evaluated at different times. Conventionally, this is measured by first exciting the system at a specific wavevector and frequency, then measuring the response. Here, we describe an alternative approach using a pair of time-separated weak measurements, and analytically show that their cross-correlation function directly recovers the dynamical structure factor. We provide numerical confirmation of this technique with a matrix product states simulation of the one-dimensional Bose-Hubbard model, weakly measured by phase contrast imaging. We explore the limits of the method and demonstrate its applicability to real experiments with limited imaging resolution.
Authors: Rémy Dassonneville, Cyril Elouard, Romain Cazali, Réouven Assouly, Audrey Bienfait, Alexia Auffèves, Benjamin Huard
Recent progress in manipulating individual quantum systems enables the exploration of engines exploiting non-classical resources. One of the most appealing is the energy provided by the inherent backaction of quantum measurements. While a handful of experiments have investigated the inner dynamics of engines fueled by measurement backaction, powering a useful task by such an engine is missing. Here we demonstrate the amplification of microwave signals by an engine fueled by repeated quantum measurements of a superconducting transmon qubit. Using feedback, the engine acts as a quantum Maxwell demon operating without a hot thermal source. Measuring the gain of this amplification constitutes a direct probing of the work output of the engine, in contrast with inferring the work by measuring the qubit state along its evolution. Observing a good agreement between both work estimation methods, our experiment validates the accuracy of the indirect method. We characterize the long-term stability of the engine as well as its robustness to transmon decoherence, loss and drifts. Our experiment exemplifies a practical usage of the energy brought by quantum measurement backaction.
Authors: Nilachal Chakrabarti, Neha Nirbhan, Arpan Bhattacharyya
In this paper, we investigate the dynamics of a non-Hermitian SSH model that arises out of the no-click limit of a monitored SSH model in the Krylov space. We find that the saturation timescale of the complexity associated with the spread of the state in the Krylov subspace increases with the measurement rate, and late time behaviour differs across the $\mathrm{PT}$ symmetry transition point. Furthermore, extending the notion of this complexity for subsystems in Krylov space, we find that the scaling of its late time value with subsystem size shows a discontinuous jump across the $\mathrm{PT}$ transition point, indicating that it can be used as a suitable order parameter for such transition but not for the measurement-induced transition. Finally, we show that a generalized measure in the Krylov subspace, which contains information about the correlation landscape, such as Quantum Fisher information, which also possesses some structural similarity with the complexity functional, can be a promising probe of the measurement-induced phase.
Authors: Bartosz Żbik, Andrzej Odrzywołek
Modeling the internal structure of self-gravitating solid and liquid bodies presents a challenge, as existing approaches are often limited to either overly simplistic constant-density approximations or more complex numerical equations of state. We present a detailed analysis of a tractable and physically motivated model for perfectly elastic, spherically symmetric self-gravitating bodies in hydrostatic equilibrium. The model employs a logarithmic equation of state (logotropic EOS) with a non-zero initial density and constant bulk modulus. Importantly, scaling properties of the model allow all solutions to be derived from a single, universal solution of an ordinary differential equation, resembling the Lane-Emden and Chandrasekhar models. The model provides new insights into stability issues and reveals oscillatory asymptotic behavior in the mass-radius relation, including the existence of both a maximum mass and a maximum radius. We derive useful, simple analytical approximations for key properties, such as central overdensity, moment of inertia, binding energy, and gravitational potential, applicable to small, metallic bodies like asteroids and moons. These new approximations could aid future research, including space mining and the scientific characterization of small Solar System bodies.
Authors: Tomer Eini, N. M. R. Peres, Yarden Mazor, Itai Epstein
Excitons in biased bilayer graphene are electrically tunable optical excitations residing in the mid-infrared (MIR) spectral range, where intrinsic optical transitions are typically scarce. Such a tunable material system with an excitonic response offer a rare platform for exploring light-matter interactions and optical hybridization of quasiparticles residing in the long wavelength spectrum. In this work, we demonstrate that when the bilayer is encapsulated in hexagonal-boron-nitride (hBN)-a material supporting optical phonons and hyperbolic-phonon-polaritons (HPhPs) in the MIR-the excitons can be tuned into resonance with the HPhP modes. We find that the overlap in energy and momentum of the two MIR quasiparticles facilitate the formation of multiple strongly coupled hybridized exciton-HPhP states. Using an electromagnetic transmission line model, we derive the dispersion relations of the hybridized states and show that they are highly affected and can be manipulated by the symmetry of the system, determining the hybridization selection rules. Our results establish a general tunable MIR platform for engineering strongly coupled quasiparticle states in biased graphene systems, opening new directions for studying and controlling light-matter interactions in the long-wavelength regime.
Authors: Michał Papaj, Lingyuan Kong, Stevan Nadj-Perge, Patrick A. Lee
Pair density modulation is a superconducting state, recently observed in exfoliated iron-based superconductor flakes, in which the superconducting gap oscillates strongly with the same periodicity as the underlying crystalline lattice. We propose a microscopic model that explains this modulation through a combination of glide-mirror symmetry breaking and the emergence of nematic superconductivity. The first ingredient results in a sublattice texture on the Fermi surface, which is aligned with the anisotropic superconducting gap of the nematic $s_\pm+d$ state. This gives rise to distinctive gap maxima and minima located on the two inequivalent iron sublattices while still being a zero-momentum pairing state. We discuss how further investigation of such modulations can give insight into the nature of the superconducting pairing, such as the signs of the order parameters and visualization of a phase transition to a mixed two-component state using local probes.
Authors: Yu-Chen Li, Tian-Gang Zhou, Shengyu Zhang, Ze Wu, Liqiang Zhao, Haochuan Yin, Xiaoxue An, Hui Zhai, Pengfei Zhang, Xinhua Peng
The emergence of the arrow of time in quantum many-body systems stems from the inherent tendency of Hamiltonian evolution to scramble quantum information and increase entanglement. While, in principle, one might counteract this temporal directionality by engineering a perfectly inverted Hamiltonian to reverse entanglement growth, such a scenario is fundamentally unstable because even minor imperfections in the backward evolution can be exponentially amplified, a hallmark of quantum many-body chaos. Therefore, successfully reversing quantum many-body dynamics demands a deep understanding of the underlying structure of quantum information scrambling and chaotic dynamics. Here, by using solid-state nuclear magnetic resonance on a macroscopic ensemble of randomly interacting spins, we measure the out-of-time-ordered correlator (OTOC) and validate key predictions of scramblon theory, a universal theoretical framework for information scrambling. Crucially, this theory enables us to isolate and mitigate errors in the OTOC caused by imperfections in the backward evolution. As a result, this protocol uncovers the anticipated exponential behavior of quantum many-body chaos and extracts the quantum Lyapunov exponent in a many-body experimental system for the first time. Our results push the fundamental limits of dynamical reversibility of complex quantum systems, with implications for quantum simulation and metrology.
Authors: Nevill Gonzalez Szwacki
We present a comprehensive first-principles investigation of boron fullerenes and two-dimensional boron sheets, unified under a coordination-based framework. By classifying over a dozen boron nanostructures, including B$_{12}$, B$_{40}$, B$_{65}$, B$_{80}$, and B$_{92}$, according to their local atomic environments (4-, 5-, and 6-fold coordination), we identify clear trends in structural stability, electronic properties, and magnetism. A universal energetic scaling relation $E_c(n) = a/n^b + E_c^{sheet}$ (with $b \approx 1$) captures the convergence of fullerene cohesive energies toward those of 2D boron phases. Notably, we establish one-to-one structural correspondences between select cages and experimentally accessible borophenes: B$_{40}$ mirrors the $\chi_3$-sheet, B$_{65}$ the $\beta_{12}$-sheet, B$_{80}$ the $\alpha$-sheet, and B$_{92}$ the $bt$-sheet. These clusters also exhibit large HOMO-LUMO gaps (e.g., $E_g = 1.78$ eV for B$_{40}$, 1.14 eV for B$_{92}$), contrasting with the metallicity of their 2D counterparts and, in the case of B$_{65}$, spontaneous spin polarization ($M = 3 \, \mu_B$). Our findings provide a predictive strategy for designing boron nanostructures by leveraging coordination fingerprints, and are further validated by the recent experimental synthesis of the B$_{80}$ cage. This work bridges zero- and two-dimensional boron chemistry, offering a roadmap for the future synthesis and application of boron-based materials.
Authors: G. Giavaras
In bilayer graphene the exact energy levels of quantum dots can be derived from the four-component continuum Hamiltonian. Here, we study the quantum dot energy levels with approximate equations and compare them with the exact levels. The starting point of our approach is the four-component continuum model and the quantum dot is defined by a continuous potential well in a uniform magnetic field. Using some simple arguments we demonstrate realistic regimes where approximate quantum dot equations can be derived. Interestingly these approximate equations can be solved semi-analytically, in the same context as a single-component Schrödinger equation. The approximate equations provide valuable insight into the physics with minimal numerical effort compared with the four-component quantum dot model. We show that the approximate quantum dot energy levels agree very well with the exact levels in a broad range of parameters and find realistic regimes where the relative error is vanishingly small.
Authors: Zipu Fan, Jinying Yang, Yuchun Chen, Ning Zhao, Xiao Zhuo, Chang Xu, Dehong Yang, Jun Zhou, Jinluo Cheng, Enke Liu, Dong Sun
The anomalous Nernst effect is the thermoelectric counterpart of the anomalous Hall effect, which can emerge in magnetic materials or topological materials without magnetic field. Such effect is critical to both fundamental topological physics and various application fields, including energy harvesting, spintronics and optoelectronics. In this work, we observe the anomalous photo-Nernst effect, which use light excitation to generate temperature gradients for the thermoelectric response. Our experiments reveal a pronounced edge photocurrent response in magnetic Weyl semimetal Co3Sn2S2 under zero magnetic field, originating from the anomalous photo-Nernst effect. The pronounced photo-Nernst current benefits from the exceptional properties of Co3Sn2S2, including the large thermoelectric coefficient, topologically enhanced anomalous response of Weyl bands and the Shockley-Ramo nature of long-range photocurrent generation. Furthermore, by comparing the nominal anomalous Nernst coefficient under different wavelength excitations, we observe a clear enhancement in the mid-infrared region, originating from the topological contribution from the large Berry curvature of Weyl bands. Our results reveal the interplay among light, magnetism, and topological order in magnetic Weyl semimetals, which not only offers insights for fundamental physics but also advances potential applications in quantum devices.
Authors: Shu-Xiang Qiao, Kai-Yue Jiang, Yu-Lin Han, Na Jiao, Ying-Jie Chen, Hong-Yan Lu, Ping Zhang
MXenes and MBenes, which are two-dimensional (2D) transition metal carbides/nitrides and borides, have been extensively studied for their impressive properties. Recently, we reported a family of transition metal sulfides MSene (M2S) with rich properties [Phys. Rev. B 111, L041404 (2025)], it is worth studying whether selenides with similar structure also have rich properties. In this work, through high-throughput screening, we present a novel family of 2D transition metal selenides, M2Se. In this family, there are fifty-eight candidate materials, of which ten are stable and metallic. Notably, eight exhibit superconductivity, among which four are superconducting topological metals. Besides, eight show charge density wave (CDW) behavior, among which five also exhibit antiferromagnetism. It is revealed that CDW originates from electron-phonon coupling rather than Fermi surface nesting. Moreover, strain can be applied to regulate the competition between CDW and superconductivity. Our findings reveal the rich properties of superconductivity, band topology, CDW, and magnetism in M2Se, providing a new platform for the controllable integration of multifunctional quantum states.
Authors: Mingjie Zhang, Zhenyu Wang, Yifan Jiang, Yaotian Liu, Kenji Watanabe, Takashi Taniguchi, Song Liu, Shiming Lei, Yongqing Li, Yang Xu
The crystallization of charge carriers, dubbed the Wigner crystal, is anticipated at low densities in clean two-dimensional electronic systems (2DES). While there has been extensive investigation across diverse platforms, probing spontaneous charge and spin ordering is hindered by disorder effects and limited interaction energies. Here, we report transport evidence for Wigner crystals with antiferromagnetic exchange interactions in high-quality, hexagonal boron nitride encapsulated monolayer MoTe2, a system that achieves a large interaction parameter (r_s) at proper hole densities. A density-tuned metal-insulator transition (MIT) occurring at 3.1E10^11 cm-2 (corresponding to r_s~32) and pronounced nonlinear charge transport in the insulating regime at low temperatures signify the formation of Wigner crystals. Thermal melting of the crystalline phase is observed below approximately 2 K via temperature-dependent nonlinear transport. Magnetoresistance measurements further reveal a substantial enhancement of spin susceptibility as approaching the MIT. The temperature dependence of spin susceptibility in the Wigner crystal phase closely follows the Curie-Weiss law, with the extracted negative Weiss constant illustrating antiferromagnetic exchange interactions. Furthermore, we have found the system exhibits metallic-like differential resistivity under finite DC bias, possibly indicating the existence of a non-equilibrium coherent state in the depinning of Wigner crystals. Our observations establish monolayer MoTe2 as a promising platform for exploring magnetic and dynamic properties of Wigner crystals.
Authors: Kensei Ushio, Shu Kamiyama, Yuto Hoshi, Ryota Mizuno, Masayuki Ochi, Kazuhiko Kuroki, Hirofumi Sakakibara
We theoretically study ambient pressure superconductivity in thin films of La$_3$Ni$_2$O$_7$. We construct model Hamiltonians adopting the crystal structure theoretically determined by fixing the in-plane lattice constant to those substrates examined in the experiment. We also construct a model based on the experimentally determined lattice structure. To the models obtained, we apply the fluctuation exchange approximation, which takes into account the full momentum and frequency dependencies of the Green function and the pairing interaction. We find that the electronic structure, including the presence/absence of the so-called $\gamma$-pocket (the Fermi surface originating from the top of the $d_{3z^2-r^2}$ bonding band) depends on the crystal structure adopted and/or the presence/absence of $+U$ correction in the band structure calculation. Nonetheless, $s\pm$-wave pairing symmetry remains robust regardless of these details in the band structure. The robustness of the $s\pm$-wave pairing mainly owes to the large sign changing superconducting gap function of the $d_{3z^2-r^2}$ bands around $(k_x,k_y)=(0,0)$ and $(k_x,k_y)=(\pi,\pi)$, which originates from the finite energy spin fluctuations. On the other hand, $T_c$ being halved from that of the pressurized bulk can only be understood by adopting the model with small $|t_\perp|$ derived from the experimentally determined crystal structure, at least within the present FLEX approach, although there may remain some other possibilities beyond this approach for the origin of the reduced $T_c$.
Authors: Yoichi Tanabe, Ngoc Han Tu, Ming-Chun Jiang, Yi Ling Chiew, Mitsutaka Haruta, Kiyohiro Adachi, David Pomaranski, Ryo Ito, Yuya Shimazaki, Daisuke Hashizume, Xiuzhen Yu, Guang-Yu Guo, Ryotaro Arita, Michihisa Yamamoto
Van der Waals heterostructures have been used to tailor atomic layers into various artificial materials through interactions at heterointerfaces. The interplay between the band gap created by the band folding of the interfacial potential and the band inversion driven by enhanced spin-orbit interaction (SOI) through band hybridization enables us to realize a two-dimensional topological insulator (2D-TI). Here we report the realization of graphene 2D-TIs by epitaxial growth of three-dimensional topological insulator (3D-TI) BiSbTeSe$_2$ ultrathin films on graphene. By increasing the BiSbTeSe$_2$ thickness from 2 nm to 9 nm to enhance SOI on graphene, the electronic state is altered from the trivial Kekul${é}$ insulator to the 2D-TI. The nonlocal transport reveals the helical edge conduction which survives up to 200 K at maximum. Our graphene 2D-TI is stable, easy to make electrical contacts, and of high quality. It offers various applications including spin-current conversion and platforms for Majorana fermions in junctions to superconductors.
Authors: Sander Driessen, Ji Zou, Even Thingstad, Jelena Klinovaja, Daniel Loss
We investigate the generation of genuine tripartite entanglement in a triangular spin-qubit system due to spatially correlated noise. In particular, we demonstrate how the formation of a highly entangled dark state -- a W state -- enables robust, long-lived tripartite entanglement. Surprisingly, we find that environmentally induced coherent coupling does not play a crucial role in sustaining this entanglement. This contrasts sharply with the two-qubit case, where the induced coupling significantly influences the entanglement dynamics. Furthermore, we explore two promising approaches to enhance the tripartite entanglement by steering the system towards the dark state: post-selection and coherent driving. Our findings offer a robust method for generating high-fidelity tripartite entangled states with potential applications in quantum computation.
Authors: Gabriel Rein, Marcin Raczkowski, Zhenjiu Wang, Toshihiro Sato, Fakher F. Assaad
Topology plays a cardinal role in explaining phases and quantum phase transitions beyond the Landau-Ginzburg-Wilson paradigm. In this study, we formulate a set of models of Dirac fermions in 2+1 dimensions with SU($N$)$\times$SU(2)$\times$U(1) symmetry that have the potential to host critical points described by field theories with topological terms. For $N=2$ it shows a rich phase diagram containing semimetallic, quantum spin Hall insulating, Kekulé valence bond solid and s-wave superconducting phases and features multiple Landau-Ginzburg-Wilson phase transitions driven by interaction strength. At $N=1$ a deconfined quantum critical point is observed. At $N=2$ one expects the critical theory to correspond to a level 2 Wess-Zumino-Witten theory in 2+1 dimensions. Here the numerical results however show a strong first order transition. Another transition can be governed by a topological $\theta$-term which is rendered irrelevant for even values of $N$ thus leading to Landau-Ginzburg-Wilson behaviour.
Authors: Jixun K. Ding, Emily Z. Zhang, Wen O. Wang, Tessa Cookmeyer, Brian Moritz, Yong Baek Kim, Thomas P. Devereaux
In light of recent experimental data indicating a substantial thermal Hall effect in square lattice antiferromagnetic Mott insulators, we investigate whether a simple Mott insulator can sustain a finite thermal Hall effect. We verify that the answer is "no" if one performs calculations within a spin-only low-energy effective spin model with non-interacting magnons. However, by performing determinant quantum Monte Carlo simulations, we show the single-band $t$-$t'$-$U$ Hubbard model coupled to an orbital magnetic field does support a finite thermal Hall effect when $t' \neq 0$ and $B \neq 0$ in the Mott insulating phase. We argue that the (carrier agnostic) necessary conditions for observing a finite thermal Hall effect are time-reversal and particle-hole symmetry breaking. By considering magnon-magnon scattering using a semi-classical Boltzmann analysis, we illustrate a physical mechanism by which finite transverse thermal conductivity may arise, consistent with our symmetry argument and numerical results. Our results contradict the conventional wisdom that square and triangular lattices with SU(2) symmetry do not support a finite thermal Hall effect and call for a critical re-examination of thermal Hall effect data in insulating magnets, as the magnon contribution should not be excluded a priori.
Authors: Koichi Oyanagi, Hossein Sepehri-Amin, Kenta Takamori, Terumasa Tadano, Takumi Imamura, Ren Nagasawa, Krishnan Mahalingam, Takamasa Hirai, Fuyuki Ando, Yuya Sakuraba, Satoru Kobayashi, Ken-ichi Uchida
This study reports the observation of the large anomalous Nernst effect in polycrystalline ferromagnetic Co$_{2}$MnGa (CMG) slabs prepared by a spark plasma sintering method. By optimizing the sintering conditions, the anomalous Nernst coefficient reaches ~7.5 $\mu$V K$^{-1}$ at room temperature, comparable to the highest value reported in the single-crystalline CMG slabs. Owing to the sizable anomalous Nernst coefficient and reduced thermal conductivity, the dimensionless figure of merit in our optimized CMG slab shows the record-high value of ~8$\times$10$^{-4}$ at room temperature. With the aid of the nano/microstructure characterization and first-principles phonon calculation, this study discusses the dependence of the transport properties on the degree of crystalline ordering and morphology of crystal-domain boundaries in the sintered CMG slabs. The results reveal a potential of polycrystalline topological materials for transverse thermoelectric applications, enabling the construction of large-scale modules.
Authors: Jun-jie Shi, Yao-hui Zhu
Unlike ordinary conductors and semiconductors, which conduct electricity through individual electrons, superconductors usually conduct electricity through pairs of electrons, known as Cooper pairs. Even after 4 decades of intense study, no one knows what holds electrons together in complex high-$T_\mathrm{c}$ cuprates and nickelates. Here, targeting the critical challenge of the pairing mechanism behind high-$T_\mathrm{c}$ superconductivity in oxides, we create a new theoretical framework by standing on the foundation of the chemical-bond$\rightarrow$structure$\rightarrow$property relationship. Considering the dominance of eV-scale ionic bonding, affinity of O$^-$ (1.46 eV) and O$^{2-}$ (-8.08 eV) and large second ionization energy ($\sim$10-20 eV) of metal atoms, we propose a groundbreaking idea of electron e$^-$ (hole h$^+$) pairing bridged by oxygen O (metal M) atoms, i.e., the ionic-bond-driven e$^-$-O-e$^-$ (h$^+$-M-h$^+$) itinerant Cooper pairing, by following the principle of "tracing electron footprints to explore pairing mechanisms". Its correctness and universality are confirmed by 32 diverse experimental evidences, especially, the STM topographic image combining with small Cooper-pair size. Any other sub-eV and covalent-binding pairing mechanisms would be doubtful. Our findings resolve a 40-year puzzle of the microscopic mechanism for high-$T_\mathrm{c}$ superconductivity and validate the feasibility of room-temperature carrier-pairing in ionic-bonded superconductors, bringing the dream of room-temperature superconductivity one step closer.
Authors: Raffaele Salioni, Rocco Martinazzo, Davide Emilio Galli, Christian Apostoli
We introduce an extension of the time-dependent variational Monte Carlo (tVMC) method that adaptively controls the expressivity of the variational quantum state during the simulation. This adaptive tVMC approach addresses numerical instabilities that arise when the variational ansatz is overparameterized or contains redundant degrees of freedom. Building on the concept of the local-in-time error (LITE), a measure of the deviation between variational and exact evolution, we introduce a procedure to quantify each parameter's contribution to reducing the LITE, using only quantities already computed in standard tVMC simulations. These relevance estimates guide the selective evolution of only the most significant parameters at each time step, while maintaining a prescribed level of accuracy. We benchmark the algorithm on quantum quenches in the one-dimensional transverse-field Ising model using both spin-Jastrow and restricted Boltzmann machine wave functions, with an emphasis on overparameterized regimes. The adaptive scheme significantly improves numerical stability and reduces the need for strong regularization, enabling reliable simulations with highly expressive variational ansätze.
Authors: A.F. Juarez Saborio, F. Bourquard, R. Galafassi, A. Claudel, L. Marty, A. Piednoir, M. Mercury, R. Fulcrand, C. Albin, V. Barnier, F. Garrelie, A. San-Miguel, F. Vialla
The unique atomic monolayer structure of graphene gives rise to a broad range of remarkable mechanical folding properties. However, significant challenges remain in effectively harnessing them in a controllable and scalable manner. In this study, we introduce an innovative approach that employs micron-scale cavities, fabricated through ultrafast laser patterning, in a stretchable polymer substrate to locally modulate adhesion and strain transfer to a graphene monolayer. This technique enables the deterministic induction of single folds in graphene with fold dimensions, width and height in the hundreds of nanometers, tunable through the geometry of the polymer cavities and the applied strain. Importantly, these folds are reversible, returning to a flat morphology with minimal structural damage, as confirmed by Raman spectroscopy. Additionally, our method allows for the creation of fields of folds with reproducible periodicity, defining clear potential for practical applications. These findings pave the way for the development of advanced devices that would leverage the strain and morphology-sensitive properties of graphene.
Authors: Qiang Gao, Zhaoyu Han, Eslam Khalaf
The superfluid stiffness fundamentally constrains the transition temperature of superconductors, especially in the strongly coupled regime. However, accurately determining this inherently quantum many-body property in microscopic models remains a significant challenge. In this work, we show how the \textit{quantum many-body bootstrap} framework, specifically the reduced density matrix (RDM) bootstrap, can be leveraged to obtain rigorous lower bounds on the superfluid stiffness in frustration free models with superconducting ground state. We numerically apply the method to a special class of frustration free models, which are known as quantum geometric nesting models, for flat-band superconductivity, where we uncover a general relation between the stiffness and the pair mass. Going beyond the familiar Hubbard case within this class, we find how additional interactions, notably simple intra-unit-cell magnetic couplings, can enhance the superfluid stiffness. Furthermore, the RDM bootstrap unexpectedly reveals that the trion-type correlations are essential for bounding the stiffness, offering new insights on the structure of these models. Straight-forward generalization of the method can lead to bounds on susceptibilities complementary to variational approaches. Our findings underscore the immense potential of the quantum many-body bootstrap as a powerful tool to derive rigorous bounds on physical quantities beyond energy.
Authors: Ziren Xie, Amir Mirzanejad, Lukas Muechler
We integrate concepts from topological band theory and strong-correlation physics with the principle of orbital symmetry conservation, which characterizes reactions as symmetry allowed or forbidden based on whether molecular orbitals cross along the reaction coordinate. Using a $4\pi$ electrocyclization as an example, we show how Green's functions generalize the concepts of symmetry allowed and symmetry forbidden reactions even in the presence of strong multi-reference correlations. We demonstrate how symmetry forbidden reactions are characterized by strong multi-reference correlations, resulting in crossings of Green's function zeros rather than poles as MO-theory would predict. Taking into account Green's functions zeros, a topological invariant is introduced that captures symmetry protected crossings of poles or zeros. We discuss the effects of symmetry breaking and outline generalizations of our approach to reactions without any conserved spatial symmetries along the reaction path. Our work lays the groundwork for systematic application of modern topological methods to chemical reactions and can be generalized to reactions involving different spin states or to excited states.
Authors: Zhiqiang Wang, Ke Wang, K. Levin
There should be no question that magnetism and superconductivity appear in close proximity in many if not most of the unconventional superconductors. These two phases are importantly correlated: the strongest manifestations of this superconducting pairing are generally associated with the weakest magnetism. It is often stated that this behavior results from a quantum critical point (QCP), although not all such superconductors fit into this category. In this paper we consider a second scenario for addressing these proximity phenomena in which no QCP is present. Although there are other examples for this latter category, most notable are those associated with very strongly paired superconductors that have insulating and magnetically ordered ``parent" materials. Here, too, one finds that ``failed" long range order is key to establishing superconductivity. This leads to the general question, which is the focus of this paper. Why, and how, in either of these contexts, does this proximal magnetism play a constructive role in helping to stabilize superconductivity? Our understanding here should help pave the way towards the discovery of new families of superconductors, which are expected to emerge on the brink of magnetism.
Authors: Kyohei Nakamura, Youichi Yanase
A supercurrent is well recognized as being of prime importance within mean-field theory, but remains largely unexplored in strongly correlated electron systems (SCES) and the quantum critical region. To clarify the impact of the supercurrent on magnetism and superconductivity near an antiferromagnetic quantum critical point, we study the two-dimensional Hubbard model based on a fluctuation exchange approximation for a current-carrying superconducting state. We show a supercurrent-induced antiferromagnetism and emergence of spin-triplet Cooper pairs. The former results from Bogoliubov Fermi surfaces, suppression in the superconducting gap, and strong correlation effects beyond the mean-field theory. Our results suggest that the supercurrent can bring out rich phenomena of superconductivity in SCES.
Authors: Jorge Martinez Romeral, Luis M.Canonico, Aron W.Cummings, Stephan Roche
We report the possibility to induce topological quantum transport in otherwise trivial systems through non-perturbative light-matter interactions, as well as the enhancement of this effect in the presence of disorder. Going beyond prior theoretical approaches, we introduce a computational framework which performs large-scale real-space quantum dynamics simulations, including carrier thermalization and disorder effects, in systems driven out of equilibrium by light or other external interactions. This methodology is illustrated in gapped single-layer and Bernal bilayer graphene but can be implemented in arbitrarily complex systems, including disordered and aperiodic systems, opening novel avenues for the design of multifunctional topological electronic devices that work in far-from-equilibrium regimes.
Authors: Jiayu Yan, Hongxuan Er, Wei Dang, Jiahuan Ren, Chao Chen, Dianxiang Ren, Fulong Dong
We investigated the attosecond transient absorption spectroscopy (ATAS) in gapped graphene by numerically solving the four-band density-matrix equations. Our results reveal that, in contrast to graphene whose fishbone-shaped spectra primarily oscillates at twice the frequency of the pump laser, the ATAS of gapped graphene exhibits a first-order harmonic component induced by the Berry connection. To gain insight into this interesting results, we employ a simplified model that considers only the nonequivalent electrons at $\Gamma$ and $\textrm{M}$ points in the Brillouin zone. This model allows us to derive an analytical expression for the ATAS contribution stemming from the Berry connection. Our analytical results qualitatively reproduce the key features observed in the numerical simulations, and reveal that the first-order harmonic component of spectra arises ont only from the Berry connections but also from the energy shifts associated with the effective mass of electrons at the $\Gamma$ and $\textrm{M}$ points. These results shed light on the complex generation mechanism of the ATAS in symmetry-broken materials.
Authors: M.V. Sadovskii
We present a brief review of some recent work on the problem of highest achievable temperature of superconducting transition $T_c$ in electron-phonon systems. The discovery of record-breaking values of $T_c$ in quite a number of hydrides under high pressure was an impressive demonstration of capabilities of electron-phonon mechanism of Cooper pairing. This lead to an increased interest on possible limitations of Eliashberg-McMillan theory as the main theory of superconductivity in a system of electrons and phonons. We shall consider some basic conclusions following from this theory and present some remarks on the limit of very strong electron-phonon coupling. We shall discuss possible limitations on the value of the coupling constant related to possible lattice and specific heat instability and conclude that within the stable metallic phase the effective pairing constant may acquire very large values. Finally we discuss some bounds for $T_c$ derived in the strong coupling limit and propose an elementary estimate of an upper limit for $T_c$, expressed via combination of fundamental physical constants.
Authors: David Antognini Silva, Yu Wang, Nicolae Atodiresei, Felix Friedrich, Stefan Blügel, Matthias Bode, Philipp Rüßmann, Artem Odobesko
Helical spin textures in one-dimensional magnetic chains on superconductors can enable topological superconductivity and host Majorana zero modes, independent of the presence of intrinsic spin-orbit coupling. Here, we show that gadolinium (Gd) adatoms, possessing large 4f magnetic moments when placed on a Nb(110) surface, establish indirect exchange interactions mediated by valence electrons, manifesting as Yu-Shiba-Rusinov states. By combining scanning tunneling microscopy and spectroscopy with density functional theory, we analyze the emergence of the Yu-Shiba-Rusinov states in single Gd atoms and Gd dimers and uncover the underlying magnetic interaction mechanisms, on the basis of which we predict by means of spin-dynamics simulations the formation of stable chiral Néel-type spin-spiral configurations in Gd chains. These findings highlight rare-earth magnets as a promising platform for precisely tuning spin-spiral ground states, an essential prerequisite for the realization of topological superconductivity.
Authors: Ashutosh Singh, Maria Sebastian, Mikhail Tokman, Alexey Belyanin
We show that chiral edge states in graphene under Quantum Hall effect conditions can be selectively probed and excited by terahertz or infrared radiation with single-quasiparticle sensitivity without affecting bulk states. Moreover, valley-selective excitation of edge states is possible with high fidelity. The underlying physical mechanism is the inevitable violation of adiabaticity and inversion symmetry breaking for electron states near the edge. This leads to the formation of Landau level-specific and valley-specific absorbance spectral peaks that are spectrally well separated from each other and from absorption by the bulk states, and have different polarization selection rules. Furthermore, inversion symmetry breaking enables coherent driving of chiral edge photocurrents due to second-order nonlinear optical rectification which becomes allowed in the electric dipole approximation.
Authors: J. F. de Oliveira Neto, F. M. A. Guimarães, Davi S. Dantas, F. M. Peeters, M. V. Milošević, A. Chaves
Within the Gross-Pitaevskii framework, we reveal the emergence of a crystallized phase of an exciton condensate in an atomically-thin anisotropic semiconductor, where screening of exciton-exciton interactions is introduced by a proximal doped graphene layer. While such screened interactions are expected to yield a hexagonal crystal lattice in the excitonic condensate in isotropic semiconductor quantum wells [see e.g. Phys. Rev. Lett. \textbf{108}, 060401 (2012)], here we show that for atomically thin semiconductors with strong electronic anisotropy, such as few-layer black phosphorus, the crystallized exciton phase acquires a parallel stripe structure - unanticipated to date. The optimal conditions for the emergence of this phase, as well as for its coexistence with excitonic superfluidity in a striped supersolid phase, are identified.
Authors: Michiya Chazono, Youichi Yanase
Finite-momentum superconductivity has become an important research topic in condensed matter physics. In particular, the orbital Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, which is stabi lized in atomically thin films by the orbital effect of an external magnetic field, has been getting attention as a fascinating finite-momentum superconducting state recently. We study the phase diagram of the trilayer Ising superconductor NbSe$_2$ in the in-plane magnetic field, taking into ac count the orbital effect, the paramagnetic effect, and the spin-orbit coupling. The finite-momentum gap structure in the high-field region is shown by a large-scale numerical calculation based on the Bogoliubov-de Gennes equation. We find an exotic superconducting phase, a layer-selective FFLO phase, in which finite-momentum Cooper pairs coexist with zero-momentum Cooper pairs, separated from the orbital FFLO phase.
Authors: Michèle Jakob, Katharina Laubscher, Patrick Del Vecchio, Anasua Chatterjee, Valla Fatemi, Stefano Bosco
Spin qubits in semiconducting quantum dots are currently limited by slow readout processes, which are orders of magnitude slower than gate operations. In contrast, Andreev spin qubits benefit from fast measurement schemes enabled by the large resonator couplings of superconducting qubits but suffer from reduced coherence during qubit operations. Here, we propose fast and high-fidelity measurement protocols based on an electrically-tunable coupling between quantum dot and Andreev spin qubits. In realistic devices, this coupling can be made sufficiently strong to enable high-fidelity readout well below microseconds, potentially enabling mid-circuit measurements. Crucially, the electrical tunability of our coupler permits to switch it off during idle periods, minimizing crosstalk and measurement back-action. Our approach is fully compatible with germanium-based devices and paves the way for scalable quantum computing architectures by leveraging the advantages of heterogeneous qubit implementations.
Authors: Joseph Gibson, Victor Drouin-Touchette, Stefanos Kourtis
We propose a quantum algorithm for approximately counting the number of solutions to planar 2-satisfiability (2SAT) formulas natively on neutral atom quantum computers. Our algorithm maps Boolean variables to atomic registers arranged in space according to a given formula, so that 2SAT constraints are enforced via the Rydberg blockade between neighboring atoms. A quench under Rydberg dynamics of an initial computational basis state produces a superposition of all solutions after a sufficiently long evolution. For almost uniform superpositions, a polynomial number of measurements is enough to estimate the solution count up to any constant multiplicative factor via sampling based counting. We demonstrate numerically that this protocol leads to almost uniform solution sampling in 1D and 2D grids and that it produces accurate counts for 2SAT instances on punctured grids, suggesting its general applicability as a heuristic for #P-complete problems.
Authors: Parameshwar R. Pasnoori, Patrick Azaria
We solve the one dimensional massive Thirring model or equivalently the sine-Gordon model in the repulsive regime with general Dirichlet boundary conditions, which are characterized by two boundary fields $\phi_{L,R}$ associated with the left and right boundaries respectively. In the presence of these boundary fields, which explicitly break the charge conjugation symmetry, the system exhibits a duality symmetry which changes the sign of the mass parameter $m_0$ and shifts the values of the boundary fields by $\phi_{L,R}\rightarrow \phi_{L,R}+\pi$. When the mass parameter $m_0<0$ and the boundary fields $\phi_{L,R}=0$, or equivalently due to duality symmetry, when the mass parameter $m_0>0$ and the boundary fields $\phi_{L,R}=\pi$, the system is at a trivial point. Here, the ground state is unique just as in the case of periodic boundary conditions. In contrast, when the mass parameter $m_0<0$ and the boundary fields $\phi_{L,R}=\pi$, and equivalently due to the duality symmetry, when the mass parameter $m_0>0$ and the boundary fields $\phi_{L,R}=0$, the system is at a topological point where it exhibits a symmetry protected topological (SPT) phase, which is characterized by the existence of zero energy bound states at both the boundaries. For a given value of the mass parameter $m_0$, we find that these phases remain stable in the presence of symmetry breaking fields at the boundary, provided they are smaller than certain critical values which depend on the strength of the interactions in the bulk. Hence, we show that the stability of the SPT and trivial phases depends on the interplay of the symmetry breaking boundary field values and the bulk interaction strength.
Authors: Fabian Oppliger, Wonjin Jang, Aldo Tarascio, Franco De Palma, Christian Reichl, Werner Wegscheider, Ville F. Maisi, Dominik Zumbühl, Pasquale Scarlino
High-efficiency single-photon detection in the microwave domain is a key enabling technology for quantum sensing, communication, and information processing. However, the extremely low energy of microwave photons (~{\mu}eV) presents a fundamental challenge, preventing direct photon-to-charge conversion as achieved in optical systems using semiconductors. Semiconductor quantum dot (QD) charge qubits offer a compelling solution due to their highly tunable energy levels in the microwave regime, enabling coherent coupling with single photons. In this work, we demonstrate microwave photon detection with an efficiency approaching 70% in the single-photon regime. We use a hybrid system comprising a double quantum dot (DQD) charge qubit electrostatically defined in a GaAs/AlGaAs heterostructure, coupled to a high-impedance Josephson junction (JJ) array cavity. We systematically optimize the hybrid device architecture to maximize the conversion efficiency, leveraging the strong charge-photon coupling and the tunable DQD tunnel coupling rates. Incoming cavity photons coherently excite the DQD qubit, which in turn generates a measurable electrical current, realizing deterministic photon-to-charge conversion. Moreover, by exploiting the independent tunability of both the DQD transition energy and the cavity resonance frequency, we characterize the system efficiency over a range of 3-5.2 GHz. Our results establish semiconductor-based cavity-QED architectures as a scalable and versatile platform for efficient microwave photon detection, opening new avenues for quantum microwave optics and hybrid quantum information technologies.
Authors: Nam Nguyen, Alex Taekyung Lee, Vijay Singh, Anh T. Ngo, Hyowon Park
La doped SrFeO$_{3}$, La$_{1/3}$Sr$_{2/3}$FeO$_{3}$, exhibits a metal-to-insulator transition accompanied by both antiferromagnetic and charge ordering states along with the Fe-O bond disproportionation below a critical temperature near 200K. Unconventionally slow charge dynamics measured in this material near the critical temperature shows that its excited charge ordering states can exhibit novel electronic structures with nontrivial energy profiles. Here, we reveal possible metastable states of charge ordering structures in La$_{1/3}$Sr$_{2/3}$FeO$_{3}$ using the first-principle and climbing image nudged elastic band methods. In the strong correlation regime, La$_{1/3}$Sr$_{2/3}$FeO$_{3}$ is an antiferromagnetic insulator with a charge ordering state of the big-small-big pattern, consistent with the experimental measurement of this material at the low temperature. As the correlation effect becomes weak, we find at least two possible metastable charge ordering states with the distinct Fe-O bond disproportionation. Remarkably, a ferroelectric metallic state emerges with the small energy barrier of $\sim$7 meV, driven by a metastable CO state of the small-medium-big pattern. The electronic structures of these metastable charge ordering states are noticeably different from those of the ground-state. Our results can provide an insightful explanation to multiple metastable charge ordering states and the slow charge dynamics of this and related oxide materials.
Authors: Antonin Badura, Dominik Kriegner, Eva Schmoranzerová, Karel Výborný, Miina Leiviskä, Rafael Lopes Seeger, Vincent Baltz, Daniel Scheffler, Sebastian Beckert, Ismaila Kounta, Lisa Michez, Libor Šmejkal, Jairo Sinova, Sebastian T. B. Goennenwein, Jakub Železný, Helena Reichlová
The component of the resistivity tensor $\rho_{ij}$ corresponding to voltage transverse to both an applied current and a magnetic field can be separated into odd and even parts with respect to the applied magnetic field. The former contains information, for example, about the ordinary or anomalous Hall effect. The latter is often ascribed to experimental artefacts and ignored. Here, we show that upon suppressing these artefacts in carefully controlled experiments, useful information remains. We first investigate the well-explored ferromagnet CoFeB, where the even part of $\rho_{yx}$ contains a contribution from the anisotropic magnetoresistance, which we confirm by Stoner--Wohlfarth modelling. We then apply our approach to magnetotransport measurements of $\rm Mn_5Si_3$ thin films, which undergo a transition from non-collinear to an altermagnetic collinear state. In this material, the even part of the transverse signal is sizable only in the low-spin-symmetry phase below $\approx 80$~K. Transverse resistivity measurements thus offer a simple and readily available probe of magnetic order transitions.
Authors: Fabio Salvati, Mikhail I. Katsnelson, Andrey A. Bagrov
Eigenstate multifractality, a hallmark of non-interacting disordered metals which can potentially be observed in many-body localized states as well, is characterized by anomalous slow dynamics and appears relevant for many areas of quantum physics from measurement-driven systems to superconductivity. We propose a novel approach to achieve non-ergodic multifractal (NEM) states without disorder by iteratively introducing defects into a crystal lattice, reshaping it from a plain structure into fractal geometry. By comprehensive analysis of the Sierpiński gasket case, we find a robust evidence of the emergence of NEM states that go beyond the conventional classification of quantum states and designate new pathways for quantum transport studies. We discuss potential experimental signatures of these states.
Authors: Yung-Yeh Chang, Kazuma Saito, Chen-Hsuan Hsu
Twisted bilayer graphene exhibits prominent correlated phenomena in two distinct regimes: a Kondo lattice near the magic angle, resembling heavy fermion systems, and a triangular correlated domain wall network under interlayer bias, akin to sliding Luttinger liquids previously introduced for cuprates. Combining these characteristics, here we investigate a system where interacting electrons in the domain wall network couple to localized spins. Owing to inter-domain-wall correlations, a two-dimensional spin helix phase emerges as a result of spatial phase coherence across parallel domain walls. Within the spin helix phase, magnons can induce a singularity, reflected in the scaling exponents of various correlation functions, accessible through electrical means. We predict observable features in magnetic resonance and anisotropic paramagnetic spin susceptibility for the spin helix and the magnon-induced singularity, serving as experimental indicators of the interplay between the Kondo lattice and sliding Luttinger liquids. Integrating critical aspects of Luttinger liquid physics, magnetism, and Kondo physics in twisted bilayer graphene, our findings offer insights into similar correlated phenomena across a broad range of twisted van der Waals structures.
Authors: Saeed S. I. Almishal, Pat Kezer, Yasuyuki Iwabuchi, Jacob T. Sivak, Sai Venkata Gayathri Ayyagari, Saugata Sarker, Matthew Furst, Gerald Bejger, Billy Yang, Simon Gelin, Nasim Alem, Ismaila Dabo, Christina M. Rost, Susan B. Sinnott, Vincent Crespi, Venkatraman Gopalan, Roman Engel-Herbert, John T. Heron, Jon-Paul Maria
This manuscript presents a working model linking chemical disorder and transport properties in correlated-electron perovskites with high-entropy formulations and a framework to actively design them. We demonstrate this new learning in epitaxial Sr$x$(Ti,Cr,Nb,Mo,W)O$3$ thin films that exhibit exceptional crystalline fidelity despite a diverse chemical formulation where most B-site species are highly misfit with respect to valence and radius. X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy confirm a unique combination of chemical disorder and structural perfection in thick epitaxial layers. This combination produces significant electron correlation, low electrical resistivity, and an optical transparency window that surpasses that of constituent end-members, with a flattened frequency- and temperature-dependent response. We address the computational challenges of modeling such systems and investigate short-range ordering using cluster expansion. These results showcase that unusual d-metal combinations access an expanded property design space that is predictable using end-member characteristics -- though unavailable to them -- thus offering performance advances in optical, spintronic, and quantum devices.
Authors: Nidhin George Mathews, Aloshious Lambai, Marcus Hans, Jochen M. Schneider, Gaurav Mohanty, Balila Nagamani Jaya
Magnetron sputtered titanium nitride (TiN) thin films are widely used as protective coatings due to their high hardness, but suffer from inherent brittleness and low fracture toughness, limiting their applicability. The multilayering of TiN films with metallic titanium (Ti) interlayers in the form of bi-layer and tri-layer systems have been studied using microcantilever fracture tests. Plastic dissipation in the Ti layer is shown to lead to an increase in crack growth resistance. The effect of the elastic-plastic mismatch between the two materials on the crack driving force, as well as the size of the fully developed plastic zone in Ti have been quantified in this work for the first time. It is shown that incorporating a Ti layer thickness of 250 nm can improve the fracture resistance by nearly ten times compared to the initiation fracture toughness in TiN, preventing catastrophic fracture of these multi-layered films. These results will aid in physics informed design of optimised thickness of metallic interlayers in multi-layered thin films.
Authors: Connor Heimig, Alexander A. Antonov, Dmytro Gryb, Thomas Possmayer, Thomas Weber, Michael Hirler, Jonas Biechteler, Luca Sortino, Leonardo de S. Menezes, Stefan A. Maier, Maxim V. Gorkunov, Yuri Kivshar, Andreas Tittl
In the strong-coupling regime, the interaction between light and matter reaches a hybridization state where the photonic and material components are inseparably linked. Using tailored states of light to break symmetries in such systems can facilitate the development of novel non-equilibrium quantum materials. Chiral optical cavities offer a promising approach for this, enabling either temporal or spatial symmetry-breaking, both of which are unachievable with conventional mirror cavities. For spatial symmetry-breaking, a cavity must discriminate the handedness of circularly polarized light, a functionality uniquely provided by chiral metamaterials. Here, we propose and demonstrate experimentally a chiral transition metal dichalcogenide (TMDC) metasurface with broken out-of-plane symmetry, allowing for the selective formation of self-hybridized exciton-polaritons with specific handedness. Our metasurface maintains maximal chirality for oblique incidence up to 20°, significantly outperforming all previously known designs, thereby transforming the angle of incidence from a constraint into a new degree of freedom for sub-nanometer-precise tuning of the cavity's resonant wavelength. Moreover, we study the chiral strong-coupling regime in nonlinear experiments and reveal the polariton-driven nature of chiral third-harmonic generation. Our results demonstrate a clear pathway towards van der Waals (vdW) metasurfaces as a novel and potent platform for chiral polaritonics with implications in a wide range of photonics research, such as non-reciprocal photonic devices and valleytronics.
Authors: Tingyu Zhang, Hiroyuki Tajima, Motoi Tachibana
We theoretically discuss quantum tunneling transport and frictions at a hadron-quark matter interface based on the Schwinger-Keldysh approach combined with the tunneling Hamiltonian, which has been developed in the context of condensed matter physics. In the inner core of massive neutron stars, it is expected that cold quark matter appears at sufficiently high densities and hence exhibits color superconductivity, surrounded by nucleon superfluids at lower densities. The perturbative expressions of the tunneling current and the friction at the interface are obtained in terms of the non-equilibrium Green's functions. We demonstrate the DC Josephson current that occurs at the hadron-quark superfluid interface in the present scheme. Our framework can be applied to various conflagrations involving the interfaces relevant to astrophysical phenomena.
Authors: Yannis Ulrich, Johannes Mitscherling, Laura Classen, Andreas P. Schnyder
We analyze the quantum geometric contribution to the intrinsic second-order nonlinear Hall effect (NLHE) for a general multiband Hamiltonian. The nonlinear conductivity, obtained in Green's function formalism, is decomposed into its quantum geometric constituents using a projector-based approach. In addition to the previously identified Berry curvature and interband quantum metric dipoles, we obtain a third term of quantum geometric origin, given by the momentum derivative of the $intraband$ quantum metric. This contribution, which we term the intraband quantum metric dipole, provides substantial corrections to the NLHE in topological magnets and becomes the dominant geometric term in topological antiferromagnets with gapped Dirac cones. Considering generalized 2D and 3D Weyl/Dirac Hamiltonians, describing a large class of topological band crossings with sizable quantum geometry, we derive analytical expressions of the NLHE, thereby revealing the individual contributions of the three quantum geometric terms. Combined with an exhaustive symmetry classification of all magnetic space groups, this analysis leads to the identification of several candidate materials expected to exhibit large intrinsic NLHE, including the antiferromagnets $\text{Yb}_3\text{Pt}_4$, $\text{CuMnAs}$, and $\text{CoNb}_3\text{S}_6$, as well as the nodal-plane material $\text{MnNb}_3\text{S}_6$. Finally, our projector-based approach yields a compact expression for the NLHE in terms of momentum derivatives of the Bloch Hamiltonian matrix alone, enabling efficient numerical evaluation of each contribution in the aforementioned materials.
Authors: Sayak Bhattacharjee, Soumya Sur, Adhip Agarwala
We introduce two classes of junctions in a toric code, a prototypical model of a $\mathbb{Z}_2$ quantum spin liquid, and study the nature of anyonic transport across them mediated by Zeeman fields. In the first class of junctions, termed potential barrier junctions, the charges sense effective static potentials and a change in the band mass. In a particular realization, while the junction is completely transparent to the electric charge, magnetic charge transmission is allowed only after a critical field strength. In the second class of junctions we stitch two toric codes with operators which do not commute at the junction. We show that the anyonic transmission gets tuned by effective pseudospin fluctuations at the junction. Using exact analytical mappings and numerical simulations, we compute charge-specific transmission probabilities. Our work, apart from uncovering the rich physical mechanisms at play in such junctions, can motivate experimental work to engineer defect structures in topologically ordered systems for tunable transport of anyonic particles.
Authors: Zeliang Sun, Gaihua Ye, Xiaohan Wan, Ning Mao, Cynthia Nnokwe, Senlei Li, Nishkarsh Agarwal, Siddhartha Sarkar, Zixin Zhai, Bing Lv, Robert Hovden, Chunhui Rita Du, Yang Zhang, Kai Sun, Rui He, Liuyan Zhao
Symmetry plays a central role in defining magnetic phases, making tunable symmetry breaking across magnetic transitions highly desirable for discovering non-trivial magnetism. Magnetic moiré superlattices, formed by twisting two-dimensional (2D) magnetic crystals, have been theoretically proposed and experimentally explored as platforms for unconventional magnetic states. However, despite recent advances, tuning symmetry breaking in moiré magnetism remains limited, as twisted 2D magnets, such as rhombohedral (R)-stacked twisted CrI_3, largely inherit the magnetic properties and symmetries of their constituent layers. Here, in hexagonal-stacked twisted double bilayer (H-tDB) CrI_3, we demonstrate clear symmetry evolution as the twist angle increases from 180^{\circ} to 190^{\circ}. While the net magnetization remains zero across this twist angle range, the magnetic phase breaks only the three-fold rotational symmetry at 180^{\circ}, but it breaks all of the rotational, mirror, and time-reversal symmetries at intermediate twist angles between 181^{\circ} and 185^{\circ}, and all broken symmetries are recovered at 190^{\circ}. These pronounced symmetry breakings at intermediate twist angles are accompanied by metamagnetic behaviors, evidenced by symmetric double hysteresis loops around zero magnetic field. Together, these results reveal that H-tDB CrI_3 at intermediate twist angles host a distinct moiré magnetic phase, featuring periodic in-plane spin textures with broken rotational, mirror, and time-reversal symmetries, which is markedly different from the out-of-plane layered antiferromagnetism in bilayer CrI_3 and the predominantly out-of-plane moiré magnetism in R-tDB CrI_3. Our work establishes H-stacked CrI_3 moiré magnets as a versatile platform for engineering magnetic properties, including and likely beyond complex spin textures.
Authors: Vitor Dantas, Héctor Ochoa, Rafael M. Fernandes, Natalia B. Perkins
We develop a theoretical framework for probing moiré phonon modes using Raman spectroscopy, and illustrate it with the example of twisted bilayer graphene (TBG). These moiré phonons arise from interlayer sliding motion in twisted 2D materials and correspond to fluctuations of the stacking order in reconstructed moiré superlattices. These include both acoustic-like phason modes and a new set of low-energy optical modes originating from the zone-folding of monolayer graphene's acoustic modes, which are accessible via Raman spectroscopy. We show that the Raman response of TBG exhibits a series of low-frequency peaks that clearly distinguish it from that of decoupled layers. We further examine the role of anharmonic interactions in shaping the phonon linewidths and demonstrate the strong dependence of the Raman spectra on both the twist angle and the polarization of the incident light. Our findings establish Raman spectroscopy as a powerful tool for exploring moiré phonons in a broad class of twisted van der Waals systems.
Authors: Harim Jang, Daniel Crawford, Khai Ton That, Lucas Schneider, Jens Wiebe, Makoto Shimizu, Harald O. Jeschke, Stephan Rachel, Roland Wiesendanger
Majorana modes offer great potential for fault-tolerant quantum computation due to their topological protection. However, for superconductor-semiconductor nanowire hybrids, intrinsic disorder makes the unambiguous detection of Majorana modes difficult. Here, we construct 1D spin chains from individual Fe atoms on the Rashba surface alloy BiAg2/Ag(111) with proximity-induced superconductivity from a Nb(110) substrate. While the Fe chains exhibit perfect crystalline order, we observe nano-scale potential disorder of the BiAg2/Ag(111)/Nb(110) heterostructure by scanning tunneling microscopy. However, this does not prevent the emergence of zero-energy modes at both ends of the Fe chains, in agreement with tight-binding calculations showing that they are only found in the topologically non-trivial regime of the phase diagram. These Majorana modes are indeed robust against potential disorder.
Authors: Samuel G. Carter, Infiter Tathfif, Charity Burgess, Brenda VanMil, Suryakanti Debata, Pratibha Dev
The silicon vacancy ($V_{Si}$) in 4H-SiC at its cubic site (V2-center) has shown significant promise for quantum technologies, due to coherent spin states, the mature material system, and stable optical emission. In these SiC-based applications, doping plays a crucial role. It can be used to control the charge state of $V_{Si}$ and formation of different types of defects. Despite its importance, there has been little research on the effects of doping. In this work, we perform a study of the effects of nitrogen doping and annealing on the photoluminescence (PL), optically-detected magnetic resonance (ODMR) contrast, and dephasing times of ensembles of V2 in epilayers of 4H-SiC. The results show an enhancement of PL that depends on the electron irradiation dose for a given electron concentration, supported by theoretical modeling of the charge state of $V_{Si}$ in the presence of nitrogen. Nitrogen substituted for carbon is shown to very efficiently donate one electron to $V_{Si}$. We also observe that the ODMR contrast can be increased from 0.5% in low doped SiC to 1.5% by nitrogen doping of $10^{17}$ to $10^{18}$ cm$^{-3}$ and annealing at 500-600 $^{\circ}$C for 1 hour, with only a 20% decrease in PL compared to unannealed. Some of the improvement in contrast is offset by a reduction in $T_2^*$ at these doping levels, but the estimated cw ODMR shot-noise limited sensitivity is still 1.6 times higher than that of undoped, unannealed SiC.
Authors: Antu Laha, Juntao Yao, Asish K. Kundu, Niraj Aryal, Anil Rajapitamahuni, Elio Vescovo, Fernando Camino, Kim Kisslinger, Lihua Zhang, Dmytro Nykypanchuk, J. Sears, J. M. Tranquada, Weiguo Yin, Qiang Li
Crystal engineering is a method for discovering new quantum materials and phases, which may be achieved by external pressure or strain. Chemical pressure is unique in that it generates internal pressure perpetually to the lattice. As an example, GdAlSi from the rare-earth ($R$) $R$Al$X$ ($X =$ Si or Ge) family of Weyl semimetals is considered. Replacing Si with the larger isovalent element Ge creates sufficiently large chemical pressure to induce a structural transition from the tetragonal structure of GdAlSi, compatible with a Weyl semimetallic state, to an orthorhombic phase in GdAlGe, resulting in an inversion-symmetry-protected nodal-line metal. We find that GdAlGe hosts an antiferromagnetic ground state with two successive orderings, at $T_\mathrm{N1}$ = 35 K and $T_\mathrm{N2}$ = 30 K. In-plane isothermal magnetization shows a magnetic field induced metamagnetic transition at 6.2 T for 2 K. Furthermore, electron-hole compensation gives rise to a large magnetoresistance of $\sim 100\%$ at 2 K and 14 T. Angle-resolved photoemission spectroscopy measurements and density functional theory calculations reveal a Dirac-like linear band dispersion over an exceptionally large energy range of $\sim$ 1.5 eV with a high Fermi velocity of $\sim 10^6$ m/s, a rare feature not observed in any magnetic topological materials.
Authors: Chang Jiang, Fan Yang, Jinshan Yang, Peng Yu, Huiying Liu, Yuda Zhang, Zehao Jia, Xiangyu Cao, Jingyi Yan, Zheng Liu, Xian-Lei Sheng, Cong Xiao, Shengyuan A. Yang, Shaoming Dong, Faxian Xiu
Intrinsic responses are of paramount importance in physics research, as they represent the inherent properties of materials, independent of extrinsic factors that vary from sample to sample, and often reveal the intriguing quantum geometry of the band structure. Here, we report the experimental discovery of a new intrinsic response in charge transport, specifically the intrinsic nonlinear planar Hall effect (NPHE), in the topological semimetal TaIrTe4. This effect is characterized by an induced Hall current that is quadratic in the driving electric field and linear in the in-plane magnetic field. The response coefficient is determined by the susceptibility tensor of Berry-connection polarizability dipole, which is an intrinsic band geometric quantity. Remarkably, the signal persists up to room temperature. Our theoretical calculations show excellent agreement with the experimental results and further elucidate the significance of a previously unknown orbital mechanism in intrinsic NPHE. This finding not only establishes a novel intrinsic material property but also opens a new route toward innovative nonlinear devices capable of operating at room temperature.
Authors: Matanat A. Mehrabova, Elshad Allahyarov, Niyazi H. Hasanov, Nurana R. Gasimova
The purpose of this work was to calculate the electronic band structure of Cd$_{1-x}$Fe$_x$Se. Ab-initio, calculations are performed in the Atomistix Toolkit program within the Density Functional Theory and Local Spin Density Approximation on Tight Tiger basis. We have used Hubbard U potential $U_{Fe} = 2.42$eV for 3d states for Fe ions. Super-cells of 8 and 64 atoms were constructed. After the construction of Cd$_{1-x}$Fe$_x$Se ($x=$ 6.25%; 25%) super-cells, atom relaxation and optimization of the crystal structure were carried out. Electronic band structure,and density of states were calculated, and total energy have been defined in antiferromagnetic and ferromagnetic phases. The band gap for the Cd$_{1-x}$Fe$_x$Se, $x=0.06$ in ferromagnetic phase is equal to $E_g=1.77$ eV, in antiferromagnetic phase $E_g=1.78$ eV. For $x=0.25$, $E_g=1.92$ eV. Antiferromagnetic phase considered more stable. Our calculations show that the band gap increases with the increases in Fe ion concentration.
Authors: Tomasz Kwapiński, Marek Dachniewicz, Marcin Kurzyna, Mieczysław Jałochowski
We analyze both the stationary and time-dependent properties of molecular states in atomic chains on a surface, some of which are composed of atomic states decoupled from the substrate - a phenomenon analogous to dark states in quantum dot systems. To illustrate this effect at the atomic scale, we performed scanning tunneling microscopy (STM) experiments on short silicon chains fabricated on a Si(553)-Au surface. In contrast to quantum dots, which typically involve characteristic energies in the meV range or lower, the atomic chains studied here operate in a high-energy regime, with energies in the eV range. Furthermore, we demonstrate that the local density of states of the chains carries clear signatures of these decoupled states, which significantly affect STM imaging. The topography becomes highly sensitive to the bias polarity, to the extent that some atomic sites may appear nearly invisible to the STM tip. Our time-resolved theoretical analysis reveals that these decoupled states emerge over a finite time interval. This oscillatory dynamical evolution, primarily driven by nearest-neighbor interactions, suggests a universal relaxation mechanism that is largely insensitive to the length of the atomic chain.
Authors: Kaveh Edalati, Alexy Bertrand, Payam Edalati, Thanh Tam Nguyen, Nariman Enikeev, Masaki Mito
High-entropy alloys (HEAs) have emerged as favorable choices for different applications, including superconductors. The present work examines the impact of nanostructuring via high-pressure torsion (HPT) on the superconducting properties of the equiatomic TiZrHfNbTa HEA. Structural characterization reveals a progressive refinement of grain size and increased dislocation density, together with partial phase transformation to an {\omega} phase with HPT processing. Magnetic susceptibility and magnetization measurements indicate a systematic enhancement in the superconducting transition temperature (from $T_c =$ 6.2 K to 7.2 K) and critical magnetic field, as well as the stabilization of the superconductivity state by HPT processing. The improvement of superconducting properties is attributed to microstructural modifications such as grain boundary density, defect generation and phase transformations, and their impact on vortex pinning, quantum confinement and electron scattering. The results suggest that nanostructuring through severe plastic deformation provides an appropriate route to optimize superconducting properties in high-entropy superconductors.
Authors: Stefano Ragni, Tomislav Miškić, Thomas Hahn, Nikolay Prokof'ev, Osor S. Barišić, Naoto Nagaosa, Cesare Franchini, Andrey S. Mishchenko
We develop an exact computational method based on numerical X-propagators for solving polaron models with arbitrary nonlinear couplings of local vibration modes to the electron density and magnitude of the hopping amplitude. Our approach covers various polaron models, some of which were impossible to treat by any existing approximation-free techniques. Moreover, it remains efficient in the most relevant but computationally challenging regime of phonon frequencies much smaller than the electron bandwidth. As a case study, we consider the double-well type nonlinear model with quadratic ($g_2<0$) and quartic ($g_4>0$) interactions describing a broad class of technologically important materials, such as quantum paraelectric compounds and halide perovskites. We observe, depending on the model parameters, three qualitatively different regimes: (i) quantum interplay of quartic and quadratic interactions which suppresses effects of the quadratic coupling, (ii) intermediate-coupling regime with exponential $\propto \exp(\alpha g_2 \Omega^{-1/4})$ scaling of the quasiparticle weight and mass renormalization, and (iii) strong-coupling asymptotic behavior.
Authors: Yaoyuan Fan, Shuoyu Shi, Lang Cao, Qiuxin Zhang, Dong Hu, Yu Wang, Xiaoji Zhou
Engineering spin polarization in dissipative bosonic systems is crucial for advancing quantum technologies, especially for applications in quantum metrology and space-based quantum simulations. This work demonstrates precise magnetic moment control in multicomponent Bose gases during evaporative cooling via tailored magnetic fields. By adjusting the magnetic field gradients, null point position, and duration, we selectively tune evaporation rates of magnetic sublevels, achieving targeted spin polarization. Theoretical models, validated by numerical simulations and Stern-Gerlach experiments, reveal how magnetic fields reshape trapping potentials and spin-dependent dissipation. The results establish a dissipative spin-selection mechanism governing polarization evolution in evaporatively cooled Bose gases and provide a framework for engineering spin-polarized quantum states.
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: Darshit Solanki, Kenji Watanabe, Takashi Taniguchi, A. K. Sood, Anindya Das
The role of twist angle ($\theta_t$) in tailoring the physical properties of heterostructures is emerging as a new paradigm in two-dimensional materials. The influence of flat electronic bands near the magic angle ($\sim$1.1$^{\circ}$) on the phononic properties of twisted bilayer graphene (t-BLG) is not well understood. In this work, we systematically investigate the G and 2D Raman modes of t-BLG samples with twist angles ranging from $\sim$0.3$^{\circ}$ to $\sim$3$^{\circ}$ using micro-Raman spectroscopy. A key finding of our work is the splitting of the G mode near the magic angle due to moiré potential induced phonon hybridization. The linewidth of the low-frequency component of the G mode (G$^-$), as well as the main component of the 2D mode, exhibits enhanced broadening near the magic angle due to increased electron-phonon coupling, driven by the emergence of flat electronic bands. Additionally, temperature-dependent Raman measurements (6-300 K) of magic-angle twisted bilayer graphene sample ($\theta_t \sim$ 1$^{\circ}$) reveal an almost tenfold increase in phonon anharmonicity-induced temperature variation in both components of the split G mode, as compared to Bernal-stacked bilayer graphene sample, further emphasizing the role of phonon hybridization in this system. These studies could be important for understanding the thermal properties of the twisted bilayer graphene systems.
Authors: S. Gabani, I. Curlik, F. Akbar, M. Giovannini, J.G. Sereni
An increasing number of Yb-based compounds fulfill the conditions for the investigation of hyperfine electro-nuclear coupling effects related to 171-Yb and 173-Yb isotopes. Among them, the lack of magnetic order down to the milikelvin range in compounds with robust localized electronic moments and their nuclear magnetism. Although reminiscences of short range magnetic interactions may be observed below 1K, such perturbation can be dodged investigating compounds located close to a quantum critical point (QCP), where quantum fluctuations prevent the development of magnetic correlations to develop. Within the family of cubic YbCu4M compounds (M = Ni, Au and Zn), we have investigated YbCu4Zn that shows a logarithmic temperature dependence: C_P /T ~ ln(T/TQ) in its electronic specific heat, as predicted for a QCP. Simultaneously, no signs of RKKY interactions are detected down to 0.03K. Due to the low Kondo temperature of its doublet ground state, the localized 4f electrons weakly couple with conduction electrons, allowing the coupling between nuclear and 4f electron moments to become relevant. However, the reminder Kondo interaction acts on the electronic hyperfine field producing a small deviation from the standard nuclear C_N ~ 1/T^2 dependence into a n < 2 power law. The expected n = 2 dependence is progressively recovered under applied magnetic field.
Authors: Guowei Wayne Tu, Evgueni T. Filipov
Basket weaving is a traditional craft used to create practical three-dimensional (3D) structures. While the geometry and aesthetics of baskets have received considerable attention, the underlying mechanics and modern engineering potential remain underexplored. This work shows that 3D woven structures offer similar stiffness yet substantially higher resilience than their non-woven continuous counterparts. We explore corner topologies that serve as building blocks to convert 2D woven sheets into 3D metamaterials that can carry compressive loads. Under small deformations, the woven corners exhibit axial stiffness similar to continuous structures because the woven ribbons are engaged with in-plane loads. Under large deformations, the woven corners can be compressed repeatedly without plastic damage because ribbons can undergo elastic local buckling. We present a modular platform to assemble woven corners into complex spatial metamaterials and demonstrate applications including damage-resilient robotic systems and metasurfaces with tailorable deformation modes. Our results explain the historic appeal of basket weaving, where readily available ribbons are crafted into 3D structures with comparable stiffness yet far superior resilience to continuous systems. The modular assembly of woven metamaterials can further revolutionize design of next-generation automotive components, consumer devices, soft robots, and more where both resilience and stiffness are essential.
Authors: Sheng-Wen Huang, Ramya Suresh, Jian Liao, Botao Du, Zachary Miles, Leonid P. Rokhinson, Yong P. Chen, Ruichao Ma
Superconducting quantum circuits provide a versatile platform for studying quantum materials by leveraging precise microwave control and utilizing the tools of circuit quantum electrodynamics (QED). Hybrid circuit devices incorporating novel quantum materials could also lead to new qubit functionalities, such as gate tunability and noise resilience. Here, we report experimental progress towards a transmon-like qubit made with a superconductor-topological insulator-superconductor (S-TI-S) Josephson junction using exfoliated BiSbTeSe2. We present a design that enables us to systematically characterize the hybrid device, from DC transport of the S-TI-S junction, to RF spectroscopy, to full circuit QED control and measurement of the hybrid qubit. In addition, we utilize a high-quality-factor superconducting cavity to characterize material and fabrication-induced losses, thereby guiding our efforts to improve device quality.
Authors: Shun Sakurai, Nariya Uchida
We investigate the interplay between chemotaxis and alignment interactions in active rod-like particles, such as E. coli and Janus rods. Starting from a discrete model of self-propelled rods with chemotactic responses, we employ a Boltzmann-Ginzburg-Landau (BGL) approach to derive coarse-grained dynamical equations for the density, polar and nematic orientational order parameters, and the concentration field of the chemoattractant. We perform a linear stability analysis for fluctuations around uniform steady states corresponding to isotropic and nematic phases. In both phases, we find that translational chemotactic response promotes instability, while rotational chemotactic response suppresses it, elucidating their contrasting effects on the onset of collective dynamics.
Authors: Shaohui Yi, Zhiyu Liao, Chenhao Liang, Sheng Zhang, Xiutong Deng, Yongjie Xie, Lincong Zheng, Yujie Wang, Yubiao Wu, Zhijun Wang, Youguo Shi, Xianggang Qiu, Bing Xu
We report on the charge dynamics of Ta$_2$Pd$_3$Te$_5$ using temperature-dependent optical spectroscopy with polarized light. We observe a metal-insulator transition characterized by the collapse of Drude response and the emergence of sharp and narrow absorption peaks at low temperatures. Unlike previous excitonic insulator candidates such as TiSe$_2$ and Ta$_2$NiSe$_5$, where the excitonic order is intertwined with charge density wave or structural instabilities, the sharp features in Ta$_2$Pd$_3$Te$_5$ point to intrinsic excitonic excitations associated with ultra-flat bands driven by many-body renormalization of the band structure via spontaneous exciton condensation. Our findings thus provide clear-cut optical evidence for exciton condensation in a bulk crystal and establish Ta$_2$Pd$_3$Te$_5$ as a promising platform for exploring correlated quantum phases and novel excitonic phenomena.
Authors: Weida Fu, Guo-Dong Zhao, Tao Hu, Wencai Yi, Hui Zhang, Alessandro Stroppa, Wei Ren, Zhongming Ren
We report the emergence of altermagnetism, a magnetic phase characterized by the coexistence of compensated spin ordering and momentum-dependent spin splitting, in graphite intercalation compounds (GICs), a prototypical material system long investigated for its tunable electronic and structural properties. Through first-principles calculations, we demonstrate that vanadium-intercalated stage-1 graphite compounds, exhibit inherent altermagnetic properties. The hexagonal crystal system and antiferromagnetic ordering of V atoms generate a magnetic space group that enforces alternating spin polarization in momentum space while maintaining zero net magnetization. The calculated band structure reveals robust altermagnetic signatures: along the high-symmetry direction, we observe a pronounced spin splitting of ~270 meV with alternating spin polarization. Crucially, the spin splitting exhibits minimal sensitivity to spin-orbit coupling (SOC) effect, highlighting the dominance of exchange interactions over relativistic effects. From Monte Carlo simulations, we predict a magnetic transition temperature ($T_m$ ) of ~228 K, indicating stable magnetic ordering above liquid nitrogen temperatures. The combination of symmetry-protected spin textures, SOC-independent splitting, and elevated $T_m$ temperature makes V-GICs as a promising candidate for spintronic applications, particularly for zero-field spin-polarized current generation and topologically robust spin transport. As the first demonstration of carbon-based alternating magnetic systems, this work offers a design paradigm for engineering spin-polarized quantum states governed by crystalline symmetry constraints.
Authors: Haohao Sheng, Jingyu Yao, Sheng Zhang, Quansheng Wu, Zhong Fang, Xi Dai, Hongming Weng, Zhijun Wang
Bose-Einstein condensation of spin-polarized triplet excitons can give rise to an intriguing spin supercurrent, enabling experimental detection of exciton condensation. In this work, we predict that Ta3X8 (X=I, Br) ferromagnetic monolayers are spin-polarized triplet excitonic insulators (EIs), based on the systematic first-principles GW calculations coupled with the Bethe-Salpeter equation (GW+BSE). The single-particle calculations of spin-polarized band structures reveal that these monolayers are bipolar magnetic semiconductors, where the highest valence band and the lowest conduction band possess opposite spin polarization. The two low-energy bands, primarily originating from Ta $d_{z^2}$ orbitals, are almost flat. The same-orbital parity and opposite-spin natures of the band-edge states effectively suppress dielectric screening, promoting the emergence of the EI state. The GW+BSE calculations reveal that the binding energy of the lowest-energy exciton is 1.499 eV for Ta3I8 monolayer and 1.986 eV for Ta3Br8 monolayer. Since both values exceed the respective GW band gaps, these results indicate a strong excitonic instability in these monolayers. A wavefunction analysis confirms that the lowest-energy exciton is a tightly bound Frenkel-like state, exhibiting a spin-polarized triplet nature with $S_z=1$. Our findings establish a valuable material platform for investigating spin-polarized triplet EIs, offering promising potential for spintronic applications.
Authors: Xiao Ma, Michael E. Cates
Non-reciprocal interactions are among the simplest mechanisms that drive a physical system out of thermal equilibrium, leading to novel phenomena such as oscillatory pattern formation. In this paper, we introduce a ternary phase separation model, with non-reciprocal interactions between two of the three phases and a spectator phase that mimics a boundary. Through numerical simulations, we uncover three distinct phase behaviours: a quasi-static regime, characterized by well-defined non-equilibrium contact angles at the three phase contact line; a limit cycle regime, with the three bulk phases rotating around the three phase contact line; and a travelling wave regime, featuring persistent directional motion. We complement our numerical findings with analytical examination of linear stability and the wave propagation speed near equilibrium. Our model provides a minimal framework for extending classical equilibrium wetting theory to active and non-equilibrium systems.
Authors: Enrico Marazzi (1), Samuel Poncé (2 and 3), Jean-Christophe Charlier (1), Gian-Marco Rignanese (2 and 3 and 4) ((1) IMCN Université catholique de Louvain Belgium, (2) ETSF Université catholique de Louvain Belgium, (3) WEL Research Institute Belgium, (4) School of Materials Science and Engineering Northwestern Polytechnical University China)
Kohn anomalies are kinks or dips in phonon dispersions which are pronounced in low-dimensional materials. We investigate the effects of non-adiabatic phonon self-energy on Kohn anomalies in one-dimensional metals by developing a model that analyzes how the adiabatic phonon frequency, electron effective mass, and electron-phonon coupling strength influence phonon mode renormalization. We introduce an electron-phonon coupling strength threshold for low-temperature system instability, providing experimentalists with a tool to predict them. Finally, we validate the predictions of our model against first-principles calculations on a 4 Å-diameter carbon nanotube.
Authors: Gabriele Bellomia, Adriano Amaricci, Massimo Capone
We demonstrate that the local nonfreeness, an unbiased measure of correlation between electrons at a single lattice site, can be computed as the mutual information between local natural spin orbitals. Using this concept, we prove that local electron correlations in the Hubbard model are fully classical: in the natural basis the local reduced density matrix is separable and no quantum correlations beyond entanglement are present. Finally, we compare different theoretical descriptions of magnetic and nonmagnetic states, showing that local classical correlations are drastically influenced by nonlocal processes. Our results confirm the relation between local classical correlations within an open system and the nonlocal correlations with its quantum environment.
Authors: Uliana E. Khodaeva, Dmitry L. Kovrizhin, Johannes Knolle
The dynamical structure factor of the transverse field Ising model (TFIM) shows universal power-law divergence at its quantum critical point, signatures of which have been arguably observed in inelastic neutron scattering studies of quantum spin chain materials, for example CoNb2O6. However, it has been recently suggested that its microscopic description is better captured in terms of a twisted Kitaev spin chain (TKSC) with bond-anisotropic couplings. Here, we present exact results for the dynamical structure factor of the TKSC across its quantum critical point, analyzing both the universal low-frequency response and the non-universal high-energy features. In addition, we explore extensions of the model including broken glide symmetry as well as the case of random, and incommensurate magnetic fields. Notably, in the latter case the fermionic excitations exhibit a localization-delocalization transition, which is manifest in the dynamical response as a distinct signature at finite frequency. We discuss the relevance of these features for the observation of quantum critical response in experiments.
Authors: Oliver Gaida, Olfa D'Angelo, Jonathan E. Kollmer
In granular hopper flow, is the clogging probability influenced by gravity? Clogging, the spontaneous arrest of granular flow through a constriction, is a fundamental and widespread phenomenon in granular processing. Accurately predicting clogging risk is essential for space-related activities. Yet, conflicting results leave us without a reliable way to extrapolate terrestrial data to low gravity. We introduce an in-bulk definition of the dimensionless granular Bond number, B, to scale clogging probability from Earth gravity to low gravity. By testing multiple lunar regolith simulants in Earth and Moon gravitational accelerations, using an active drop tower, we reveal that low gravity significantly increases clogging risk, challenging previous findings. We observe a gravity-induced shift in the critical orifice below which clogging occurs by up to one order of magnitude. Scaling data with the Bond number unifies scattered results into a state diagram predicting clogging across materials and gravitational accelerations. Our findings provide a practical tool for anticipating granular clogging in reduced gravity, informing future space missions.
Authors: Milena Petkovic, Natasha Dropka, Xia Tang, Janina Zittel
The Czochralski (Cz) method is a widely used process for growing high-quality single crystals, critical for applications in semiconductors, optics, and advanced materials. Achieving optimal growth conditions requires precise control of process and furnace design parameters. Still, data scarcity -- especially for new materials -- limits the application of machine learning (ML) in predictive modeling and optimization. This study proposes a transfer learning approach to overcome this limitation by adapting ML models trained on a higher data volume of one source material (Si) to a lower data volume of another target material (Ge and GaAs). The materials were deliberately selected to assess the robustness of the transfer learning approach in handling varying data similarity, with Cz-Ge being similar to Cz-Si, and GaAs grown via the liquid encapsulated Czochralski method (LEC), which differs from Cz-Si. We explore various transfer learning strategies, including Warm Start, Merged Training, and Hyperparameters Transfer, and evaluate multiple ML architectures across two different materials. Our results demonstrate that transfer learning significantly enhances predictive accuracy with minimal data, providing a practical framework for optimizing Cz growth parameters across diverse materials.
Authors: Bidisha Mukherjee, Amit Raj Singh, Garima Mishra
We investigate the role of bubble positioning in the force-induced melting of double-stranded DNA using two distinct approaches: Brownian Dynamics simulations and the Gaussian Network Model. We isolate the effect of bubble positioning by using DNA molecules with 50% AT - 50% GC base-pair composition which ensures constant enthalpy. Our results reveal that it is not just the sequence itself, but its specific arrangement that influences DNA stability. We examine two types of DNA sequences containing a block of either AT or GC base-pairs, resulting in the formation of a large bubble or a smaller bubble within the DNA, respectively. By systematically shifting these blocks along the strand, we investigate how their positioning influences the force-temperature phase diagram of DNA. Our Brownian dynamics simulations reveal that, at high forces, melting of the entire DNA strand is initiated after stretching $\approx 9$ GC base-pairs, independent of the specific base-pair sequence. In contrast, no such characteristic length scale is observed in the Gaussian network model. Our study suggests that free strand entropy plays a significant role in determining the force-temperature phase diagram of the DNA.
Authors: Anton Klimek, Benjamin A. Dalton, Lucas Tepper, Roland R. Netz
Proteins often exhibit subdiffusive configurational dynamics. The origins of this subdiffusion are still unresolved. We investigate the impact of non-Markovian friction and the free energy landscape on the dynamics of fast-folding proteins in terms of the mean squared displacement (MSD) and the mean first-passage-time (MFPT) of the folding reaction coordinate. We find the friction memory kernel from published molecular dynamics (MD) simulations to be well-described by a hierarchical multi-exponential function, which gives rise to subdiffusion in the MSD over a finite range of time. We show that friction memory effects in fast-folding proteins dominate the scaling behavior of the MSD compared to effects due to the folding free energy landscape. As a consequence, Markovian models are insufficient for capturing the folding dynamics, as quantified by the MSD and the MFPT, even when including coordinate-dependent friction. Our results demonstrate the importance of memory effects in protein folding and conformational dynamics and explicitly show that subdiffusion in fast-folding protein dynamics originates from memory effects, not from the free energy landscape and not from coordinate-dependent friction.
Authors: Halyna Butovych, Jaroslav Ilnytskyi, Erkki Lahderanta, Taras Patsahan
Contamination of water by heavy metal ions represents a significant environmental concern. Among various remediation methods, chelation has proven to be an effective technique in water treatment processes. This study investigates the chelating properties of linear polyethyleneimine (PEI) and its complexation with divalent mercury ions (Hg2+) in aqueous solution. Atomistic molecular dynamics (MD) simulations were carried out using the OPLS/AA force field to examine the microscopic structure of PEI-Hg2+ complexes. PEI chains of varying lengths were considered, and it was found that a single linear PEI molecule containing ten amino groups is capable of coordinating up to four Hg2+ ions. The stability of the resulting complexes was further supported by density functional theory (DFT) calculations.
Authors: Ioanna Karagianni, Ioannis Panagiotopoulos
The coarse-grained interactions between Néel skyrmions, stabilized by interfacial Dzyaloshinskii-Moriya coupling (iDMI), are studied through the properties of their hexagonal lattices by micromagnetic simulations. The interactions with the film edges are excluded by imposing periodic boundary conditions. The dependence of skyrmion size and interaction energy on the distance is derived. Two types of behavior are observed depending on the value of iDMI compared to the critical value Dc above which the skyrmion size diverges: For iDMI < Dc the skyrmions acquire a finite size that saturates at maximum value independent of the skyrmion distance that corresponds to the one of the isolated skyrmion. This energy is above that of the homogeneous ferromagnetic state. For iDMI > Dc the skyrmions tend to increase in size to the extent that their neighboring skyrmions permit and finite size skyrmions can be stabilized only in arrays due to their mutual repulsion. These configurations have energy below that of the homogeneous ferromagnetic state.
Authors: Seungjun Lee, Eng Hock Lee, Young-Kyun Kwon, Steven J. Koester, Phaedon Avouris, Vladimir Cherkassky, Jerry Tersoff, Tony Low
The energy band alignment at the interface of van der Waals heterostructures (vdWHs) is a key design parameter for next-generation electronic and optoelectronic devices. Although the Anderson and midgap models have been widely adopted for bulk semiconductor heterostructures, they exhibit severe limitations when applied to vdWHs, particularly for type-III systems. Based on first-principles calculations for approximately $10^3$ vdWHs, we demonstrate these traditional models miss a critical dipole arising from interlayer charge spillage. We introduce a generalized linear response (gLR) model that includes this dipole through a quantum capacitance term while remaining analytically compact. With only two readily computed inputs, the charge neutrality level offset and the sum of the isolated-layer bandgaps, the gLR reproduces DFT band line-ups with $r^2\sim$0.9 across type-I, II, and III stacks. Machine-learning feature analysis confirms that these two descriptors dominate the underlying physics, indicating the model is near-minimal and broadly transferable. The gLR framework therefore provides both mechanistic insight and a fast, accurate surrogate for high-throughput screening of the vast vdW heterostructure design space.
Authors: Yinqi Chen, Cheng Xu, Yang Zhang, Constantin Schrade
A recent experiment has reported unconventional superconductivity in twisted bilayer MoTe$_2$, emerging from a normal state that exhibits a finite anomalous Hall effect -- a signature of intrinsic chirality. Motivated by this discovery, we construct a continuum model for twisted MoTe$_2$ constrained by lattice symmetries from first-principles calculations that captures the moiré-induced inversion symmetry breaking even in the absence of a displacement field. Building on this model, we show that repulsive interactions give rise to finite-momentum superconductivity via the Kohn-Luttinger mechanism in this chiral moiré system. Remarkably, the finite-momentum superconducting state can arise solely from internal symmetry breaking of the moiré superlattice, differentiating it from previously studied cases that require external fields. It further features a nonreciprocal quasiparticle dispersion and an intrinsic superconducting diode effect. Our results highlight a novel route to unconventional superconducting states in twisted transition metal dichalcogenides moiré systems, driven entirely by intrinsic symmetry-breaking effects.
Authors: Jordan T. McCourt, Ethan G. Arnault, Merve Baksi, Samuel J. Poage, Salva Salmani-Rezaie, Divine P. Kumah, Kaveh Ahadi, Gleb Finkelstein
Two-dimensional electron gases (2DEGs) formed at complex oxide interfaces offer a unique platform to engineer quantum nanostructures. However, scalable fabrication of locally addressable devices in these materials remains challenging. Here, we demonstrate an efficient fabrication approach by patterning narrow constrictions in a superconducting KTaO3-based heterostructure. The constrictions are individually tunable via the coplanar side gates formed within the same 2DEG plane. Our technique leverages the high dielectric permittivity of KTaO3 (epsilon_r ~ 5000) to achieve strong electrostatic modulation of the superconducting 2DEG. Transport measurements through the constriction reveal a range of transport regimes: Within the superconducting state, we demonstrate efficient modulation of the critical current and Berezinskii Kosterlitz Thouless (BKT) transition temperature at the weak link. Further tuning of the gate voltage reveals an unexpectedly regular Coulomb blockade pattern. All of these states are achievable with a side gate voltage |V_SG| < 1 V. The fabrication process is scalable and versatile, enabling a platform both to make superconducting field-effect transistors and to study a wide array of physical phenomena present at complex oxide interfaces.
Authors: B. Sriram Shastry, Emil A. Yuzbashyan, Aniket Patra
Starting from a generalization of Weyl's relations in finite dimension $N$, we show that the Heisenberg commutation relations can be satisfied in a specific $N-1$ dimensional subspace, and display a linear map for projecting operators to this subspace. This setup is used to construct a hierarchy of parameter-dependent commuting matrices in $N$ dimensions. This family of commuting matrices is then related to Type-1 matrices representing quantum integrable models. The commuting matrices find an interesting application in quantum computation, specifically in Grover's database search problem. Each member of the hierarchy serves as a candidate Hamiltonian for quantum adiabatic evolution and, in some cases, achieves higher fidelity than standard choices -- thus offering improved performance.
Authors: Dibyendu Sardar, Marcin Gronowski, Michał Tomza, John L. Bohn
Accurate \textit{ab initio} potential energy surfaces are essential to understand and predict collisional outcomes in ultracold molecular systems. In this study, we explore the intermolecular interactions between two laser-cooled CaF molecules, both in their ground and excited electronic states, aiming to understand the mechanisms behind the observed collisional losses on the non-reactive, spin-polarized surface of the CaF+CaF system. Using state-of-the-art \textit{ab initio} methods, we compute twelve electronic states of the Ca$_2$F$_2$ complex within the rigid rotor approximation applied to CaF. Calculating the potential energy surfaces for the excited electronic states of Ca$_2$F$_2$ is challenging and computationally expensive. Our approach employs the multireference configuration interaction method, restricted to single and double excitations, along with a reasonably large active space to ensure the convergence in the excited states. We also compute the spin-orbit coupling between the ground state and the lowest spin-polarized triplet state, as well as the spin-spin coupling within the lowest triplet state (1) $^3\mathrm{A}'$. Additionally, we determine the electric transition dipole moments for the (1) $^3\mathrm{A}'$-(2) $^3\mathrm{A}'$ and (1) $^3\mathrm{A}'$-(1) $^3\mathrm{A}''$ transitions. Notably, we find that the lowest spin-polarized state (1) $^3\mathrm{A}'$, shifted by 1064 nm of laser light from the optical dipole trap, intersects several electronically excited states. Finally, by analyzing the potential energy surfaces, we discuss two plausible pathways that may account for the observed collisional losses on the spin-polarized surface of the CaF+CaF system.
Authors: Kenric P. Nelson
Nonextensive Statistical Mechanics (NSM) has developed into a powerful toolset for modeling and analyzing complex systems. Despite its many successes, a puzzle arose early in its development. The constraints on the Tsallis entropy are in the form of an escort distribution with elements proportional to $p_i^q$, but this same factor within the Tsallis entropy function is not normalized. This led to consideration of the Normalized Tsallis Entropy (NTE); however, the normalization proved to make the function unstable. I will provide evidence that the coupled entropy, which divides NTE by $1 + d\kappa$, where $d$ is the dimension and $\kappa$ is the coupling, may provide the necessary robustness necessary for applications like machine learning. The definition for the coupled entropy and its maximizing distributions, the coupled exponential family, arises from clarifying how the number of independent random variables $(q)$ is composed of the nonlinear properties of complex systems, $q=1+\frac{\alpha\kappa}{1+d\kappa}$, where $\alpha$ is the nonlinear parameter governing the shape of distributions near their location and $\kappa$ is the parameter determining the asymptotic tail decay. Foundationally, for complex systems, the coupling is the measure of nonlinearity inducing non-exponential distributions and the degree of nonadditivity entropy. As such, the coupling is a strong candidate as a measure of statistical complexity.
Authors: Mohammad Nooraiepour, Mohammad Masoudi, Hannelore Derluyn, Pascale Senechal, Peter Moonen, Helge Hellevang
Salt precipitation during CO$_2$ storage in saline aquifers presents challenges for injectivity and containment, with broader implications for soil salinization and cultural heritage preservation. This study utilizes time-lapse X-ray and spectral micro-computed tomography, scanning electron microscopy, and deep learning-assisted image analysis to investigate halite crystallization and brine consumption in porous medium. We identified three-dimensional halite growth structures functioning as a secondary porous medium. Visualizing the spatio-temporal dynamics of salt-brine coexistence and halite precipitation revealed critical insights into the self-enhancing nature of salt growth. Expanding gas-liquid contact surfaces and initial crystal nucleation sites significantly enhanced evaporation and growth rates. Hydrophilic halite crystals attract brine films, establishing a feedback loop that perpetuates growth. The encapsulation of brine between grain surfaces and umbrella-like salt crusts was observed. Delineating the self-enhancing growth, including the role of capillary forces and surface-interface processes, is crucial for improving CO$_2$ injection efficiency and integrity, as well as for addressing environmental challenges related to soil salinization.
Authors: Reese E. Jones, Adrian Buganza Tepole, Jan N. Fuhg
Multi-well potentials are ubiquitous in science, modeling phenomena such as phase transitions, dynamic instabilities, and multimodal behavior across physics, chemistry, and biology. In contrast to non-smooth minimum-of-mixture representations, we propose a differentiable and convex formulation based on a log-sum-exponential (LSE) mixture of input convex neural network (ICNN) modes. This log-sum-exponential input convex neural network (LSE-ICNN) provides a smooth surrogate that retains convexity within basins and allows for gradient-based learning and inference. A key feature of the LSE-ICNN is its ability to automatically discover both the number of modes and the scale of transitions through sparse regression, enabling adaptive and parsimonious modeling. We demonstrate the versatility of the LSE-ICNN across diverse domains, including mechanochemical phase transformations, microstructural elastic instabilities, conservative biological gene circuits, and variational inference for multimodal probability distributions. These examples highlight the effectiveness of the LSE-ICNN in capturing complex multimodal landscapes while preserving differentiability, making it broadly applicable in data-driven modeling, optimization, and physical simulation.
Authors: Samad Hajinazar, Eva Zurek
Version 14 of XtalOpt, evolutionary multi-objective global optimization algorithm for crystal structure prediction, is now available for download from its official website this https URL. The new version of the code is designed to perform ground state search for novel crystal structures with variable composition by integrating a suite of ab initio methods alongside classical and machine-learning potentials for structural relaxation. The multi-objective search framework has been further enhanced through the introduction of Pareto optimization, enabling efficient discovery of functional materials. Here, we describe the implemented methodologies, provide detailed instructions for their use, and present an overview of additional improvements included in XtalOpt version 14.
Authors: Jaime A. Berkovich, Noah S. David, Markus J. Buehler
Cellular automata (CA) provide a minimal formalism for investigating how simple local interactions generate rich spatiotemporal behavior in domains as diverse as traffic flow, ecology, tissue morphogenesis and crystal growth. However, automatically discovering the local update rules for a given phenomenon and using them for quantitative prediction remains challenging. Here we present AutomataGPT, a decoder-only transformer pretrained on around 1 million simulated trajectories that span 100 distinct two-dimensional binary deterministic CA rules on toroidal grids. When evaluated on previously unseen rules drawn from the same CA family, AutomataGPT attains 98.5% perfect one-step forecasts and reconstructs the governing update rule with up to 96% functional (application) accuracy and 82% exact rule-matrix match. These results demonstrate that large-scale pretraining over wider regions of rule space yields substantial generalization in both the forward (state forecasting) and inverse (rule inference) problems, without hand-crafted priors. By showing that transformer models can faithfully infer and execute CA dynamics from data alone, our work lays the groundwork for abstracting real-world dynamical phenomena into data-efficient CA surrogates, opening avenues in biology, tissue engineering, physics and AI-driven scientific discovery.
Authors: Bijit Mukherjee, Michał Tomza
We propose a coherent optical population transfer of weakly bound field-linked tetratomic molecules (FL tetramers) to deeper bound states using stimulated Raman adiabatic passage (STIRAP). We consider static-electric-field shielded polar alkali-metal diatomic molecules and corresponding FL tetramers in their $\textrm{X}^1\Sigma^+ + \textrm{X}^1\Sigma^+$ ground electronic state. We show that the excited metastable $\textrm{X}^1\Sigma^+ + \textrm{b}^3\Pi$ electronic manifold supports FL tetramers in a broader range of electric fields with collisional shielding extended to zero field. We calculate the Franck-Condon factors between the ground and excited FL tetramers and show that they are highly tunable with the electric field. We also predict photoassociation (PA) of ground-state shielded molecules to the excited FL states in free-bound optical transitions. We propose proof-of-principle experiments to implement STIRAP and PA using FL tetramers, paving the way for the formation of deeply bound ultracold polyatomic molecules.
Authors: Akarsh Aurora, Alexis R Devitre, Angus PC Wylie, Jonas A Rajagopal, Michael P Short
Commercial fusion power plants demand magnet materials that retain structural integrity and thermal conductivity while operating under the bombardment of energetic neutrons at cryogenic temperatures. Understanding how thermo-mechanical properties evolve under such extreme loads is crucial for selecting materials with high radiation tolerance and predictable failure mechanisms. Presented here is a facility that combines cryogenic transient grating spectroscopy (TGS) with simultaneous ion irradiation, enabling in-situ measurements of thermal diffusivity and surface acoustic wave (SAW) frequency spectra. Employing copper as a benchmark material, an irradiation was performed at 30 K with 12.4 MeV $\text{Cu}^{6+}$ ions producing a final fluence of $1.9 \times 10^{17}$ ions/m$^2$. Over the irradiation period, thermal diffusivity nearly halved from an initial value of $1.2 \times 10^{-4}$ $\text{m}^2/\text{s}$ while SAW speed did not show significant change, maintaining a value of $2162\pm18$ m/s. Given its real-time monitoring capability and the numerous candidate materials that remain uncharacterized under fusion magnet operating conditions, this facility is poised to deliver new scientific insights into fusion magnet material degradation trends, contributing to improved design criteria and operational certainty for forthcoming fusion power plants.
Authors: Elijah Pelofske, Frank Barrows, Pratik Sathe, Cristiano Nisoli
Quantum annealers have emerged as versatile and controllable platforms for experimenting on exotic spin systems that model quantum materials. However, quantum annealing experiments have yet to explore magnetic memory and hysteresis, features seemingly at odds with hardware designed to escape metastable states via quantum tunneling, favoring forgetfulness. Here, we present a general protocol to experiment on magnetic hysteresis in a transverse-field Ising model. We implement it on three D-Wave superconducting flux qubit annealers, using up to thousands of spins, and explore both ferromagnetic and disordered Ising models across contrasting graph topologies. Crucially, we observe robust memory retention in hysteresis loops, establishing quantum annealers as a platform for probing non-equilibrium emergent magnetic phenomena. This approach enables many topics of future exploration including return point memory and hysteresis in frustrated or topologically ordered systems, thus broadening the role of analog quantum computers into foundational questions in condensed matter physics.
Authors: Brian R. Pollard, Saman Alavi
Ronald Wilfrid Gurney is one of the lesser-known research students of the Cavendish Laboratory in the mid 1920s. Gurney made significant contributions to the application of quantum mechanics to problems related to tunneling of alpha-particles from nuclei, to formation of images in photographic plates, the understanding of the origin of color-centres in salt crystals, and in the theory of semiconductors. He was the first physicist to apply quantum mechanics to the theory of electrochemistry and ionic solutions. He also made fundamental contributions to ballistics research. Gurney wrote a number of textbooks on fundamental and applied quantum mechanics in a distinctive style which are still useful as educational resources. In addition to his scientific contributions, he travelled extensively, and during and after World War II worked in the United States. During the cold war, he got entangled in the Klaus Fuchs affair and lost his employment. He died at the age of 54 in 1953 from a stroke. With the approach of the 100th year anniversary of quantum mechanics, it is timely to commemorate the life and contributions of this somewhat forgotten physicist.
Authors: Ali Binai Motlagh, Grant Wilbur, Nour Allam, Giannis Tolis, Lilly Daw, S. ONeal, Dennis G. Deppe, Kimberley C. Hall
We extend the recently developed NARP scheme for laser-triggered single-photon sources to the simultaneous excitation of multiple emitters with varying transition energies, laying the groundwork for wavelength-division multiplexing in quantum optical networks. Our Multi-NARP scheme does not rely on polarization filtering and thus enables the near-unity extraction efficiency of single photons from each quantum dot. Our approach also offers the advantages of robustness to variations in the laser pulse parameters and immunity to excitation-induced dephasing tied to electron-phonon coupling. We show that simultaneous triggering of at least 10 emitters is possible, enabling the development of high-bandwidth quantum networks.
Authors: Francesco Belli, Sean Torres, Julia Contreras-Garcìa, Eva Zurek
Hydrogen-based materials are able to possess extremely high superconducting critical temperatures, \tc s, due to hydrogen's low atomic mass and strong electron-phonon interaction. Recently, a descriptor based on the Electron Localization Function (ELF) has enabled the rapid estimation of the \tc\ of hydrogen-containing compounds from electronic networking properties, but its applicability has been limited by the small size and homogeneity of the training dataset used. Herein, the model is re-examined compiling a publicly available combined dataset of 244 binary and ternary hydride superconductors. Our analysis shows that though ELF-based networking remains a valuable descriptor, its predictive power declines with increasing compositional complexity. However, by introducing the molecularity index, defined as the highest value of the ELF at which two hydrogen atoms connect, and applying symbolic regression, the accuracy of the predictions can be substantially enhanced. These results establish a more robust framework for assessing superconductivity in hydride materials, facilitating accelerated screening of novel candidates through integration with crystal structure prediction methods or high-throughput searches.
Authors: Neha Mahuli (1), Joaquin Minguzzi (1), Jiansong Gao (1), Rachel Resnick (2), Sandra Diez (3), Cosmic Raj (1), Guillaume Marcaud (1), Matthew Hunt (1), Loren Swenson (1), Jefferson Rose (1), Oskar Painter (1), Ignace Jarrige (1) ((1) AWS Center for Quantum Computing, Pasadena, CA, USA, (2) Google Research, (3) National Institute of Standards and Technology)
We present a dry surface treatment combining atomic layer etching and deposition (ALE and ALD) to mitigate dielectric loss in fully fabricated superconducting quantum devices formed from aluminum thin films on silicon. The treatment, performed as a final processing step prior to device packaging, starts by conformally removing the native metal oxide and fabrication residues from the exposed surfaces through ALE before \textit{in situ} encapsulating the metal surfaces with a thin dielectric layer using ALD. We measure a two-fold reduction in loss attributed to two-level system (TLS) absorption in treated aluminum-based resonators and planar transmon qubits. Treated transmons with compact capacitor plates and gaps achieve median $Q$ and $T_1$ values of $3.69 \pm 0.42 \times 10^6$ and $196 \pm 22$~$\mu$s, respectively. These improvements were found to be sustained over several months. We discuss how the combination of ALE and ALD reverses fabrication-induced surface damages to significantly and durably improve device performance via a reduction of the TLS defect density in the capacitive elements.
Authors: Zhengni Yang, Rui Yang, Weijian Han, Qixin Liu
This paper introduces a novel deep-learning approach to predict true stress-strain curves of high-strength steels from small punch test (SPT) load-displacement data. The proposed approach uses Gramian Angular Field (GAF) to transform load-displacement sequences into images, capturing spatial-temporal features and employs a Sequence-to-Sequence (Seq2Seq) model with an LSTM-based encoder-decoder architecture, enhanced by multi-head cross-attention to improved accuracy. Experimental results demonstrate that the proposed approach achieves superior prediction accuracy, with minimum and maximum mean absolute errors of 0.15 MPa and 5.58 MPa, respectively. The proposed method offers a promising alternative to traditional experimental techniques in materials science, enhancing the accuracy and efficiency of true stress-strain relationship predictions.
Authors: Alexander Jochim, Stefan Bornholdt
Why are human societies unstable? Theories based on the observation of recurring patterns in historical data indicate that economic inequality, as well as social factors are key drivers. So far, models of this phenomenon are more macroscopic in nature. However, basic mechanisms at work could be accessible to minimal mathematical models. Here we combine a simple mechanism for economic growth with a mechanism for the spreading of social dissatisfaction. Broad wealth distributions generated by the economic mechanism eventually trigger social unrest and the destruction of wealth, leading to an emerging pattern of boom and bust. We find that the model time scales compare well with empirical data. The model emphasizes the role of broad (power law) wealth distributions for dynamical social phenomena.
Authors: Akshat Rana, Pooja Lamba, Atanu Ghosh, Siddharth Dhomkar, Rama K. Kamineni
Imaging of microwave magnetic fields with nano-scale resolution has interesting applications. Specifically, detecting the orientation of the microwave fields is useful in condensed matter physics and quantum control. However, most of the existing methods for microwave field imaging are limited to detecting the magnitude of the fields. Due to their small sensor size and favorable optical and spin properties, nitrogen-vacancy (NV) centers in diamond are highly suitable for imaging dc and ac magnetic fields. The reported methods for detecting the orientation of microwave magnetic fields use pulsed Rabi frequency measurements. Here, we demonstrate imaging of the orientation of microwave magnetic fields by only using continuous-wave experiments on NV centers. This simplifies the sensor apparatus and is particularly advantageous in applications where pulsing of the target microwave field is not possible. The method requires static bias magnetic field oriented perpendicular to the quantization axis of NV centers. We detect the direction of an arbitrary microwave magnetic field using NV centers of two different orientations. Moreover, we demonstrate that the projection of the microwave fields onto a plane can be imaged using NV centers of single orientation. It can be straightforwardly implemented using a single NV center.
Authors: Paniz Foshat, Shima Poorgholam-khanjari, Valentino Seferai, Hua Feng, Susan Johny, Oleg A. Mukhanov, Matthew Hutchings, Robert H. Hadfield, Martin Weides, Kaveh Delfanazari
Exchanging energy below the superconducting gap introduces quasiparticle energy distributions in superconducting quantum circuits, which will be responsible for their decoherence. This study examines the impact of quasiparticle energy on the performance of NbN superconducting microwave coplanar waveguide resonators on silicon chips. We measured the resonance frequency and internal quality factor in response to temperature sweeps to evaluate the effect of quasiparticle dynamics. Moreover, by calculating the complex conductivity of the NbN film, we identified the contribution of quasiparticle density to the experimental results.
Authors: Teng Wang, Lu Jing, Fiona C.Y. Kwok, Yuri D. Sobral, Thomas Weinhart, Anthony R. Thornton
Granular flow down an inclined plane is ubiquitous in geophysical and industrial applications. On rough inclines, the flow exhibits Bagnold's velocity profile and follows the so-called $\mu(I)$ local rheology. On insufficiently rough or smooth inclines, however, velocity slip occurs at the bottom and a basal layer with strong agitation emerges below the bulk, which is not predicted by the local rheology. Here, we use discrete element method simulations to study detailed dynamics of the basal layer in granular flows down both smooth and rough inclines. We control the roughness via a dimensionless parameter, $R_a$, varied systematically from 0 (flat, frictional plane) to near 1 (very rough plane). Three flow regimes are identified: a slip regime ($R_a \lesssim 0.45$) where a dilated basal layer appears, a no-slip regime ($R_a \gtrsim 0.6$) and an intermediate transition regime. In the slip regime, the kinematics profiles (velocity, shear rate and granular temperature) of the basal layer strongly deviate from Bagnold's profiles. General basal slip laws are developed which express the slip velocity as a function of the local shear rate (or granular temperature), base roughness and slope angle. Moreover, the basal layer thickness is insensitive to flow conditions but depends somewhat on the inter-particle coefficient of restitution. Finally, we show that the rheological properties of the basal layer do not follow the $\mu(I)$ rheology, but are captured by Bagnold's stress scaling and an extended kinetic theory for granular flows. Our findings can help develop more predictive granular flow models in the future.
Authors: Alessandro Petrini, Claudio Conti, Davide Pierangeli
Optical neural networks are emerging as a powerful and versatile tool for processing optical signals directly in the optical domain with superior speed, integrability, and functionality. Their application to optical polarization enables neuromorphic polarization sensors, but their operation is limited to fully-polarized light. Here, we demonstrate single-shot analysis of partially-polarized beams with a photonic random neural network (PRNN). The PRNN is composed of a series of optical layers implemented by a stack of scattering media and a few trainable digital nodes. The setup infers the degree-of-polarization and the Stokes parameters of the polarized component with precision comparable to off-the-shelf polarimeters. The use of several optical layers allows to enhance the accuracy, reduce the sensor size, and minimize digital costs, demonstrating the advantage of a deep optical encoder for processing polarization information. Our results point out photonic neural networks as fast, compact, broadband, low-cost polarimeters that are widely applicable from sensing to imaging.
Authors: Xin Wang, Xu-Yang Hou, Yan He, Hao Guo
Topological properties of quantum systems at finite temperatures, described by mixed states, pose significant challenges due to the triviality of the Uhlmann bundle. We introduce the thermal Uhlmann-Chern number, a generalization of the Chern number, to characterize the topological properties of mixed states. By inserting the density matrix into the Chern character, we introduce the thermal Uhlmann-Chern number, a generalization of the Chern number that reduces to the pure-state value in the zero-temperature limit and vanishes at infinite temperature, providing a framework to study the temperature-dependent evolution of topological features in mixed states. We provide, for the first time, a rigorous mathematical proof that the first- and higher-order Uhlmann-Chern numbers converge to the corresponding Chern numbers in the zero-temperature limit, differing only by a factor of $1/D$ for $D$-fold degenerate ground states. We demonstrate the utility of this framework through applications to a two-level system, the coherent state model, the 2D Haldane model, and a four-band model, highlighting the temperature-dependent behavior of topological invariants. Our results establish a robust bridge between the topological properties of pure and mixed states, offering new insights into finite-temperature topological phases.
Authors: Ildoo Kim
The most studies on the stability of foam bubbles investigated the mechanical stability of thin films between bubbles due to the drainage by gravity. In the current work, we take an alternative approach by assuming the rupture of bubbles as a series of random events and by investigating the time evolution of the size distribution of foam bubbles over a long time up to several hours. For this purpose, we first prepared layers of bubbles on Petri dishes by shaking soap solutions of a few different concentrations, and then we monitored the Petri dishes by using a time-lapse video imaging technique. We analyzed the captured images by custom software to count the bubble size distribution with respect to the initial concentration and elapsed time. From the statistics on our data, we find that the total bubble volume decreases exponentially in time, and the exponent, i.e. the mean lifetime, is a function of the bubble size. The mean lifetimes of larger bubbles are observed to be shorter than those of smaller bubbles, by approximately a factor of 2.
Authors: Yuqi Qing, Yu-Qin Chen, Shi-Xin Zhang
We investigate the quantum dynamics of a one-dimensional quasiperiodic system featuring a single-particle mobility edge (SPME), described by the generalized Aubry-André (GAA) model. This model offers a unique platform to study the consequences of coexisting localized and extended eigenstates, which contrasts sharply with the abrupt localization transition in the standard Aubry-André model. We analyze the system's response to a quantum quench through two complementary probes: entanglement entropy (EE) and subsystem information capacity (SIC). We find that the SPME induces a smooth crossover in all dynamical signatures. The EE saturation value exhibits a persistent volume-law scaling in the mobility-edge phase, with an entropy density that continuously decreases as the number of available extended states decreases. Complementing this, the SIC profile interpolates between the linear ramp characteristic of extended systems and the information trapping behavior of localized ones, directly visualizing the mixed nature of the underlying spectrum. Our results establish unambiguous dynamical fingerprints of a mobility edge, providing a crucial non-interacting benchmark for understanding information and entanglement dynamics in more complex systems with mixed phases.
Authors: O. Daneshmandi, M. Alidadi, Y.M. Banad, S. S. Sharif
We present a Solid-State Optical Magnetometer (SOM) based on black phosphorus (BP) multilayers, offering a compact, scalable, and highly sensitive alternative to traditional atomic-based magnetometers. Utilizing BP's intrinsic linear dichroism in a metasurface cavity, the SOM achieves sub-nanotesla precision and vector magnetic field sensing. BP enhances light-matter interactions, enabling tunable optical responses driven by Lorentz force-induced cavity deformation. Optimized metasurface unit cells increase polarization-dependent absorption, improving detection sensitivity. Finite Element Method simulations show high linearity (R-squared > 0.999), tunable dynamic range, and adjustable sensitivity via current modulation. At 200 microamps, the SOM reaches a sensitivity of 31.25 picotesla, while lower currents expand the dynamic range up to +-10 nanotesla. This tunability allows for application-specific optimization in areas such as biomagnetic sensing, metrology, and industrial field detection. Unlike SQUIDs and optically pumped magnetometers, the BP-based SOM operates at room temperature and nanoscale dimensions with comparable sensitivity, eliminating the need for cryogenics or vapor cells. Power consumption remains under 1 microwatt, far below conventional technologies. This work establishes BP metasurface integration as a promising platform for low-power, miniaturized, and high-performance magnetic field sensing.
Authors: Haifeng Tang, Hong-Yi Wang, Zhong Wang, Xiao-Liang Qi
Quantum entanglement is affected by unitary evolution, which spreads the entanglement through the whole system, and also by measurements, which usually tends to disentangle subsystems from the rest. Their competition has been known to result in the measurement-induced phase transition. But more intriguingly, measurement alone has the ability to drive a system into different entanglement phases. In this work, we map the entanglement evolution under unitaries and/or measurements into a classical spin problem. This framework is used to understand a myriad of random circuit models analytically, including measurement-induced and measurement-only transitions. Regarding many-body joint measurements, a lower bound of measurement range that is necessary for a global scrambled phase is derived. Moreover, emergent continuous symmetries (U(1) or SU(2)) are discovered in some random measurement models in the large-$d$ (qudit dimension) limit. The emergent continuous symmetry allows a variety of spin dynamics phenomena to find their counterparts in random circuit models.
Authors: Premjith Thekkeppatt, Edwin Baaij, Tijs van Roon, Klaasjan van Druten, Florian Schreck
We report on the design and characterization of a high-power amplifier with an output power of 36.5 dBm for a frequency range of 50 MHz to 1000 MHz with a total gain of 40 dB. The amplifier is optimized for driving acousto-optic and electro-optic modulators for ultracold atom experiments. This amplifier is a 19 inch rack unit, with a power efficiency of >35 %, and 0.01 dBm long-term stability. Schematics and other design materials are publicly available under an open hardware license.
Authors: Tanay Paul, Allison M. Green, Delia J. Milliron, Thomas M. Truskett
Multilayer assemblies of metal nanoparticles can act as photonic structures, where collective plasmon resonances hybridize with cavity modes to create plasmon-polariton states. For sufficiently strong coupling, plasmon polaritons qualitatively alter the optical properties of light-matter systems, with applications ranging from sensing to solar energy. However, results from experimental studies have raised questions about the role of nanoparticle structural disorder in plasmon-polariton formation and light-matter coupling in plasmonic assemblies. Understanding how disorder affects optical properties has practical implications since methods for assembling low-defect nanoparticle superlattices are slow and scale poorly. Modeling realistic disorder requires large system sizes, which is challenging using conventional electromagnetic simulations. We employ Brownian dynamics simulations to construct large-scale nanoparticle multilayers with controlled structural order. We investigate their optical response using a superposition T-matrix method with 2-D periodic boundary conditions. We find that while structural disorder broadens the polaritonic stop band and the near-field hot-spot distribution, the polariton dispersion and coupling strength remain unaltered. To understand effects of nanoparticle composition, we consider assemblies with model particles mimicking gold or tin-doped indium oxide (ITO) nanocrystals. Losses due to higher damping in ITO nanocrystals prevent their assemblies from achieving the deep strong coupling of gold nanoparticle multilayers, although the former still exhibit ultrastrong coupling. We demonstrate that while computationally efficient mutual polarization method calculations employing the quasistatic approximation modestly overestimate the strength of the collective plasmon, they reproduce the polariton dispersion relations determined by electrodynamic simulations.
Authors: Vladislav Efremkin, Julian Heske, Thomas D. Kühne, Emil Prodan
Quantifying the configuration space and the Gibbs measure of thermally disordered condensed matter systems has been a long standing problem. The challenge is to avoid the Gibbs paradox, which forbids any ordering or labeling of the atoms. Our key observation is that the lattice of a thermally disordered condensed matter system, in either solid, liquid or gas phase, can be fully reconstructed from the Voronoi cells of the atoms alone, even if these Voronoi cells are disassembled and randomly scrambled. In the example of the crystalline phase of silicon, the statistics of the Voronoi cells reveals the existence of four, and only four, large facets that are present with probability one for all temperatures up to the solid-liquid melting line. These four largest facets, which separate nearest-neighboring atoms, can be also be used to reconstruct the lattice of the crystal. Hence, their collection supplies the optimal representation of the configuration of the crystal. We conjecture that the existence of Voronoi facets that, despite their large thermal fluctuations, survive with probability one up to the melting temperature, is the fundamental signature of the crystalline solid phase and therefore key to quantifying the Gibbs measure over the entire solid phase.
Authors: Guochu Deng
Experimental data collected from a triple-axis spectrometer (TAS) are typically analysed by considering the instrument resolution, as the resolution of a TAS instrument is often complex and significantly influences the measured results. Two Python packages, TasVisAn and InsPy, have been developed to visualize and analyse data from TAS instruments - particularly from the cold-neutron TAS Sika and the thermal-neutron TAS Taipan at the Australian Centre for Neutron Scattering. TasVisAn offers a range of functions, including data importing, reduction, plotting, contour mapping, convolution fitting, and more, for data collected on TAS instruments, especially on Sika and Taipan. It also supports data reduction of the current trendy multi-analyser and multiplexing TAS instruments, including the multiplexing mode of Sika. Besides, it includes scan simulation and batch file validation tools for both Taipan and Sika, assisting users in designing and planning experiments in advance. InsPy is a general-purpose Python package designed to calculate the four-dimensional (4D) instrument resolution in momentum-energy space for any TAS instrument. Combined with InsPy, TasVisAn supports both instrument resolution calculation and resolution-convoluted data fitting. Its flexible external data import feature further allows TasVisAn to be adapted for the visualization and convolution analysis of inelastic neutron scattering data across various TAS instruments.
Authors: Vladislav D. Kurilovich, Gabrielle Roberts, Leigh S. Martin, Matt McEwen, Alec Eickbusch, Lara Faoro, Lev B. Ioffe, Juan Atalaya, Alexander Bilmes, John Mark Kreikebaum, Andreas Bengtsson, Paul Klimov, Matthew Neeley, Wojciech Mruczkiewicz, Kevin Miao, Igor L. Aleiner, Julian Kelly, Yu Chen, Kevin Satzinger, Alex Opremcak
One of the roadblocks towards the implementation of a fault-tolerant superconducting quantum processor is impacts of ionizing radiation with the qubit substrate. Such impacts temporarily elevate the density of quasiparticles (QPs) across the device, leading to correlated qubit error bursts. The most damaging errors, $T_1$ errors, stem from QP tunneling across the qubit Josephson junctions (JJs). Recently, we demonstrated that this type of error can be strongly suppressed by engineering the profile of superconducting gap at the JJs in a way that prevents QP tunneling. In this work, we identify a new type of impact-induced correlated error that persists in the presence of gap engineering. We observe that impacts shift the frequencies of the affected qubits, and thus lead to correlated phase errors. The frequency shifts are systematically negative, reach values up to $3\,{\rm MHz}$, and last for $\sim 1\,{\rm ms}$. We provide evidence that the shifts originate from QP-qubit interactions in the JJ region. Further, we demonstrate that the shift-induced phase errors can be detrimental to the performance of quantum error correction protocols.
Authors: Yoshihito Kuno, Takahiro Orito, Ikuo Ichinose
We investigate a critical many-body system by introducing a Rényi generalized mutual information, connecting between Rényi mutual information and Rényi Shannon mutual information. This Rényi generalized mutual information can offer more experimentally accessible alternative than the conventional entanglement entropy. As a critical many-body state, we focus on the critical transverse-field Ising model (TFIM) described by the Ising conformal field theory (CFT). We show that even if we modify the non-selective projective measurement assumed in Rényi Shannon mutual information by replacing the measurement into decoherence by environment, the Rényi generalized Shannon mutual information maintains the CFT properties such as subsystem CFT scaling law and its central charge observed through both the conventional Rényi Shannon mutual information and Rényi mutual information. Furthermore, we apply a local decoherence to the critical ground state of the TFIM and numerically observe the Rényi generalized mutual information by changing the parameter controlling environment effect (corresponding to the strength of measurement) in the Rényi generalized mutual information and the strength of the decoherence to which the entire system subjects. We find that Rényi-$2$ type central charge connected to the central charge is fairly robust, indicating the strong robustness of the Ising CFT properties against local decoherence by environment.
Authors: Alejandro Castro, Tuan Minh Pham, Ernesto Ortega, David Machado
Xenophobic interactions play a role as important as homophilic ones in shaping many dynamical processes on social networks, such as opinion formation, social balance, or epidemic spreading. In this paper, we use belief propagation and Monte Carlo simulations on tree-like signed graphs to predict that a sufficient propensity to xenophobia can impede a consensus that would otherwise emerge via a phase transition. As the strength of xenophobic interactions and the rationality of individuals with respect to social stress decrease, this transition changes from continuous to discontinuous, with a strong dependence on the initial conditions. The size of the parameter region where consensus can be reached from any initial condition decays as a power-law function of the number of discussed topics.
Authors: J. Wijnen, J. Parker, M. Gagliano, E. Martínez-Pañeda
We combine state-of-the-art thermo-metallurgical welding process modelling with coupled diffusion-elastic-plastic phase field fracture simulations to predict the failure states of hydrogen transport pipelines. This enables quantitatively resolving residual stress states and the role of brittle, hard regions of the weld such as the heat affected zone (HAZ). Failure pressures can be efficiently quantified as a function of asset state (existing defects), materials and weld procedures adopted, and hydrogen purity. Importantly, simulations spanning numerous relevant conditions (defect size and orientations) are used to build \emph{Virtual} Failure Assessment Diagrams (FADs), enabling a straightforward uptake of this mechanistic approach in fitness-for-service assessment. Model predictions are in very good agreement with FAD approaches from the standards but show that the latter are not conservative when resolving the heterogeneous nature of the weld microstructure. Appropriate, \emph{mechanistic} FAD safety factors are established that account for the role of residual stresses and hard, brittle weld regions.
Authors: Zejian Li, Anna Delmonte, Rosario Fazio
We study monitored quantum dynamics of infinite-range interacting bosonic systems in the thermodynamic limit. We show that under semiclassical assumptions, the quantum fluctuations along single monitored trajectories adopt a deterministic limit for both quantum-jump and state-diffusion unravelings, and can be exactly solved. In particular, the hierarchical structure of the equations of motion explains the coincidence of entanglement phase transitions and dissipative phase transitions found in previous finite-size numerical studies. We illustrate the findings on a Bose-Hubbard dimer and a collective spin system.
Authors: Sergio Cerezo-Roquebrún, Simon Hands, Alejandro Bermudez
We explore the finite-density phase diagram of the single-flavour Gross-Neveu-Wilson (GNW) model using matrix product state (MPS) simulations. At zero temperature and along the symmetry line of the phase diagram, we find a sequence of inhomogeneous ground states that arise through a real-space version of the mechanism of Hilbert-space fragmentation. For weak interactions, doping the symmetry-protected topological (SPT) phase of the GNW model leads to localized charges or holes at periodic arrangements of immobile topological defects separating the fragmented subchains: a topological crystal. Increasing the interactions, we observe a transition into a parity-broken phase with a pseudoscalar condensate displaying a modulated periodic pattern. This soliton lattice is a sequence of topological charges corresponding to anti-kinks, which also bind the doped fermions at their respective centers. Out of this symmetry line, we show that quasi-spiral profiles appear with a characteristic wavevector set by the density $k = 2{\pi}{\rho}$, providing non-perturbative evidence for chiral spirals beyond the large-N limit. These results demonstrate that various exotic inhomogeneous phases can arise in lattice field theories, and motivate the use of quantum simulators to confirm such QCD-inspired phenomena in future experiments.
Authors: Hirakjyoti Sarma, Nilakshi Das
The structure and dynamics of a harmonically confined three dimensional finite dust cluster are investigated via both Langevin Dynamics (LD) and frictionless Molecular Dynamics (fMD) simulation. The static structure of the system is analyzed through the Radial Distribution Function, Center-two-particle correlation function(C2P) and angular correlation function. The intra-shell angular correlation, Radial Distribution Function and C2P remains largely unaffected by the dynamics employed. However, the inter-shell angular correlation exhibits sharp peaks at irregular angular intervals in fMD which are not seen in LD indicating strongly correlated motion of the two spherical shells in the cluster in fMD. The single particle dynamics of the cluster is characterized by the Van - Hove self autocorrelation function and Mean Squared Displacement (MSD). Notably, the Van - Hove autocorrelation function in fMD simulations exhibits narrower width and higher peak height as compared to the LD simulations, suggesting greater particle mobility in LD. Trajectory analysis reveals a rotational motion of the particles about a common axis in fMD which disappears with progressively increasing friction coefficient. We show that the disappearance of rotational motion with the introduction of neutral friction in the dynamics is due to the much faster relaxation of the interparticle distance as well as interparticle angular separation in LD as compared to fMD.
Authors: Dinesh Wagle, Daniel Stoeffler, Loic Temdie, Mojtaba Taghipour Kaffash, Vincent Castel, H. Majjad, R. Bernard, Yves Henry, Matthieu Bailleul, M. Benjamin Jungfleisch, Vincent Vlaminck
A caustic is a mathematical concept describing the beam formation when the beam envelope is reflected or refracted by a manifold. While caustics are common in a wide range of physical systems, caustics typically exhibit a reciprocal wave propagation and are challenging to control. Here, we utilize the highly anisotropic dispersion and inherent non-reciprocity of a magnonic system to shape non-reciprocal emission of caustic-like spin wave beams in an extended 200 nm thick yttrium iron garnet (YIG) film from a nano-constricted rf waveguide. We introduce a near-field diffraction model to study spin-wave beamforming in homogeneous in-plane magnetized thin films, and reveal the propagation of non-reciprocal spin-wave beams directly emitted from the nanoconstriction by spatially resolved micro-focused Brillouin light spectroscopy (BLS). The experimental results agree well with both micromagnetic simulation, and the near-field diffraction model. The proposed method can be readily implemented to study spin-wave interference at the sub-micron scale, which is central to the development of wave-based computing applications and magnonic devices.
Authors: Nassim Derriche, George Sawatzky
We present a novel and efficient real space, semiclassical model of electric polarization with general applicability to any system in which screening plays an important role. This model includes the effects of both atomic and bond polarizabilities, the latter originating from the modification of local bond charge transfer energies induced by polarizing charges. The nonlinear interference of multiple polarization clouds and the emergence of local field effects are highlighted as key phenomena highly influencing the short-range screening of the Coulomb interaction. As a representative system to showcase this model, the screened interaction between doped holes in the CuO$_2$ planes of cuprate high-temperature superconductors is investigated. This leads to the emergence of striking direction-dependent short-range minima in their Coulomb repulsion, which can strongly reduce the need for retardation effects and allow for an enhancement of the attractive interaction resulting from the exchange of bosons between two electrons or holes. This in turn enhances T$_C$, shortens the Cooper pair coherence length and supports the materialization of the pseudogap phase anisotropy observed in many high-T$_C$ superconductors.
Authors: William Legrand, Yana Kemna, Stefan Schären, Hanchen Wang, Davit Petrosyan, Luise Holder, Richard Schlitz, Myriam H. Aguirre, Michaela Lammel, Pietro Gambardella
The synthesis of nm-thick epitaxial films of iron garnets by physical vapor deposition has opened up exciting opportunities for the on-chip generation and processing of microwave signals encoded in magnons. However, iron garnet thin films suffer from demanding lattice-matching and stoichiometry requirements. Here a new approach to their synthesis is developed, enabling a precise and continuous tuning of iron garnet compositions based on the co-sputtering of binary oxides. By substituting a controlled proportion of iron with additional yttrium, Y$_{3}$(Y$_{x}$Fe$_{5-x}$)O$_{12}$ films of high crystalline quality are obtained, combining a widely tunable lattice parameter and excellent magnetization dynamics. This enables iron garnet thin films suited for cryogenic applications, which have long remained impractical due to microwave losses caused by paramagnetic garnet substrates. Low-temperature ferromagnetic resonance confirms the elimination of substrate paramagnetic losses for Y$_{3}$(Y$_{x}$Fe$_{5-x}$)O$_{12}$ films lattice-matched to Y$_{3}$Sc$_{2}$Ga$_{3}$O$_{12}$ (YSGG), a diamagnetic substrate. The Y$_{3}$(Y$_{x}$Fe$_{5-x}$)O$_{12}$ system can be matched to other substrates such as (Gd,Y)$_{3}$Sc$_{2}$Ga$_{3}$O$_{12}$. Bi-substituted films of (Bi$_{0.8}$Y$_{2.2}$)Fe$_{5}$O$_{12}$ also have ideal lattice matching to YSGG, demonstrating the versatility of this approach. This opens unprecedented options for cation substitutions in iron garnet films, offering a promising avenue to new properties and quantum magnonic devices operating in low-temperature environments.
Authors: Priya Sharma, Jens Koch, Eran Ginossar
Superconducting circuits can exhibit quantized energy levels and long coherence times. Harnessing the anharmonicity offered by Josephson junctions, such circuits have been successfully employed as qubits, quantum limited amplifiers and sensors. Here, we consider superfluidity as the charge-neutral analogue of superconductivity. Both dissipationless mass flow and Josephson tunneling have been demonstrated in superfluid helium. We propose a quantum device, consisting of a superfluid weak link and a mechanical element. The superfluid motion in this device is quantized. The resulting discrete energy levels are resolvable at millikelvin temperatures essential to maintaining the superfluid state. Appropriate device engineering can yield the necessary nonlinearity to realize qubit functionality. Hence, this device can potentially operate as a charge-neutral, superfluid quantum bit with micron-sized dimensions and millisecond scale coherence time. We show that this quantum regime is within reach for a range of device designs.
Authors: Allan N. Kaufman, Bruce I. Cohen, Alain J. Brizard
Presented here is a transcription of the lecture notes from Professor Allan N. Kaufman's graduate statistical mechanics course at Berkeley from the 1972-1973 academic year. Part 1 addresses equilibrium statistical mechanics with topics: fundamentals, classical fluids and other systems, chemical equilibrium, and long-range interactions. Part 2 addresses non-equilibrium statistical mechanics with topics: fundamentals, Brownian motion, Liouville and Klimontovich equations, Landau equation, Markov processes and Fokker-Planck equation, linear response and transport theory, and an introduction to non-equilibrium quantum statistical mechanics.
Authors: Arindam Mallick, Alexei Andreanov
We consider tight-binding models on Bravais lattices with anisotropic onsite potentials that vary along a given direction and are constant along the transverse one. Inspired by our previous work on flat bands in anti-\(\mathcal{PT}\) symmetric Hamiltonians [Mallick et al., Phys.~Rev.~A 105, L021305 (2022)], we construct an anti-\(\mathcal{PT}\) symmetric Hamiltonians with an \(E=0\) flat band by tuning the hoppings and the shapes of potentials. This construction is illustrated for the square lattice with bounded and unbounded potentials. Unlike flat bands in short-ranged translationally invariant Hamiltonians, we conjecture that the considered \(E=0\) flat bands do not host compact localized states. Instead the flat-band eigenstates exhibit a localization transition along the potential direction upon increasing the potential strength for bounded potentials. For unbounded potentials flat-band eigenstates are always localized irrespective of the potential strength.
Authors: Tu Hong, Xiao Yan Xu
Non-Fermi liquids are an important topic in condensed matter physics, as their characteristics challenge the framework of traditional Fermi liquid theory and reveal the complex behavior of electrons in strongly interacting systems. Despite some progress in this field, linear-in-temperature resistivity and inverse-in-frequency tail of optical conductivity are unresolved issues in non-Fermi liquids. Both the experimentally observed smeared region and the theoretically predicted marginal Fermi liquid suggest that spatial disorder seems to be an important driver of these phenomena. By performing large-scale determinant quantum Monte Carlo (DQMC) simulations in the ferromagnetic spin-fermion model at finite $N$, beyond the large-$N$ used in previous theoretical work, we investigated the role of spatial disorder in the critical Fermi surface (FS) of this model. We proposed a corrected theory of our system, which is based on a modified Eliashberg theory and a universal theory of strange metals. This theory agrees well with the data obtained from DQMC, particularly in capturing the $\omega \ln \omega$ type self-energy characteristic of marginal Fermi liquid behavior, though temperature limitations prevent us from observing the linear-in-temperature scattering rate. Our findings offer strong and unbiased validation of the universal theory of strange metals, broaden the applicability of the modified Eliashberg theory, and provide insights for numerically searching for marginal Fermi liquid and linear-in-temperature resistivity.
Authors: J. E. Hirsch
In Entropy 24, 83 (2022) [1], titled "The Law of Entropy Increase and the Meissner Effect", A. Nikulov claims that the Meissner effect exhibited by type I superconductors violates the second law of thermodynamics. Contrary to this claim, I show that the Meissner effect is consistent with the second law of thermodynamics provided that a mechanism exists for the supercurrent to start and stop without generation of Joule heat. The theory of hole superconductivity provides such a mechanism, the conventional theory of superconductivity does not. It requires the existence of hole carriers in the normal state of the system.
Authors: Jocelyn L. Mendes, Hyun Jun Shin, Jae Yeon Seo, Nara Lee, Young Jai Choi, Joel B. Varley, Scott K. Cushing
Controlling the effects of photoexcited polarons in transition metal oxides can enable the long timescale charge separation necessary for renewable energy applications as well as controlling new quantum phases through dynamically tunable electron-phonon coupling. In previously studied transition metal oxides, polaron formation is facilitated by a photoexcited ligand-to-metal charge transfer (LMCT). When the polaron is formed, oxygen atoms move away from iron centers, which increases carrier localization at the metal center and decreases charge hopping. Studies of yttrium iron garnet and erbium iron oxide have suggested that strong electron and spin correlations can modulate photoexcited polaron formation. To understand the interplay between strong spin and electronic correlations in highly polar materials, we studied gadolinium iron oxide (GdFeO3), which selectively forms photoexcited polarons through an Fe-O-Fe superexchange inter-action. Excitation-wavelength-dependent transient extreme ultraviolet (XUV) spectroscopy selectively excites LMCT and metal-to-metal charge transfer transitions (MMCT). The LMCT transition suppresses photoexcited polaron formation due to the balance between superexchange and Hubbard interactions, while MMCT transitions result in photoexcited polaron formation within 250+/-40 fs. Ab initio theory demonstrates that electron and hole polarons localize on iron centers following MMCT. In addition to understanding how strong electronic and spin correlations can control strong electron-phonon coupling, these experiments separately measure electron and hole polaron interactions on neighboring metal centers for the first time, providing insight into a large range of charge-transfer and Mott-Hubbard insulators.
Authors: Chuan Chen, Inti Sodemann Villadiego
We compute the spectra of anyon quasiparticles in all three super-selection sectors of the Kitaev model (i.e., visons, fermions and bosons), perturbed by a Zeeman field away from its exactly solvable limit, to gain insights on the competition of its non-abelian spin-liquid with other nearby phases, such as the mysterious intermediate state observed in the antiferromagnetic model. Both for the ferro- and antiferro-magnetic models we find that the fermions and visons become gapless at nearly identical critical Zeeman couplings. In the ferromagnetic model this is consistent with a direct transition into a polarized state. In the anti-ferromagnetic model this implies that previous theories of the intermediate phase viewed as a spin liquid with a different fermion Chern number are inadequate, as they presume that the vison gap does not close. In the antiferromagnetic model we also find that a bosonic quasiparticle becomes gapless at nearly the same critical field as the fermions and visons. This boson carries the quantum numbers of an anti-ferromagnetic order parameter, suggesting that the intermediate phase has spontaneously broken symmetry with this order.
Authors: Serafim S. Babkin, Benjamin Joecker, Karsten Flensberg, Maksym Serbyn, Jeroen Danon
Technology involving hybrid superconductor-semiconductor materials is a promising avenue for engineering quantum devices for information storage, manipulation, and transmission. Proximity-induced superconducting correlations are an essential part of such devices. While the proximity effect in the conduction band of common semiconductors is well understood, its manifestation in confined hole gases, realized for instance in germanium, is an active area of research. Lower-dimensional hole-based systems, particularly in germanium, are emerging as an attractive platform for a variety of solid-state quantum devices, due to their combination of efficient spin and charge control and long coherence times. The recent experimental realization of the proximity effect in germanium thus calls for a theoretical description that is tailored to hole gases. In this work, we propose a simple model to describe proximity-induced superconductivity in two-dimensional hole gases, incorporating both the heavy-hole (HH) and light-hole (LH) bands. We start from the Luttinger-Kohn model, introduce three parameters that characterize hopping across the superconductor-semiconductor interface, and derive explicit intraband and interband effective pairing terms for the HH and LH bands. Unlike previous approaches, our theory provides a quantitative relationship between induced pairings and interface properties. Restricting our general model to an experimentally relevant case where only the HH band crosses the chemical potential, we predict the coexistence of $s$-wave and $d$-wave singlet pairings, along with triplet-type pairings, and modified Zeeman and Rashba spin-orbit couplings. Our results thus present a starting point for theoretical modeling of quantum devices based on proximitized hole gases, fueling further progress in quantum technology.
Authors: Luis A. Peña Ardila, Arturo Camacho-Guardian
Polarons have emerged as a powerful concept across many-fields in physics to study an impurity coupled to a quantum bath. The interplay between impurity physics and the formation of composite objects remains a relevant problem to understand how few- and many-body states are robust towards complex environments and polaron physics. In most cases, impurities are point-like objects. The question we address here is how quasiparticle properties are affected when impurities possess an internal structure. The simplest yet fundamental structure for the impurity is a dimer state. Here, we investigate the polaronic properties of a dimer dressed by the elementary excitations of a bosonic bath. We solve the two-body impurity-impurity problem to determine the position and broadening of the bound state and consider the polaron dressing using a field-theory approach. We demonstrate the emergence of different dressed dimer regimes, where polaron dressing drives a dimer from a well-defined to an ill-defined bound state.
Authors: Ruibin Xu, B.N.J. Persson
We present experimental wear data for polymethyl methacrylate (PMMA) sliding on tile, sandpaper, and polished steel surfaces, as well as for soda-lime, borosilicate, and quartz glass sliding on sandpaper. The results are compared with a recently developed theory \cite{ToBe} of sliding wear based on crack propagation (fatigue), originally formulated for elastic contact and here extended to include plasticity. The elastoplastic wear model predicts wear rates that agree reasonably well with the experimental results for PMMA and soda-lime glass. However, deviations observed for quartz suggest that material-specific deformation mechanisms, particularly the differences between crystalline and amorphous structures, may need to be considered for accurate wear predictions across different materials. In addition, the model reveals a non-monotonic dependence of the wear rate on the penetration hardness $\sigma_{\rm P}$. Thus, for plastically soft material, the wear rate increases with increasing $\sigma_{\rm P}$, while for hard materials, it decreases. This contrasts with Archard's wear law, where the wear rate decreases monotonically with increasing $\sigma_{\rm P}$.
Authors: Kishor Nepal, Aashish Gautam, Chinonso Ugwumadu, David Drabold
We present new atomistic models of amorphous silicon (a-Si) and hydrogenated amorphous silicon (a-Si:H) surfaces. The a-Si model included 4096 atoms and was obtained using local orbital density functional theory. By analyzing a slab model (periodic in two dimensions with a slab about 44 Å thick), we observed a strong correlation between surface structure and surface charge density, which might be compared to STM experiments. Hydrogen atoms added near the under-coordinated surface atoms passivate dangling bonds and induce structural rearrangements. We analyze the electronic structure, including the localization of the states, and note resonant mixing between bulk and surface defect structures. We also compute the classical normal modes of the hydrogenated a-Si and compare them to experiments where possible. Our work is a step toward understanding the meaning of ``surface reconstruction" for a noncrystalline material.
Authors: A. Nonato (1), G.G.S. Teles (1), C. C. Silva (1), R. X. Silva (2), Juan S. Rodríguez-Hernández (3), C.W.A. Paschoal (3), A. S. de Menezes (4), C.C. Santos (4) ((1) Coordenação de Ciências Naturais Física, Universidade Federal do Maranhão, Centro de Ciências de Bacabal, (2) Centro de Ciência e Tecnologia em Energia e Sustentabilidade (CETENS), Universidade Federal do Recôncavo da Bahia, (3) Departamento de Física, Universidade Federal do Ceará, Campus do Pici, (4) Departamento de Física, Universidade Federal do Maranhão, Centro de Ciências de Exatas CCET)
We present a study of low-concentration Zn (II) impurities in L-Alanine Single Crystal (ZNLA) employing resonant Raman scattering and optical absorption spectroscopy. By analyzing the relative integrated intensity of the selective vibrational modes, we observe a resonant enhancement of Raman-active modes near the UV absorption band, associated with vibrations of the amino and carboxyl groups in ZNLA. These findings suggest that zinc cations occupy an interstitial position coordinated by amino and carboxyl groups. Also, ZNLA single crystal shows a strong antiresonance behavior for some modes associated with amino and carboxyl groups. The antiresonance model in the cross-section allowed the estimation of the bandgap to be 3.8 eV, which perfectly agrees with the direct bandgap obtained from the absorption spectrum (3.75 eV). Finally, our approach proves to be useful for detecting interactions between transition metal ion impurities and intramolecular structures in other transition metal-doped organic amino acid systems.
Authors: Hidetoshi Wada, Tiantian Zhang, Shuichi Murakami
Recent studies showed that topologically trivial insulators may have fractionally quantized corner charges due to the topological invariant called a filling anomaly. Such crystal shapes in three dimensions are restricted to vertex-transitive polyhedra, which are classified into spherical and cylindrical families. The previous works derived formulas of the fractional corner charge for the spherical family, which corresponds to the tetrahedral and cubic space groups (SGs). In this study, we derive all the corner charge formulas for the cylindrical family, which corresponds to the orthorhombic, tetragonal, hexagonal, and trigonal crystal shapes. We show that all the real-space formulas of the filling anomaly for the cylindrical SGs are universally determined by the total charges at the Wyckoff position (WP) 1a. Moreover, we derive the k-space formulas of the corner charge for the cylindrical cases with time-reversal symmetry (TRS). From our results, we also show that CsLi$_{2}$Cl_{3}, KN_{3}, and Li_{3}N are candidate materials with a quantized corner charge by using the ab initio calculations. Together with our previous work, we exhaust corner charge formulas for all the SGs and crystal shapes having quantized corner charges.
Authors: D. Michel Pino, Rubén Seoane-Souto, Maria José Calderón, Ramón Aguado, José Carlos Abadillo-Uriel
Hybrid superconductor-semiconductor systems have received a great deal of attention in the last few years because of their potential for quantum engineering, including novel qubits and topological devices. The proximity effect, the process by which the semiconductor inherits superconducting correlations, is an essential physical mechanism of such hybrids. Recent experiments have demonstrated the proximity effect in hole-based semiconductors, but, in contrast to electrons, the precise mechanism by which the hole bands acquire superconducting correlations remains an open question. In addition, hole spins exhibit a complex strong spin-orbit interaction, with largely anisotropic responses to electric and magnetic fields, further motivating the importance of understanding the interplay between such effects and the proximity effect. In this work, we analyze this physics with focus on germanium-based two-dimensional gases. Specifically, we develop an effective theory supported by full numerics, allowing us to extract various analytical expressions and predict different types of superconducting correlations including non-standard forms of singlet and triplet pairing mechanisms with non-trivial momentum dependence; as well as different Zeeman and Rashba spin-orbit contributions. This, together with their precise dependence on electric and magnetic fields, allows us to make specific experimental predictions, including the emergence of f-type superconductivity, Bogoliubov Fermi surfaces, and gapless regimes caused by large in-plane magnetic fields.
Authors: Guo-Qing Zhang, Ling-Zhi Tang, L. F. Quezada, Shi-Hai Dong, Dan-Wei Zhang
Recent studies of 2D moiré materials have opened opportunities for advancing condensed matter physics. However, the effect of 1D moiré potentials on topological and correlated phases remains largely unexplored. Here we reveal a sequence of trivial-to-topological transitions and periodic-moiré-spin density waves induced by the 1D commensurate moiré potentials for spin-1/2 fermionic atoms. Such reentrant topology from a trivial phase is absent without the moiré potential and can be understood as the renormalization of topological parameters by the moiré strength. We then unveil the critical exponent and localization properties of the single-particle eigenstates. The periodic spin density wave of many-body ground states is contributed by the moiré potential, and is enhanced by on-site interactions but suppressed by nearest-neighbor interactions. Our results enrich the topological physics with multiple transitions and spin-density orders in 1D moiré systems, and the realization of the proposed model is promising in near-future ultracold atom setups.
Authors: G. Zhao, Y. Wang, X.-F. Qian
We conduct a systematic analysis of cavity effects on the decay dynamics of an open magnonic system. The Purcell effect on the magnon oscillator decay is thoroughly examined for both driven and non-driven scenarios. Analytical conditions are determined to distinguish between strong and weak coupling regimes, corresponding to oscillatory and pure decay behaviors respectively. Additionally, our theory also predicts the decay of the photon mode within the cavity-magnonic open system, demonstrating excellent agreement with existing experimental data. Our findings and methodologies can provide valuable insights for advancing research in cavity magnonic quantum control, quantum information processing, and the development of magnonic quantum devices.
Authors: Takato Yoshimura, Lucas Sá
We address the longstanding challenge in quantum many-body theory of reconciling unitary dynamics with irreversible relaxation. In classical chaos, the unitary evolution operator develops Ruelle-Pollicott (RP) resonances inside the unit circle in the continuum limit, leading to mixing. In the semiclassical limit, chaotic single-particle quantum systems relax with the same RP resonances. In contrast, the theory of quantum many-body RP resonances and their link to irreversibility remain underdeveloped. Here, we relate the spectral form factor to the sum of autocorrelation functions and, in generic many-body lattice systems without conservation laws, argue that all quantum many-body RP resonances converge inside the unit disk, highlighting the role of nonunitary and the thermodynamic limit. While we conjecture this picture to be general, we analytically prove the emergence of irreversibility in the random phase model (RPM), a paradigmatic Floquet quantum circuit model, in the limit of large local Hilbert space dimension. To this end, we couple it to local environments and compute the exact time evolution of autocorrelation functions, the dissipative form factor, and out-of-time-order correlation functions (OTOCs). Although valid for any dissipation strength, we then focus on weak dissipation to clarify the origin of irreversibility in unitary systems. When the dissipationless limit is taken after the thermodynamic limit, the unitary quantum map develops an infinite tower of decaying RP resonances -- chaotic systems display so-called anomalous relaxation. We also show that the OTOC in the RPM can undergo a two-stage relaxation and that during the second stage, the approach to the stationary value is again controlled by the leading RP resonance. [See the paper for the full abstract.]
Authors: Peerasait Prachaseree, Emma Lejeune
Random fiber networks form the structural foundation of numerous biological tissues and engineered materials. From a mechanics perspective, understanding the structure-function relationships of random fiber networks is particularly interesting because when external force is applied to these networks, only a small subset of fibers will actually carry the majority of the load. Specifically, these load-bearing fibers propagate through the network to form load paths, also called force chains. However, the relationship between fiber network geometric structure, force chains, and the overall mechanical behavior of random fiber network structures remains poorly understood. To this end, we implement a finite element model of random fiber networks with geometrically exact beam elements, and use this model to explore random fiber network mechanical behavior. Our focus is twofold. First, we explore the mechanical behavior of single fiber chains and random fiber networks. Second, we propose and validate an interpretable analytical approach to predicting fiber network mechanics from structural information alone. Key findings include insight into the critical strain-stiffening transition point for single fiber chains and fiber networks generated from a Voronoi diagram, and a connection between force chains and the distance-weighted graph shortest paths that arise by treating fiber networks as spatial graph structures. This work marks an important step towards mapping the structure-function relationships of random fiber networks undergoing large deformations. Additionally, with our code distributed under open-source licenses, we hope that future researchers can directly build on our work to address related problems beyond the scope defined here.
Authors: Saeed S. I. Almishal, Pat Kezer, Yasuyuki Iwabuchi, Jacob T. Sivak, Sai Venkata Gayathri Ayyagari, Saugata Sarker, Matthew Furst, Gerald Bejger, Billy Yang, Simon Gelin, Nasim Alem, Ismaila Dabo, Christina M. Rost, Susan B. Sinnott, Vincent Crespi, Venkatraman Gopalan, Roman Engel-Herbert, John T. Heron, Jon-Paul Maria
This manuscript presents a working model linking chemical disorder and transport properties in correlated-electron perovskites with high-entropy formulations and a framework to actively design them. We demonstrate this new learning in epitaxial Sr$x$(Ti,Cr,Nb,Mo,W)O$3$ thin films that exhibit exceptional crystalline fidelity despite a diverse chemical formulation where most B-site species are highly misfit with respect to valence and radius. X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy confirm a unique combination of chemical disorder and structural perfection in thick epitaxial layers. This combination produces significant electron correlation, low electrical resistivity, and an optical transparency window that surpasses that of constituent end-members, with a flattened frequency- and temperature-dependent response. We address the computational challenges of modeling such systems and investigate short-range ordering using cluster expansion. These results showcase that unusual d-metal combinations access an expanded property design space that is predictable using end-member characteristics -- though unavailable to them -- thus offering performance advances in optical, spintronic, and quantum devices.
Authors: Yao Du, Jonas Veenstra, Ryan van Mastrigt, Corentin Coulais
Learning to change shape is a fundamental strategy of adaptation and evolution of living organisms, from bacteria and cells to tissues and animals. Human-made materials can also exhibit advanced shape morphing capabilities, but lack the ability to learn. Here, we build metamaterials that can learn complex shape-changing responses using a contrastive learning scheme. By being shown examples of the target shape changes, our metamaterials are able to learn those shape changes by progressively updating internal learning degrees of freedom -- the local stiffnesses. Unlike traditional materials that are designed once and for all, our metamaterials have the ability to forget and learn new shape changes in sequence, to learn multiple shape changes that break reciprocity, and to learn multistable shape changes, which in turn allows them to perform reflex gripping actions and locomotion. Our findings establish metamaterials as an exciting platform for physical learning, which in turn opens avenues for the use of physical learning to design adaptive materials and robots.
Authors: Zhangkai Cao, Shuning Tan, Ji Liu, Xiaosen Yang, Tao Ying, Ho-Kin Tang, Cho-Tung Yip
Motivated by significant discrepancies between experimental observations of electron-doped cuprates and numerical results of the Hubbard model, we investigate the role of nearest-neighbor (NN) electron interactions $V$ by studying the $t-U-V$ model on square lattices. Upon doping $\delta$= 0.153, by using constrained path quantum Monte Carlo (CPQMC) method, we find that NN electron attraction $V$ can notably drive an exotic $p$-wave spin-triplet pairing, while the NN electron repulsion $V$ will suppress the $d_{x^2-y^2}$-wave ($d$-wave) pairing and triggers the $d_{xy}$-wave pairing. Especially in the intermediate coupling regime, as NN repulsion increases, the intensity of $d_{xy}$-wave pairing also increases, further suppressing the presence of $d$-wave pairing, which may help explain the notable suppression of $d$-wave pairing in electron-doped cuprate superconductors. Besides the pairing phase, we also find that the NN electron attraction $V$ has no significant effect on spin density wave (SDW) and charge density wave (CDW), but repulsion $V$ significantly enhanced CDW and suppressed SDW. Our study suggests the $t-U-V$ Hubbard model can serve as the minimal model to capture the essential physics of the electron-doped cuprates.
Authors: Luciano Jacopo DOnofrio, Maria Teresa Mercaldo, Wojciech Brzezicki, Adam Klosinski, Federico Mazzola, Carmine Ortix, Mario Cuoco
The control of spin and orbital angular momentum without relying on magnetic materials is commonly accomplished by breaking of inversion symmetry, which enables charge-to-spin conversion and spin selectivity in electron transfer processes occurring in chiral media. In contrast to this perspective, we show that orbital moment filtering can be accomplished in centrosymmetric systems: the electron states can be selectively manipulated allowing for the preferential transfer of electrons with a particular orbital momentum orientation. We find that orbital moment filtering is indeed efficiently controlled through orbital couplings that break both mirror and rotational symmetries. We provide the symmetry conditions required for the electron transmission to achieve orbital filtering and relate them to the orientation of the orbital moment. The presence of atomic spin-orbit interaction in the centrosymmetric transmission medium leads to the selective filtering of spin and orbital moments. Our findings allow to identify optimal regimes for having highly efficient simultaneous spin and orbital moment filtering.
Authors: Adrián Begué, Maria Grazia Proietti, José Ignacio Arnaudas, Miguel Ciria
The large magnetostriction in FeGa alloys is relevant for manifold applications, but for thin films, it can play a prominent role in controlling the strength of the magnetic anisotropy. Bulk samples show values depending on the extensive preparation procedure compendium, which is limited in its temperature range for high-quality thin-film synthesis. Here, we present a study of the magnetoelastic coupling coefficients $B_1$ and $B_2$ in epitaxial FeGa thin films below 50 nm deposited on the MgO(001) surface at 150 $^\circ$C by the cantilever method. Series of films with 22, 28, and 33 at. % Ga do not show thickness-dependent variations for $B_1$ and $B_2$, but $-B_1$ for the 22 at. % Ga composition is 10 MPa, roughly 2 times the bulk value and smaller than the bulk-like value of $-B_1$=12.1 MPa obtained for a film with 17 at. % Ga. This enhancement is correlated with the A2 crystal structure for the film rather than the coexistence with D0$_3$ or other ordered nanometric precipitates proposed for bulk samples. Synchrotron diffraction excludes the formation of long-range L6$_0$, or D0$_3$ precipitates in samples with (001)A2 peaks at concentrations around 25 at. % Ga, which implies partial chemical disorder. The analysis of extended x-ray absorption fine structure measurements points to a D0$_3$ local order with a residual number of Ga-Ga pairs. Considering that the substrate quenches the movable strain in the A2 phase described in dual-phase structures, our results point to the important role of the electronic structure of the iron atoms modified by the presence of Ga in the alloy. This effect enlarges $B_1$ in films with the A2 phase, stabilized using epitaxial growth.
Authors: Yuya Ominato, Masahito Mochizuki
We theoretically discover possible dc-current induction and high-harmonic generation from photodriven chiral fermions in B20-type semimetals irradiated with circularly polarized light as nonlinear optical responses with several unconventional properties. First, we find multiple sign changes of the induced bulk dc photocurrent as a function of light parameters, which is ascribed to the nature of asymmetric photon-dressed bands in chiral systems. Moreover, we observe a parity-dependent directivity of high-harmonic generation where the odd- and even-order harmonics have intensities only in directions perpendicular and parallel to the polarization plane, respectively, which can be understood from dynamical symmetry of the present photodriven chiral systems.
Authors: Srinivas V. Mandyam, Weicen Dong, Xiaoxian Yan, Binru Zhao, Elen Duverger-Nedellec, Junfa Lin, Tianlong Xia, Zhiying Zhao, Xi Chen, Jie Ma, Hui Xing, F. Malte Grosche, Matteo Baggioli
Nowotny chimney ladder (NCL) crystals present physical properties in between the contrasting paradigms of ideal crystal and amorphous solid, making them promising candidates for thermoelectric applications due to their inherently low thermal conductivity. Here, we report an extensive experimental characterization of the thermodynamic and thermoelectric transport properties of a large class of NCL materials, focusing on the intermetallic compound Ru$_2$Sn$_{3}$. We show that the heat capacity of these NCL compounds exhibits a boson-peak-like glassy anomaly between $8$ K and $14$ K. By combining experimental measurements with density functional theory (DFT), we attribute its microscopic origin to extremely low-energy optical phonons that universally appear as a consequence of the chimney ladder sublattice structure. Additionally, the measured thermal conductivity and the thermoelectric response present distinct anomalous glass-like features that strongly correlate with the dynamics of the low-lying optical phonons revealed by DFT. Our work demonstrates that low-energy optical modes in ordered crystals can induce glassy behavior, outlining a pathway to design metallic materials with low thermal conductivity and unique thermoelectric properties without the need for disorder or strong electronic correlations.
Authors: G. Giavaras, Ruben Seoane Souto, Maria Jose Calderon, Ramon Aguado
Leveraging the higher harmonics content of the Josephson potential in a superconducting circuit offers a promising route in the search for new qubits with increased protection against decoherence. In this work, we demonstrate how the flux tunability of a hybrid semiconductor-superconductor Josephson junction based on a single full-shell nanowire enables this possibility. Near one flux quantum, $\Phi\approx \Phi_0=h/2e$, we find that the qubit system can be tuned from a gatemon regime to a parity-protected regime with qubit eigenstates localized in phase space in the $0$ and $\pi$ minima of the Josephson potential ($\cos 2\varphi_0$). Estimates of qubit coherence and relaxation times due to different noise sources are presented.
Authors: Lei Gioia, Ryan Thorngren
We construct Hamiltonian models on a 3+1d cubic lattice for a single Weyl fermion and for a single Weyl doublet protected by exact (as opposed to emergent) chiral symmetries. In the former, we find a not-on-site, non-compact chiral symmetry which can be viewed as a Hamiltonian analog of the Ginsparg-Wilson symmetry in Euclidean lattice models of Weyl fermions. In the latter, we combine an on-site $U(1)$ symmetry with a not-on-site $U(1)$ symmetry, which together generate the $SU(2)$ flavor symmetry of the doublet at low energies, while in the UV they generate an algebra known in integrability as the Onsager algebra. This latter model is in fact the celebrated magnetic Weyl semimetal which is known to have a chiral anomaly from the action of $U(1)$ and crystalline translation, that gives rise to an anomalous Hall response - however reinterpreted in our language, it has two exact $U(1)$ symmetries that gives rise to the global $SU(2)$ anomaly which protects the gaplessness even when crystalline translations are broken. We also construct an exact symmetry-protected single Dirac cone in 2+1d with the $U(1) \rtimes T$ parity anomaly. Our constructions evade both old and recently-proven no-go theorems by using not-on-siteness in a crucial way, showing our results are sharp.
Authors: Nozomi Higashino, Yasuhiro Tada
We study creation of quasi-particles in fractional Chern insulators (FCI) under magnetic fields. We consider two representative models, the Kapit-Mueller model and the checkerboard model, which have distinct band properties in terms of the quantum geometry. The former satisfies the so-called ideal condition and well mimics the lowest Landau level, while the latter is not ideal for realization of FCI states. It is found within exact diagonalization that both quasi-holes and quasi-electrons are stably created by the magnetic fields in the Kapit-Mueller model. On the other hand, stability of the quasi-particle creation depends on directions of the magnetic field in the checkerboard model. Although the quasi-electron creation is stable under a magnetic field, the quasi-hole creation and the underlying FCI state are unstable for the opposite field direction, leading to a field-induced non-FCI state. We point out that this difference can be understood based on the multiband quantum geometry in the presence of the magnetic fields.
Authors: Long Zhang, Guangxin Ni, Junjie He, Guoying Gao
Altermagnets with non-relativistic momentum-dependent spin splitting and compensated net magnetic moments have recently garnered significant interest in spintronics, particularly as pinning layers in magnetic tunnel junctions (MTJs). However, room-temperature (RT) altermagnet-based MTJs with tunable tunneling magnetoresistance (TMR) or electroresistance (TER) modulated by multiferroicity remains largely unexplored. Here, we propose an experimentally fabricable above-RT multiferroic MTJ, comprising an altermagnetic metal, ferroelectric barrier, and ferromagnetic metal-epitomized by a CrSb/In2Se3/Fe3GaTe2 heterostructure. Our calculations with first-principles and nonequilibrium Green function method indicate that the architecture enables magnetically switchable TER, electrically tunable TMR, and dual-mode controllable spin filtering. To disentangle the roles of ferroelectricity and the tunnel barrier, non-ferroelectric Sb2Se3 and a vacuum gap are exploited as control cases. Remarkably, the system achieves TMR up to 2308 %, TER of 707 %, and near-perfect spin filtering efficiency. Both TMR and TER are considerable for CrSb/In2Se3/Fe3GaTe2 with either Cr or Sb interface. These findings demonstrate the above-RT multiferroic altermagnet-based MTJs and highlight their exciting potential as a versatile platform for next-generation spin dynamics, magnetic-sensing and quantum logic nano-devices.
Authors: Justus Teller, Christian Schäfer, Kristof Moors, Benjamin Bennemann, Matvey Lyatti, Florian Lentz, Detlev Grützmacher, Roman-Pascal Riwar, Thomas Schäpers
We study the frustration pattern of a square lattice with in-situ fabricated Nb-Pt-Nb four-terminal Josephson junctions. The four-terminal geometry gives rise to a checker board pattern of alternating fluxes f, f' piercing the plaquettes, which stabilizes the Berezinskii-Kosterlitz-Thouless transition even at irrational flux quanta per plaquette, due to an unequal repartition of integer flux sum f+f' into alternating plaquettes. This type of frustrated frustration manifests as a beating pattern of the dc resistance, with state configurations at the resistance dips gradually changing between the conventional zero-flux and half-flux states. Hence, the four-terminal Josephson junction array offers a promising platform to study previously unexplored flux and vortex configurations, and provides an estimate on the spatial expansion of the four-terminal Josephson junction central weak link area.
Authors: Lan-Ye He, Xin-Man Ye, Dao-Xin Yao
We investigate the squared sublattice magnetizations and magnetic excitations of a $S=1/2$ trilayer antiferromagnetic Heisenberg model with interlayer interaction $J_{\bot}$ and intralayer interaction $J_{//}$ by employing stochastic series expansion quantum Monte Carlo (SSE-QMC) and stochastic analytic continuation (SAC) methods. Compared with the bilayer model, the trilayer model has one inner layer and two outer layers. The change in its symmetry can lead to special magnetic excitations. Our study reveals that the maximum of the magnetization of the outer sublattice corresponds to smaller ratio parameter $g={J_{//}}/{J_{\bot}}$, a finding that is verified using the finite-size extrapolation. As $g$ decreases, the excitation spectra gradually evolve from a degenerate magnon mode with continua to low-energy and high-energy branches. Particularly when $g$ is small enough, like $0.02$, the high-energy spectrum further splits into characteristic doublon ($\approx J_{\bot}$) and quarton ($\approx 1.5 J_{\bot}$) spectral bands. Moreover, the accuracy of the magnetic excitations is confirmed through the SpinW software package and the dispersion relations derived through the linear spin wave theory. Our results provide an important reference for experiments, which can be directly compared with experimental data from inelastic neutron scattering results to verify and guide the accuracy of experimental detection.
Authors: Rashmi Kandari, Rudolf Podgornik, Sunita Kumari
Precisely controlling the surface charge of zwitterionic macromolecules is crucial for tailoring their properties and optimizing them for specific applications. Here, we present a generalized calculation scheme for determining the screening length in solutions containing zwitterionic macroions, where the charge of the macroion is controlled by the electrolyte solution. This scheme bypasses the need to solve the Poisson Boltzmann equation by expressing the inverse screening parameter in terms of the derivative of pressure with respect to chemical potential. The scheme reveals that the screening length has two components: one related to the Debye length with effective charges, and another stemming from the macroion surface dissociation equilibrium, which exhibits a screening resonance behavior. Furthermore, we find that the nonuniform surface charge distribution induced by pH responsive charge regulation strongly affects the screening behavior. The charge regulation properties of macroions, even in dilute solutions, are a key factor in the screening of electrostatic interactions, offering insights into complex biological and nanomaterial systems.
Authors: Christian Gualerzi, Leonardo Pisani, Pierbiagio Pieri
We investigate the mechanical stability of Bose-Fermi mixtures at zero temperature in the presence of a tunable Feshbach resonance, which induces a competition between boson condensation and boson-fermion pairing when the boson density is smaller than the fermion density. Using a many-body diagrammatic approach validated by fixed-node Quantum Monte Carlo calculations and supported by recent experimental observations, we determine the minimal amount of boson-boson repulsion required to guarantee the stability of the mixture across the entire range of boson-fermion interactions from weak to strong coupling. Our stability phase diagrams indicate that mixtures with boson-to-fermion mass ratios near two, such as the $^{87}$Rb-$^{40}$K system, exhibit optimal stability conditions. Moreover, by applying our results to a recent experiment with a $^{23}$Na-$^{40}$K mixture, we find that the boson-boson repulsion was insufficient to ensure stability, suggesting that the experimental timescale was short enough to avoid mechanical collapse. On the other hand, we also show that even in the absence of boson-boson repulsion, Bose-Fermi mixtures become intrinsically stable beyond a certain coupling strength, preceding the quantum phase transition associated with the vanishing of the bosonic condensate. We thus propose an experimental protocol for observing this quantum phase transition in a mechanically stable configuration.
Authors: A. E. Koshelev
The possibility of driving vortex lines with an oscillating magnetic field could be useful in many applications. For example, it can be used for the removal of undesired trapped flux from contactless elements of superconducting devices. We investigate the dynamics of vortex lines in a superconducting film with a ratchet thickness profile driven by an oscillating magnetic field applied parallel to the film. We numerically simulate the dynamics of a single flux line modeled as an elastic string with a variable length. We explore the behavior for different frequencies and amplitudes of the oscillating magnetic field and find several dynamic regimes. For moderate frequencies, the average velocity is finite only within specific amplitude ranges. A notable feature is the presence of extended velocity plateaus, which correspond to regimes when the line moves by integer multiples of the spatial period $w$ during integer multiples of the time period $T$. The transitions to these plateau states are rather steep, especially at low frequencies. The plateau at velocity $w/T$ dominates at intermediate frequencies but vanishes at high frequencies. The onset field amplitude of finite velocity nonmonotonically depends on the frequency and passes through a minimum at a certain frequency value. At low frequencies, the velocity exceeds $w/T$ and progressively increases with the amplitude. These findings provide valuable insights into the dynamic behavior of vortex lines driven by oscillating magnetic field in patterned superconducting films, offering potential pathways for controlling the magnetic flux in superconducting devices.
Authors: F. Katmis, V. Lauter, R. Yagan, L.S. Brandt, A.M. Cheghabouri, H. Zhou, J.W. Freeland, C.I.L. de Araujo, M.E. Jamer, D. Heiman, M.C. Onbasli, J. S. Moodera
Topological spin configurations, such as soliton-like spin texture and Dirac electron assemblies, have emerged in recent years in both fundamental science and technological applications. Achieving stable topological spin textures at room-temperature is crucial for enabling these structures as long-range information carriers. However, their creation and manipulation processes have encountered difficulties due to multi-step field training techniques and competitive interactions. Thus, a spontaneous ground state for multi-dimensional topological spin textures is desirable, as skyrmions form swirling, hedgehog-like spin structures in two dimensions, while hopfions emerge as their twisted three-dimensional counterparts. Here, we report the first observation of robust and reproducible topological spin textures of hopfions and skyrmions observed at room temperature and in zero magnetic field, which are stabilized by geometric confinement and protected by interfacial magnetism in a ferromagnet/topological insulator/ferromagnet trilayer heterostructure. These skyrmion-hopfion configurations are directly observed at room temperature with Lorenz transmission electron microscopy. Using micromagnetic modelling, the experimental observations of hopfion-skyrmion assemblies are reproduced. Our model reveals a complete picture of how spontaneously organized skyrmion lattices encircled by hopfion rings are controlled by surface electrons, uniaxial anisotropy and Dzyaloshinskii-Moriya interaction, all at ambient temperature. Our study provides evidence that topological chiral spin textures can facilitate the development of magnetically defined information carriers. These stable structures hold promise for ultralow-power and high-density information processing, paving the way for the next generation of topologically defined devices.
Authors: Alexandra Jurgens, James P. Crutchfield
A prediction makes a claim about a system's future given knowledge of its past. A retrodiction makes a claim about its past given knowledge of its future. The bidirectional machine is an ambidextrous hidden Markov chain that does both optimally by making explicit in its state structure all statistical correlation in a stochastic process. We introduce an informational taxonomy to profile these correlations via a suite of multivariate information measures. While prior results laid out the different kinds of information contained in isolated measurement of a bit, the associated informations were challenging to calculate explicitly. Overcoming this via bidirectional machine states, we expand that analysis to prediction and retrodiction. The result highlights fourteen new interpretable and calculable measures that characterize a process' informational structure. In addition, we introduce a labeling and indexing scheme that systematizes information-theoretic analyses of complex multivariate systems. Operationalizing this, we provide algorithms to directly calculate all of these quantities in closed form for finitely-modeled processes.
Authors: Xiaoyu Zhang, Taoni Bao
Accurate modeling of spin-orbit coupling and noncollinear magnetism in materials requires noncollinear density functionals within the two-component generalized Kohn-Sham (GKS) framework, yet constructing and implementing noncollinear functionals remains challenging. Recently, a methodology was proposed to extend collinear functionals into noncollinear ones, successfully defining noncollinear functionals and their derivatives. However, the initial implementation involved a systematic approach to differentiate energy over density matrix elements rather than the derivatives of the energy functional with respect to density, presenting challenges for integration with periodic boundary condition-density functional theory (PBC-DFT) software. We have derived a novel set of working equations based on the original methodology, which provides noncollinear energy functionals and their derivatives. These working equations have been implemented in our noncollinear functional ensemble named NCXC, ensuring numerical stability and transferability without the need for incorporating derivatives of basis functions. This implementation is expected to facilitate compatibility with most DFT software packages. We demonstrate some preliminary applications in periodic systems, including noncollinear magnetism in spin spirals, band structures in topological insulators, and band gaps in semiconducting inorganic materials, using NCXC.
Authors: Hossein Hosseinabadi, Yaroslav Tserkovnyak, Eugene Demler, Jamir Marino
We uncover a new class of dynamical quantum instability in driven magnets leading to emergent enhancement of antiferromagnetic correlations even for purely ferromagnetic microscopic couplings. A primary parametric amplification creates a frequency-tuned nested magnon distribution in momentum space, which seeds a secondary instability marked by the emergence of enhanced antiferromagnetic correlations, mirroring the instability of nested Fermi surfaces in electronic systems. In sharp contrast to the fermionic case, however, the magnon-driven instability is intrinsically non-equilibrium and fundamentally inaccessible in thermal physics. Its quantum mechanical origin sets it apart from classical instabilities such as Faraday and modulation instabilities, which underlie several instances of dynamical behavior observed in magnetic and cold-atom systems.
Authors: Cliff Sun, Alexey Bezryadin
An ordinary superconducting quantum interference device (SQUID) contains two weak links connected in parallel. We model a multiple-wire SQUID (MW-SQUID), generalized in two ways. First, the number of weak links, which are provided by parallel superconducting nanowires, is larger than two. Second, the current-phase relationship of each nanowire is assumed linear, which is typical for a homogeneous superconducting thin wire. For such MW-SQUIDs, our model predicts that the critical current ($I_c$) is a multi-valued function of the magnetic field. We also calculate vorticity stability regions (VSR), i.e., regions in the current-magnetic field plane in which, for a given distribution of vortices, the currents in all wires are below their critical values, so the vortices do not move between the cells. The VSRs have rhombic shapes in the case of two-wire SQUIDS and have more complicated shapes in the case of many nanowires. We present a classification of such VSRs and determine conditions under which VSR is disjoint, leading to 100\% supercurrent modulation and quantum phase transitions. According to the model, the maximum critical current curves obey $IB$ symmetry, while each VSR obeys $IBV$ symmetry. The model predicts conditions at which MW-SQUID exhibits a perfect diode effect in which the critical current of one polarity is zero while it is not zero for the opposite polarity of the bias current. We also provide a classification of the stability regions produced by (1) completely symmetric, (2) phase disordered, (3) position disordered, (4) critical current disordered, and (5) completely disordered multi-wire SQUIDs.
Authors: Yuanji Xu, Xintao Jin, Haoyuan Tang, Fuyang Tian
The study of magnetism in two-dimensional materials has garnered significant interest, driven by fundamental investigations into low-dimensional magnetic phenomena and their potential for applications in spintronic devices. Through dynamical mean-field theory calculations, we demonstrate that Ni$_{3}$GeTe$_{2}$ exhibits flat-band characteristics resulting from the geometric frustration of its layered triangular lattice. These flat bands are further renormalized due to electronic correlation. Our calculations reveal that the magnetic order of Ni atoms is significantly influenced by both the Coulomb interaction and Hund's coupling, indicating that the physics of Ni atoms is situated in an intermediate region between Hundness and Mottness. Additionally, our results show that Ni atoms experience significant spin fluctuations in their local moments, maintaining paramagnetism at low temperatures. Furthermore, we investigate the effect of vacancies, finding a substantial suppression of the density of states at the Fermi level. The physical mechanisms uncovered by our study provide a comprehensive understanding of the novel properties exhibited in this material.
Authors: Yu Zhao, Yidun Wan
Topologically ordered matter phases have been regarded as beyond the Landau-Ginzburg symmetry breaking paradigm of matter phases. Recent studies of anyon condensation in topological phases, however, may fit topological phases back in the Landau-Ginzburg paradigm. To truly do so, we realized that the string-net model of topological phases is in fact an effective lattice gauge theory coupled with anyonic matter once two modifications are made: (1) We reinterpret anyons as matter fields coupled to lattice gauge fields, thus extending the HGW model to a genuine Hamiltonian lattice gauge theory. (2) By explicitly incorporating the internal degrees of freedom of anyons, we construct an enlarged Hilbert space that supports well-defined gauge transformations and covariant coupling, restoring the analogy with conventional lattice gauge field theory. In this modified string-net model, topological phase transitions induced by anyon condensation and their consequent phenomena, such as order parameter fields, coherent states, Goldstone modes, and gapping gauge degrees of freedom, can be formulated exactly as Landau's effective theory of the Higgs mechanism. To facilitate the understanding, we also compare anyon condensation to/with the Higgs boson condensation in the electroweak theory and the Cooper pair condensation.
Authors: S W Lovesey
A material in possession of localized 4f-electron magnetism and delocalized 3d-electron or band magnetism can often present A material in possession of localized 4f-electron magnetism and delocalized 3d-electron or band magnetism can often present enigmatic physical phenomena, and there has been a longstanding interest in the kagome metal YbFe6Ge6. More recently, because of an investigation of a so-called anomalous Hall effect, or topological Hall effect, and magnetic neutron Bragg diffraction [W. Yao et al., Phys. Rev. Lett. 134, 186501 (2025)]. Iron moments in the two-dimensional layers of a hexagonal nuclear structure undergo collinear antiferromagnetic order below a temperature 500 K. The moments depart from the c axis in a spontaneous transition at 63 K to an orthorhombic structure. The magnetism of Yb ions appears to behave independently, which can be confirmed using resonant x-ray diffraction enhanced by a Fe atomic resonance. The inferred magnetic space group is a P(parity)T(time)-symmetric (anti-inversion collinear antiferromagnet. A linear magnetoelectric effect is allowed, as in historically important chromium sesquioxide, and Kerr rotation and the piezomagnetic effect are forbidden. Symmetry informed Bragg diffraction patterns for future x-ray and neutron experiments are shown to be rich in Fe magnetic properties of orthorhombic YbFe6Ge6, including space-spin correlations, anapoles and Dirac quadrupoles familiar in high-Tc ceramic superconductors.
Authors: Anna Chmiel, Julian Sienkiewicz
We consider a coupled system mimicking opinion formation under the influence of a group of $q$ neighbors ($q$-lobby) that consists of an Ising part governed by temperature-like parameter $T$ and a voter dynamics parameterized by noise probability $p$ (independence of choice). Using rigorous analytical calculations backed by extensive Monte Carlo simulations, we examine the interplay between these two quantities. Based on the theory of phase transitions, we derive the relation between $T$ and $p$ at the critical line dividing the ordered and disordered phases, which takes a very simple and generic form $T(p-a)=b$ in the high temperature limit. For specific lobby sizes, we show where the temperature are noise are balanced, and we hint that for large $q$, the temperature-like dynamics prevails.
Authors: J. L. Costa, E. Santos, J. B. S. Mendes, A. Azevedo
We study inverse spin and orbital Hall effects in 19 transition metals using spin-pumping driven by ferromagnetic resonance. Spin-to-charge conversion was measured in YIG/X(5), while orbital-to-charge conversion was probed in YIG/Pt(2)/X(5) heterostructures. Here, X represents the different transition metals. Surprisingly, the orbital contribution overwhelmingly dominates over the spin response, clarifying the challenge of disentangling these effects. Our results largely agree with first-principles predictions for spin and orbital Hall conductivities but reveal discrepancies in select materials. These findings emphasize the fundamental role of the orbital Hall effect, and position orbitronics as a pivotal frontier in condensed matter physics.
Authors: Fan Zhang, Haowei Li, Wei Yi
We study the gas-liquid transition in a binary Bose-Einstein condensate, where the two Zeeman-shifted hyperfine spin components are coupled by cavity-assisted Raman processes. Below a critical Zeeman field, the cavity becomes superradiant for an infinitesimally small pumping strength, where the enhanced superradiance is facilitated by the simultaneous formation of quantum droplet, a self-bound liquid phase stabilized by quantum fluctuations. Above the critical Zeeman field, the gas-liquid transition only takes place at a finite pumping strength after the system becomes superradiant. As the back action of the gas-liquid transition, the superradiant cavity field undergoes an abrupt jump at the first-order transition point. Furthermore, as a result of the fixed density ratio of the quantum droplet, the cavity field exhibits a linear scaling with the pumping strength in the liquid phase. These features serve as prominent signals for the cavity-mediated gas-liquid transition and coexistence, which derive from the interplay of Zeeman field, cavity-assisted spin mixing, and quantum fluctuations.
Authors: Ujjal Roy, Sourav Manna, Souvik Chakraborty, Kenji Watanabe, Takashi Taniguchi, Ankur Das, Moshe Goldstein, Yuval Gefen, Anindya Das
Considering a range of candidate quantum phases of matter, half-integer thermal conductance ($\kappa_{\text{th}}$) is believed to be an unambiguous evidence of non-Abelian states. It has been long known that such half-integer values arise due to the presence of Majorana edge modes, representing a significant step towards topological quantum computing platforms. Here, we challenge this prevailing notion by presenting a comprehensive theoretical and experimental study where half-integer two-terminal thermal conductance plateau is realized employing Abelian phases. Our proposed setup features a confined geometry of bilayer graphene, interfacing distinct particle-like and hole-like integer quantum Hall states. Each segment of the device exhibits full charge and thermal equilibration. Our approach is amenable to generalization to other quantum Hall platforms, and may give rise to other values of fractional (electrical and thermal) quantized transport. Our study demonstrates that the observation of robust non-integer values of thermal conductance can arise as a manifestation of mundane equilibration dynamics as opposed to underlying non-trivial topology.
Authors: Killian Sheriff, Daniel Xiao, Yifan Cao, Lewis R. Owen, Rodrigo Freitas
Materials properties depend strongly on chemical composition, i.e., the relative amounts of each chemical element. Changes in composition lead to entirely different chemical arrangements, which vary in complexity from perfectly ordered (i.e., stoichiometric compounds) to completely disordered (i.e., solid solutions). Accurately capturing this range of chemical arrangements remains a major challenge, limiting the predictive accuracy of machine learning potentials (MLPs) in materials modeling. Here, we combine information theory and machine learning to optimize the sampling of chemical motifs and design MLPs that effectively capture the behavior of metallic alloys across their entire compositional and structural landscape. The effectiveness of this approach is demonstrated by predicting the compositional dependence of various material properties - including stacking-fault energies, short-range order, heat capacities, and phase diagrams - for the AuPt and CuAu binary alloys, the ternary CrCoNi, and the TiTaVW high-entropy alloy. Extensive comparison against experimental data demonstrates the robustness of this approach in enabling materials modeling with high physical fidelity.
Authors: Simon Brunner, Christian F. Schmidt, Stefan Floerchinger
We consider excitations of a spin-1 Bose-Einstein-condensate (BEC) in the vicinity of different mean-field configurations and derive mappings to emergent relativistic quantum field theories minimally coupled to curved acoustic spacetimes. The quantum fields are typically identified with Nambu-Goldstone bosons, such that the structure of the analogue quantum field theories on curved spacetimes depends on the (spontaneous) symmetry breaking pattern of the respective ground-state. The emergent spacetime geometries are independent of each other and exhibit bi-metricity in the polar and antiferromagnetic phase, whereas one has tri-metricity in the ferromagnetic phase. Compared to scalar BECs, the spinor degrees of freedom allow to investigate massive vector and scalar fields where the former is a spin-nematic rotation mode in the polar phase which can be cast into a Proca field that is minimally coupled to a curved spacetime that emerges on length scales larger than the spin-healing length. Finally, we specify the Zeeman couplings and the condensate trap to be spacetime-dependent such that a cosmological FLRW-metric can be achieved. This work enables a pathway towards quantum-simulating cosmological particle production of Proca quanta via quenching the quadratic Zeeman-coefficient or via magnetic field ramps, which both result in the creation of spin-nematic squeezed states.
Authors: Saeid Ansari, R. Jafari, Alireza Akbari, Mehdi Abdi
Dynamical quantum phase transitions (DQPTs) have been studied in the extended XY model under both noiseless and noisy linear driven staggered field cases. In the time-independent staggered field case, the model exhibits a single critical point where the transition occurs from the spin-liquid phase to the antiferromagnetic phase. In the noiseless ramp case, unlike the transverse field XY model where DQPT always occurs for a quench crossing the single critical point, there is a critical sweep velocity above which the kinks corresponding to a DQPT are completely removed. Furthermore, in this case there are only two critical modes whose excitation probability is one-half. In the presence of a Gaussian white noise, we find that this critical sweep velocity decreases by increasing the noise strength, and scales linearly with the square of the noise intensity. A surprising result occurs when the noise intensity and sweep velocity are about the same order of magnitude, the number of critical modes is significantly increased, signalling a region with multiple critical modes. Furthermore, our findings indicate that the scaling of the dynamical free energy near the DQPTs time is the same for both noiseless and noisy ramp quenches.
Authors: Sasan Kheiri, R. Jafari, S. Mahdavifar, Ehsan Nedaaee Oskoee, Alireza Akbari
In most lattice models, gap closing typically occurs at high-symmetry points in the Brillouin zone. In the transverse field Ising model with cluster interaction, besides the gap closing at high-symmetry points, the gap closing at the quantum phase transition between paramagnetic and cluster phases of the model can be moved by tuning the strength of the cluster interaction. We take advantage of this property to examine the nonequilibrium dynamics of the model in the framework of dynamical quantum phase transitions (DQPTs) after a noiseless and noisy ramp of the transverse magnetic field. The numerical results show that DQPTs always happen if the starting or ending point of the quench field is restricted between two critical points. In other ways, there is always critical sweep velocity above which DQPTs disappear. Our finding reveals that noise modifies drastically the dynamical phase diagram of the model. We find that the critical sweep velocity decreases by enhancing the noise intensity and scales linearly with the square of noise intensity for weak and strong noise. Moreover, the region with multi-critical modes induced in the dynamical phase diagram by noise. The sweep velocity under which the system enters the multi-critical modes (MCMs) region increases by enhancing the noise and scales linearly with the square of noise intensity
Authors: Stephen Whitelam
We introduce a generative modeling framework for thermodynamic computing, in which structured data is synthesized from noise by the natural time evolution of a physical system governed by Langevin dynamics. While conventional diffusion models use neural networks to perform denoising, here the information needed to generate structure from noise is encoded by the dynamics of a thermodynamic system. Training proceeds by maximizing the probability with which the computer generates the reverse of a noising trajectory, which ensures that the computer generates data with minimal heat emission. We demonstrate this framework within a digital simulation of a thermodynamic computer. If realized in analog hardware, such a system would function as a generative model that produces structured samples without the need for artificially-injected noise or active control of denoising.
Authors: D. S. Grebenkov
We revise the classical problem of characterizing first exit times of a harmonically trapped particle whose motion is described by one- or multi-dimensional Ornstein-Uhlenbeck process. We start by recalling the main derivation steps of a propagator using Langevin and Fokker-Planck equations. The mean exit time, the moment-generating function, and the survival probability are then expressed through confluent hypergeometric functions and thoroughly analyzed. We also present a rapidly converging series representation of confluent hypergeometric functions that is particularly well suited for numerical computation of eigenvalues and eigenfunctions of the governing Fokker-Planck operator. We discuss several applications of first exit times such as detection of time intervals during which motor proteins exert a constant force onto a tracer in optical tweezers single-particle tracking experiments; adhesion bond dissociation under mechanical stress; characterization of active periods of trend following and mean-reverting strategies in algorithmic trading on stock markets; relation to the distribution of first crossing times of a moving boundary by Brownian motion. Some extensions are described, including diffusion under quadratic double-well potential and anomalous diffusion.
Authors: Maxwell J D Ramstead, Dalton A R Sakthivadivel, Karl J Friston
This paper presents a meta-theory of the usage of the free energy principle (FEP) and examines its scope in the modelling of physical systems. We consider the so-called `map-territory fallacy' and the fallacious reification of model properties. By showing that the FEP is a consistent, physics-inspired theory of inferences of inferences, we disprove the assertion that the map-territory fallacy contradicts the principled usage of the FEP. As such, we argue that deploying the map-territory fallacy to criticise the use of the FEP and Bayesian mechanics itself constitutes a fallacy: what we call the {\it map-territory fallacy fallacy}. In so doing, we emphasise a few key points: the uniqueness of the FEP as a model of particles or agents that model their environments; the restoration of convention to the FEP via its relation to the principle of constrained maximum entropy; the `Jaynes optimality' of the FEP under this relation; and finally, the way that this meta-theoretical approach to the FEP clarifies its utility and scope as a formal modelling tool. Taken together, these features make the FEP, uniquely, {\it the} ideal model of generic systems in statistical physics.
Authors: Itai Arad, Raz Firanko, Rahul Jain
We show an area law in the mutual information for the maximally-mixed state $\Omega$ in the ground space of general Hamiltonians, which is independent of the underlying ground space degeneracy. Our result assumes the existence of a `good' approximation to the ground state projector (a good AGSP), a crucial ingredient in previous area-law proofs. Such approximations have been explicitly derived for 1D gapped local Hamiltonians and 2D frustration-free locally-gapped Hamiltonians. As a corollary, we show that in 1D gapped local Hamiltonians, for any $\varepsilon>0$ and any bi-partition $L\cup L^c$ of the system, \begin{align*} \mathrm I_{\max}^\varepsilon (L:L^c)_{\Omega} \le \mathrm O \big( \log (|L|\log(d))+\log(1/\varepsilon)\big), \end{align*} where $|L|$ represents the number of sites in $L$, $d$ is the dimension of a site and $ \mathrm I_{\max}^\varepsilon (L:L^c)_{\Omega} $ represents the $\varepsilon$-\emph{smoothed maximum mutual information} with respect to the $L:L^c$ partition in $\Omega$. From this bound we then conclude $\mathrm I (L:L^c)_\Omega \le \mathrm O\big(\log(|L|\log(d))\big)$ -- an area law for the mutual information in 1D systems with a logarithmic correction. In addition, we show that $\Omega$ can be approximated in trace norm up to $\varepsilon$ with a state of Schmidt rank of at most $\mathrm{poly}(|L|/\varepsilon)$, leading to a good MPO approximation for $\Omega$ with polynomial bond dimension. Similar corollaries are derived for the mutual information of 2D frustration-free and locally-gapped local Hamiltonians.
Authors: Yu-Qin Chen, Shuo Liu, Shi-Xin Zhang
In this study, we explore the information capacity of open quantum systems, focusing on the effective channels formed by the subsystem of random quantum circuits and quantum Hamiltonian evolution. By analyzing the subsystem information capacity, which is closely linked to quantum coherent information of these effective quantum channels, we uncover a diverse range of dynamical and steady behaviors depending on the types of evolution. Therefore, the subsystem information capacity serves as a valuable tool for studying the intrinsic nature of various dynamical phases, such as integrable, localized, thermalized, and topological systems. We also reveal the impact of different initial information encoding schemes on information dynamics including one-to-one, one-to-many, and many-to-many. To support our findings, we provide representative examples for numerical simulations, including random quantum circuits with or without mid-circuit measurements, random Clifford Floquet circuits, free and interacting Aubry-André models, and Su-Schrieffer-Heeger models. These numerical results are further quantitatively explained using the effective statistical model mapping and the quasiparticle picture in the cases of random circuits and non-interacting Hamiltonian dynamics, respectively.
Authors: Luke Eilers, Raoul-Martin Memmesheimer, Sven Goedeke
State-of-the-art neural network training methods depend on the gradient of the network function. Therefore, they cannot be applied to networks whose activation functions do not have useful derivatives, such as binary and discrete-time spiking neural networks. To overcome this problem, the activation function's derivative is commonly substituted with a surrogate derivative, giving rise to surrogate gradient learning (SGL). This method works well in practice but lacks theoretical foundation. The neural tangent kernel (NTK) has proven successful in the analysis of gradient descent. Here, we provide a generalization of the NTK, which we call the surrogate gradient NTK, that enables the analysis of SGL. First, we study a naive extension of the NTK to activation functions with jumps, demonstrating that gradient descent for such activation functions is also ill-posed in the infinite-width limit. To address this problem, we generalize the NTK to gradient descent with surrogate derivatives, i.e., SGL. We carefully define this generalization and expand the existing key theorems on the NTK with mathematical rigor. Further, we illustrate our findings with numerical experiments. Finally, we numerically compare SGL in networks with sign activation function and finite width to kernel regression with the surrogate gradient NTK; the results confirm that the surrogate gradient NTK provides a good characterization of SGL.
Authors: Peng Zhang, Jing-Yuan Chen
Since the inception of lattice QCD, a natural definition for the Yang-Mills instanton on lattice has been long sought for. In a recent work, one of authors showed the natural solution has to be organized in terms of bundle gerbes in higher homotopy theory / higher category theory, and introduced the principles for such a categorical construction. To pave the way towards actual numerical implementation in the near future, nonetheless, an explicit construction is necessary. In this paper we provide such an explicit construction for $SU(2)$ gauge theory, with technical aspects inspired by Lüscher's 1982 geometrical construction. We will see how the latter is in a suitable sense a saddle point approximation to the full categorical construction. The generalization to $SU(N)$ will be discussed. The construction also allows for a natural definition of lattice Chern-Simons-Yang-Mills theory in three spacetime dimensions.
Authors: Rabeeya Hamid, Demeng Feng, Pournima Narayanan, Justin S. Edwards, Manchen Hu, Emma Belliveau, Minjeong Kim, Sanket Deshpande, Chenghao Wan, Linda Pucurimay, David A. Czaplewski, Daniel N. Congreve, Mikhail A. Kats
Frequency upconversion, which converts low-energy photons into higher-energy ones, typically requires intense coherent illumination to drive nonlinear processes or the use of externally driven optoelectronic devices. Here, we demonstrate an upconversion system that converts low-intensity (down to ~10-7 W/cm$^2$) incoherent near-infrared (NIR) light into the visible, reaching intensities perceptible by the human eye, without the use of any external power input. Our upconverting element is enabled by the following ingredients: (1) photon upconversion via triplet-triplet annihilation in a bulk heterojunction of the organic semiconductors Y6 and rubrene; (2) plasmonic enhancement of absorption and field intensity in the heterojunction layer; (3) collection enhancement using a dichroic thin-film assembly. To enable high-resolution imaging, the upconverting element is inserted at an intermediate image plane of a dual-wavelength telescope system, which preserves the relative directionality of rays between the incident NIR light and output visible light. Our all-passive upconversion imaging system will enable NIR imaging and sensing in low-light environments under energy constraints.
Authors: Sridevi Kuriyattil, Pablo M. Poggi, Jonathan D. Pritchard, Johannes Kombe, Andrew J. Daley
Quantum states featuring extensive multipartite entanglement are a resource for quantum-enhanced metrology, with sensitivity up to the Heisenberg limit. However, robust generation of these states using unitary dynamics typically requires all-to-all interactions among particles. Here, we demonstrate that optimal states for quantum sensing can be generated with sparse interaction graphs featuring only a logarithmic number of couplings per particle. We show that specific sparse graphs with long-range interactions can approximate the dynamics of all-to-all spin models, such as the one-axis twisting model, even for large system sizes. The resulting sparse coupling graphs and protocol can also be efficiently implemented using dynamic reconfiguration of atoms in optical tweezers.
Authors: Alice Doimo, Giorgio Nicoletti, Davide Bernardi, Prajwal Padmanabha
Spatial metapopulation models are fundamental to theoretical ecology, enabling to study how landscape structure influences global species dynamics. Traditional models, including recent generalizations, often rely on the deterministic limit of stochastic processes, assuming large population sizes. However, stochasticity - arising from dispersal events and population fluctuations - profoundly shapes ecological dynamics. In this work, we extend the classical metapopulation framework to account for finite populations, examining the impact of stochasticity on species persistence and dynamics. Specifically, we analyze how the limited capacity of local habitats influences survival, deriving analytical expressions for the finite-size scaling of the survival probability near the critical transition between survival and extinction. Crucially, we demonstrate that the deterministic metapopulation capacity plays a fundamental role in the statistics of survival probability and extinction time moments. These results provide a robust foundation for integrating demographic stochasticity into classical metapopulation models and their extensions.
Authors: Rishabh Jha, Salvatore R. Manmana, Stefan Kehrein
Generic non-equilibrium many-body systems display a linear growth of bipartite entanglement entropy in time, followed by a volume law saturation. In stark contrast, the Page curve dynamics of black hole physics shows that the entropy peaks at the Page time $t_{\text{Page}}$ and then decreases to zero. Here, we investigate such Page-like behavior of the von Neumann entropy in a model of strongly correlated spinless fermions in a typical system-environment setup, and characterize the properties of the Page curve dynamics in the presence of interactions using numerically exact matrix product states methods. The two phases of growth, namely the linear growth and the bending down, are shown to be separated by a non-analyticity in the min-entropy before $t_{\text{Page}}$, which separates two different quantum phases, realized as the respective ground states of the corresponding entanglement (or equivalently, modular) Hamiltonian. We confirm and generalize, by introducing interactions, the findings of \href{this https URL}{Phys. Rev. B 109, 224308 (2024)} for a free spinless fermionic chain where the corresponding entanglement Hamiltonian undergoes a quantum phase transition at the point of non-analyticity. However, in the presence of interactions, a scaling analysis gives a non-zero critical time for the non-analyticity in the thermodynamic limit only for weak to intermediate interaction strengths, while the dynamics leading to the non-analyticity becomes \textit{instantaneous} for interactions large enough. We present a physical picture explaining these findings.
Authors: Oleksandr Gamayun, Murtaza Ali Mir, Oleg Lychkovskiy, Zoran Ristivojevic
Quantum observables of generic many-body systems exhibit a universal pattern of growth in the Krylov space of operators. This pattern becomes particularly manifest in the Lanczos basis, where the evolution superoperator assumes the tridiagonal form. According to the universal operator growth hypothesis, the nonzero elements of the superoperator, known as Lanczos coefficients, grow asymptotically linearly. We introduce and explore broad families of Lanczos coefficients that are consistent with the universal operator growth and lead to the exactly solvable dynamics. Within these families, the subleading terms of asymptotic expansion of the Lanczos sequence can be controlled and fine-tuned to produce diverse dynamical patterns. For one of the families, the Krylov complexity is computed exactly.
Authors: Pawel Szczypkowski, Adrian Makowski, Wojciech Zwoliński, Katarzyna Prorok, Piotr Wasylczyk, Artur Bednarkiewicz, Radek Lapkiewicz
Achieving high-resolution optical imaging deep within heterogeneous and scattering media remains a fundamental challenge in biological microscopy, where conventional techniques are hindered by multiple light scattering and absorption. Here, we present a non-invasive imaging approach that harnesses the nonlinear response of luminescent labels in conjunction with the statistical and spatial properties of speckle patterns - an effect of random light interference. Using avalanching nanoparticles (ANPs) with strong photoluminescence nonlinearity, we demonstrate that random speckle illumination can be converted into a single, localized, sub-diffraction excitation spot. This spot can be scanned across the sample using the angular memory effect, enabling high-resolution imaging through a scattering layer. Our method is general, fast, and cost-effective. It requires no wavefront shaping, no feedback, and no reconstruction algorithm, offering a powerful new route to deep, high-resolution imaging through complex media.
Authors: Jonathan B. Curtis, Amir Yacoby, Eugene Demler
Atomic scale qubits, as may be realized in nitrogen vacancy (NV) centers in diamond, offer the opportunity to study magnetic field noise with nanometer scale spatial resolution. Using these spin qubits, one can learn a great deal about the magnetic-field noise correlations, and correspondingly the collective-mode spectra, in quantum materials and devices. However, to date these tools have been essentially restricted to studying Gaussian noise processes -- equivalent to linear-response. In this work we will show how to extend these techniques beyond the Gaussian regime and show how to unambiguously measure higher-order magnetic noise cumulants in a local, spatially resolved way. We unveil two protocols for doing this; the first uses a single spin-qubit and different dynamical decoupling sequences to extract non-Markovian and non-Gaussian spin-echo noise. The second protocol uses two-qubit coincidence measurements to study spatially non-local cumulants in the magnetic noise. We then demonstrate the utility of these protocols by considering a model of a bath of non-interacting two-level systems, as well as a model involving spatially correlated magnetic fluctuations near a second-order Ising phase transition. In both cases, we highlight how this technique can be used to measure in a real many-body system how fluctuation dynamics converge towards the central limit theorem as a function of effective bath size. We then conclude by discussing some promising applications and extensions of this method.
Authors: Barak Budnick, Ofer Biham, Eytan Katzav
We present analytical results for the effect of preferential node deletion on the structure of networks that evolve via node addition and preferential attachment. To this end, we consider a preferential-attachment-preferential-deletion (PAPD) model, in which at each time step, with probability $P_{\rm add}$ there is a growth step where an isolated node is added to the network, followed by the addition of $m$ edges, where each edge connects a node selected uniformly at random to a node selected preferentially in proportion to its degree. Alternatively, with probability $P_{\rm del}=1-P_{\rm add}$ there is a contraction step, in which a preferentially selected node is deleted and its links are erased. The balance between the growth and contraction processes is captured by the growth/contraction rate $\eta=P_{\rm add}-P_{\rm del}$. For $0 < \eta \le 1$ the overall process is of network growth, while for $-1\le\eta<0$ the overall process is of network contraction. Using the master equation and the generating function formalism, we study the time-dependent degree distribution $P_t(k)$. It is found that for each value of $m>0$ there is a critical value $\eta_c(m)=-(m-2)/(m+2)$ such that for $\eta_c(m)<\eta\le1$ the degree distribution $P_t(k)$ converges towards a stationary distribution $P_{\rm st}(k)$. In the special case of pure growth, where $\eta=1$, the model is reduced to a preferential attachment growth model and $P_{\rm st}(k)$ exhibits a power-law tail, which is a characteristic of scale-free networks. In contrast, for $\eta_c(m)<\eta<1$ the distribution $P_{\rm st}(k)$ exhibits an exponential tail, which has a well-defined this http URL implies a phase transition at $\eta=1$, in contrast with the preferential-attachment-random-deletion (PARD) model [B. Budnick, O. Biham and E. Katzav, J. Stat. Mech. 013401 (2025)], in which the power-law tail remains intact as long as $\eta>0$.
Authors: Yi-Xuan Wang, Yuval Gefen
Lindbladian dynamics of open systems may be employed to steer a many-body system towards a non-trivial ground state of a local Hamiltonian. Such protocols provide us with tunable platforms facilitating the engineering and study of non-trivial many-body states. Steering towards a degenerate ground state manifold provides us with a protected platform to employ many-body states as a resource for quantum information processing. Notably, ground states of frustrated local Hamiltonians have been known not to be amenable to steering protocols. Revisiting this intricate physics we report two new results: (i) we find a broad class of (geometrically) frustrated local Hamiltonians for which steering of the ground state manifold is possible through a sequence of discrete steering steps. Following the steering dynamics, states within the degenerate ground-state manifold keep evolving in a non-stationary manner. (ii) For the class of Hamiltonians with ground states which are non-steerable through local superoperators, we derive a "glass floor" on how close to the ground state one can get implementing a steering protocol. This is expressed invoking the concept of cooling-by-steering (a lower bound of the achievable temperature), or through an upper bound of the achievable fidelity. Our work provides a systematic outline for studying quantum state manipulation of a broad class of strongly correlated states.
Authors: Marvin Lenk, Sayak Biswas, Anna Posazhennikova, Johann Kroha
One of the fundamental problems of quantum statistical physics is how an ideally isolated quantum system can ever reach thermal equilibrium behavior despite the unitary time evolution of quantum-mechanical systems. Here, we study, via explicit time evolution for the generic model system of an interacting, trapped Bose gas with discrete single-particle levels, how the measurement of one or more observables subdivides the system into observed and non-observed Hilbert subspaces and the tracing over the non-measured quantum numbers defines an effective, thermodynamic bath, induces the entanglement of the observed Hilbert subspace with the bath, and leads to a bi-exponential approach of the entanglement entropy and of the measured observables to thermal equilibrium behavior as a function of time. We find this to be more generally fulfilled than in the scenario of the eigenstate thermalization hypothesis (ETH), namely for both local particle occupation numbers and non-local density correlation functions, and independent of the specific initial quantum state of the time evolution.
Authors: Bao Pham, Gabriel Raya, Matteo Negri, Mohammed J. Zaki, Luca Ambrogioni, Dmitry Krotov
Hopfield networks are associative memory (AM) systems, designed for storing and retrieving patterns as local minima of an energy landscape. In the classical Hopfield model, an interesting phenomenon occurs when the amount of training data reaches its critical memory load $- spurious\,\,states$, or unintended stable points, emerge at the end of the retrieval dynamics, leading to incorrect recall. In this work, we examine diffusion models, commonly used in generative modeling, from the perspective of AMs. The training phase of diffusion model is conceptualized as memory encoding (training data is stored in the memory). The generation phase is viewed as an attempt of memory retrieval. In the small data regime the diffusion model exhibits a strong memorization phase, where the network creates distinct basins of attraction around each sample in the training set, akin to the Hopfield model below the critical memory load. In the large data regime, a different phase appears where an increase in the size of the training set fosters the creation of new attractor states that correspond to manifolds of the generated samples. Spurious states appear at the boundary of this transition and correspond to emergent attractor states, which are absent in the training set, but, at the same time, have distinct basins of attraction around them. Our findings provide: a novel perspective on the memorization-generalization phenomenon in diffusion models via the lens of AMs, theoretical prediction of existence of spurious states, empirical validation of this prediction in commonly-used diffusion models.
Authors: Tomer Eini, N. M. R. Peres, Yarden Mazor, Itai Epstein
Excitons in biased bilayer graphene are electrically tunable optical excitations residing in the mid-infrared (MIR) spectral range, where intrinsic optical transitions are typically scarce. Such a tunable material system with an excitonic response offer a rare platform for exploring light-matter interactions and optical hybridization of quasiparticles residing in the long wavelength spectrum. In this work, we demonstrate that when the bilayer is encapsulated in hexagonal-boron-nitride (hBN)-a material supporting optical phonons and hyperbolic-phonon-polaritons (HPhPs) in the MIR-the excitons can be tuned into resonance with the HPhP modes. We find that the overlap in energy and momentum of the two MIR quasiparticles facilitate the formation of multiple strongly coupled hybridized exciton-HPhP states. Using an electromagnetic transmission line model, we derive the dispersion relations of the hybridized states and show that they are highly affected and can be manipulated by the symmetry of the system, determining the hybridization selection rules. Our results establish a general tunable MIR platform for engineering strongly coupled quasiparticle states in biased graphene systems, opening new directions for studying and controlling light-matter interactions in the long-wavelength regime.
Authors: Tadashi Takayanagi
Holographic duality describes gravitational theories in terms of quantum many-body systems. In holography, quantum information theory provides a crucial tool that directly connects microscopic structures of these systems to the geometries of gravitational spacetimes. One manifestation is that the entanglement entropy in quantum many-body systems can be calculated from the area of an extremal surface in the corresponding gravitational spacetime. This implies that a gravitational spacetime can emerge from an enormous number of entangled qubits. In this Essay, I will discuss open problems in this area of research, considering recent developments and outlining future prospects towards a complete understanding of quantum gravity. The first step in this direction is to understand what kind of quantum circuits each holographic spacetime corresponds to, drawing on recent developments in quantum complexity theories and studying concrete examples of holography in string theory. Next, we should extend the concept of holography to general spacetimes, e.g., those spacetimes which appear in realistic cosmologies, by utilizing the connections between quantum information and holography. To address the fundamental question of how time emerges, I will propose the concepts of pseudo-entropy and time-like entanglement as a useful tool in our exploration.
Authors: Felix Fritzsch, Pieter W. Claeys
Recent experimental and theoretical developments in many-body quantum systems motivate the study of their out-of-equilibrium properties through multi-time correlation functions. We consider the dynamics of higher-order out-of-time-order correlators (OTOCs) in a minimal circuit model for quantum dynamics. This model mimics the dynamics of a structured subsystem locally coupled to a maximally random environment. We prove the exponential decay of all higher-order OTOCs and fully characterize the relevant time scales, showing how local operators approach free independence at late times. We show that the effects of the environment on the local subsystem can be captured in a higher-order influence matrix, which allows for a Markovian description of the dynamics provided an auxiliary degree of freedom is introduced. This degree of freedom directly yields a dynamical picture for the OTOCs in terms of free cumulants from free probability, consistent with recent predictions from the full eigenstate thermalization hypothesis (ETH). This approach and the relevant influence matrix are expected to be applicable in more general settings and present a first step to characterizing quantum memory in higher-order OTOCs.
Authors: Albert M. Varonov, Todor M. Mishonov
Recently using Scanning Josephson Tunneling Microscopy (SJTM) in the group of Séamus Davis a super-modulation of the superconducting order parameter induced by super-modulation of the distance $\delta$ between planar Cu and apical O was observed in [O'Mahony et al, On the electron pairing mechanism of copper-oxide high temperature superconductivity, PNAS Vol. 119(37), e2207449119 (2022)]. The authors conclude: "concurrence of prediction from strong correlation theory... with these observations indicates that... super-exchange is the electron pairing mechanism of Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$." Additionally, the charge transfer energy $\mathcal{E}$, probably between O2$p_z$ and Cu$3d_{x^2-y^2}$ levels was studied by SJTM, too. In our current theoretical study we use LCAO approximation and Hilbert space spanned on 5 atomic orbitals: Cu$4s$, Cu$3d_{x^2-y^2}$, O2$p_x$, O2$p_y$, O2$p_z$. For the only super-exchange amplitude $J_{sd}$ we use the Kondo double electron exchange between Cu$4s$ and Cu$3d_{x^2-y^2}$ orbitals and its anti-ferromagnetic sign is determined by adjacent to the copper ion in-plane oxygen orbitals. Within this approximations we have calculated: "Measured dependence of... electron-pair density $n_p$ on the displacement $\delta$ of the apical O atoms from the planar Cu atoms" on [O'Mahony et al., Fig. 5C] and obtained an excellent accuracy. We discuss that the correlation between the shape of Fermi contour and the critical temperature of optimally hole-doped cuprates can be considered as an analogue of the isotope effect of phonon superconductors. The analyzed SJTM experiment is one of the best confirmations of the [J. Röhler, Plane dimpling and Cu4s hybridization in YBa$_2$Cu$_3$O$_{7-x}$, Physica B: Cond. Matt. Vol. 284-288, 1041 (2000)] idea that the hybridization of Cu$4s$ with conduction band leads to increasing of $T_c$.
Authors: Jeet Shah, Laura Shou, Jeremy Shuler, Victor Galitski
The thermodynamic limit is foundational to statistical mechanics, underlying our understanding of many-body phases. It assumes that, as the system size grows infinitely at fixed density of particles, unambiguous macroscopic phases emerge that are independent of the system's boundary shape. We present explicit quantum spin and dimer Hamiltonians whose ground states violate this principle. Our construction relies on the previous mathematical work on classical dimers on the Aztec diamond and the square-octagon fortress, where geometry-dependent phase behaviors are observed in the infinite-size limit. We reverse engineer quantum spin Hamiltonians on the square and the square-octagon lattices whose ground states at the Rokhsar-Kivelson points are described by classical dimer coverings. On diamond-shaped domains, we find macroscopic boundary regions exhibiting distinct quantum phases from those on square-shaped domains. We study the nature of these phases by calculating the dimer-dimer and vison correlators and adapt Kasteleyn matrix based analytical and numerical methods for computing the vison correlator, which are significantly more efficient than standard Monte Carlo techniques. Our results show that the square-octagon lattice supports a single gapped short-range entangled phase, with exponentially decaying dimer correlators and a constant vison correlator. When the same model is considered on a diamond-shaped domain, an additional ordered phase emerges near the corners, where the dimers are in a staggered pattern.
Authors: Wen O. Wang, Edwin W. Huang, Brian Moritz, Thomas P. Devereaux
We compute high-resolution angle-resolved photoemission spectroscopy of the Hubbard model using the unbiased determinant quantum Monte Carlo algorithm, revealing an asymmetry between electron and hole doping. Electron doping exhibits more coherent quasiparticles and stronger antiferromagnetic correlations compared to hole doping. At low doping, a nodal-antinodal dichotomy on the Fermi surface is observed, similar to cuprate experiments. The dichotomy reflects the momentum dependence of the Mott gap, as manifested in both the spectral function and the self-energy. For hole doping, we observe a transition towards the pseudogap, without signature of pocket formation. The simulated nuclear magnetic resonance pseudogap temperatures do not necessarily agree with the temperature determined by spectroscopy. These findings collectively suggest the pseudogap is a smooth crossover driven by strong correlations.
Authors: Pavel A. Andreev, Mariya Iv. Trukhanova
We present the analytical theory of the electromagnon resonance for the multiferroics of spin origin. We consider the spin density evolution under the influence of magnetoelectric coupling in the presence of the electromagnetic wave. The dielectric permeability is found for the eigen-wave perturbations accompanied by perturbations of the electric field. The imaginary part of the dielectric permeability is found as the function of the applied electric field frequency, while the frequency of the eigen-waves is found from the dispersion equation as the function of the wave vector and parameters of the system. The result shows the existence of two peaks. One sharp peak is associated with the magnon resonance, while the second wide peak at the approximately four times smaller frequency is interpreted as the electromagnon resonance in accordance with existing experimental data.
Authors: Wen L. Liu, Jun Jian, Ning X. Zheng, Hui Tang, Ji Z. Wu, Yu Q. Li, Wen X. Zhang, Jie Ma, Suo T. Jia
Dilute-gas Bose-Einstein condensates are an exceptionally versatile testbed for the investigation of physics phenomenon especially the well-known classical system. Here we use a degenerate Bose gas of sodium atoms confined in an optical dipole trap to simulate the matter-wave on the swing. Under the driving of Anti-Sisyphus process, the swing was excited successfully. Moreover, the spin echo like behavior and collective-mode excitation appear during the oscillation of matter-wave swing, manifesting the quantum nature of the system beyond its classical counterpart. Our work lays the foundation for matter-wave on the swing and more generally points to a future of practical applications for the motional quantum states linked with quantum information science.
Authors: Xiaoyue Zhou, Yi Chan, Siyuan Zhu, Fu Deng, Wei Bai, Jingdi Zhang
We report on an ultrafast terahertz spectroscopic study on the dynamics of free carriers and the pertinent bulk plasmons in Hg$_{0.8}$Cd$_{0.2}$Te (MCT) film, a narrowband semiconductor accommodating three dimensional massless Kane fermions. The ultrabroadband terahertz source enables the investigation of the lightly doped equilibrium state in the presence of plasmon-phonon hybridization through the heavily doped excited state, primarily dominated by plasmons. Without the recourse to the resource consuming cryogenic high magnetic field spectroscopy that hinges on observable related to the interband transition, we show that the massless band dispersion can instead be conveniently perceived by the room temperature study of the intraband transition through the determination of the plasmon carrier density relationship. We found the plasma frequency in MCT scales with the cube root of carrier density, in contrast with the square root scaling in the conventional massive fermion system of parabolic band dispersion. This work also answers the curious question of whether the MCT can maintain its massless Kane fermion character in case the strict gapless condition is deviated from. The method presented herein provides a convenient approach to identifying the landscape of both massless and massive band dispersion.
Authors: Yuncheng Mao, Ju Zhou, Myrta Grüning, Claudio Attaccalite
We study the shift current in two two-dimensional (2D) Janus transition metal dichalcogenides: molybdenum diselenide (MoSSe) and tungsten diselenide (WSSe). The shift current is evaluated using a real-time approach, in which the coupling with an external field is described in terms of a dynamical Berry phase. This approach incorporates electron-hole interactions and quasiparticle band structure renormalization through an effective Hamiltonian derived from many-body perturbation theory. We find that the shift current is strongly enhanced in correspondence of C excitons. An analysis in terms of the electron-hole pairs reveals that electron and hole are localized on different atoms, and thus following an optical excitation, the center of the electron charge is shifted thus giving rise to a significant photocurrent. These results highlight the role played by excitons in the shift-current response of Janus TMDs and demonstrate that these materials are promising building blocks for future photovoltaic devices.
Authors: Tsz Fung Poon, King Yau Yip, Ying Kit Tsui, Lingfei Wang, Kai Ham Yu, Wei Zhang, Zheyu Wang, Taketo Nakatani, Chishiro Michioka, Hiroaki Ueda, Siu Tung Lam, Kwing To Lai, Swee K. Goh
Kagome metal AV$_3$Sb$_5$ (A=K, Rb, Cs) has emerged as an intriguing platform for exploring the interplay between superconductivity and other quantum states. Among the three compounds, RbV$_3$Sb$_5$ has a notably lower superconducting critical temperature ($T_c$) at ambient pressure, posing challenges in exploring the superconducting state. For instance, the upper critical field ($H_{c2}$) is small and thus difficult to measure accurately against other control parameters. Hence, enhancing superconductivity would facilitate $H_{c2}$ measurements, providing insights into key superconducting properties such as the dimensionality. In this letter, we report the tuning of the $T_c$ in RbV$_3$Sb$_5$ through the application of biaxial strain. Utilizing a negative thermal expansion material ZrW$_2$O$_8$ as a substrate, we achieve a substantial biaxial strain of $\epsilon=1.50\%$, resulting in a remarkable 75\% enhancement in $T_c$. We investigate the $H_{c2}$ as a function of temperature, revealing a transition from multi-band to single-band superconductivity with increasing tensile strain. Additionally, we study the $H_{c2}$ as a function of field angle, revealing a plausible correlation between the $T_c$ enhancement and the change in dimensionality of the superconductivity under tensile strain. Further analysis quantitatively illustrates a transition towards two-dimensional superconductivity in RbV$_3$Sb$_5$ when subjected to tensile strain. Our work demonstrates that the application of biaxial strain allows for the tuning of both the $T_c$ and superconducting dimensionality in RbV$_3$Sb$_5$.
Authors: Ming-Qiang Ren, Qiang-Jun Cheng, Hui-Hui He, Ze-Xian Deng, Fang-Jun Cheng, Yong-Wei Wang, Cong-Cong Lou, Qinghua Zhang, Lin Gu, Kai Liu, Xu-Cun Ma, Qi-Kun Xue, Can-Li Song
Interfacial interactions often promote the emergence of unusual phenomena in two-dimensional systems, including high-temperature superconductivity. Here, we report the observation of full-gap superconductivity with a maximal spectroscopic temperature up to 26 K in a BaAs monolayer grown on ferropnictide Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ (abbreviated as BFCA) epitaxial films. The superconducting gap remains robust even when the thickness of underlying BFCA is reduced to the monolayer limit, in contrast to the rapid suppression of $T_\textrm{c}$ in standalone BFCA thin films. We reveal that the exceptional crystallinity of the BaAs/BFCA heterostructures, featured by their remarkable electronic and geometric uniformities, is crucial for the emergent full-gap superconductivity with mean-field temperature dependence and pronounced bound states within magnetic vortices. Our findings open up new avenues to unravel the mysteries of unconventional superconductivity in ferropnictides and advance the development of FeAs-based heterostructures.
Authors: Meng Zhang, Ming Qin, Yanqiu Sun, Siyuan Hong, Yanwu Xie
The coexistence of superconductivity and ferroelectricity is rare due to their conflicting requirements: superconductivity relies on free charge carriers, whereas ferroelectricity typically occurs in insulating systems. At LaAlO3/KTaO3 interfaces, we demonstrate the coexistence of two-dimensional superconductivity and ferroelectricity, enabled by the unique properties of KTaO3 as a quantum paraelectric. Systematic gating and poling experiments reveal a universal enhancement of the superconducting transition temperature (Tc) by 0.2-0.6 K and bistable transport properties, including hysteresis, strongly suggesting the existence of switchable ferroelectric polarization in the interfacial conducting layer. Hysteresis loops indicate robust ferroelectricity below 50 K. The Tc enhancement is attributed to ferroelectric polarization-induced reduction in dielectric constant, which narrows the interfacial potential well, confining carriers closer to the interface. The bistability arises from switchable ferroelectric polarization, which modulates the potential well depending on polarization direction. These findings establish a straightforward mechanism coupling ferroelectricity and superconductivity, providing a promising platform for exploring their interplay.
Authors: Gregory Behrendt, Sebastian Deffner
Endoreversible engine cycles are a cornerstone of finite-time thermodynamics. We show that endoreversible Stirling engines operating with a one-component plasma as working medium run at maximal power output with the Curzon-Ahlborn efficiency. As a main result, we elucidate that this is actually a consequence of the fact that the caloric equation of state depends only linearly on temperature and only additively on volume. In particular, neither the exact form of the mechanical equation of state, nor the full fundamental relation are required. Thus, our findings immediately generalize to a larger class of working plasmas, far beyond simple ideal gases. In addition, we show that for plasmas described by the photonic equation of state the efficiency is significantly lower. This is in stark contrast to endoreversible Otto cycles, for which photonic engines have an efficiency larger than the Curzon-Ahlborn efficiency.
Authors: Fan Yang, Maria Zelenayova, Paolo Molignini, Emil J. Bergholtz
The non-Hermitian bulk-boundary correspondence features an interplay between the non-Hermitian skin effect and anomalous boundary-mode behavior. Whereas the skin effect is known to manifest itself in quantum dynamics in the form of chiral damping, it has remained less clear what impact the boundary modes may have. Here we derive experimentally accessible signatures of the boundary modes. We also establish clear criteria, based on the effective generalized Brillouin zone, that determine when bulk and boundary effects can be dynamically discerned using the Liouvillian separation gap. This leads to telltale signatures in both stable regimes -- where particle number remains finite -- and in the unstable regimes -- where a macroscopic boundary mode population occurs.
Authors: W. Ebeling
Honoring the hundredth anniversary of the birthday of Ihor R. Yuknovskii we analyze new developments in the statistical thermodynamics of Coulomb systems. The basic idea of this work is to demonstrate that the exponential potential used in the first papers of Yukhnovskii is an appropriate reference system for a description of classical and quantum charged particle systems. We briefly discuss the collaboration between the groups of Ihor R. Yuknovskii in Lviv and Günter Kelbg in Rostock and analyze several approaches based on pair correlation functions and cluster expansion in the classical as well as in the quantum case. Finally, we discuss the progress in the statistical description of bound states of three particles as in helium plasmas and in MgCl$_2$-solutions in the classical case and present new results regarding the influence of three-particle bound states. In particular, we give new expressions for the cluster integrals and the mass action functions of helium atoms and ionic triple associates as well as for the equation of state (EoS).
Authors: Abid, Luneng Zhao, Ju Huang, Yongjia Zheng, Yuta Sato, Qingyun Lin, Zhen Han, Chunxia Yang, Tianyu Wang, Bill Herve Nduwarugira, Yicheng Ma, Lingfeng Wang, Yige Zheng, Hang Wang, Salman Ullah, Afzal Khan, Qi Zhang, Wenbin Li, Junfeng Gao, Bingfeng Ju, Feng Ding, Yan Li, Kazu Suenaga, Shigeo Maruyama, Huayong Yang, Rong Xiang
In this work, we present the synthesis of tin disulfide (SnS2) nanotubes (NTs) with preferred chiral angle. A sacrificial template is used to create channels of boron nitride nanotubes (BNNTs) with an optimized diameter of 4-5 nm, inside of which SnS2 NTs are formed with the high yield and structural purity. Atomic resolution imaging and nano-area electron diffraction reveal that these synthesized SnS2 NTs prefer to have an armchair configuration with a probability of approximately 85%. Calculations using density functional theory (DFT) reveal a negligible difference in the formation energy between armchair and zigzag NTs, suggesting that structural stability does not play a key role in this chirality-selective growth. However, a detailed TEM investigation revealed that some SnS2 nanoribbons are found connected to the ends of SnS2 NTs, and that these nanoribbons primarily have a zigzag configuration. Subsequent DFT and machine learning potential molecular dynamic simulations verify that nanoribbons with zigzag configurations are more stable than armchair ones, and indeed zigzag nanoribbons aligned along the BNNT axis tend to roll up to form an armchair SnS2 NTs. Finally, this "zigzag nanoribbon to armchair nanotube" transition hypothesis is verified by in-situ high-resolution transmission electron microscopy, in which the transformation of SnS2 nanoribbons into a nanotube is reproduced in real time. This work is the first demonstration of preferred-chirality growth of transition metal dichalcogenide nanotubes.
Authors: M.P. Telenkov, Yu.A. Mityagin, D.S.Korchagin
The electron scattering with longitudinal polar optical phonons in a quantizing magnetic field tilted to the plane of quantum well layers is studied. The scattering rate's behavior at variation of the magnetic field magnitude and orientation is established.
Authors: Julian Amette Estrada, Marc E. Brachet, Pablo D. Mininni
Quantum turbulence shares many similarities with classical turbulence in the isotropic and homogeneous case, despite the inviscid and quantized nature of its vortices. However, when quantum fluids are subjected to rotation, their turbulent dynamics depart significantly from the classical expectations. We explore the phenomenology of rotating quantum turbulence, emphasizing how rotation introduces new regimes with no classical analogs. We review recent theoretical, experimental, and numerical developments, and present new numerical results that map out distinct dynamical regimes arising from the interplay of rotation, quantization, non-linearities, and condensed matter regimes. In particular, we show the importance of distinguishing the dynamics of rotating quantum fluids in the slowly rotating, rapidly rotating, and low Landau level regimes. The findings have implications for the dynamics of liquid helium, atomic Bose-Einstein condensates, and neutron stars, and show how rotating quantum fluids can serve as a unique platform bridging turbulence theory and condensed matter physics revealing novel states of out-of-equilibrium quantum matter.
Authors: Giniyat Khaliullin, Jiří Chaloupka
We propose a theory for bilayer nickelate materials, where a large tetragonal field - intrinsic or induced by epitaxial strain - lifts the orbital degeneracy and localizes the $3z^2-r^2$ orbital states. These states host local spins $S=1/2$ bound into singlets by strong interlayer coupling, and their dynamics is described by weakly dispersive singlet-triplet excitations ("triplons"). The charge carriers occupy the wide bands of $x^2-y^2$ symmetry, and their Cooper pairing is mediated by the high-energy triplon excitations. As the $x^2-y^2$ band filling increases, i.e. moving further away from the Ni$^{3+}$ valence state, the indirect Ruderman-Kittel-Kasuya-Yosida interactions between local spins induce spin-density-wave order via triplon condensation. Implications of the model for compressively strained La$_3$Ni$_2$O$_7$ films and electron doped oxychloride Sr$_3$Ni$_2$O$_5$Cl$_2$ are discussed.
Authors: Jiří Chaloupka, Giniyat Khaliullin
We theoretically study quasi-two-dimensional nickel compounds, where the nickel ions assume Ni$^{2+}$ $d^8$ valence state and feature a low-spin $S=0$ ground state quasidegenerate with $S=1$ ionic excitations. Such a level structure is supported by square-planar coordination of nickel ions or a suitable substitution of apical oxygens. We construct the corresponding singlet-triplet exchange model and explore its phase diagram and excitation spectrum. By hole doping, we further introduce mobile Ni$^{3+}$ $d^7$ ionic configurations with effective spins $S=1/2$, and analyze their interactions with the $d^8$ singlet-triplet background. The interplay with the triplet excitations in the $d^8$ sector is found to have a deep impact on the propagation of the doped hole-like charge carriers and is identified as a powerful source of Cooper pairing among them.
Authors: Sang Yong Song, Gábor B. Halász, Jiaqiang Yan, Benjamin J. Lawrie, Petro Maksymovych
We investigate the orbitally resolved superconducting properties of bulk FeSe using scanning tunneling microscopy (STM). We find that the spectral weights of both the large $\Delta_1$ and small $\Delta_2$ superconducting gaps remain nearly unchanged at the top Se sites as the STM tip approaches atomic contact. In contrast, the spectral weight of $\Delta_2$ increases significantly at the Fe and bottom Se sites. These results suggest that the gap $\Delta_2$ is localized in the xy-plane and likely associated with the dxy orbital band. Furthermore, we observe a long-range suppression of the large gap $\Delta_1$ near one-dimensional (1D) defects such as twin boundaries, wrinkles, and step edges, whereas $\Delta_2$ remains robust. This indicates that the two superconducting gaps respond differently to such 1D defects. High-resolution measurement using a Pb-coated tip reveals localized in-gap states near 1D defects, indicating possible defect-induced magnetism. Our findings highlight the contrasting behaviors of gap $\Delta_1$ and gap $\Delta_2$ in response to local electronic and magnetic environments and provide real-space evidence for orbital-selective superconductivity.
Authors: A. Baumketner, D. Anokhin, Ya. Patsahan
We investigate the effect of the excluded volume of surfactant ligands on the shape of incipient quantum dots (QDs) to which they are attached. We consider a model in which ligands are represented by hard-sphere particles that are bound to the surface of a nanoparticle (NC) that is cast in the shape of a prism. It is found in Monte Carlo simulations that the ensemble of relevant NC conformations consists of a small number of specific states that take on the form of nanoplates and nanorods. The shape of these states can be well described by the derived theoretical models. At increasing ligand density, the free energy of different states is seen to be approximately the same, suggesting that excluded volume interactions among ligands acts to narrow down the conformational space accessible to an NC without creating a statistical preference for any particular configuration.
Authors: M. S. Bulakhov, A. S. Peletminskii, P. P. Kostrobij, I. A. Ryzha, Yu. V. Slyusarenko
An approach to the theoretical study of effects and phenomena in quantum gases interacting with radiation is proposed. The approach is based on a modification of the canonical transformation method, which was once used to diagonalize Hamiltonians describing the interaction of electrons with phonons in a solid. The capabilities of the method are demonstrated by studying the influence of photons on the spectral characteristics of atoms of quantum gases interacting with radiation. Within the framework of the developed approach, the effect of "dressing" atoms of quantum gases by a cloud of virtual photons is investigated and expressions for the energy characteristics of such dressed atoms - quasiparticles are obtained. The problem of defining the concept of the effective mass of such quasiparticles is discussed.
Authors: Valerio Lucarini, Manuel Santos Gutierrez, John Moroney, Niccolò Zagli
The link between forced and free fluctuations for nonequilibrium systems can be described via a generalized version of the celebrated fluctuation-dissipation theorem. The use of the formalism of the Koopman operator makes it possible to deliver an intepretable form of the response operators written as a sum of exponentially decaying terms, each associated one-to-one with a mode of natural variability of the system. Here we showcase on a stochastically forced version of the celebrated Lorenz '63 model the feasibility and skill of such an approach by considering different Koopman dictionaries, which allows us to treat also seamlessly coarse-graining approaches like the Ulam method. Our findings provide support for the development of response theory-based investigation methods also in an equation-agnostic, data-driven environment.
Authors: Yixin Zhang, Cristian Batista, Yang Zhang
Antiferromagnetism and superconductivity are often viewed as competing orders in correlated electron systems. Here, we demonstrate that kinetic frustration in hole motion facilitates their coexistence within the square-lattice repulsive Hubbard model. Combining exact analytical solutions on tailored geometries with large-scale numerical simulations, we reveal a robust pairing mechanism: holes on opposite sublattices behave as if they carry opposite effective charges due to spin singlet formation from kinetic frustration. This emergent property suppresses phase separation and fosters a coherent $d$-wave superconducting channel embedded within a long-range antiferromagnetic background. Our findings establish a minimal yet broadly applicable framework for stabilizing strong-coupling superconductivity in doped Mott insulators.
Authors: Phil Russ, Mi Yan, Nicholas Kowalski, Laura Wadleigh, Vito W. Scarola, Brian DeMarco
Disorder can be applied to transform conducting to insulating states by localizing individual quantum particles. The interplay between disorder and interactions in many-particle systems leads to a richer tapestry of quantum phase transitions. Here, we report the measurement in an ultracold lattice gas of a disorder-induced transition from a state with small disorder-independent compressibility to a state for which compressibility increases with disorder. At zero temperature this is the transition from a Mott insulator (MI) to a Bose glass (BG), both of which are insulating states. This transformation is observed using measurements of core compressibility. By determining how double occupancy changes with atom number, we identify the threshold disorder strength required to switch from disorder-independent MI-like to disorder-dependent BG-like compressible behavior.
Authors: Jin Shang, Yinqiao Wang, Deng Pan, Yuliang Jin, Jie Zhang
The jamming transition between flow and amorphous-solid states exhibits paradoxical properties characterized by hyperuniformity (suppressed spatial fluctuations) and criticality (hyperfluctuations), whose origin remains unclear. Here we model the jamming transition by a topological satisfiability transition in a minimum network model with simultaneously hyperuniform distributions of contacts, diverging length scales and scale-free clusters. We show that these phenomena stem from isostaticity and mechanical stability: the former imposes a global equality, and the latter local inequalities on arbitrary sub-systems. This dual constraint bounds contact number fluctuations from both above and below, limiting them to scale with the surface area. The hyperuniform and critical exponents of the network model align with those of frictionless jamming, suggesting a new universality class of non-equilibrium phase transitions. Our results provide a minimal, dynamics-independent framework for jamming criticality and hyperuniformity in disordered systems.
Authors: Farhad Kamarei, Evan Breedlove, Oscar Lopez-Pamies
This paper presents a macroscopic theory, alongside its numerical implementation, aimed at describing, explaining, and predicting the nucleation and propagation of fracture in viscoelastic materials subjected to quasistatic loading conditions. The focus is on polymers, in particular, on elastomers. To this end, the starting point of this work is devoted to summarizing the large body of experimental results on how elastomers deform, nucleate cracks, and propagate cracks when subjected to mechanical loads. When viewed collectively, the experiments make it plain that there are three basic ingredients that any attempt at a complete macroscopic theory of fracture in elastomers ought to account for: i) the viscoelasticity of the elastomer; ii) its strength; and iii) its fracture energy. A theory is then introduced that accounts for all these three basic ingredients by extending the phase-field theory initiated by Kumar, Francfort, and Lopez-Pamies (J. Mech. Phys. Solids 112 (2018), 523--551) for elastic brittle materials to seamlessly incorporate viscous energy dissipation by deformation, a generalized strength surface that is a hypersurface in stress-deformation space (and not just in stress space as for elastic brittle materials), and the pertinent Griffith criticality condition for materials that dissipate energy not just by the creation of surface but also by deformation, in this case, by viscous deformation (Shrimali and Lopez-Pamies (2023) Extreme Mech. Lett. 58, 101944). From an applications point of view, the proposed theory amounts to solving an initial-boundary-value problem comprised of two nonlinear PDEs coupled with a nonlinear ODE for the deformation field, a tensorial internal variable, and the phase field. A robust scheme is presented to generate solutions for these equations.
Authors: Dimitrios Mataragkas, Alexandros Vasilopoulos, Nikolaos G. Fytas, Dong-Hee Kim
We investigate the spin-$1$ Blume-Capel model on an infinite strip of the triangular lattice using the transfer-matrix method combined with a sparse-matrix factorization technique. Through finite-size scaling analysis of numerically exact spectra for strip widths up to $L = 19$, we accurately locate the tricritical point improving upon recent Monte Carlo estimates. In the first-order regime, we observe exponential scaling of the spectral gap, reflecting the linear growth of interfacial tension as the temperature decreases below the tricritical point. Finally, we validate our tricritical point estimate through precise agreement with conformal field theory predictions for the tricritical Ising universality class. Our results underscore the continued utility of the transfer-matrix approach for studying phase transitions in complex lattice models.
Authors: Till Welker, Ricard Alert
Via mechanisms not accessible at equilibrium, self-propelled particles can form phases with positional order, such as crystals, and with orientational order, such as polar flocks. However, the interplay between these two types of order remains relatively unexplored. Here, we address this point by studying crystals of active particles that turn either towards or away from each other, which can be experimentally realised with phoretic or Janus colloids or with elastically-coupled walker robots. We show that, depending on how these interactions vary with interparticle distance, the particles align along directions determined by the underlying crystalline lattice. To explain the results, we map the orientational dynamics of the active crystal onto a lattice of spins that interact via (anti-)ferromagnetic alignment with each other plus nematic alignment with the lattice directions. Our findings indicate that orientational and positional order can be strongly coupled in active crystals, thus suggesting strategies to control orientational order by engineering the underlying crystalline lattice.
Authors: E. Langmann, J. Lenells
We study an extension of the 2D Fermi--Hubbard model, which was recently introduced in [Das et al., Phys. Rev. Lett. 132, 263402 (2024)] and shown to describe altermagnetism that can be studied in cold atom systems. Using an updated Hartree--Fock method that can detect instabilities towards phase separation, we show that the model is in a mixed phase in large parts of the parameter regime at half-filling. We argue that the occurrence of a mixed phase is an indication of exotic physics which, in this model, occurs in parameter regimes accessible in cold atom experiments.
Authors: Bernhard E. Lüscher, Mark H. Fischer
Time-reversal-symmetry breaking is generally understood to be detrimental for superconductivity. However, recent experiments found superconductivity emerging out of a normal state showing a finite anomalous Hall effect, indicative of time-reversal-symmetry breaking, in diverse systems from kagome metals, $1T'$-WS$_2$, to twisted MoTe$_2$ and rhombohedral graphene. Motivated by these findings, we study the stability of superconducting orders and the mechanisms that suppress superconductivity in the prototypical anomalous Hall system, the Haldane model, where complex hopping parameters result in loop-current order with a compensated flux pattern. We find that neither spin-singlet nor spin-triplet states are generically suppressed, but the real-space sublattice structure plays a crucial role in the stability of the orders. Interestingly, the nearest-neighbor chiral states of $d\pm id$ or $p\pm i p$ symmetry couple linearly to the flux, such that the two otherwise degenerate chiralities split under finite flux. As an experimental probe to distinguish the various orders in this system, we study the anomalous thermal Hall effect, $\kappa_{xy} / T$, which vanishes at zero temperature for topologically trivial superconducting states, but reaches a finite value corresponding to the Chern number in a topologically non-trivial superconducting state. Our results illustrate that broken time-reversal symmetry through a finite flux is neither generically destructive for superconductivity, nor does it imply non-trivial topological order of the emerging superconducting state. However, in the case of multiple competing pairing channels, the loop-current order can favor a chiral superconducting state.
Authors: Charly Beulenkamp, Krzysztof P. Zamarski, Robert C. Bird, C. Ruth Le Sueur, Jeremy M. Hutson, Manuele Landini, Hanns-Christoph Nägerl
We report the creation of an ultracold gas of bosonic $^{39}$K$^{133}$Cs molecules. We first demonstrate a cooling strategy relying on sympathetic cooling of $^{133}$Cs to produce an ultracold mixture. From this mixture, weakly bound molecules are formed using a Feshbach resonance at 361.7 G. The molecular gas contains $7.6(10)\times 10^3$ molecules with a lifetime of about 130 ms, limited by two-body decay. We perform Feshbach spectroscopy to observe several new interspecies resonances and characterize the bound state used for magnetoassociation. Finally, we fit the combined results to obtain improved K-Cs interaction potentials. This provides a good starting point for the creation of ultracold samples of ground-state $^{39}$K$^{133}$Cs molecules.
Authors: Robert S. Hoy
We show that for a standard continuously-polydisperse model with particle-diameter distribution $P(\sigma) \propto \sigma^{-3}$ and polydispersity index $\Delta$, employing a combination of standard SWAP moves and transient degree of freedom (TDOF) moves during a Lubachevsky-Stillinger-like particle-growth process dramatically increases the generated packings' jamming densities $\phi_{\rm J}(\Delta)$ and coordination numbers $Z_{\rm J}(\Delta)$, for a wide range of $\Delta$. We find that the fractional increase in $\phi_{\rm J}(\Delta)$ obtained by employing these moves first increases rapidly with $\Delta$, then plateaus at $6-7\%$ over the range $0.10 \lesssim \Delta \leq 50$; the obtained $\phi_{\rm J}$ are as high as $0.747$ (for $\Delta = 0.50$). These density increases are achieved without producing crystallization or fractionation. SWAP and TDOF moves also reduce packings' rattler populations by as much as 96% and increase their bulk moduli by as much as 154%.
Authors: Mehrana R. Nejad
Starting from a three-dimensional description of an active nematic layer, we employ an asymptotic theory to derive a series of low-dimensional continuum models that capture the coupled dynamics of flat and curved films, including variations in film thickness, shape deformations, internal velocity fields, and the dynamics of orientational order. Using this asymptotic theory, we investigate instabilities driven by activity in both the nematic and isotropic phases for cylindrical and flat films. In the flat case, we demonstrate that incorporating shape and thickness variations fundamentally alters the bend and splay nature of instabilities compared to conventional two dimensional nematic instabilities. In the isotropic phase, we find that both extensile and contractile activity can induce nematic order, in contrast with active nematics on fixed surfaces, where only extensile activity leads to ordering. For the case of curved geometries such as a cylindrical film, we reveal that thickness and shape instabilities are inherently coupled. In the isotropic phase, the emergence of nematic order triggers both thickness and shape instabilities. In the nematic phase, contractile activity induces thickness instabilities, which in turn drive geometric deformations. Our results highlight the crucial interplay between activity, thickness variations, and curvature, providing new insights into the behavior of active nematic films beyond the conventional two dimensional paradigm that has been studied to date.
Authors: E. Langmann, J. Lenells
We show that the standard textbook description of (restricted) Hartree--Fock theory for (Fermi) Hubbard-like models is in need of an update, and we present such an update allowing us to correct basic and established results in the condensed matter physics literature that are qualitatively wrong. Our update amounts to adding a test which reliably checks the thermodynamic stability of solutions of Hartree--Fock equations. This stability test makes it possible to detect, by simple means and with certainty, regions in phase space where the model exhibits mixed phases where two conventional phases coexist and translation invariance is broken in complicated ways; in such a mixed phase, unconventional physics is to be expected. Our results show that mixed phases are ubiquitous in Hubbard-like models in arbitrary dimensions.
Authors: Ankur Majumder, Sudeshna Sen
The Mott-Hubbard metal-insulator transition is a paradigmatic phenomenon where Coulomb interactions between electrons drive a metal-insulator phase transition. It has been extensively studied within the Hubbard model, where a quantum critical transition occurs at a finite temperature second-order critical point. This work investigates the Mott metal-insulator transition in a modified periodic Anderson model that may be viewed as a three-orbital lattice model including an interacting, localized orbital coupled to a delocalized conduction orbital via a second conduction orbital. This model could also be viewed as a bilayer model involving a conventional periodic Anderson model layer coupled to a metallic layer. Within the dynamical mean field theory, this model possesses a strictly zero temperature quantum critical point separating a Fermi liquid and a Mott insulating phase. By employing a simplified version of the dynamical mean field theory, namely, the two-site or linearized dynamical mean field theory, we provide an analytical estimate of the critical parameter strengths at which the transition occurs at zero temperature. We also provide an analytical estimate of the single-site von Neumann entanglement entropy. This measure can be used as a robust identifier for the phase transition. We extend these calculations to their cluster version to incorporate short-range, non-local spatial correlations and discuss their effects on the transition observed in this model.
Authors: Porhouy Minh, Steven W. Hall, Ryan S. DeFever, Sapna Sarupria
Modulating liquid-to-solid transitions and the resulting crystalline structure for tailored properties is much desired. Colloidal systems are exemplary to this end, but the fundamental knowledge gaps in relating the influence of intermolecular interactions to crystallization behavior continue to hinder progress. In this study, we address this knowledge gap by studying nucleation and growth in systems with modified Lennard-Jones potential. Specifically, we study the commonly used 12-6 potential and a softer 7-6 potential. The thermodynamic state point for the study is chosen such that both systems are investigated at the same level of supercooling and pressure. Under these conditions, we find that the nucleation rate for both systems is comparable. Interestingly, the nucleation pathways and resulting crystal structures are different. In the 12-6 system, nucleation and growth occur predominantly through the FCC structure. Softening the potential alters the critical nucleus composition and introduces two distinct nucleation pathways. One pathway predominantly leads to the nucleus with a body-centered cubic (BCC) structure, while the other favors the face-centered cubic (FCC) arrangement. Our study illustrates that polymorph selection can be achieved through modifications to intermolecular interactions without impacting nucleation kinetics. The results have significant implications in designing approaches for polymorph selection and modulating self-assembly mechanisms.
Authors: Keun Hyuk Ahn
The Su-Schrieffer-Heeger model is extended to the three and higher dimensional systems. Nearly or absolutely flat midgap surface and hypersurface bands are predicted based on the topological analysis, which do not require fine tuning of parameters. By adding the on-site Coulomb interaction for the three dimensional systems, we computationally show that the large difference in the band widths between the surface and the bulk leads to the strongly correlated phenomena, specifically magnetism, confined only on the surface. Possible experimental realizations in solid state materials and metamaterials are discussed.
Authors: Yun Kim, Dingbin Huang, Deyuan Lyu, Haoyue Sun, Jian-Ping Wang, Paul A. Crowell, Xiaojia Wang
Spintronics has emerged as a key technology for fast and non-volatile memory with great CMOS compatibility. As the building blocks for these cutting-edge devices, magnetic materials require precise characterization of their critical properties, such as the effective anisotropy field ($H_{\rm{k,eff}}$, related to magnetic stability) and damping ($\alpha$ key factor in device energy efficiency). Accurate measurements of these properties are essential for designing and fabricating high-performance spintronic devices. Among advanced metrology techniques, Time-resolved Magneto-Optical Kerr Effect (TR-MOKE) stands out for its superb temporal and spatial resolutions, surpassing traditional methods like ferromagnetic resonance (FMR). However, the full potential of TR-MOKE has not yet been fully pledged due to the lack of systematic optimization and robust operational guidelines. In this study, we address this gap by developing experimentally validated guidelines for optimizing TR-MOKE metrology across materials with perpendicular magnetic anisotropy (PMA) and in-plane magnetic anisotropy (IMA). Our work identifies the optimal ranges of the field angle to simultaneously achieve high signal amplitudes and improve measurement sensitivities to $H_{\rm{k,eff}}$ and $\alpha$. By suppressing the influence of inhomogeneities and boosting sensitivity, our work significantly enhances TR-MOKE capability to extract magnetic properties with high accuracy and reliability. This optimization framework positions TR-MOKE as an indispensable tool for advancing spintronics, paving the way for energy-efficient and high-speed devices that will redefine the landscape of modern computing and memory technologies.
Authors: K. Guratinder, R. D. Johnson, D. Prabhakaran, R. A. Taylor, F. Lang, S. J. Blundell, L. S. Taran, S. V. Streltsov, T. J. Williams, S. R. Giblin, T. Fennell, K. Schmalzl, C. Stock
CoTi$_{2}$O$_{5}$ has the paradox that low temperature static magnetic order is incompatible with the crystal structure owing to a mirror plane that exactly frustrates magnetic interactions. Despite no observable structural distortion with diffraction, CoTi$_{2}$O$_{5}$ does magnetically order below $T_{\rm N}$ $\sim$ 25 K with the breaking of spin ground state degeneracy proposed to be a realization of the spin Jahn-Teller effect in analogy to the celebrated orbital Jahn-Teller transition. We apply neutron and Raman spectroscopy to study the dynamics of this transition in CoTi$_{2}$O$_{5}$. We find anomalous acoustics associated with a symmetry breaking strain that characterizes the spin Jahn-Teller transition. Crucially, the energy of this phonon coincides with the energy scale of the magnetic excitations, and has the same symmetry of an optic mode, observed with Raman spectroscopy, which atypically softens in energy with decreasing temperature. Taken together, we propose that the energetics of the spin Jahn-Teller effect in CoTi$_{2}$O$_{5}$ are related to cooperative magnetoelastic fluctuations as opposed to conventional soft critical dynamics which typically drive large measurable static displacements.
Authors: Yu-Xiao Jiang, Zi-Jia Cheng, Qiaozhi Xu, Md Shafayat Hossain, Xian P. Yang, Jia-Xin Yin, Maksim Litskevich, Tyler A. Cochran, Byunghoon Kim, Eduardo Miranda, Sheng Ran, Rafael M. Fernandes, M. Zahid Hasan
The Kondo lattice mode, as one of the most fundamental models in condensed matter physics, has been employed to describe a wide range of quantum materials such as heavy fermions, transition metal dichalcogenides and two-dimensional Moire systems. Discovering new phases on Kondo lattice and unveiling their mechanisms are crucial to the understanding of strongly correlated systems. Here, in a layered Kondo magnet USbTe, we observe a spin-textured nematic state and visualize a heavy electronic liquid-crystal phase. Employing scanning tunneling microscopy and spectroscopy (STM/STS), we visualize a tetragonal symmetry breaking of heavy electronic states around the Fermi level. Through systematically investigating the temperature and energy dependence of spectroscopic data, we find that the nematic state coincides with the formation of heavy quasi-particles driven by band hybridization. Remarkably, using spin polarized STM, we demonstrate that the nematic state is spin polarized, which not only suggests its intrinsically electronic nature, but also represents the unique magnetic texture of nematic heavy fermions. Our findings unveil a novel correlation-mediated order whose mechanism is inherently tied to Kondo-lattice physics. The observation of heavy nematic states enriches the phase diagram of correlated systems and provides a rare platform to explore the interplay of Kondo physics, spontaneous symmetry breaking and quantum criticality.
Authors: L.A. Kroo, R.A. Nicholson, M.W Boehm, S.K. Baier, G.H. McKinley
Here we present an experimentally practical and robust method to compute the transient extensional viscosity from exponential shear on a wide variety of viscoelastic complex fluids. To achieve this, we derive an analytical, frame-invariant continuum solution for the exponential shear material function, valid over all Weissenberg numbers. Specifically, we amend the original framework of Doshi and Dealy proposed in 1987 to explicitly address the effect of rotation of material elements, due to the presence of vorticity. Modern strain-controlled rheometers can access a wide range of effective Hencky strain rates in exponential shear (approximately within a range of 0.01 to 7 s^-1) and up to an effective Hencky strain of approximately 6 -- sufficient range to observe finite extensibility for many polymeric fluids. We quantify the kinematic, transducer-based, and instability-related experimental limitations of the method, establishing firm windows of data validity. The new material function is tested on a number of different example fluids. We show that these exponentially increasing strain histories are capable of producing "strong flow" -- generating stress-growth dynamics consistent with coil-stretch conformational changes in polymer solutions exhibited in extensional flows (Wi > 0.5). We then demonstrate that the method can reach finite extensibility for a 0.3 % wt. PIB solution. The method is then quantitatively validated (with no fitted parameters) against a traditional extensional technique, Capillary Break-Up Extensional Rheometry (CaBER) using the same PIB solution. Questions related to generality of this approach are addressed, including discussions on multi-mode relaxation and shear thinning.
Authors: Eungkyun Kim, Yu-Hsin Chen, Naomi Pieczulewski, Jimy Encomendero, David Anthony Muller, Debdeep Jena, Huili Grace Xing
AlN has the largest bandgap in the wurtzite III-nitride semiconductor family, making it an ideal barrier for a thin GaN channel to achieve strong carrier confinement in field-effect transistors, analogous to silicon-on-insulator technology. Unlike SiO$_2$/Si/SiO$_2$, AlN/GaN/AlN can be grown fully epitaxially, enabling high carrier mobilities suitable for high-frequency applications. However, developing these heterostructures and related devices has been hindered by challenges in strain management, polarization effects, defect control and charge trapping. Here, the AlN single-crystal high electron mobility transistor (XHEMT) is introduced, a new nitride transistor technology designed to address these issues. The XHEMT structure features a pseudomorphic GaN channel sandwiched between AlN layers, grown on single-crystal AlN substrates. First-generation XHEMTs demonstrate RF performance on par with the state-of-the-art GaN HEMTs, achieving 5.92 W/mm output power and 65% peak power-added efficiency at 10 GHz under 17 V drain bias. These devices overcome several limitations present in conventional GaN HEMTs, which are grown on lattice-mismatched foreign substrates that introduce undesirable dislocations and exacerbated thermal resistance. With the recent availability of 100-mm AlN substrates and AlN's high thermal conductivity (340 W/m$\cdot$K), XHEMTs show strong potential for next-generation RF electronics.
Authors: Shantanu Singh, Boyang Zhao, Christopher E. Stevens, Mythili Surendran, Tzu-Chi Huang, Bi-Hsuan Lin, Joshua R. Hendrickson, Jayakanth Ravichandran
Chalcogenides and oxy-chalcogenides, including complex chalcogenides and transition metal dichalcogenides, are emerging semiconductors with direct or indirect band gaps within the visible spectrum. These materials are being explored for various photonic and electronic applications, such as photodetectors, photovoltaics, and phase-change electronics. Understanding the fundamental properties of these materials is crucial for optimizing their functionalities. Therefore, the availability of large, high-quality single crystals of chalcogenides and oxy-chalcogenides is essential for a better comprehension of their structure and properties. In this study, we present a novel crystal growth method that utilizes the exchange reaction between BaS and ZrCl$_4$/ HfCl$_4$. By carefully controlling the stoichiometric ratio of the binary sulfide to the chloride, we can grow single crystals of several materials, such as ZrS$_2$, HfS$_2$, BaZrS$_3$, and ZrOS. This method results in large single crystals with a short reaction time of 24 to 48 hours. High-resolution thin film diffraction and single-crystal X-ray diffraction confirm the quality of the crystals produced through this exchange reaction. We also report the optical properties of these materials investigated using photoluminescence and Raman measurements. The chloride exchange reaction method paves the way for the synthesis of single crystals of chalcogenides and oxy-chalcogenide systems with a short reaction time but with low mosaicity and can be an alternative growth technique for single crystals of materials that are difficult to synthesize using conventional growth techniques.
Authors: Wojciech Nowakowski, Krzysztof Pomorski
The quaternionic description of semiconductor single-electron devices is given in the single-electron regime. The conversion scheme of complex value Hamiltonian into a quaternion is formulated for the case of single-electron semiconductor qubit and many electrostatically interacting qubits. In particular, the quantum evolution operator is presented in quaternion form for the case of one and many electrostatically interacting quantum bodies.
Authors: Eduardo Velasco Stock, Roberto da Silva, Sebastian Gonçalves
We propose a mean-field (MF) approximation for the recurrence relation governing the dynamics of $m$ species of particles on a square lattice, and we simultaneously perform Monte Carlo (MC) simulations under identical initial conditions to emulate the intricate motion observed in environments such as subway corridors and scramble crossings in large cities. Each species moves according to transition probabilities influenced by its respective static floor field and the state of neighboring cells. To illustrate the methodology, we analyze statistical fluctuations in the spatial distribution for $m = 1$, $m = 2$, and $m = 4$ and for different regimes of average density and biased movement. A numerical comparison is conducted to determine the best agreement between the MC simulations and the MF approximation considering a renormalization exponent $\beta$ that optimizes the fit between methods. Finally, we report a phenomenon we term "Gaussian-to-Gaussian" behavior, in which an initially normal distribution of particles becomes distorted due to interactions among same and opposing species, passes through a transient regime, and eventually returns to a Gaussian-like profile in the steady state, after multiple rounds of motion under periodic boundary conditions.
Authors: Kevin Hernández, Elías Castellanos
Quantum droplets formed by rubidium, lithium, and sodium atoms have been analyzed in this paper by using a logarithmic-type Gross-Pitaevskii equation. Variational methods and numerical techniques were employed to solve the corresponding nonlinear equations. A disk-shaped Bose-Einstein condensate was analyzed to assess its radial evolution. Additionally, free expansion under rotation of the BEC was studied. Compression and expansion around the equilibrium radius were observed in different scenarios, predicting self-confinement, which implies the formation of quantum droplets originating from a BEC state. Briefly, the physical aspects of the system and the possible formation of Bose-nova effects are discussed.
Authors: Leonardo Garibaldi Rigon, Yongjoo Baek
A recent experiment [Son et al., Soft Matter, 2024, 20,2777-2788] showed that self-propelled particles confined within a circular boundary filled with granular medium spontaneously form a motile cluster that stays on the boundary. This cluster exhibits persistent (counter)clockwise motion driven by symmetry breaking, which arises from a positive feedback between the asymmetry of the cluster and those of the surrounding granular medium. To investigate this symmetry-breaking mechanism in broader contexts, we propose and analyze the dynamics of an active hinge moving through a crowded two-dimensional channel. Through extensive numerical simulations, we find that the lifetime of the hinge's motile state varies nonmonotonically with both the packing fraction of the granular medium and the strength of self-propulsion. Furthermore, we observe an abrupt transition in the configuration of passive particles that sustain hinge motility as the hinge's maximum angle relative to the channel wall increases. These findings point to the possibility of designing superstructures composed of passive granular media doped with a small number of active elements, whose dynamics modes can be switched by tuning the properties of their components.
Authors: Yun Liu, Zu-Jian Ying
Dipole-dipole interaction (DDI) possesses characteristics different from the conventional isotropic s-wave interaction in Bose-Einstein condensates (BECs), the interplay of DDI with spin-orbit coupling (SOC) and rotation may induce novel quantum properties. We systematically analyze the effects of the DDI, Weyl-like SOC, rotation and trap anharmonicity in the ground state of two-componen BECs. The interplay of these factors leads to a kaleidoscope of quantum states of quantum defects and quantum droplets in lattice, wheel and ring forms of distributions, with transitions of topology of density and a critical behavior in varying the parameters. We also show a bunch of exotic spin topological structures, including centric vortex surrounded by layers of spin flows, compound topological structure of edge defect, and various coexistence states of skyrmions with different topological charge. In particular, we find quarter skyrmions and other possible fractional skyrmions. Rashba-type SOC and Weyl-like SOC are compared as well. Our study implies that one can manipulate both the density topology and the spin topological structure via these tunable parameters in BECs. The abundant variations of the topological structures and particularly the revealed critical behavior may provide various quantum resources for potential applications in quantum metrology.
Authors: L.A. Kroo, R.A. Nicholson, M.W Boehm, S.K. Baier, P.A. Underhill, G.H. McKinley
Building off recent advances on how to practically use exponential shear in a torsional rheometer to compute transient planar extensional viscosity (Kroo et al. 2025a), we extend the technique to cyclic tensile measurements in complex fluids and soft solids. An novel input strain waveform provides a unifying approach that smoothly interpolates between exponential shear (ES) and oscillatory shear (SAOS/MAOS/LAOS) as a flow type parameter is varied. Analogous to cyclic tensile fatigue tests in solids, or the process of chewing in the oral cavity, this complex strain history is used to quantify the evolution of extensional material properties at large strains over sequential cycles of stretch. In the limit of large Hencky strain rates, the waveform locally increases exponentially and generates a period of strong material stretching. This allows for the direct computation of a transient planar extensional viscosity within specific domains of the periodic function. We demonstrate this technique on a set of model fluids, and then apply it to complex multiphase materials that mutate. These latter fluids exhibit progressive evolution in their rheological properties over repeated cycles of extensional deformation. Here we focus on two examples: a delicate foodstuff material (melted provolone cheese) which systematically decreases its extensional response over successive stretching cycles, mutating at a rate that is directly dependent on the effective Hencky strain rate. We contrast this with a PVA-borax solution which exhibits precisely the opposite effect during successive stretching cycles: increasing its planar extensional response over successive cycles, as interchain associative interactions (controlled via stretching) build structure within the fluid. These results highlight a promising new approach to study bulk extensional properties during cyclical stretching of complex fluids.
Authors: Ping Yang, Wanxiang Feng, Siyuan Liu, Shan Guan, Liwei Wen, Wei Jiang, Gui-Bin Liu, Yugui Yao
In this work, we reveal giant magneto-optical responses in two-dimensional(2D) antiferromagnets with nearly flat electronic bands, based on first-principles calculations and group-theoretical analysis. We identify a record-large second-order magneto-optical Schafer-Hubert(SH) effect, featuring a polarization rotation angle of 28 degree, in monolayer antiferromagnetic RuOCl2, driven by flatband-enhanced interband optical transitions. Both the valence and conduction bands exhibit pronounced directional flatness, giving rise to highly anisotropic optical absorption and broadband hyperbolic frequency windows spanning the entire visible spectrum. This anisotropy leads to an exceptionally strong linear dichroism (LD) reaching 50%, far exceeding values reported in other 2D magnetic systems. Remarkably, the giant SH effect and LD appear at distinct photon energies, reflecting a momentum-direction-dependent crossover between flat and dispersive bands. Both responses are further amplified with increasing RuOCl2 film thickness. Our results establish flat-band antiferromagnets as a fertile platform for realizing giant nonlinear magneto-optical effects and open new avenues for 2D opto-spintronic device applications.
Authors: Asir Intisar Khan, Jeong-Kyu Kim, Urmita Sikder, Koushik Das, Thomas Rodriguez, Rohith Soman, Srabanti Chowdhury, Sayeef Salahuddin
For high-electron-mobility transistors based on two-dimensional electron gas (2DEG) within a quantum well, such as those based on AlGaN/GaN heterostructure, a Schottky-gate is used to maximize the amount of charge that can be induced and thereby the current that can be achieved. However, the Schottky-gate also leads to very high leakage current through the gate electrode. Adding a conventional dielectric layer between the nitride layers and gate metal can reduce leakage; but this comes at the price of a reduced drain current. Here, we used a ferroic HfO2-ZrO2 bilayer as the gate dielectric and achieved a simultaneous increase in the ON current and decrease in the leakage current, a combination otherwise not attainable with conventional dielectrics. This approach surpasses the conventional limits of Schottky GaN transistors and provides a new pathway to improve performance in transistors based on 2DEG.
Authors: Siya Zhu, Doguhan Sariturk, Raymundo Arroyave
High-entropy alloys (HEAs) have attracted increasing attention due to their unique structural and functional properties. In the study of HEAs, thermodynamic properties and phase stability play a crucial role, making phase diagram calculations significantly important. However, phase diagram calculations with conventional CALPHAD assessments based on experimental or ab-initio data can be expensive. With the emergence of machine-learning interatomic potentials (MLIPs), we have developed a program named PhaseForge, which integrates MLIPs into the Alloy Theoretic Automated Toolkit (ATAT) framework using our MLIP calculation library, MaterialsFramework, to enable efficient exploration of alloy phase diagrams. Moreover, our workflow can also serve as a benchmarking tool for evaluating the quality of different MLIPs.
Authors: Jiahao Chen, Wentao Tang, Xingzhou Tang, Yang Ding, Jie Ni, Yuxi Chen, Bingxiang Li, Rui Zhang, Juan de Pablo, Yanqing Lu
Skyrmions, originally from condensed matter physics, have been widely explored in various physical systems, including soft matter. A crucial challenge in manipulating topological solitary waves like skyrmions is controlling their flow on demand. Here, we control the arbitrary moving direction of skyrmions in a chiral liquid crystal system by adjusting the bias of the applied alternate current electric field. Specifically, the velocity, including both moving direction and speed can be continuously changed. The motion control of skyrmions originates from the symmetry breaking of the topological structure induced by flexoelectric-polarization effect. The omnidirectional control of topological solitons opens new avenues in light-steering and racetrack memories.
Authors: Gerhard H. Fecher, Roshnee Sahoo, Claudia Felser
MnPtGa is a hexagonal intermetallic compound with a rich variety of magnetic order. Its magnetic state is reported to range from collinear ferromagnetism, to non-collinear skyrmion type order. MnPtGa is a system with strongly localized magnetic moments at the Mn atoms as was demonstrated using calculations for disordered local moments. The magnetic moments at the Mn sites stay at about 3.9 bohr even above the calculated magnetic transition temperatures (TN = 220 K or TC = 285 K). In the present work, a special emphasis was focused on the possible non-collinear magnetic order using first principles calculations. The investigations included magnetic anisotropy, static noncollinear order in form of spin canting and dynamic non-collinearity in spin spirals. It is found that the energy differences between ferromagnetic, antiferromagnetic, canted, or spiral magnetic order are in the order of not more than 30 meV, which is in the order of thermal energies at ambient temperature. This hints that a particular magnetic state - including skyrmions, antiskyrmions or spin glass transitions - may be forced when an external field is applied at finite temperature.
Authors: Shreya Debnath, Kuntal Bhattacharyya, Saurabh Basu
Spin-phonon coupling and its efficacy in inducing multiple topological phase transitions in a frustrated kagome antiferromagnet have not been addressed in the literature. To this end, we study the ramifications of invoking optical phonons in a non-collinear antiferromagnet via two different kinds of coupling mechanisms, namely, a local and a non-local one, which are distinct in their macroscopic origin. In the case of a local spin-phonon coupling, a single phonon mode affects the magnetic interactions, whereas in the non-local case, two neighbouring phonon modes are involved in the energy renormalization, and it would be worthwhile to compare and contrast the two. To tackle these phonons, we propose an analytical approach through a canonical spin-Peierls transformation applied to magnons, that renders a hybridization between the magnons and the phonon modes and yields a magnon-polaron quasiparticle state. In both the coupling regimes, the robust support of the topological signatures is derived systematically from the bulk and edge spectral properties of the magnon-polaron bands that are characterized by their corresponding Chern numbers. Thereafter, we witness transitions from one topological phase to another solely via tuning the spin-phonon coupling strength. Moreover, these transitions significantly impact the behavior of the thermal Hall conductivity, which aid in discerning distinct topological phases. Additionally, the explicit dependencies on the temperature and the external magnetic field are explored in inducing topological phase transitions associated with the magnon-polaron bands. Thus, our work serves as an ideal platform to probe the interplay of frustrated magnetism and polaronic physics.
Authors: Dominik Szczȩśniak
Breaking the intrinsic chirality of quasiparticles in graphene enables the emergence of new and intriguing phases. One such paradigmatic example is the bond density wave, which leads to a Kekulé-ordered structure and underpins exotic electronic states where electron-phonon interactions can play a fundamental role. Here, it is shown that the relevant physics of these correlations can be resolved locally, according to the behavior of interatomic characteristics. For this purpose a robust distance-dependent framework for describing electronic structure of graphene with Kekulé bond order is presented. Given this insight, the strength of electron-phonon interactions is found to scale linearly with the electronic coupling, contributing to a uniform picture of this relationship in distorted graphene structures. Moreover, it is shown that the introduced distortion yields a strongly non-uniform spatial distribution of the pairing strength that eventually leads to the induction of periodically distributed domains of enhanced electron-phonon coupling. These findings help elucidate certain peculiar aspects of phonon-mediated phenomena in graphene, particularly the associated superconducting phase, and offer potential pathways for their further engineering.
Authors: Seungho Lee, Se Kwon Kim
We derive an effective field theory for a noncollinear altermagnet and magnons on top of the noncollinear ground state from an altermagnetic Heisenberg model. We obtain the ground-state phase diagram, revealing a noncollinear phase and four distinct collinear phases. The ground state of the noncollinear phase fully breaks the spin rotational symmetry, while the ground state of the collinear phases possesses unbroken $\mathrm{SO}(2)$ symmetry. The resulting effective field theory for the noncollinear phase is an $\mathrm{SO}(3)$ sigma model in which the magnonic excitation has three independent degrees of freedom and exhibits the $d$-wave-like anisotropic linear dispersion. We also discuss possible topological solitons, including $\mathbb{Z}_2$ vortices.
Authors: Kuangjie Chen, Yang Qi, Zheng Yan, Xiaopeng Li
Recent advances in Rydberg tweezer arrays bring novel opportunities for programmable quantum simulations beyond previous capabilities. In this work, we investigate a bosonic t-J-V model currently realized with Rydberg atoms. Through large-scale quantum Monte Carlo simulations, we uncover an emergent double supersolid (DSS) phase with the coexistence of two superfluids and crystalline order. Tunable long-range tunneling and repulsive hole-hole interactions enable a rich phase diagram featuring a double superfluid phase, a DSS phase, and an antiferromagnetic insulator. Intriguingly, within the DSS regime we observe an unconventional thermal enhancement of crystalline order. Our results establish the bosonic t-J-V model as a promising and experimentally accessible platform for exploring exotic quantum phases in Rydberg atom arrays.
Authors: Peter Hatton, Blas Pedro Uberuaga, Danny Perez
Chemically complex materials (CCMs) exhibit extraordinary functional properties but pose significant challenges for atomistic modeling due to their vast configurational heterogeneity. We introduce Hop-Decorate (HopDec), a high-throughput, Python-based atomistic workflow that automates the generation of defect transport data in CCMs. HopDec integrates accelerated molecular dynamics with a novel redecoration algorithm to efficiently sample migration pathways across chemically diverse local environments. The method constructs a defect-state graph in which transitions are associated with distributions of kinetic and thermodynamic parameters, enabling direct input into kinetic Monte Carlo and other mesoscale models. We demonstrate HopDec's capabilities through applications to a Cu-Ni alloy and the spinel oxide (Fe,Ni)Cr2O4, revealing simple predictive relationships in the former and complex migration behaviors driven by cation disorder in the latter. These results highlight HopDec's ability to extract physically meaningful trends and support reduced-order or machine-learned models of defect kinetics, bridging atomic-scale simulations and mesoscale predictions in complex material systems.
Authors: Soumya Shephalika Behera, Isha, Arvind Kumar Yogi, V R Rao Medicherla, Parasmani Rajput, Archana Sagdeo, Jaspreet Singh, Vasant Sathe, R J Choudhary
The structural distortions, orbital correlations, and electronic states in cobalt ferrite (CoFe2O4) were investigated using complementary characterisation techniques, including SR-XRD, HAXPES, XANES, EXAFS, and Raman spectroscopy. SR-XRD confirms phase purity and reveals a temperature-dependent superlattice reflection between 200 K and 100 K, consistent with the emergence of short-range orbital ordering driven by cooperative Jahn-Teller distortion (JTD). The disappearance of this feature below 100 K signals orbital freezing and the onset of a glass-like orbital state. HAXPES measurements show multiplet splitting and charge-transfer satellite features in the Co and Fe 2p core levels, indicating mixed valence states and strong electron correlations. XANES analysis reveals hybridized p-d states and local coordination distortions. Temperature-dependent EXAFS measurements indicate increasing local disorder-particularly in Fe-O and Fe-Fe octahedral bonds as evidenced by enhanced Debye-Waller factors. These distortions, attributed to cation redistribution and oxygen vacancies, are static and asymmetric, primarily affecting the octahedral sublattice. Notably, signatures of cooperative Jahn-Teller distortions emerge in the intermediate temperature range (200-100 K) and disappear upon further cooling. Raman spectroscopy further supports these findings, revealing phonon anomalies and enhanced spin-phonon coupling in the same temperature range. Magnetic measurements indicate spin reorientation and exchange interaction anomalies that align with the orbital behaviour. Together, these results hint at a frustrated orbital state in CoFe2O4 possibly involving cooperative Jahn-Teller distortions, disrupted long-range coherence, and orbital glass behaviour offering new insights into the coupling of orbital, spin, and lattice degrees of freedom in spinel systems.
Authors: Udai Prakash Tyagi, Partha Goswami
This communication presents an examination of a two-dimensional, non-Hermitian Su -Schrieffer-Heeger (SSH) model, which is differentiated from its conventional Hermitian counterpart by incorporating gain and/or loss terms, mathematically represented by imaginary on-site potentials. The time-reversal symmetry is disrupted due to these on-site potentials. Exceptional points in a non-Hermitian system feature eigenvalue coalescence and non-trivial eigenvector degeneracies. Utilization of the rank-nullity theorem and graphical analysis of the phase rigidity factor enable identification of true exceptional points. Furthermore, this investigation achieves vectorized Zak phase quantization and examines a topolectric RLC circuit to derive the corresponding topological boundary resonance condition and the quantum Hall susceptance. Although Chern number quantization is not feasible, staggered hopping amplitudes corresponding to unit-cell lattice sites lead to broken inversion symmetry with non-zero Berry curvature, resulting in finite anomalous Nernst conductivity.
Authors: Felix Zahner, Felix Nickel, Roberto Lo Conte, Tim Drevelow, Roland Wiesendanger, Stefan Heinze, Kirsten von Bergmann
The interplay of magnetism and superconductivity can lead to intriguing emergent phenomena. Here we combine two different two-dimensional antiferromagnetic magnet-superconductor hybrids (MSH) and study their properties using spin-polarized scanning tunneling microscopy. Both MSHs show the characteristics of a topological nodal point superconducting phase with edge modes to the trivial substrate superconductor. At the boundary between the two MSHs we find low-energy modes which are spin-polarized. Based on a tight-binding model we can explain the experimental observations by considering two different topological nodal point superconductors. This gives rise to spin-polarized chiral edge modes that connect topological nodal points of the two different MSH. We demonstrate via the complex band structure that due to an asymmetric lateral decay these edge modes are spin-polarized, regardless of the details of the spin structure at the boundary. The presence of spin-polarized edge states between different topological superconductors enables advanced functional design for the exploitation of MSHs as a platform for topology-based applications.
Authors: Sanchar Sharma, Christina Psaroudaki
Magnets have recently emerged as promising candidates for quantum computing, particularly using topologically-protected nanoscale spin textures. While the quantum dynamics of such spin textures has been theoretically studied, direct experimental evidence of their non-classical behavior remains an open challenge. To address this, we propose to employ Brillouin light scattering (BLS) as a method to probe the quantum nature of skyrmions in frustrated magnets. We show that, for a specific geometry, classical skyrmions produce symmetric sidebands in the BLS spectrum, whereas quantum skyrmions exhibit a distinct asymmetry arising from vacuum fluctuations of their rotation. By studying the photon-skyrmion interaction, we calculate the BLS spectrum using a quantum master equation and show that sideband asymmetry serves as a robust witness of energy level quantization. We find that this asymmetry is pronounced at low temperatures, and can be controlled by input laser power. These findings establish a concrete protocol for the optical detection of non-classical features in spin textures, paving the way for exploring their role in quantum applications.
Authors: Yongxu Fu, Yi Zhang
Non-Hermitian quantum systems exhibit various interesting and inter-connected spectral, topological, and boundary-sensitive features. By introducing conditional boundary conditions (CBCs) for non-Hermitian quantum systems, we explore a winding-control mechanism that selectively collapses specific periodic boundary condition (PBC) spectra onto their open boundary condition (OBC) counterparts, guided by their specific winding numbers, together with a composite reconstruction of the Brillouin zone (BZ) and generalized Brillouin zone (GBZ). The corresponding eigenstates also manifest nontrivial skin effects or extended behaviors arising from the interplay between BZ and GBZ structures. Furthermore, we can generalize our control by incorporating similarity transformations and holomorphic mappings with the boundary controls. We demonstrate the winding control numerically within various models, which enriches our knowledge of non-Hermitian physics across the spectrum, topology, and bulk-boundary correspondence.
Authors: Aravindh S. Shankar, Jasper Steenbergen, Stephan Plugge, Koenraad Schalm
We show that two Yukawa-SYK models with a weak tunneling contact can have an exotic hybrid superconducting thermofield-double-like state that is holographically dual to a traversable wormhole connecting two black holes with charged scalar hair. The hybrid superconducting thermo-field-double/wormhole state is distinguishable by anomalous scaling of revival oscillations in the fermionic Green's function, but also in a unique Andreev-revival in the anomalous Green's function. The existence of this TFD/wormhole state surprisingly shows that the some quantum critical effects can survive the phase transition to superconductivity. This Andreev-revival is in principle an accessible signature of the transition to the TFD/wormhole phase detectable in the ac-Josephson current.
Authors: Jack Griffiths, Steven A. Wrathmall, Simon A. Gardiner
Precise determination of thermodynamic parameters in ultracold Bose gases remains challenging due to the destructive nature of conventional measurement techniques and inherent experimental uncertainties. We demonstrate an artificial intelligence approach for rapid, non-destructive estimation of the chemical potential and temperature from single-shot, in situ imaged density profiles of finite-temperature Bose gases. Our convolutional neural network is trained exclusively on quasi-2D `pancake' condensates in harmonic trap configurations. It achieves parameter extraction within fractions of a second. The model also demonstrates zero-shot generalisation across both trap geometry and thermalisation dynamics, successfully estimating thermodynamic parameters for toroidally trapped condensates with errors of only a few nanokelvin despite no prior exposure to such geometries during training, and maintaining predictive accuracy during dynamic thermalisation processes after a relatively brief evolution without explicit training on non-equilibrium states. These results suggest that supervised learning can overcome traditional limitations in ultracold atom thermometry, with extension to broader geometric configurations, temperature ranges, and additional parameters potentially enabling comprehensive real-time analysis of quantum gas experiments. Such capabilities could significantly streamline experimental workflows whilst improving measurement precision across a range of quantum fluid systems.
Authors: S. Subakti (1), D. Wolf (1), O. Zaiets (1 and 2), S. Parkin (3), A. Lubk (1 and 2 and 4) ((1) Leibniz Institute for Solid State and Materials Research Dresden, Germany, (2) Institute of Solid State and Materials Physics, TU Dresden, Germany, (3) Department for Nano-Systems from Ions, Spins, and Electrons (NISE), Max Planck Institute of Microstructure Physics, Germany, (4) Würzburg--Dresden Cluster of Excellence this http URL, TU Dresden, Germany)
Crystal structure symmetry of Fe-deficient $\text{Fe}_{\text{2.9}}\text{GeTe}_{\text{2}}$ at room temperature has been investigated by a combination of selected-area electron diffraction (SAED) and convergent-beam electron diffraction (CBED). By symmetry analysis of CBED patterns along different zone axis, the space group of $\text{Fe}_{\text{2.9}}\text{GeTe}_{\text{2}}$ at room-temperature has been identified as $P6_3mc$ (No.186), which derives from the high-symmetry parent system $\text{Fe}_{\text{3}}\text{GeTe}_{\text{2}}$ ($P6_3/mmc$) by breaking the mirror symmetry along the six-fold rotation axis. The $P3m1$ (No.156) space group previously reported for $\text{Fe}_{\text{2.9}}\text{GeTe}_{\text{2}}$ is a subgroup of $P6_3mc$ suggesting further possible symmetry breaks in this non-stochiometric system.
Authors: Edvards Strods, Martins Zubkins, Viktors Vibornijs, Dmitrii Moldarev, Anatolijs Sarakovskis, Karlis Kundzins, Emija Letko, Daniel Primetzhofer, Juris Purans
Oxygen-containing yttrium hydride (YHO) and molybdenum trioxide (MoO$_3$) bilayer films (YHO/MoO$_3$) are produced using reactive magnetron sputtering, and their photochromic properties are investigated in relation to the thickness and density of the MoO$_3$ layer. Compared to single YHO films, the YHO/MoO$_3$ films exhibit faster coloration and larger contrast, with both parameters adjustable by varying the thickness or deposition pressure of the MoO$_3$ layer. Transparent YHO/MoO$_3$ films (~75% at 550 nm) demonstrate a photochromic contrast of up to 60%, significantly higher than the 25-30% contrast observed for single YHO films after 20 hours of UVA-violet light exposure. This enhancement arises from hydrogen intercalation from the (200)-textured polycrystalline YHO film into the X-ray amorphous MoO$_3$, leading to the formation of molybdenum bronze (HxMoO$_3$), as confirmed by X-ray photoelectron and optical spectroscopies. However, the darkened YHO/MoO$_3$ films do not fully recover to their initial transparency after illumination due to the irreversible nature of the coloured MoO$_3$ layer. Most of the hydrogen intercalated into MoO$_3$ originates from the YHO layer during the initial darkening process. Furthermore, the bilayer films are chemically unstable, exhibiting gradual darkening over time even without intentional UV illumination, as confirmed by nuclear reaction analysis.
Authors: Shu-Tong Guan, Jin An
Topological Josephson junctions enable nonreciprocal transport involving Majorana fermions (MFs). Here we examine a topological Josephson junction with mixed $s$+$p$-wave pairing, where topological phase transition can be driven by adjusting the ratio between the pairing components. There exist two exact symmetrically positioned zero-energy level crossings for the Andreev-bound states, which can be shifted by external fields, and can be destroyed or recreated in pairs by a time-reversal breaking Zeeman field or inhomogeneities, exhibiting band-like structure. The dependence of the shift on the Zeeman field is linear when the two $p$-wave $\boldsymbol{d}$-vectors on both sides are identical while quadratic when they are distinct. Near the topological phase transition, the topological $p$-wave dominant junctions host MF-induced pronounced superconducting diode effect with high efficiency factor $Q$ up to 30 %, in contrast to the trivial $s$-wave dominant junctions possessing relatively small $Q$.
Authors: Mohammad Dehghani, Dominic Waldhoer, Angus Gentles, Pedram Khakbaz, Rainer Minixhofer, Michael Waltl
We present a comprehensive ab initio study of the influence of band structure corrections, particularly the electron effective mass, on the phonon-limited electron drift and Hall mobilities of GaAs. Our approach is based on the DFT+$U$ method, combined with an iterative solution of the linearized Boltzmann transport equation using the Wannier interpolation technique. We show how this framework allows for accurate refinements of the electronic band structure and phonon dispersion, leading to improved predictions for transport properties. In particular, by varying the Hubbard parameters to purposefully tune the conduction band features, allowing us to reproduce bands with different electron effective mass, we systematically investigate the relationship between mobility and effective mass. In this context, our results show close agreement with semi-empirical relations that follow a power-law dependence. Moreover, this approach can be used to indirectly incorporate temperature effects into the band structure, enabling efficient evaluation of temperature-dependent electron mobilities. Our mobility results exhibit good agreement with experimental data and are comparable to previously reported values obtained using the computationally expensive GW method.
Authors: Yanchen Wu, Martin Z. Bazant, Allan S. Myerson, Richard D. Braatz
Heterogeneous nucleation at surface edges is pervasive across nature and industry, yet the role of line tension, arising from asymmetric capillary interactions at geometric singularities, remains poorly understood. Herein we develop a generalized nucleation theory that explicitly incorporates line tension induced by edge pinning, thereby extending classical frameworks to account for nanoscale confinement and interfacial asymmetry. Through analytical treatment of droplet formation within geometrically defined nanopores, we derive a closed-form expression for the edge-pinned line tension as a function of Laplace pressure, pore geometry, and wettability. This formulation reveals that line tension can significantly reshape the nucleation energy landscape, introducing nontrivial dependencies on contact angle and pore morphology. Our results uncover a tunable, geometry-mediated mechanism for controlling nucleation barriers, offering predictive insight into phase transitions in confined environments and suggesting new strategies for design in applications ranging from nanofluidics to crystallization control.
Authors: Daniel Boyanovsky
Dynamical axion (quasi) particles are emergent collective excitations in topological magnetic insulators that break parity and time reversal invariance or in Weyl semimetals. They couple to electromagnetism via a topological Chern-Simons term, leading to their decay into two photons. We extend the Weisskopf-Wigner formulation of atomic spontaneous emission to the quantum field theory of dynamical axion quasiparticles, allowing us to obtain the quantum two-photon state emerging from axion decay in real time. This state features \emph{hyperentanglement} in momentum and polarization with a distinct polarization pattern, a consequence of the parity and time reversal breaking of the axion-photon interaction. Polarization aspects of this two-photon state are studied by introducing quantum Stokes operators. Whereas the two-photon quantum state features vanishing \emph{averages} of the degree of polarization and polarization asymmetry, there are non-trivial momentum correlations of the Stokes operators. In particular momentum correlations of the \emph{polarization asymmetry} can be obtained directly from coincident momentum and polarization resolved two photon detection. Correlations of Stokes operators are directly related to momentum and polarization resolved Hanbury-Brown Twiss second order coherences. This relationship suggests two-photon correlations as a direct probe of dynamical axion quasiparticles. Similarities and differences with parametrically down converted photons and other systems where spontaneous emission yield hyperentangled two photon states are recognized, suggesting experimental avenues similar to tests of Bell inequalities to probe dynamical axion quasiparticles with coincident two photon detection.
Authors: Dominic Schuh, Janik Kreit, Evan Berkowitz, Lena Funcke, Thomas Luu, Kim A. Nicoli, Marcel Rodekamp
We present the first proof of principle that normalizing flows can accurately learn the Boltzmann distribution of the fermionic Hubbard model - a key framework for describing the electronic structure of graphene and related materials. State-of-the-art methods like Hybrid Monte Carlo often suffer from ergodicity issues near the time-continuum limit, leading to biased estimates. Leveraging symmetry-aware architectures as well as independent and identically distributed sampling, our approach resolves these issues and achieves significant speed-ups over traditional methods.
Authors: Max T. Birch, Yukako Fujishiro, Ilya Belopolski, Masataka Mogi, Yi-Ling Chiew, Xiuzhen Yu, Naoto Nagaosa, Minoru Kawamura, Yoshinori Tokura
The emergent properties of materials are defined by the symmetries of their underlying atomic, spin and charge order. The explorations of symmetry breaking effects are therefore usually limited by the intrinsic properties of known, stable materials. In recent years, advances in focused ion beam (FIB) fabrication have enabled the nanostructuring of bulk crystals into ultraprecise transport devices [1-4], facilitating the investigation of geometrical effects on mesoscopic length scales. In this work, we expand such explorations into three-dimensional (3D), curvilinear shapes, by sculpting helical nanostructure devices from single crystals of the high-mobility, centrosymmetric magnetic Weyl semimetal Co$_3$Sn$_2$S$_2$ [5,6]. The combination of the imposed chiral geometry and intrinsic ferromagnetism yields nonreciprocal electron transport [7-9]. The high coercivity results in an anomalous, reversable diode effect remnant under zero applied magnetic field, which is orders of magnitude larger than can be explained by a classical self-field mechanism. We argue the enhancement originates from the high carrier mobility and the resulting quasi-ballistic transport: the conduction electron mean free path approaches the length scale of the curvature, resulting in increased asymmetrical scattering at the boundaries. We further demonstrate the inverse effect of the nonreciprocal transport: the field-free, current-induced switching of the magnetisation. The results establish the vast potential of 3D nanosculpting to explore and enrich the functionality of quantum materials.
Authors: David Allemeier, İsmet İnönü Kaya, M. Selim Hanay, Kamil L. Ekinci
We study the noisy dynamics of two coupled bistable modes of a nanomechanical beam. When de-coupled, each driven mode obeys the Duffing equation of motion, with a well-defined bistable region in the frequency domain. When both modes are driven, intermodal dispersive coupling emerges due to the amplitude dependence of the modal frequencies and leads to coupled states of the two modes. We map out the dynamics of the system by sweeping the drive frequencies of both modes in the presence of added noise. The system then samples all accessible states at each combination of frequencies, with the probability of each stable state being proportional to its occupancy time at steady state. In the frequency domain, the system exhibits four stable regions -- one for each coupled state -- which are separated by five curves. These curves are reminiscent of coexistence curves in an equilibrium phase diagram: each curve is defined by robust inter-state transitions, with equal probabilities of finding the system in the two contiguous states. Remarkably, the curves intersect in two triple points, where the system now transitions between three distinct contiguous states. A physical analogy can be made between this nonequilibrium system and a multi-phase thermodynamic system, with possible applications in computing, precision sensing, and signal processing.
Authors: Daniel Staros, Abdulgani Annaberdiyev, Kevin Gasperich, Anouar Benali, Panchapakesan Ganesh, Brenda Rubenstein
The many-body fixed-node and fixed-phase spin-orbit Diffusion Monte Carlo (DMC) methods are applied to accurately predict the fundamental gap of monolayer CrI$_3$ - the first experimentally-realized 2D material with intrinsic magnetism. The fundamental gap obtained, 2.9(1)~eV, agrees well with the highest peak in optical spectroscopy measurements and a previous $GW$ result. We numerically show that as expected in DMC the same value of the fundamental gap is obtained in the thermodynamic limit using both neutral promotions and the standard quasiparticle definition of the gap based on the ionization potential and electron affinity. Additional analysis of the differences between density matrices formed in different bases using configuration interaction calculations explains why a single-reference trial wave function can produce an accurate excitation. We find that accounting for electron correlation is more crucial than accounting for spin-orbit effects in determining the fundamental gap. These results highlight how DMC can be used to benchmark 2D material physics and emphasize the importance of using beyond-DFT methods for studying 2D materials.
Authors: Jozef Genzor, Roman Krčmár, Hiroshi Ueda, Denis Kochan, Andrej Gendiar, Tomotoshi Nishino
The critical behavior of the classical Ising model on a three-dimensional fractal lattice with Hausdorff dimension $d_H = \ln32 / \ln4 = 2.5$ is investigated using the higher-order tensor renormalization group (HOTRG) method. We determine the critical temperature $T_c \approx 2.65231$ and the critical exponents for magnetization $\beta \approx 0.059$ and field response $\delta \approx 35$. Unlike a previously studied 2D fractal with $d_H \approx 1.792$, the specific heat for this 3D fractal exhibits a divergent singularity at $T_c$. The results are compared with those for regular lattices and other fractal structures to elucidate the role of dimensionality in critical phenomena.
Authors: Graham Kimbell (1), Ulderico Filippozzi (2), Stefano Gariglio (1), Marc Gabay (3), Andreas Glatz (4 and 5), Andrey Varlamov (6 and 7), Andrea Caviglia (1) ((1) Department of Quantum Matter Physics, University of Geneva, Geneva, Switzerland, (2) Kavli Institute of Nanoscience, Delft University of Technology, Delft, Netherlands, (3) Laboratoire de Physique des Solides, Universite Paris Saclay, CNRS UMR 8502, Orsay Cedex, France, (4) Materials Science Division, Argonne National Laboratory, Argonne, Illinois, USA, (5) Department of Physics, Northern Illinois University, DeKalb, Illinois, USA, (6) Institute of Superconductivity and Innovative Materials (CNR-SPIN) Rome, Italy, (7) Lombard Institute ''Academy of Sciences and Letters'', Milan, Italy)
We investigate tunable superconducting transitions in (111)$\mathrm{LaAlO}_3/\mathrm{KTaO}_3$ field-effect devices. Large increases in conductivity, associated with superconducting fluctuations, are observed far above the transition temperature. However, the standard Aslamazov-Larkin paraconductivity model significantly underestimates the effect observed here. We use a model that includes conductivity corrections from normal state quasiparticle interference together with all contributions from superconducting fluctuations evaluated at arbitrary temperatures and in the short-wavelength limit. Through analysis of the magnetoconductance and resistive transitions, we find that the large conductivity increase can be explained by a combination of weak anti-localization and Maki-Thompson superconducting fluctuations. Both contributions are enabled by a strong temperature dependence of the electron's decoherence time compatible with an electron-phonon scattering scenario. We find that conductivity corrections are modulated by the electrostatic field effect, that governs a competition between normal-state quasiparticle interference and superconducting fluctuations.
Authors: Zhen Cao, Siying Li, Zhendong Li, Xinyi Liu, Zhigang Wu, Mingyuan Sun
Recent experiments demonstrate that rapidly rotating Bose-Einstein condensates (BECs) near the lowest Landau level can self-organize into interaction-driven persistent droplet arrays. Inspired by this discovery, we investigate the formation and dynamics of single droplet and droplet arrays in rapidly rotating BECs. Guided by a rigorous theorem on localized many-body states for 2D interacting systems in a magnetic field, we construct single droplet and droplet arrays states which are shown to be stationary solutions to the Gross-Pitaevskii equation in the rotating frame. The single droplet is shown to be dynamically stable, which underpins its role as the basic unit in a droplet array. The stability of the droplet arrays is demonstrated by their dynamic formation from a phase engineered initial condensate. Our study sheds light onto the nature of the droplet state in a rapidly rotating BEC and offers a new approach for generating and manipulating quantum droplet arrays through designing the initial condensate phase.
Authors: Domantas Burba, Gediminas Juzeliūnas
We present a general framework for engineering two-dimensional (2D) sub-wavelength topological optical lattices using spatially dependent atomic dark states in a $\Lambda$-type configuration of the atom-light coupling. By properly designing the spatial profiles of the laser fields inducing coupling between the atomic internal states, we show how to generate sub-wavelength Kronig-Penney-like geometric scalar potential accompanied by narrow and strong patches of the synthetic magnetic field localized in the same areas as the scalar potential. These sharply peaked magnetic fluxes are compensated by a smooth background magnetic field of opposite sign, resulting in zero net flux per unit cell while still enabling topologically nontrivial band structures. Specifically, for sufficiently narrow peaks, their influence is minimum, and the behavior of the system in a remaining smooth background magnetic field resembles the Landau problem, allowing for the formation of nearly flat energy bands with unit Chern numbers. Numerical analysis confirms the existence of ideal Chern bands and the robustness of the topological phases against non-adiabatic effects and losses. This makes the scheme well-suited for simulating quantum Hall systems and fractional Chern insulators in ultracold atomic gases, offering a new platform for exploring strongly correlated topological phases with high tunability.
Authors: Sanjay Dharmavaram, Basant Lal Sharma
The complex physics of self-assembly in colloidal crystals on deformable interfaces and surfaces poses interesting possibilities for the designability and synthesis of next-generation metamaterials. The goal of this article is to characterize instabilities arising in colloidal crystals assembled on fluid membranes. The colloidal particles are modeled as pair-wise interacting point particles, constrained to lie on a fluid membrane and yet free to reorganize, and the membrane's elastic energy is modeled via the Helfrich energy. We find that when a collection of particles is arranged on a planar membrane in some regular fashion -- such as periodic lattice -- then the regular configuration admits bifurcations to non-planar configurations. Using the Bloch-wave anstaz for the mode of instabilities, we present a parameteric analysis of the boundary between the stable and unstable regimes. We find that instabilities can occur through two distinct kinds of modes, when the parameters belong in certain physically interesting regimes, referred to as long-wavenumber modes ($L$ modes) and short-wavenumber modes ($S$ modes) in the article. We discuss some connections between these results and recent experiments, as well as the open problem of budding in biomembranes.
Authors: Vira Shyta, Jeroen van den Brink, Flavio S. Nogueira
The low-energy effective description of Weyl semimetals is defined by the axion electrodynamics, which captures the effects arising due to the presence of nodes of opposite chirality in the electronic structure. Here we explore the magnetoelectric response of time-reversal breaking (TRB) Weyl superconductors in the London regime. The influence of the axion contribution leads to an increase in the London penetration depth$-$a behavior that can be anticipated by first considering the photon spectrum of a TRB Weyl semimetal. Moreover, we find that both the Meissner state and the vortex phase feature an interplay between the electric and magnetic fields. This leads to a nonvanishing electromagnetic angular momentum, which we calculate for a number of geometrical configurations.
Authors: T. Granzow, A. Aravindhan, Y. Nouchokgwe, V. Kovacova, S. Glinsek, S. Hirose, T. Usui, H. Uršič, I. Goričan, W. Jo, C.-H. Hong, E. Defay
Ferroelectrics show a phase transition to a paraelectric phase at a well-defined transition temperature. Introducing disorder makes this transition diffuse, and the system becomes a relaxor. Since the degree of (dis-)order is usually manipulated by varying the chemical composition, it is difficult to establish a direct relationship between disorder and the degree of diffuseness. Perovskite structured lead scandium tantalate (Pb[Sc$_{1/2}$Ta$_{1/2}$]O$_3$, PST) offers the opportunity to tune the character of the transition by thermal annealing without changing the stoichiometry. Here it is demonstrated that there is a linear correlation between the structural ordering, quantified by the intensity ratio $S$ of the pseudocubic (111)/(200) x-ray diffraction peaks, and the diffuseness parameter $\gamma$ deduced from temperature-dependent dielectric spectroscopy. The relation is universal, independent of whether the sample is a thin film, multilayer capacitor or bulk ceramic, and also independent of the absolute value of the dielectric permittivity.
Authors: Nandlal Pingua, Himani Rautela, Roni Chatterjee, Smarajit Karmakar, Pinaki Chaudhuri, Shiladitya Sengupta
We report observations of unusal \emph{first} plastic events in silica and metallic glasses in the shear startup regime at applied strain two orders of magnitude smaller than yield strain. The (non-Affine) particle displacement field during these events have complex real space structure with multiple disconnected cores of high displacement appearing at the \emph{same} applied strain under athermal quasistatic simple shear deformation, and identified by a ``cell based cluster analysis'' method. By monitoring the stress relaxation during the first plastic event by Langevin dynamics simulation, we directly show the cascade nature of these events. Thus these first plastic events are reminiscent of avalanches in the post-yielding steady state, but unlike the steady state avalanches, we show that these events are not system spanning. To understand the nature of these events, we tune three factors that are known to affect brittleness of a glass. These are (i) sample preparation history, (ii) inter-particle interactions and (iii) rigidity of the background matrix applying a ``soft matrix'' probe recently developed by some of us. In each case we show that such first plastic events are more probable in more ductile glasses. Our observations are consistent with the picture that more ductile materials are softer, implying that understanding the role of softness may be a promising route to develop microscopic quantifiers of brittleness and thus clarifying the physical origin of brittle-to-ductile transition.
Authors: Adam D. Smith, Wenjun Ding, Yogesh K. Vohra, Cheng-Chien Chen
Recent experiments demonstrate a "robust superconductivity phenomenon" in niobium-based alloys, where the superconducting state remains intact and the critical temperature ($T_c$) is largely unaffected by external pressure well above tens of gigapascal (GPa) into the megabar regime ($\ge 100 GPa$). Motivated by these observations, we perform first-principles electron-phonon calculations for body-centered cubic Nb and NbTi crystals, as well as for special quasi-random structures of Nb$_{0.5}$Ti$_{0.5}$ and (NbTa)$_{0.7}$(HfZrTi)$_{0.3}$ high-entropy alloy (HEA). The calculations unravel the underlying mechanism of robust superconductivity, stemming from a compensation effect between varying electronic and phonon properties under pressure. The results also reveal how structural and chemical disorders modify the superconducting state. The first-principles $T_c$ values agree quantitatively with the experiments throughout the entire pressure range under study. Our work thereby paves the way for exploring superconducting HEAs under pressure via advanced first-principles simulations.
Authors: Alessio Squarcini, Piotr Nowakowski, Douglas B. Abraham, Anna Maciołek
We employ a procedure that enables us to calculate the excess free energies for a finite Ising cylinder with domain walls analytically. This procedure transparently covers all possible configurations of the domain walls under given boundary conditions and allows for a physical interpretation in terms of coarse-grained quantities such as surface and point tensions. The resulting integrals contain all the information about finite-size effects; we extract them by careful asymptotic analysis using the steepest descent method. To this end, we exactly determine the steepest descent path and analyse its features. For the general class of integrals, which are usually found in the study of systems with inclined domain walls, knowledge of the steepest descent path is necessary to detect possible intersections with poles of the integrand in the complex plane.
Authors: Lorenzo Cirigliano
Clustering and degree correlations are ubiquitous in real-world complex networks. Yet, understanding their role in critical phenomena remains a challenge for theoretical studies. Here, we provide the exact solution of site percolation in a model for strongly clustered random graphs, with many overlapping loops and heterogeneous degree distribution. We systematically compare the exact solution with mean-field predictions obtained from a treelike random rewiring of the network, which preserves only the degree sequence. Our results demonstrate a nontrivial interplay between degree heterogeneity, correlations and network topology, which can significantly alter both the percolation threshold and the critical exponents predicted by the mean-field. These findings highlight the need for new approaches, beyond the heterogeneous mean-field theory, to accurately describe phase transitions in complex networks with realistic topological features.
Authors: Roman Krcmar, Jozef Genzor, Andrej Gendiar, Tomotoshi Nishino
The Corner Transfer Matrix Renormalization Group (CTMRG) algorithm is modified to measure the magnetization at the boundary of the system, including the corners of the square-shaped lattice. Using automatic differentiation, we calculate the magnetization's first derivative, allowing us to determine the boundary critical exponent $\beta$ accurately.
Authors: Simon Widmann, Siddhartha Dam, Johannes Düreth, Christian G. Mayer, Romain Daviet, Carl Philipp Zelle, David Laibacher, Monika Emmerling, Martin Kamp, Sebastian Diehl, Simon Betzold, Sebastian Klembt, Sven Höfling
Equilibrium and nonequilibrium states of matter can exhibit fundamentally different behavior. A key example is the Kardar-Parisi-Zhang universality class in two spatial dimensions (2D KPZ), where microscopic deviations from equilibrium give rise to macroscopic scaling laws without equilibrium counterparts. While extensively studied theoretically, direct experimental evidence of 2D KPZ scaling has remained limited to interface growth so far. Here, we report the observation of universal scaling consistent with the KPZ universality class in 2D exciton-polariton condensates -- quantum fluids of light that are inherently driven and dissipative, thus breaking equilibrium conditions. Using momentum-resolved photoluminescence spectroscopy as well as space- and time-resolved interferometry, we probe the phase correlations across microscopically different systems, varying drive conditions in two distinct lattice geometries. Our analysis reveals correlation dynamics and scaling exponents in excellent agreement with 2D KPZ predictions. These results establish exciton-polariton condensates as a robust experimental platform for exploring 2D nonequilibrium universality quantitatively, and open new avenues for investigating the emergence of coherence in interacting quantum systems far from equilibrium.
Authors: J. Schwardt, J. C. Budich
We introduce and benchmark a stochastic local search heuristic for the NP-complete satisfiability problem 3-SAT that drastically outperforms existing solvers in the notoriously difficult realm of critically hard instances. Our construction is based on the crucial observation that well established previous approaches such as WalkSAT are prone to get stuck in local minima that are distinguished from true solutions by a larger number of oversatisfied combinatorial constraints. To address this issue, the proposed algorithm, coined DOCSAT, dissipates oversatisfied constraints (DOC), i.e. reduces their unfavorable abundance so as to render them critical. We analyze and benchmark our algorithm on a randomly generated sample of hard but satisfiable 3-SAT instances with varying problem sizes up to N=15000. Quite remarkably, we find that DOCSAT outperforms both WalkSAT and other well known algorithms including the complete solver Kissat, even when comparing its ability to solve the hardest quintile of the sample to the average performance of its competitors. The essence of DOCSAT may be seen as a way of harnessing statistical structure beyond the primary cost function of a combinatorial problem to avoid or escape local minima traps in stochastic local search, which opens avenues for generalization to other optimization problems.
Authors: Julius Kullig, Jan Wiersig, Henning Schomerus
The nonorthogonality of modes in open systems significantly modifies their resonant response, resulting in quantitative and qualitative deviations from Breit-Wigner resonance relations. For isolated resonances with a Lorentzian lineshape, the deviations amount to an enhancement of the resonance linewidth by the Petermann factor (PF), given by the overlap of left and right eigenmodes of the underlying effectively non-Hermitian Hamiltonian. The PF diverges at exceptional points (EPs), where resonance frequencies degenerate, and right and left eigenmodes are orthogonal to each other. This divergence signifies a qualitative departure from a Lorentzian lineshape, which has gained recent attention. In this work, we extend this concept to EPs, and describe how this EP PF manifests in a variety of physical scenarios. Firstly, we identify this PF in physical terms as an enhancement of the response of a system to external or parametric perturbations. Utilizing two natural orthogonally projected reference systems based on the right and left eigenvectors, we show that each choice carries a precise geometric interpretation that naturally extends the notion of the PF for isolated resonances to EPs. The two choices can be combined into an overall EP PF, which again can be expressed in purely geometric terms. Secondly, we illuminate the geometric mechanisms that determine the size of the EP PF, by considering the role of modes participating in the degeneracy and those that remain spectrally separated. Thirdly, we design a system to study the EP PF in a specific physical setup, consisting of two microrings coupled to a waveguide with embedded semitransparent mirrors. This example shows our approach yields a more accurate spectral response strength than conventional truncation. These results complete the description of systems at EPs in the same way as the original PF does for isolated resonances.
Authors: Manmeet Kaur, Somendra M. Bhattacharjee
This work presents a unified perspective on thermal equilibrium and quantum dynamics by examining the simplest quantum system, a qubit, as a foundational model. We show that both the thermal partition function and the Loschmidt amplitude can be understood as extensions of a single analytic function along different paths in the complex plane. The zeros of Loschmidt amplitude encode dynamical features such as orthogonality, rate function singularities, and quantum speed limits, in analogy with the role of partition function zeros in equilibrium statistical mechanics. We further establish, through the Cauchy-Riemann equations, that the high-temperature specific heat corresponds to early-time evolution. The discussion follows a pedagogical progression from a single qubit to an interacting spin chain.
Authors: Longlong Wu, David Yang, Wei Wang, Shinjae Yoo, Ross J. Harder, Wonsuk Cha, Aiguo Li, Ian K. Robinson
Quantitative visualization of internal deformation fields in crystalline materials helps bridge the gap between theoretical models and practical applications. Applying Bragg coherent diffraction imaging under X-ray dynamical diffraction conditions provides a promising approach to the longstanding challenge of investigating the deformation fields in micron-sized crystals. Here, we present an automatic differentiation-based Artificial Intelligence method that integrates dynamical scattering theory to accurately reconstruct deformation fields in large crystals. Using this forward model, our simulated and experimental results demonstrate that three-dimensional local strain information inside a large crystal can be accurately reconstructed under coherent X-ray dynamical diffraction conditions with Bragg coherent X-ray diffraction imaging. These findings open an avenue for extending the investigation of local deformation fields to microscale crystals while maintaining nanoscale resolution, leveraging the enhanced coherence and brightness of advanced X-ray sources.
Authors: Ajit Dash, Suyash Pati Tripathi, Dimitrios Georgakopoulos, MengKe Feng, Steve Yianni, Ensar Vahapoglu, Md Mamunur Rahman, Shai Bonen, Owen Brace, Jonathan Y. Huang, Wee Han Lim, Kok Wai Chan, Will Gilbert, Arne Laucht, Andrea Morello, Andre Saraiva, Christopher C. Escott, Sorin P. Voinigescu, Andrew S. Dzurak, Tuomo Tanttu
Utilizing quantum effects in nanoscopic devices has in the past mostly been accessible through academic cleanrooms and research foundries. Opening the quantum frontier for wider industrial applications likely requires the scale of well-established complementary metal-oxide-semiconductor (CMOS) foundries for manufacturing transistor-based quantum devices operable above subkelvin temperatures. Here, we operate a commercial 22-nm-node fully depleted silicon-on-insulator (FDSOI) CMOS device as dual parallel-connected charge-pumps for the implementation of a quantum current standard in the International System of Units (SI). We measure the accuracy of (1.2 +/- 0.1)E-3 A/A for this scalable architecture at 50 MHz with reference to SI-traceable voltage and resistance standards in a pumped helium system. Looking ahead we propose a practical monolithic CMOS chip that incorporates one million parallel-connected charge pumps along with on-chip control electronics. This can be operated as a table-top primary standard, generating quantum currents up to microampere levels.
Authors: Eran Bouchbinder
Frictional sliding, e.g., earthquakes along geological faults, are mediated either by frictional crack-like ruptures, where interfacial (fault) slip is accumulated during the entire sliding event, or by frictional pulse-like ruptures, featuring a finite length over which slip is accumulated. Our basic understanding of slip pulses, which are believed to dominate most crustal earthquakes, is still incomplete. Here, building on recent progress, we present an analytic equation of motion for rate-and-state frictional slip pulses, which are intrinsically unstable spatiotemporal objects, in terms of a single degree of freedom. The predictions of the equation are supported by large-scale simulations of growing pulses and reveal the origin of the slow development of their instability, which explains the dynamic relevance of pulses in a broad range of natural and manmade frictional systems.
Authors: D. Prokop, M. Mrkvickova, J. Tungli, Z. Bonaventura, P. Dvorak, S. Kadlec, T. Hoder
The decay of electrical charge on a dielectric surface in nitrogen-C4F7N (Novec4710, C4) mixtures is investigated using measurement of electric field via in-situ electric field-induced second harmonic (EFISH) technique. The charge is deposited on the surface of the alumina by generating a barrier discharge in the gap, and the amount of charge is determined from electrical current measurements and numerical modeling. For different admixtures (0, 10, and 50 percent) of C4F7N in nitrogen, the presence of surface charge is detected even 60 hours after charge deposition. It is found that C4F7N admixture lead to a significantly longer-lasting surface charge, indicating a slower charge decay. Using an isothermal charge decay model, charge traps are identified for pure nitrogen charge deposition, which are in agreement with results found in the literature. Charge deposition in C4F7N admixtures leads to modification or creation of new traps with higher trap energies. The EFISH measurements are used to determine the C4F7N nonlinear hyperpolarizability tensor component. Direct comparison of the experimental results from two developed methods (EFISH and electrical measurements) and the numerical model gives a closer insight into the surface charge spread over the dielectrics, resulting in surface charge density estimation.
Authors: Arjun Bagchi, Aritra Banerjee, Prateksh Dhivakar, Saikat Mondal, Ashish Shukla
The Carroll group arises in the vanishing speed of light limit of the Poincaré group and was initially discarded as just a mathematical curiosity. However, recent developments have proved otherwise. Carroll and conformal Carroll symmetries are now ubiquitous, appearing in diverse physical phenomena starting from condensed matter physics to quantum gravity. This review aims to provide the reader a gateway into this fast-developing field. After an introduction and setting the stage with basics of the symmetry in question, we detail the construction of Carrollian and Carrollian Conformal field theories (CCFT). We then focus on applications. By far the most popular of these applications is in the context of the construction of holography in asymptotically flat spacetimes (AFS) in terms of a co-dimension one dual CCFT. We review the early work on AFS$_3$ /CCFT$_2$ before delving into an in-depth analysis for the construction of the dual to 4D AFS. Two other important sets of applications are in hydrodynamics and in condensed matter physics, which we discuss in detail. Carroll hydrodynamics is introduced as the $c\to 0$ limit of relativistic hydrodynamics first and then reconstructed from a symmetry based approach. Relations to ultrarelativistic flows and connections to the quark-gluon plasma are discussed with concrete examples of the Bjorken and Gubser flow models. In condensed matter applications, we cover connections to fractons, flat bands, and phase separation in Luttinger liquid models. To conclude, we give very brief outlines of other topics of interest including string theory and black hole horizons.
Authors: N. Massa, F. Cavaliere, D. Ferraro
Motivated by recent developments in the field of multilevel quantum batteries, we present the model of a quantum device for energy storage with anharmonic level spacing, based on a superconducting circuit in the transmon regime. It is charged via the sequential interaction with a collection of identical and independent ancillary two-level systems. By means of a numerical analysis we show that, in case these ancillas are coherent, this kind of quantum battery can achieve remarkable performances for what it concerns the control of the stored energy and its extraction in regimes of parameters within reach in nowadays quantum circuits.
Authors: Michael Foltýn, Michal Kvapil, Tomáš Šikola, Michal Horák
Bismuth nanoparticles are being investigated due to their reported photothermal and photocatalytic properties. In this study, we synthesised spherical bismuth nanoparticles (50-600 nm) and investigated their structural and optical properties at the single particle level using analytical transmission electron microscopy. Our experimental results, supported by numerical simulations, demonstrate that bismuth nanoparticles support localised surface plasmon resonances, which can be tuned from the near-infrared to the ultraviolet spectral region by changing the nanoparticle size. Furthermore, plasmonic resonances demonstrate stability across the entire spectral bandwidth, enhancing the attractiveness of bismuth nanoparticles for applications over a wide spectral range. Bismuth's lower cost, biocompatibility, and oxidation resistance make it a suitable candidate for utilisation, particularly in industrial and large-scale plasmonic applications.
Authors: Hana Vargová
We rigorously analyze the global tripartite entanglement in a Heisenberg trimer with mixed spins-($1$,$1/2$,$1$) under varying exchange couplings between dissimilar and identical spins, magnetic fields, and temperatures. The global tripartite entanglement is quantified using the geometric mean of all three bipartite contributions, evaluated through negativity. We precisely map the regions of parameter space in which the trimer system exhibits spontaneous global entanglement. In addition, we classify the nature of the tripartite entangled states based on the distribution of reduced bipartite negativities among the spin dimers in the trimer. We further examine the thermal stability of global tripartite entanglement throughout the full parameter space. Special attention is given to the theoretical prediction of thermal robustness in a real three-spin complex, [Ni(bapa)(H$_2$0)]$_2$Cu(pba)(ClO$_4$)$_2$, where bapa stands for bis($3$-aminopropyl)amine, and pba denotes $1$,$3$-propylenebis(oxamato), which serves as an experimental realization of the mixed-spin ($1$,$1/2$,$1$) Heisenberg trimer. Notably, global entanglement in this system is predicted to persist up to approximately $100$ K and magnetic fields approaching $210$ T. Moreover, we uncover a thermally induced activation of robust global entanglement in regions where the ground state is biseparable. The magnitude of this thermal entanglement is remarkably high, nearly reaching a value of $1/2$, which has not been reported before. Finally, we propose a connection between the theoretically predicted tripartite entanglement, quantified via negativity derived from the density matrix, and the quantities measured directly or indirectly from various experiments.
Authors: Hana Vargová, Jozef Strečka
The genuine tetrapartite entanglement of a mixed spin-(1/2,1) Heisenberg tetramer is quantified according to the three different approaches incorporated all seven global bisections existing within the tetrapartite system. The degree of entanglement of each bisection is evaluated through the bipartite negativity at zero and non-zero temperature taking into account ferromagnetic and antiferromagnetic type of intra- ($J$) and inter-dimer ($J_1$) exchange coupling inside the square plaquette. Three utilized quantification methods based on the generalization of (i) a genuine tripartite negativity, (ii) a Coffman, Kundu and Wootters monogamy relation and (iii) a geometric average of complete trisections, result to the qualitatively and almost quantitatively identical behavior of a genuine tetrapartite negativity. It is shown that the genuine tetrapartite negativity exclusively arises from the antiferromagnetic-inter dimer $J_1>0$ coupling, whereas the character of with respect to $J$ ($J>0$ or $J<0$) determines its zero-temperature magnitude and its thermal stability with respect to the magnetic field and temperature. As is demonstrated for $0
Authors: Minoru Eto, Kentaro Nishimura, Muneto Nitta
Dislocations, as topological defects in crystal lattices, are fundamental to understanding plasticity in materials. Similar periodic structures also arise in continuum field theories, such as chiral soliton lattices (CSLs), which appear in condensed matter systems like chiral magnets and in high-energy contexts such as quantum chromodynamics in strong magnetic field or under rapid rotation. This work investigates whether dislocations can dynamically form within such emergent CSLs. The chiral sine-Gordon model, reduced from the aforementioned examples by certain truncations, is useful to determine the ground state but it cannot describe time evolution, lacks dynamical formation or leads to singular dislocations, because its equations of motion do not contain a topological term. We propose a field-theoretical model including the topological term coupled to external fields resolving these issues by modifying the topological term so it affects the dynamics. Using numerical simulations, we study the real-time formation of CSLs in two and three spatial dimensions. In 2D, edge dislocations emerge spontaneously, guiding soliton growth and later annihilating to leave a stable CSL. In 3D, both edge and screw dislocations form; the latter exhibits helical structure influenced by the external field. We find stable double helical screw dislocations looking like a double helix staircase or DNA. We then demonstrate the formation of helical dislocations and analyze how the external field strength affects CSL density and formation speed. Our results provide a novel theoretical framework for understanding dislocations in solitonic structures, connecting high-energy field theory with materials science phenomena.
Authors: Valerij Gurin
The plasmonic optical absorption of the silica glasses containing copper selenide nanoparticles is simulated on the basis of Drude theory. The plasmonic resonance absorption is studied in dependence on plasmonic frequency, damping factor and the matrix dielectric function. The charge carrier concentration in the nanoparticles is evaluated through the plasmonic frequency for the spectra of closest correspondence to experimental. The plasmon resonance position and the width of maxima are varied throughout the visible and near-IR ranges for the above parameters of experimental glasses with Cu2-xSe nanoparticles.
Authors: Xiao-Wen Shang, Shu-Yi Liang, Guan-Ju Yan, Xin-Yang Jiang, Zi-Ming Yin, Hao Tang, Jian-Peng Dou, Ze-Kun Jiang, Yu-Quan Peng, Xian-Min Jin
Quantum interference and entanglement are in the core of quantum computations. The fast spread of information in the quantum circuit helps to mitigate the circuit depth. Although the information scrambling in the closed systems has been proposed and tested in the digital circuits, how to measure the evolution of quantum correlations between systems and environments remains a delicate and open question. Here, we propose a photonic circuit to investigate the information scrambling in an open quantum system by implementing the collision model with cascaded Mach-Zehnder interferometers. We numerically simulate the photon propagation and find that the tripartite mutual information strongly depends on the system-environment and environment-environment interactions. We further reduce the number of observables and the number of shots required to reconstruct the density matrix by designing an enhanced compressed sensing. Our results provide a reconfigurable photonic platform for simulating open quantum systems and pave the way for exploring controllable dissipation and non-Markovianity in discrete-variable photonic computing.
Authors: Fabrizio Ramírez, David Villaseñor, Viani S. Morales-Guzmán, Darly Y. Castro, Jorge G. Hirsch
Light-matter systems that exhibit two-photon interactions have emerged as powerful platforms for exploring quantum applications. In this work, we focus on the two-photon Dicke model, a system of significant experimental relevance that displays spectral collapse and undergoes a phase transition from a normal to a superradiant phase. We analyze the normal phase, where a classical limit with two degrees of freedom can be derived using a mean-field approximation. Our study presents a detailed investigation of the loss of integrability in the two-photon Dicke model, employing both quantum and classical diagnostics. These results allow us to explore various dynamical features of the system, including the onset of chaos and the existence of mixed phase-space behavior.
Authors: Dawid Paszko, Christopher J. Turner, Dominic C. Rose, Arijeet Pal
The Lindblad equation for open quantum systems is central to our understanding of coherence and entanglement in the presence of Markovian dissipation. In closed quantum systems Hilbert-space fragmentation is an effective mechanism for slowing decoherence in the presence of constrained interactions. We develop a general mechanism for operator-space fragmentation of mixed states, undergoing Lindbladian evolution generated by frustration-free Hamiltonians and Pauli-string jump operators. The interplay of generator algebras of dissipative and unitary dynamics leads to a hierarchical partitioning of operator and real space into dynamically disconnected subspaces, which we elucidate using the bond and commutant algebras of superoperators. This fragmentation fundamentally constrains information spreading in open systems and provides new mechanisms to control highly entangled quantum states and dynamics. Our approach yields two key advances. Firstly, we introduce frustration graphs in operator space as a compact representation to construct effective non-Hermitian Hamiltonians in individual fragments and diagnose their free-fermion solvability. Secondly, using these methods we uncover a range of universal dynamical regimes in Pauli-Lindblad models, exhibiting symmetry enriched quantum chaos and integrability in operator-space fragments. Furthermore, we show dissipation-driven phase transitions corresponding to exceptional points in the Lindbladian spectrum whose signatures are captured by spectral statistics and operator dynamics. These results establish operator-space fragmentation as a fundamental principle for open quantum systems, with immediate implications for quantum error correction, where protected subspaces could emerge naturally from fragmentation. Our framework provides a systematic approach to discover and characterize novel non-equilibrium phases in open quantum many-body systems.
Authors: Jiahao Chen, Xingzhou Tang, Yang Ding, Susanta Chakraborty, Satoshi Aya, Bingxiang Li, Yanqing Lu
Polar solitons, i.e., solitonic waves accompanying asymmetry of geometry or phase, have garnered attention in polar systems, such as ferroelectric or magnetoelectric materials, where they play a critical role in topological transitions and nonreciprocal responses to external fields. A key question is whether such polar solitons can emerge in nonpolar systems, where intrinsic polarity is absent. Here, we demonstrate an unprecedented polar soliton with nematic order in a nonpolar and chiral liquid crystal system by applying an alternating electric field. The soliton is corn-kernel-shaped, displaying a pair of oppositely charged topological defects at its two ends. While head-to-head collision between the solitons leads to repulsion, head-to-tail collision attracts the solitons into a single polar soliton. A rich variety of solitonic kinetics, such as rectilinear translation and circulation motions, can be activated by controlling the voltage and frequency of an electric field. Simulations reveal that the formation of the polar solitons is achieved through balancing the electric and nematic elastic energies, while the flexoelectric effect drives their rotational behaviors. The discovery of polar solitons in nonpolar systems expands the understanding of topological solitons, opening new avenues for dynamic control in soft matter systems, with potential applications in nonreciprocal responsive materials and topological information storage.
Authors: Guillermo Serrera, Yoshito Y. Tanaka, Pablo Albella
Light-matter interactions generally involve momentum exchange between incident photons and the target object giving rise to optical forces and torques. While typically weak, they become significant at the nanoscale, driving intense research interest in the exploitation of photon recoil to drive micro- and nanostructures. While great progress has been attained in controlling transversal degrees of freedom, three-dimensional movement remains challenging, particularly due to the impractical realization of pulling forces that oppose the direction of incident light. Here we theoretically present a novel nanomotor design that enables control over both transverse and longitudinal motion. This design exploits coupling between an azimuthally polarized Bessel beam and a dielectric glass cylinder to realistically achieve optical pulling forces. At the same time, asymmetric plasmonic dimers, embedded within the cylinder, provide lateral motion, through asymmetric scattering under plane wave illumination. We further demonstrate that unwanted displacements and rotations can be restrained, even at long illumination times. Our design unlocks a new degree of freedom in motion control, allowing for pulling, pushing, and lateral movement by simply tuning the polarization or switching between plane waves and Bessel beams.
Authors: Seungjae Lee, Lennart J. Kuklinski, Moritz Thümler, Marc Timme
The emergence of synchrony essentially underlies the functionality of many systems across physics, biology and engineering. In all established synchronization phase transitions so far, a stable synchronous state is connected to a stable incoherent state: For continuous transitions, stable synchrony directly connects to stable incoherence at a critical point, whereas for discontinuous transitions, stable synchrony is connected to stable incoherence via an additional unstable branch. Here we present a novel type of transition between synchrony and incoherence where the synchronous state does not connect to the state of incoherence. We uncover such transitions in the complexified Kuramoto model with their variables and coupling strength parameter analytically continued. Deriving a self-consistency equation for a quaternion order parameter that we propose helps to mathematically pin down the mechanisms underlying this transition type. Local numerical analysis suggests that the transition is linked to a Hopf bifurcation destabilizing synchrony, in contrast to branching point bifurcations established for the transition between synchrony and incoherence so far.
Authors: Nazli Ugur Koyluoglu, Shankari V. Rajagopal, Gabriel L. Moreau, Jacob A. Hines, Ognjen Marković, Monika Schleier-Smith
We propose a robust approach to spin squeezing with local interactions that approaches the Heisenberg limit of phase sensitivity. To generate the requisite entanglement, we generalize the paradigmatic two-axis countertwisting Hamiltonian -- akin to squeezing by parametric amplification -- to systems with power-law interactions, incorporating a Heisenberg coupling that aids in spreading correlations and protects the collective spin coherence. The resulting time to approach the Heisenberg limit scales sublinearly with particle number in 2D dipolar and 3D van der Waals interacting systems. Our protocol is robust to disorder and density fluctuations, and can be implemented in near-term experiments with molecules, Rydberg atoms, and solid-state spins.
Authors: Aferdita Xhameni, Antonio Lombardo
We demonstrate high accuracy classification for handwritten digits from the MNIST dataset ($\sim$98.00$\%$) and RGB images from the CIFAR-10 dataset ($\sim$86.80$\%$) by using resistive memories based on a 2D van-der-Waals semiconductor: hafnium disulfide (HfS$_2$). These memories are fabricated via dry thermal oxidation, forming vertical crossbar HfO$_x$S$_y$/HfS$_2$ devices with a highly-ordered oxide-semiconductor structure. Our devices operate without electroforming or current compliance and exhibit multi-state, non-volatile resistive switching, allowing resistance to be tuned using voltage pulse trains. Using low-energy potentiation and depression pulses (0.7V-0.995V, 160ns-350ns), we achieve 31 ($\sim$5 bits) stable conductance states with high linearity, symmetry, and low variation over 100 cycles. Key performance metrics-such as weight update, quantisation, and retention-are extracted from these experimental devices. These characteristics are used to simulate neural networks with our resistive memories as weights. Neural networks are trained on state-of-the-art (SOTA) digital hardware (CUDA cores) and a baseline inference accuracy is extracted. IBM's Analog Hardware Acceleration Kit (AIHWKIT) is used to modify and remap digital weights in the pretrained network, based on the characteristics of our devices. Simulations account for factors like conductance linearity, device variation, and converter resolution. In both image recognition tasks, we demonstrate excellent performance, similar to SOTA, with only $<$0.07$\%$ and $<$1.00$\%$ difference in inference accuracy for the MNIST and CIFAR-10 datasets respectively. The forming-free, compliance-free operation, fast switching, low energy consumption, and high accuracy classification demonstrate the potential of HfO$_x$S$_y$/HfS$_2$-based resistive memories for energy-efficient neural network acceleration and neuromorphic computing.
Authors: Roman Krčmár, Mária Zelenayová, Jozef Genzor, Libor Caha, Peter Rapčan, Tomotoshi Nishino, Andrej Gendiar
Phase transition of the two- and three-state quantum Potts models on the Sierpiński pyramid are studied by means of a tensor network framework, the higher-order tensor renormalization group method. Critical values of the transverse magnetic field and the magnetic exponent $\beta$ are evaluated. Despite the fact that the Hausdorff dimension of the Sierpiński pyramid is exactly two $( = \log_2^{~} 4)$, the obtained critical properties show that the effective dimension is lower than two.
Authors: Alberto Pérez de Alba Ortíz, Bernd Ensing
We present a molecular simulation method to simultaneously find multiple transition pathways, and their associated free-energy profiles. The scheme extends path-metadynamics (PMD) [Phys. Rev. Lett. 109, 020601 (2012)] with multiple paths and repulsive walkers (multiPMD). We illustrate multiPMD for two C7eq-to-C7ax paths in Ace-Ala-Nme and six PPII-to-PPII paths in Ace-(Pro)4-Nme. We also show a scheme to render an interpretable "PathMap", showing the free energy ridges between paths, as well as the branching and merging of the transition channels. MultiPMD is a flexible and promising method for systems with competing or controversial pathways, which appear in many biomolecular systems, including proteins and nucleic acids.
Authors: Yuehui Li, Bo Han, Xiaolong Yang, Ruilin Mao, Fachen Liu, Ruochen Shi, Ruishi Qi, Xiaorui Hao, Ning Li, Bingyao Liu, Xiaomei Li, Jinlong Du, Ji Chen, Wu Li, Peng Gao
Nanoscale defects such as dislocations, have a significant impact on the phonon thermal transport properties in non-metallic materials. To unravel these effects, understanding of defect phonon modes is essential. Herein, at the atomic scale, the localized phonons of individual dislocation at a Si/Ge interface are measured via monochromated electron energy loss spectroscopy in a scanning transmission electron microscope. These modes are then correlated with the local microstructure, further revealing the dislocation effects on the local thermal transport properties. The dislocation causes phonon redshift in several milli-electron-volts within about two to four nanometers of the core, where both of the strain field and Ge-segregation play roles. With the presence of dislocation, the local interfacial thermal conductance can be either enhanced or reduced, depending on the complex interaction and competition between lattice-disorder (dislocation) and element-disorder (heterointerface mixing and Ge-segregation) at the interface. These findings provide valuable insights to improve the thermal properties of thermoelectric generators and thermal management systems through proper defect engineering.
Authors: Giacomo Bighin, Puneet A. Murthy, Nicolò Defenu, Tilman Enss
Achieving strong interactions in fermionic many-body systems is a major theme of research in condensed matter physics. It is well-known that interactions between fermions can be mediated through a bosonic medium, such as a phonon bath or Bose-Einstein condensate (BEC). Here we show that such induced attraction can be resonantly enhanced when the bosonic medium is a two-component spinor BEC. The strongest interaction is achieved by tuning the boson-boson scattering to the quantum critical spinodal point of the BEC where the sound velocity vanishes. The fermion pairing gap and the superconducting critical temperature can thus be dramatically enhanced. We propose two experimental realizations of this scenario, with exciton-polariton systems in two-dimensional semiconductors and ultracold atomic Bose-Fermi mixtures.
Authors: Kui Zhao, Jianfei Xiao, Huaiyuan Liu, Linfeng Tu, Yiwen Ma, Jiangbo He, Mingli Liu, Ruiyang Jiang, Zhongmou Jia, Shang Zhu, Yunteng Shi, Zhaozheng Lyu, Jie Shen, Guangtong Liu, Li Lu, Fanming Qu
The application of in-plane magnetic fields to Josephson junctions enables fundamental exploration of quantum phenomena, including Zeeman-driven 0-$\pi$ transitions and planar topological superconductivity. However, intrinsic orbital effects arising from nanoscale rippled geometries in practical devices can dominate phase interference signatures, complicating their interpretation. Here, we experimentally probe superconducting interference in NbTiN weak-link Josephson junctions under combined perpendicular and in-plane magnetic fields. The critical supercurrent reveals a distinct diamond-shaped interference pattern, with nodes progressively opening and evolving into V-shaped features, reminiscent of suppression-recovery patterns associated with 0-$\pi$ transitions. We theoretically analyze the interplay between orbital effects from rippled geometries and non-uniform supercurrent density distributions, demonstrating that their synergistic interaction could reproduce the experimentally observed interference evolution. Our findings elucidate how geometric imperfections and current inhomogeneity cooperatively reshape phase interference, providing critical insights into orbital-dominated phenomena in Josephson systems.
Authors: Samyak Jain, Rickmoy Samanta
We construct viscous fluid flow sourced by a force dipole embedded in a cylindrical fluid membrane, coupled to external embedding fluids. We find analytic expressions for the flow, in the limit of infinitely long and thin tubular membranes. We utilize this solution to formulate the in-plane dynamics of a pair of pusher-type dipoles along the cylinder surface. We find that a mutually perpendicular dipole pair move together along helical geodesics, thus acting as curvature checkers, analogous to vortex dipoles. Since the cylindrical geometry breaks the in-plane rotational symmetry of the membrane, there is a difference in flows along the axial and transverse directions of the cylinder. This in turn leads to anisotropic hydrodynamic interaction between the dipoles and is remarkably different from flat and spherical fluid membranes. In particular, the flow along the compact direction of the cylinder has a local rigid rotation term (independent of the angular coordinate but decays along the axis of the cylinder). Due to this feature of the flow, we observe that the interacting dipole pair initially situated along the axial direction exhibits an overall drift along the compact angular direction of the tubular fluid membrane. We find that the drift for the dipole pair increases linearly with time. Our results are relevant for non-equilibrium dynamics of motor proteins in tubular membranes arising in nature, as well as in-vitro experiments (25).
Authors: Léopold Van Brandt, Jean-Charles Delvenne
An extension of fluctuation-dissipation theorem is used to derive a "speed limit" theorem for nonlinear electronic devices. This speed limit provides a lower bound on the dissipation that is incurred when transferring a given amount of electric charge in a certain amount of time with a certain noise level (average variance of the current). This bound, which implies a high energy dissipation for fast, low-noise operations (such as switching a bit in a digital memory), brings together recent results of stochastic thermodynamics into a form that is usable for practical nonlinear electronic circuits, as we illustrate on a switching circuit made of an nMOS pass gate in a state-of-the-art industrial technology.
Authors: Manato Fujimoto, Daniel E. Parker, Junkai Dong, Eslam Khalaf, Ashvin Vishwanath, Patrick Ledwith
The rise of moiré materials has led to experimental realizations of integer and fractional Chern insulators in small or vanishing magnetic fields. At the same time, a set of minimal conditions sufficient to guarantee a Abelian fractional state in a flat band were identified, namely "ideal" or "vortexable" quantum geometry. Such vortexable bands share essential features with the lowest Landau level, while excluding the need for more fine-tuned aspects such as flat Berry curvature. A natural and important generalization is to ask if such conditions can be extended to capture the quantum geometry of higher Landau levels, particularly the first (1LL), where non-Abelian states at $\nu = 1/2,2/5$ are known to be competitive. The possibility of realizing these states at zero magnetic field , and perhaps even more exotic ones, could become a reality if we could identify the essential structure of the 1LL in Chern bands. In this work, we introduce a precise definition of 1LL quantum geometry, along with a figure of merit that measures how closely a given band approaches the 1LL. We apply the definition to identify two models with 1LL structure -- a toy model of double bilayer twisted graphene and a more realistic model of strained Bernal graphene.
Authors: Thomas Blommel, Jason Kaye, Yuta Murakami, Emanuel Gull, Denis Golež
Using a state-of-the-art numerical scheme, we show that the Higgs mode under excitation exhibits chirped oscillations and exponential decay when fluctuations are included. This is in stark contrast to conventional BCS collisionless dynamics which predict power-law decay and the absence of chirping. The chirped amplitude mode enables us to determine the local modification of the effective potential even when the system is in a long-lived prethermal state. We then show that this chirped amplitude mode is an experimentally observable quantity since the photoinduced (super)current in pump-probe experiments serves as an efficient proxy for the order parameter dynamics, including the chirped dynamics. Our result is based on the attractive Hubbard model using dynamical mean-field theory within the symmetry-broken state after a excitation across the superconducting gap. Since the collective response involves long timescales, we extend the hierarchical low-rank compression method for nonequilibrium Green's functions to symmetry-broken states and show that it serves as an efficient representation despite long-lived memory kernels.
Authors: Qinghua He, Wenlong Gao, Feng Liu
Conventional topological materials rely on band-specific mechanisms -- such as band inversion or spin-orbit coupling -- to realize nontrivial topological invariants. Here, we introduce a symmetry-driven paradigm for generating topological states, exploiting a translational symmetry $\mathcal{L}$ that couples two maximal Wyckoff positions. This symmetry induces robust band degeneracies independent of band structure details, allowing us to classify $\mathcal{L}$ as trivial or nontrivial by quantized electric multipoles. Crucially, for nontrivial $\mathcal{L}$, symmetry-protected edge and corner states emerge universally across all symmetry-compatible insulating, semi-metallic, and metallic phases, irrespective of specific band structure. We demonstrate this in a $C_4$-symmetric model and validate it using an experimentally feasible dielectric photonic crystal engineered with $\mathcal{L}$ symmetry. Through full-wave simulation, we observe directional edge modes and localized corner modes, with the former selectively excited by harmonic point sources spatially shifted by $\mathcal{L}$ at a fixed frequency.
Authors: Karl J Friston, Maxwell J D Ramstead, Dalton A R Sakthivadivel
We discuss an approach to mathematically modelling systems made of objects that are coupled together, using generative models of the dependence relationships between states (or trajectories) of the things comprising such systems. This broad class includes open or non-equilibrium systems and is especially relevant to self-organising systems. The ensuing variational free energy principle (FEP) has certain advantages over using random dynamical systems explicitly, notably, by being more tractable and offering a parsimonious explanation of why the joint system evolves in the way that it does, based on the properties of the coupling between system components. Using the FEP allows us to model the dynamics of an object as if it were a process of variational inference, because variational free energy (or surprisal) is a Lyapunov function for its dynamics. In short, we argue that using generative models to represent and track relations among subsystems leads us to a particular statistical theory of interacting systems. Conversely, this theory enables us to construct nested models that respect the known relations among subsystems. We point out that the fact that a physical object conforms to the FEP does not necessarily imply that this object performs inference in the literal sense; rather, it is a useful explanatory fiction which replaces the `explicit' dynamics of the object with an `implicit' flow on free energy gradients -- a fiction that may or may not be entertained by the object itself.
Authors: Debashish Mondal, Rekha Kumari, Tanay Nag, Arijit Saha
We theoretically investigate the transport signature of single and multiple Floquet Majorana end modes~(FMEMs), appearing in an experimentally feasible setup with Rashba nanowire~(NW) placed in closed proximity to a conventional $s$-wave superconductor, in the presence of an external Zeeman field. Periodic drive causes the anomalous $\pi$-modes to emerge in addition to the regular $0$-modes in the driven system where the former does not exhibit any static analog. For single $0$- and/or $\pi$-FMEM, differential conductance exhibits a quantized value of $2e^{2}/h$ while we consider the sum over all the photon sectors, supporting Floquet sum rule. We examine the stability of this summed conductance against random onsite disorder. We further investigate the summed conductance in several cases hosting multiple~(more than one) $0$- or $\pi$-modes at the end of the NW. In these cases, we obtain quantized values of $n_{M}\times 2e^{2}/h$ in summed differential conductance with $n_{M}$ being the number of modes~($0$ or $\pi$) localized at one end of the NW. We repeat our analysis for another experimentally realizable model system known as helical Shiba chain. Moreover, we corroborate our results by computing the differential conductance for FMEMs using non-equilibrium Green's function method. Our work opens up the possibility of studying the transport signatures of FMEMs in these realistic models.
Authors: Wai Kit Ng, Jakub Dranczewski, Anna Fischer, T V Raziman, Dhruv Saxena, Tobias Farchy, Kilian Stenning, Jonathan Peters, Heinz Schmid, Will R Branford, Mauricio Barahona, Kirsten Moselund, Riccardo Sapienza, Jack C. Gartside
With the growing prevalence of AI, demand increases for hardware that mimics the brain's ability to extract structure from limited data. In the retina, ganglion cells detect features from sparse inputs via lateral inhibition, where neurons antagonistically suppress activity of neighbouring cells. Biological neurons exhibit diverse heterogeneous nonlinear responses, linked to robust learning and strong performance in low-data regimes. Here, we introduce a bio-inspired 'retinomorphic' photonic system where spatially-competing lasing modes in a network laser act as heterogeneous, inhibitively-coupled neurons - enabling few-shot classification and segmentation. This compact (150 micron) silicon-compatible scheme addresses key challenges in photonic computing: physical nonlinearity and spatial footprint. We report 98.05% and 87.85% accuracy on MNIST and Fashion-MNIST, and 90.12% on BreaKHis cancer diagnosis - outperforming software CNNs including EfficientNet in few-shot and class-imbalanced regimes. We demonstrate combined segmentation and classification on the HAM10k skin lesion dataset, achieving DICE and Jaccard scores of 84.49% and 74.80%. These results establish a new class of nonlinear photonic hardware for versatile, data-efficient neuromorphic computing.
Authors: Pablo Rodriguez-Lopez, Mauro Antezza
We analyze the impact of spatial non-locality and losses in the electromagnetic response of graphene on the Casimir-Lifshitz interaction. To this purpose, we calculate the Casimir-Lifshitz force (CLF) between a gold sphere and a graphene-coated SiO$_2$ plane and compare our finding with the recent experiment in PRL {\bf 126}, 206802 (2021) and PRB {\bf 104}, 085436 (2021). We calculated the CLF using three different models for the electromagnetic response of graphene: electric conductivity using a non-local and lossy Kubo model, electric conductivity using the local and lossy Kubo model, and the non-local and lossless polarization operator model. The relation between these three models has been recently explored in PRB {\bf 111}, 115428 (2025). We show that, for the parameters of the available experiments, the theoretical predictions for the Casimir-Lifshitz force using the three models are practically identical (having a relative differences smaller than $10^{-3}$). This implies that for those given experiments, both non-local and lossy effects in the graphene response are completely negligible. We also find that this experiment cannot distinguish between the Drude and Plasma prescriptions for the involved materials (gold and graphene). Our findings are relevant for present and future comparisons with experimental measurement of the Casimir-Lifshitz force involving graphene structures. Indeed, we show that an extremely simple local Kubo model for the electric conductivity, explicitly depending on Dirac mass, chemical potential, losses and temperature, is largely enough for a totally comprehensive comparison with typical experimental configurations. We also show how the Polarization tensor must be used and modified in general, for phenomena needing a more fine response function, i.e. requiring both the spatial non-locality and losses.
Authors: Fang Xie, Lei Chen, Yuan Fang, Qimiao Si
The moiré structure of AB-stacked $\rm{MoTe_2/WSe_2}$ represents a natural platform to realize Kondo lattice models, due to the discrepancy of the bandwidth between the individual layers. Here, we study this system at the commensurate filling of $\nu_{\rm tot}=2$. Our focus is on the $1+1$ filling setting of $\nu_{\rm Mo} =\nu_{\rm W}=1$, which enables a Kondo lattice description. We find a Kondo semimetal due to the sizable intra-orbital hopping among the electrons in the $\rm{MoTe_2}$ layer. The Kondo-driven (emergent) flat band is naturally pinned to the Fermi energy. When combined with the inherent topology of the electronic structure, a topological Kondo semimetal phase ensues. We calculate the valley Hall response and, due to the breaking of inversion symmetry, also identify a spontaneous Hall effect. There is a Berry curvature dodecapole, which leads to a fourth-order spontaneous Hall effect in the perturbative regime of the electric field that is further amplified in the non-perturbative regime. As such, the system provides a tunable setting to simulate topological Kondo semimetals. Finally, we discuss the pathways that connect the physics realized here to the Weyl Kondo semimetals and their proximate phases that have been advanced in recent years in topological Kondo lattice models and materials.
Authors: Saikat Mondal, Adhip Agarwala
In interacting topological systems, Landau-like order parameters interplay with the band topology of fermions. The physics of domain formation in such systems can get significantly altered due to the presence of topological fermions. In this work we show that coupling a topological fermionic field to a scalar field can drastically modify the nucleation processes of the scalar field. We find that existence of non-trivial fermionic boundary modes on the nucleating droplets of the scalar field leads to substantial quantum corrections to the surface tension. This leads to an increase in the size of the critical nucleus beyond which unrestricted droplet growth happens. To illustrate the phenomena we devise a minimal model of fermions in a Chern insulating system coupled to a classical Ising field in two spatial dimensions. Using a combination of analytic and numerical methods we conclusively demonstrate that topological phases have a characteristic quantum surface tension. Apart from material systems, our work opens up a host of questions regarding the impact of fermionic topological terms on classical phase transitions and associated criticality.
Authors: Mateus Marques, Bruno M. de Souza Melo, Alexandre R. Rocha, Caio Lewenkopf, Luis G. G. V. Dias da Silva
We explore the phase diagram of the Mott metal-insulator transition (MIT), focusing on the effects of particle-hole asymmetry (PHA) in the single-band Hubbard model. Our dynamical mean-field theory (DMFT) study reveals that the introduction of PHA in the model significantly influences the critical temperature ($T_c$) and interaction strength ($U_c$), as well as the size of the co-existence region of metallic and insulating phases at low temperatures. Specifically, as the system is moved away from particle-hole symmetry, $T_c$ decreases and $U_c$ increases, indicating a suppression of the insulating phase and the strengthening of the metallic behavior. Additionally, the first-order transition line between metallic and insulating phases is better defined in the model with PHA, leading to a reduced co-existence region at $T
Authors: Alpin N. Tatan, Osamu Sugino
We study new superconductor candidates in functionalized MXenes Zr$_2$NS$_2$, Zr$_2$NCl$_2$, and Sc$_2$NCl$_2$ with $\textit{ab initio}$ calculations based on density functional theory for superconductors (SCDFT). The superconducting transition temperature $(T_c)$ at ambient pressure is predicted to reach 9.48 K (Zr$_2$NS$_2$), with potential further improvements under applied strain. We note that the changes in the profiles of superconducting gap $(\Delta)$ and electron-phonon coupling $(\lambda)$ across the Fermi surface may be influenced by their modified electronic bandstructure components.
Authors: Junhui Cao, Alexey Kavokin
The BCS theory has achieved widespread success in describing conventional superconductivity. However, when the length scale reaches the atomic limit, the reduced dimensionality may lead to the quantum breakdown resulting in unpredictable superconducting behaviors. It has been exper imentally evidenced that the critical temperature is strongly enhanced in the monolayer films of FeSe/STO and epitaxial Aluminum. Here, we propose the exciton mechanism of superconductivity as a possible reason for the enhanced superconductivity in hybrid superconductor-semiconductor structures. The exciton-induced Cooper pairing may lead to the larger energy gaps and higher critical temperatures as compared to those caused by the phonon induced superconductivity. A detailed comparison of the theory and experimental results of Ref. 1 reveals the possibility of exciton-induced superconductivity in thin films of Aluminum near the monolayer limit.
Authors: Jordan R. Sawchuk, David A. Sivak
Optimal control of stochastic systems plays a central role in nonequilibrium physics, with applications in the study of biological molecular motors and the design of single-molecule experiments. While exact analytic solutions to optimization problems are rare, under slow driving conditions, the problem can be reformulated geometrically solely in terms of equilibrium properties. In this framework, minimum-work protocols are geodesics on a thermodynamic manifold whose metric is a generalized friction tensor. Here, we introduce a new foundation for this friction-tensor formalism for conservatively driven systems. Under complete control of the potential energy, a global thermodynamic manifold (on which points are identified with instantaneous energy landscapes) has as its metric a full-control friction tensor. Arbitrary partial-control friction tensors arise naturally as inherited metrics on submanifolds of this global manifold. Leveraging a simple mathematical relationship between system dynamics and the geometry of the global manifold, we derive new expressions for the friction tensor that offer powerful tools for interpretation and computation of friction tensors and minimum-work protocols. Our results elucidate a connection between relaxation and dissipation in slowly driven systems and suggest optimization heuristics. We demonstrate the utility of these developments in three illustrative examples.
Authors: Xun-Jiang Luo, Fengcheng Wu
In a class of systems, there are gapped boundary-localized states described by a boundary Hamiltonian. The topological classification of gapped boundary Hamiltonians, same as the standard tenfold way for gapped bulk states, can lead to the emergence of boundary topological insulators (TIs) and superconductors (TSCs). In this work, we present a theoretical study of boundary TIs and TSCs of the full Altland-Zirnbauer tenfold symmetry classes. Based on the boundary projection analyses for a $d$-dimensional Dirac continuum model, we demonstrate that nontrivial boundary topology can arise at a $(d-n)$-dimensional boundary if the Dirac model incorporates ($n+1$) mass terms with $0
Authors: Aiden V. Harbick, Mark K. Transtrum
Modern superconducting radio frequency (SRF) applications demand precise control over material properties across multiple length scales - from microscopic composition, to mesoscopic defect structures, to macroscopic cavity geometry. We present a time-dependent Ginzburg-Landau (TDGL) framework that incorporates spatially varying parameters derived from experimental measurements and ab initio calculations, enabling realistic, sample-specific simulations. As a demonstration, we model Sn-deficient islands in Nb$_3$Sn and calculate the field at which vortex nucleation first occurs for various defect configurations. These thresholds serve as a predictive tool for identifying defects likely to degrade SRF cavity performance. We then simulate the resulting dissipation and show how aggregate contributions from multiple small defects can reproduce trends consistent with high-field $Q$-slope behavior observed experimentally. Our results offer a pathway for connecting microscopic defect properties to macroscopic SRF performance using a computationally efficient mesoscopic model.
Authors: Hyeong-Tark Han, Jae Sung Lee, Jae-Hyung Jeon
Thermodynamic uncertainty relations (TURs) delineate tradeoff relations between the thermodynamic cost and the magnitude of an observable's fluctuation. While TURs have been established for various nonequilibrium systems, their applicability to systems influenced by active noise remains largely unexplored. Here, we present an explicit expression of TUR for systems with active Ornstein-Uhlenbeck particles (AOUPs). Our findings reveal that active noise introduces modifications to the terms associated with the thermodynamic cost in the TUR expression. The altered thermodynamic cost encompasses not only the conventional entropy production but also the energy consumption induced by the active noise. We examine the capability of this TUR as an accurate estimator of the extent of anomalous diffusion in systems with active noise driven by a constant force in free space. By introducing the concept of a contracted probability density function, we derive a steady-state TUR tailored to this system. Moreover, through the adoption of a new scaling parameter, we enhance and optimize the TUR bound further. Our results demonstrate that active noise tends to hinder accurate estimation of the anomalous diffusion extent. Our study offers a systematic approach for exploring the fluctuation nature of biological systems operating in active environments.
Authors: Juan C. Petit, Saswati Ganguly, Matthias Sperl
We investigate the vibrational properties of polycrystalline monodisperse and disordered bidisperse granular packings during jamming and unjamming using discrete element method simulations. Both systems deviate from Debye scaling at low frequencies $(\omega)$, but only bidisperse packings exhibit a low-$\omega$ plateau. The low $\omega$ exponent ($\alpha$) in bidisperse packings evolves smoothly from zero (plateau) to near one (Debye scaling) with increasing packing fraction, whereas in polycrystalline packings, it changes discontinuously near jamming/unjamming, due to the nature of the contact network rearrangements. Despite structural modifications during the compression-decompression cycle, the exponent remains unchanged at the same distance from jamming density, regardless of the history. Nonaffine displacements and contact orientational order further confirm that structural features that impact low-$\omega$ vibrational states and, hence, mechanical properties are largely restored upon decompression, reinforcing vibrational similarities between jamming and unjamming states.
Authors: Botond Tyukodi, Fernando Caballero, Daichi Hayakawa, Douglas M. Hall, W. Benjamin Rogers, Gregory M. Grason, Michael F. Hagan
Recent advances in synthetic methods enable designing subunits that self-assemble into structures with precise, finite sizes and well-defined architectures, but yields are frequently suppressed by the formation of off-target metastable structures. Increasing the complexity (the number of distinct subunit types) can inhibit off-target structures, but leads to slower kinetics and higher synthesis costs. Here, we study icosahedral shells formed of programmable triangular subunits as a model system, and identify design principles that produce the highest target yield at the lowest complexity. We use a symmetry-based construction to create a range of design complexities, starting from the maximal symmetry Caspar-Klug assembly up to the fully addressable, zero-symmetry assembly. Kinetic Monte Carlo simulations reveal that the most prominent defects leading to off-target assemblies are disclinations at sites of rotational symmetry. We derive symmetry-based rules for identifying the optimal (lowest-complexity, highest-symmetry) design that inhibits these disclinations, leading to robust, high-fidelity assembly of targets with arbitrarily large, yet precise, finite sizes. The optimal complexity varies non-monotonically with target size, with `magic' sizes appearing for high-symmetry designs in which symmetry axes do not intersect vertices of the triangular net. The optimal designs at magic sizes require 12 times fewer inequivalent interaction-types than the (minimal symmetry) fully addressable construction, which greatly reduces the timescale and experimental cost required to achieve high fidelity assembly of large targets. This symmetry-based principle for pruning off-target assembly generalizes to diverse architectures with different topologies.
Authors: Abhishek Yadav, Francesco Caravelli, David Wolpert
Mismatch cost (MMC) is a universally applicable lower bound on both the entropy production (EP) of any fixed physical process across a given time interval. In this work we use MMC for the first time to lower-bound the amount of work dissipated by running a high-level or assembler-level computer program. To begin, we extend previous results concerning MMC to prove that it scales at least linearly with the total heat flow in the worst case over initial distributions. This establishes that - in contrast to results like the thermodynamic speed limit theorem or thermodynamic uncertainty relations - it is often a substantial fraction of the work dissipated on macroscopic scales. We also prove that the MMC lower bound over a given time interval never decreases if the time interval is subdivided into a sequence of sub-intervals, and that the bound often increases. Armed with these results, we then introduce a general framework for computing the minimal EP (i.e., the MMC) associated with running any computer program on any physical system that implements a modern digital computer. Crucially, this framework holds completely independently of the microscopic physical details of that system. Next we apply this general framework to compare lower bounds on the EP incurred by running two canonical sorting algorithms, bubble sort and Bucket sort. This enables us to investigate how thermodynamic cost depends on features like input size and structure (e.g., with or without repeated entries). Finally, we extend the framework to programs that call subroutines.
Authors: Carolin Wille, Maksimilian Usoltcev, Jens Eisert, Alexander Altland
This work proposes a minimal model extending the duality between classical statistical spin systems and fermionic systems beyond the case of free fermions. A Jordan-Wigner transformation applied to a two-dimensional tensor network maps the partition sum of a classical statistical mechanics model to a Grassmann variable integral, structurally similar to the path integral for interacting fermions in two dimensions. The resulting model is simple, featuring only two parameters: one governing spin-spin interaction (dual to effective hopping strength in the fermionic picture), the other measuring the deviation from the free fermion limit. Nevertheless, it exhibits a rich phase diagram, partially stabilized by elements of topology, and featuring three phases meeting at a tricritical point. Besides the interpretation as a spin and fermionic system, the model is closely related to loop gas and vertex models and can be interpreted as a parity-preserving (non-unitary) circuit. Its minimal construction makes it an ideal reference system for studying non-linearities in tensor networks and deriving results by means of duality.
Authors: Greta Lupi, Jose L. Lado
Impurities in quantum materials have provided successful strategies for learning properties of complex states, ranging from unconventional superconductors to topological insulators. In quantum magnetism, inferring the Hamiltonian of an engineered system becomes a challenging open problem in the presence of complex interactions. Here we show how a supervised machine-learning technique can be used to infer Hamiltonian parameters from atomically engineered quantum magnets by inferring fluctuations of the ground states due to the presence of impurities. We demonstrate our methodology both with a fermionic model with spin-orbit coupling, as well as with many-body spin models with long-range exchange and anisotropic exchange interactions. We show that our approach enables performing Hamiltonian extraction in the presence of significant noise, providing a strategy to perform Hamiltonian learning with experimental observables in atomic-scale quantum magnets. Our results establish a strategy to perform Hamiltonian learning by exploiting the impact of impurities in complex quantum many-body states.
Authors: Jesper Byggmästar, Damian Sobieraj, Jan S. Wróbel, Daniel K. Schreiber, Osman El-Atwani, Enrique Martinez, Duc Nguyen-Manh
Tungsten-based low-activation high-entropy alloys are possible candidates for next-generation fusion reactors due to their exceptional tolerance to irradiation, thermal loads, and stress. We develop an accurate and efficient machine-learned interatomic potential for the W-Ta-Cr-V system and use it in hybrid Monte Carlo molecular dynamics simulations of ordering and segregation to all common types of defects in WTaCrV. The predictions are compared to atom probe tomography analysis of segregation and precipitation in WTaCrV thin films. By also considering two other alloys, WTaV and MoNbTaVW, we are able to draw general conclusions about preferred segregation in refractory alloys and the reasons behind it, guiding future alloy design and elucidating experimental observations. We show that the experimentally observed CrV precipitates in WTaCrV form semicoherent bcc-to-bcc interfaces with the surrounding matrix, as coherent precipitates are not thermodynamically stable due to excessive lattice mismatch. The predictions from simulations align well with our atom probe tomography analysis as well as previous experimental observations.
Authors: Benjamin A. Levitan, Yuval Oreg, Erez Berg
We propose a mechanism which can generate supercurrents in spin-orbit coupled superconductors with charged magnetic inclusions. The basic idea is that through spin-orbit interaction, the in-plane electric field near the edge of each inclusion appears to the electrons as an effective spin-dependent gauge field; if Cooper pairs can be partially spin polarized, then each pair experiences a nonzero net transverse pseudo-gauge field. We explore the phenomenology of our mechanism within a Ginzburg-Landau theory, with parameters determined from a microscopic model. Depending on parameters, our mechanism can either enhance or reduce the total magnetization upon superconducting condensation. Given an appropriate distribution of inclusions, we show how our mechanism can generate superconducting vortices without any applied orbital magnetic field. Our mechanism can produce similar qualitative behavior to the ``magnetic memory effect'' observed in 4Hb-TaS$_2$. However, the magnitude of the effect in that material seems larger than our model can naturally explain.
Authors: Peter Lunts, Aavishkar A. Patel, Subir Sachdev
We describe the evolution of low-temperature thermopower across Fermi-volume-changing quantum phase transitions in Kondo lattice models without translational symmetry breaking. This transition moves from a heavy Fermi liquid with a conventional Luttinger-volume large Fermi surface to a 'FL*' state, characterized by a small Fermi surface and a spin liquid with fractionalized excitations. The onset of the large Fermi surface phase is driven by the condensation of a Higgs field that carries a unit gauge charge under an emergent U(1) gauge field. We consider the case with spatially random Kondo exchange, as this leads to strange metal behavior in electrical transport. We find a large asymmetric thermopower in a 'skewed' marginal Fermi liquid, with similarities to the skewed non-Fermi liquid of Georges and Mravlje (arXiv:2102.13224). Our findings are consistent with recent observations in heavy fermion compounds (Z.-Y. Cao et al., arXiv:2408.13604), and describe an enhancement of thermopower on the large Fermi surface side as well as a non-monotonic behavior on the small Fermi surface side. Our results also apply to single-band Hubbard models and the pseudogap transition in the cuprates. In the ancilla framework, single-band models exhibit an inverted Kondo lattice transition: the small Fermi surface pseudogap state corresponds to the condensed Higgs state. This inversion results in an enhancement of thermopower on the pseudogap side in our theory, consistent with observations in the cuprates (C. Collignon et al., arXiv:2011.14927; A. Gourgout et al., arXiv:2106.05959). We argue that these observations support a non-symmetry-breaking Fermi-volume-changing transition as the underlying description of the onset of the pseudogap in the cuprates.
Authors: Renjie Zhang, Bocheng Yu, Hengxin Tan, Yiwei Cheng, Feiran Shen, Junye Yang, Dan Mu, Xinru Han, Alfred Zong, Quanxin Hu, Xuezhi Chen, Yudong Hu, Chengnuo Meng, Junchao Ren, Junqin Li, Zhenhua Chen, Zhengtai Liu, Mao Ye, Makoto Hashimoto, Donghui Lu, Shifeng Jin, Binghai Yan, Lunhua He, Ziqiang Wang, Tian Shang, Yaobo Huang, Baiqing Lv, Hong Ding
Orbital selectivity is pivotal in dictating the phase diagrams of multiorbital systems, with prominent examples including the orbital-selective Mott phase and superconductivity, etc. The intercalation of anisotropic layers represents an effective method for enhancing orbital selectivity and, thereby shaping the low-energy physics of multiorbital systems. Despite its potential, related experimental studies remain limited. In this work, we systematically examine the interplay between orbital selectivity and magnetism in the newly discovered anisotropic kagome TbTi3Bi4 single crystal, and report a unidirectional, orbital-selective band reconstruction within the antiferromagnetic (AFM) state. By combining soft X-ray and vacuum ultraviolet angle-resolved photoemission spectroscopy (ARPES) measurements with orbital-resolved density functional theory (DFT) calculations, we identify that the band reconstruction is a manifestation of the AFM order, driven by a 1/3 nesting instability of the intercalated Tb 5dxz orbitals. Such an orbital-selective modulation leads the unusual momentum-dependent band folding and the emergence of symmetry-protected Dirac cones only at the M1 point. More importantly, the discovery of orbital-selective 3 x 1 AFM order offers crucial insights into the underlying mechanism of the fractional magnetization plateau in this Kagome AFM metal. Our findings not only underscore the essential role of both conducting and localized electrons in determining the magnetic orders of LnTi3Bi4 (Ln = Lanthanide) kagome metals but also offer a pathway for manipulating magnetism through selective control of anisotropic electronic structures.
Authors: Pengwei Zhao, Jiahao Yang, Gang v. Chen
Ferroelectricity has been one major focus in modern fundamental research and technological application. We consider the physical origin of improper ferroelectricity in Mott insulating materials. Beyond the well-known Katsura-Nagaosa-Balatsky's inverse Dzyaloshinskii-Moriya mechanism for the noncollinearly ordered magnets, we point out the induction of the electric polarizations in the multipolar ordered Mott insulators. Using the multiflavor representation for the multipolar magnetic moments, we can show the crossover or transition from the pure inverse Dzyaloshinskii-Moriya mechanism to the pure multipolar origin for the ferroelectricity, and also incorporate the intermediate regime with the mixture of both origins. We expect our results to inspire a reexamination of ferroelectricity in the multipolar-ordered magnets.
Authors: Syed Yunus Ali, Rafna Rafeek, Debasish Mondal
We consider a Geometric Brownian Information Engine to explore the effects of finite cycle time $(\tau)$ on the extractable work, power, and efficiency. We incorporate an error-free feedback controller that converts the information obtained about the state of overdamped Brownian particles, confined within a 2-D monolobal geometry, into extractable work. The performance of the information engine depends on the cycle period $(\tau)$, measurement distance $(x_m)$, and feedback location $(x_f)$ of the controller. Upon increasing the feedback cycle time, the engine transitions from a high non-equilibrium steady state to a completely relaxed state. We set the measurement distance at an optimum position related to a fully relaxed state ($x_m^* \sim 0.6 \sigma$). When the cycle time is finite and short ($\tau <\tau_r$), the best information processing occurs with a shorter distance of the feedback site. While increasing the cycle time towards a fully relaxed state ($\tau \gg \tau_r$), the maximum extractable work that can be achieved with a feedback location is set to be twice that of $x_m^*$, as expected. When the cycle time ($\tau$) is longer than the relaxation time ($\tau_r$), the maximum power is achieved when the scaled feedback location is exactly double the optimum measurement distance ($x_f^{*}=2x_m^*$). In contrast, when $\tau < \tau_r$, the maximum power is achieved when the feedback site is set at a lower value. As the $\tau$ increases, the maximum average power decreases. In the limit of a long $\tau$, the highest efficiency as well extractable work is attained when $x_f$ is located at $2x_m$, regardless of the level of entropic control. As the dominance of entropic control increases, the extractable work and efficiency in the fully relaxed state decrease due to higher information loss during relaxation.
Authors: Paolo G. Radaelli, Gautam Gurung
We present a formalism based on colour symmetry to analyse the momentum-space spin textures of non-collinear antiferromagnets. We show that, out of the spin textures allowed by the magnetic point group, \textcolor{\altcolor} {one can extract a component that is invariant by general rotations in spin space, and can exist in the absence of spin-orbit coupling, in complete analogy to spin textures in altermagnets}. We demonstrate this approach in the case of three complex, non-collinear magnets, Mn$_3$Ir(Ge,Si), Pb$_2$MnO$_4$ and Mn$_3$GaN. For Mn$_3$GaN, we also show that the predictions of colour-symmetry analysis are consistent with density functional theory calculations performed on the same system both with and without spin-orbit coupling.
Authors: Balázs Nagyfalusi, László Szunyogh, Krisztián Palotás
An ab initio scheme based on the Kubo-Greenwood linear response theory of exchange torque correlation is presented to calculate intrinsic Gilbert damping parameters in magnets of reduced dimensions. The method implemented into the real-space Korringa-Kohn-Rostoker (RS-KKR) Greens' function framework enables to obtain diagonal elements of the atomic-site-dependent on-site and non-local Gilbert damping tensor. Going from the 3D bulk and surfaces of iron and cobalt ferromagnets addressed in our previous work [Phys. Rev. B 109, 094417 (2024)], in the present paper monolayers of Fe and Co on (001)- and (111)-oriented Cu, Ag, and Au substrates are studied, and particularly the substrate-dependent trends are compared. Furthermore, the Gilbert damping parameters are calculated for Fe and Co adatoms and dimers on (001)-oriented substrates. It is investigated how the damping parameter of single adatoms depends on their vertical position. This dependence is quantified in relation to the adatoms' density of states at the Fermi energy showing a non-monotonic behavior. By rotating the spin moment of the adatoms and collinear magnetic dimers, an anisotropic behavior of the damping is revealed. Finally, a significant, three- to ten-times increase of the on-site Gilbert damping is found in antiferromagnetic dimers in comparison to the ferromagnetic ones, whilst the inter-site damping is even more enhanced.
Authors: Huan Wang, Shangguo Zhu, Yun Long, Mingbo Pu, Xiangang Luo
Ultracold atoms, typically manipulated by scalar beams with uniform polarization, have propelled advances in quantum simulation, computation, and metrology. Yet, vector beams (VBs) -- structured light with spatially varying polarization -- remain unexplored in this context, despite their enhanced tunability and broad optical applications. Here, we demonstrate a novel scheme to generate synthetic gauge fields in ultracold atoms via VB-mediated coupling of internal states. This approach enables angular stripe phases across an expanded parameter range, achieving a three-order-of-magnitude enhancement in the phase diagram and facilitating experimental observation. We further present an all-optical method to create topologically nontrivial giant skyrmions in spin space, with tunable topology governed by VB parameters. Our findings establish VBs as powerful tools for quantum control and the exploration of exotic quantum states and phases.
Authors: Taiki Sato, Hiroaki Ishizuka
Using a microscopic model, we show that the electron-electron interaction of flat bands deviates significantly from the Coulomb interaction. In particular, we find that large-momentum scattering is enhanced at $\theta\lesssim4^\circ$, with a non-monotonic momentum dependence appearing near the magic angle. For $\theta \gtrsim 1.2^\circ$, the enhanced large-momentum scattering can be attributed to the compact Wannier function. On the other hand, for $\theta\lesssim1.2^\circ$, the nonmonotonic momentum dependence of the interaction matrix cannot be explained by a simple Wannier orbital, indicating a nontrivial modification to the el-el interaction. Notably, the range of angles $\theta$ where the large-momentum scattering is enhanced differs from the magic angles at which nearly-flat bands emerge, suggesting that the angle dependence of material properties provides information about the effect of interaction. The results highlight unusual features of the interaction in moiré graphene.
Authors: Daan Verraes, Tom Braeckevelt, Nick Bultinck, Veronique Van Speybroeck
We conduct first-principles simulations of pressurized La$_3$Ni$_2$O$_7$, a material in which a recent series of experiments has found signs of high-temperature superconductivity. In the pressure range where superconductivity is observed, we find a significant increase in the Hubbard U parameter (i.e. the strength of on-site repulsion) for the maximally localized Wannier states comprising the density functional theory (DFT) bands crossing the Fermi energy. We attribute this increase in U to reduced screening by the nearby La 5d bands - an effect that is sensitive to the pressure-driven crystal structure. Our results therefore indicate that the superconducting region in the La$_3$Ni$_2$O$_7$ phase diagram coincides with a region of enhanced electronic correlations. Ab initio molecular dynamics simulations extend these trends to finite temperatures, providing insights into the experimentally observed transition lines. Finally, we explore intrinsic chemical pressure using DFT simulations of Ac$_3$Ni$_2$O$_7$.
Authors: Thomas Rocke, James Kermode
The problem of constructing a dataset for MLIP development which gives the maximum quality in the minimum amount of compute time is complex, and can be approached in a number of ways. We introduce a ``Bayesian selection" approach for selecting from a candidate set of structures, and compare the effectiveness of this method against other common approaches in the task of constructing ideal datasets targeting Silicon surface energies. We show that the Bayesian selection method performs much better than Simple Random Sampling at this task (for example, the error on the (100) surface energy is 4.3x lower in the low data regime), and is competitive with a variety of existing selection methods, using ACE and MACE features.
Authors: L. L. Lage, A. B. Félix, S. dos A. Sousa-Júnior, A. Latgé, Tarik P. Cysne
We study the spectral properties and local topology of the Kane-Mele-Rashba model on a Sierpinski Carpet (SC) fractal, constructed from a rectangular flake with an underlying honeycomb arrangement and open boundary conditions. When the system parameters correspond to a topologically trivial phase, the energy spectrum is characterized solely by bulk states that are not significantly modified by the system's fractality. For parameters corresponding to the quantum spin Hall insulator (QSHI) phase, in addition to bulk states, the energy spectrum exhibits in-gap topological states that are strongly influenced by the fractal geometry. As the fractal generation increases, the in-gap topological states acquire a staircase profile, which translates into sharp peaks in the density of states. We also show that both the QSHI and the trivial phase exhibit a large gap in the valence-projected spin spectrum, allowing the use of the local spin Chern marker (LSCM) to index the local topology of the system. Fractality does not affect this gap, allowing the application of LSCM to higher fractal generations. Our results explore the LSCM versatility, showing its potential to access local topology in complex geometries such as fractal systems.
Authors: Grzegorz Centała, Jarosław W. Kłos
This study investigates magneto-rotational coupling as a distinct contribution to magnetoelastic interactions, which can be influenced by magnetic anisotropy. We determine magneto-rotational coupling coefficients that incorporate the shape anisotropy of a magnetic nanoelement (strip) and demonstrate that this type of coupling can be modified through geometric adjustments. Furthermore, we analyze the magneto-rotational contribution to the magnetoelastic field in a ferromagnetic strip embedded in a nonmagnetic substrate. Both Rayleigh and Love waves are considered sources of the magnetoelastic field, and we examine how the strength of the magneto-rotational coupling varies with the direction of the magnetization, and the aspect ratio of the strip cross-section. We analyze the changes of the magneto-rotational contribution to the magnetoelastic field with an increasing thickness-to-width ratio, assuming a fixed magnetization direction corresponding to the strongest magnetoelastic coupling. For Love wave, the contribution of the out-of-plane component increases monotonically, while that of the in-plane component decreases monotonically. In the case of the Rayleigh wave, only the out-of-plane component contributes, and it approaches zero as the cross-section becomes square. These findings enhance the understanding of magneto-rotational coupling in magnonic nanostructures.
Authors: John C. Sunil, Richard A. Blythe, Martin R. Evans, Satya N. Majumdar
We consider a discrete-time continuous-space random walk, with a symmetric jump distribution, under stochastic resetting. Associated with the random walker are cost functions for jumps and resets, and we calculate the distribution of the total cost for the random walker up to the first passage to the target. By using the backward master equation approach we demonstrate that the distribution of the total cost up to the first passage to the target can be reduced to a Wiener-Hopf integral equation. The resulting integral equation can be exactly solved (in Laplace space) for arbitrary cost functions for the jump and selected functions for the reset cost. We show that the large cost behaviour is dominated by resetting or the jump distribution according to the choice of the jump distribution. In the important case of a Laplace jump distribution, which corresponds to run-and-tumble particle dynamics, and linear costs for jumps and resetting, the Wiener-Hopf equation simplifies to a differential equation which can easily be solved.
Authors: Yitao Sun, Marcel Niedermeier, Tiago V. C. Antão, Adolfo O. Fumega, Jose L. Lado
Moiré and super-moiré materials provide exceptional platforms to engineer exotic correlated quantum matter. The vast number of sites required to model moiré systems in real space remains a formidable challenge due to the immense computational resources required. Super-moiré materials push this requirement to the limit, where millions or even billions of sites need to be considered, a requirement beyond the capabilities of conventional methods for interacting systems. Here, we establish a methodology that allows solving correlated states in systems reaching a billion sites, that exploits tensor-network representations of real-space Hamiltonians and self-consistent real-space mean-field equations. Our method combines a tensor-network kernel polynomial method with quantics tensor cross interpolation algorithm, enabling us to solve exponentially large models, including those whose single particle Hamiltonian is too large to be stored explicitly. We demonstrate our methodology with super-moiré systems featuring spatially modulated hoppings, many-body interactions and domain walls, showing that it allows access to self-consistent symmetry broken states and spectral functions of real-space models reaching a billion sites. Our methodology provides a strategy to solve exceptionally large interacting problems, providing a widely applicable strategy to compute correlated super-moiré quantum matter.
Authors: Joshua Althüser, Götz S. Uhrig
We numerically study the collective excitations present in isotropic superconductors including a screened Coulomb interaction. By varying the screening strength, we analyze its impact on the system. We use a formulation of the effective phonon-mediated interaction between electrons that depends on the energy transfer between particles, rather than being a constant in a small energy shell around the Fermi edge. This justifies considering also rather large attractive interactions. We compute the system's Green's functions using the iterated equations of motion (iEoM) approach, which ultimately enables a quantitative analysis of collective excitations. For weak couplings, we identify the well-known amplitude (Higgs) mode at the two-particle continuum's lower edge and the phase (Anderson-Bogoliubov) mode at $\omega = 0$ for a neutral system, which shifts to higher energies as the Coulomb interaction is switched on. As the phononic coupling is increased, the Higgs mode separates from the continuum, and additional phase and amplitude modes appear, persisting even in the presence Coulomb interactions.
Authors: Liam L.H. Lau, Andreas Gleis, Daniel Kaplan, Premala Chandra, Piers Coleman
We examine the interplay between electron correlations and phonons in an Anderson-Holstein impurity model with an Einstein phonon. When the phonons are slow compared to charge fluctuations (frequency $\omega_0 \ll U/2$, the onsite Coulomb scale $U/2$), we demonstrate analytically that the expected phonon-mediated reduction of interactions is completely suppressed, even in the strong coupling regime. This suppression arises from the oscillator's inability to respond to rapid charge fluctuations, manifested as a compensation effect between the polaronic cloud and the excited-state phonons associated with valence fluctuations. We identify a novel frozen mixed valence phase, above a threshold dimensionless electron-phonon coupling $\alpha^*$ when the phonons are slow, where the static phonon cloud locks the impurity into specific valence configurations, potentially explaining the puzzling coexistence of mixed valence behavior and insulating properties in materials like rust. Conversely, when the phonon is fast ($\omega_0 \gtrsim U/2$), the system exhibits conventional polaronic behavior with renormalized onsite interactions effectively $U_{\text{eff}}$ due to phonon mediated attraction, with additional satellite features in the local spectral function due to phonon excitations. Using numerical renormalization group (NRG) calculations, a fully dynamic renormalization technique, we confirm these behaviors in both regimes. These findings have important implications for strongly correlated systems where phonon energy scales may be comparable to the Coulomb scale, such as in twisted bilayer graphene, necessitating careful consideration of interaction renormalizations in theoretical models.
Authors: Minsu Yi, Panayotis Benetatos
We introduce a simple theoretical model, the Freely Jointed Chain with quenched hinges (qFJC), which captures the quenched disorder in the local bending stiffness of the polymer. In this article, we analyze the tensile elasticity of the qFJC in the Gibbs (fixed-force) ensemble. For finite-size systems, we obtain a recurrence relation of the exact free energy, which allows us to calculate the exact force-extension relation numerically for an arbitrary size of the system. In the thermodynamic limit, when $L({\rm contour \;length})\gg L_p({\rm persistence \;length})$, we obtain a framework to deal with quenched disorder in the polymer configuration. This allows us to obtain the response function for the discrete and continuous qFJC in the thermodynamic limit. It turns out that the extension of the continuous qFJC can be cast in a simple form. Furthermore, we have applied our analysis to rod-coil multiblock copolymers.
Authors: Alireza Akbari, Peter Thalmeier
The surface tunneling microscope (STM) method probes the itinerant conduction electron spectrum which is influenced by the presence of collective order parameters. It may in fact be used as a tool to obtain important information about their microscopic nature, for example the gap symmetry in unconventional superconductors. Surprisingly it has been found that the STM spectrum can also identify magnetic order of completely localised electrons, e.g., incommensurate helical structure of 4f electron moments, as observed in the compound GdRu$_2$Si$_2$. This is due to the fact that the exchange coupling of conduction states to the localised subsystem reconstructs the itinerant bands which then leaves an imprint on the STM spectrum. We develop a theory based on this idea that shows firstly the appearance of STM satellite peaks at the wave vector of localised moment helical order for the pure surface. Secondly we derive the quasiparticle interference spectrum in Born approximation due to the presence of surface impurities which contains information on the reconstruction process of itinerant states caused by the localised helical order. Furthermore we show that within full $t$-matrix approach impurity bound states are also influenced by the exchange coupling to helical magnetic order.
Authors: Tigran V. Shahbazyan
We develop a non-Lorentzian analytical model for quantum emitters (QE) resonantly coupled to localized surface plasmons (LSP) in metal-dielectric structures. Using the explicit form of LSP Green function, we derive non-Lorentzian version of semiclassical Maxwell-Bloch equations that describe LSPs directly in terms of metal complex dielectric function rather than via Lorentzian resonances. For a single QE resonantly coupled to an LSP, we obtain an analytical expression for effective optical polarizability of the hybrid system which, in the Lorentzian approximation, recovers the results of the classical coupled oscillators model. We demonstrate that non-Lorentzian effects originating from temporal dispersion of the metal dielectric function affect significantly the optical spectra as the hybrid system transitions to the strong coupling regime. Specifically, in contrast to results of Lorentzian models, the main spectral weight in the system scattering spectra is shifted toward the lower energy polaritonic band, consistent with the experiment.
Authors: Dallas R. Trinkle (Materials Science and Engineering, University of Illinois, Urbana-Champaign)
We compute the phase separation of the immiscible liquid alloy Fe-Cu-Ni. Our computational approach uses a virtual semigrand canonical Widom approach to determine differences in excess chemical potentials between different species. Using an embedded atom potential for Fe-Cu-Ni, we simulate liquid states over a range of compositions and temperatures. This raw data is then fit to Redlich-Kister polynomials for the Gibbs free energy with a simple temperature dependence. Using the analytic form, we can determine the phase diagram for the ternary liquid, compute the miscibility gap and spinodal decomposition as a function of temperature for this EAM potential. In addition, we compute density as a function of composition and temperature, and predict pair correlation functions. We use static structure factors to estimate the second derivative of the Gibbs free energy (the $S^0$ method) and compare with our fit Gibbs free energy. Finally, using a nonequilibrium Hamiltonian integration method, we separately compute absolute Gibbs free energies for the pure liquid states; this shows that our endpoints are accurate to within 1 meV for our ternary Gibbs free energy, as well as the absolute Gibbs free energy for the ternary liquid.
Authors: A. Shekhter, M. K. Chan R. D. McDonald, N. Harrison
According to Zaanen's interpretation of Homes' empirical law~[Zaanen, {\it Nature} {\bf 430}, 512 (2004)], the superconducting transition temperatures in the cuprates are high because their metallic states are as viscous as quantum mechanics permits. Here, we show that Homes' law in fact implies three key points: (i) the resistivity is linear in temperature in the normal state near the transition temperature; (ii) the dimensionless coefficient of proportionality of the relaxation rate with temperature is of order unity -- the so-called universal Planckian relaxation rate; and (iii) the logarithmically broad applicability of this law arises from an unusually wide range of effective masses throughout the cuprate phase diagram. In fact, a universal Planckian relaxation rate implies Homes' law only if the mechanism of mass renormalization is independent of the Planckian relaxation.
Authors: Ivan Abilio, Krisztián Palotás
The revised Chen's derivative rule for electron tunneling is implemented to enable computationally efficient first-principles-based calculations of the differential conductance dI/dV for scanning tunneling spectroscopy (STS) simulations. The probing tip is included through a single tip apex atom, and its electronic structure can be modeled as a linear combination of electron orbitals of various symmetries, or can be directly transferred from first-principles electronic structure calculations. By taking pristine and boron- or nitrogen-doped graphene sheets as sample surfaces, the reliability of our implementation is demonstrated by comparing its results to those obtained by the Tersoff-Hamann and Bardeen's electron tunneling models. It is highlighted that the energy-resolved direct and interference contributions to dI/dV arising from the tip's electron orbitals result in a fingerprint of the particular combined surface-tip system. The significant difference between the electron acceptor boron and donor nitrogen dopants in graphene is reflected in their dI/dV fingerprints. The presented theoretical method allows for an unprecedented physical understanding of the electron tunneling process in terms of tip-orbital-resolved energy-dependent dI/dV maps, that is anticipated to be extremely useful for investigating the local electronic properties of novel material surfaces in the future.
Authors: O. Busel, D. Polishchuk, A. Kravets, V. Korenivski
We observe strongly nonlinear spin dynamics in ferro-/antiferro-magnetic multilayers, controlled by the number of bilayers in the system, layer thicknesses, as well as temperature, peaking in magnitude near the Néel point of the antiferromagnetic layers just above room temperature. Well above the Néel transition, the individual ferromagnetic layers are exchange decoupled and resonate independently. As the temperature is lowered toward the Néel point, the ferromagnetic proximity effect through the thin antiferromagnetic spacers transforms the system into a weakly coupled macrospin chain along the film normal, which exhibits pronounced standing spin-wave resonance modes, comparable in intensity to the uniform resonance in the ferromagnetic layers. These findings are supported by our micromagnetic simulations showing clear spin-wave profiles with precessional phase lag along the macrospin chain. Well below the Néel transition, the FeMn layers order strongly antiferromagnetically and exchange-pin the ferromagnetic layers to effectively make the multilayer one macrospin. The appearance and intensity of the high-frequency spin-wave modes can thus be conveniently controlled by thermal gating the multilayer. The nonlinearity in the microwave response of the demonstrated material can approach 100\%, large compared to nonlinear materials used in e.g. optics, with second-harmonic generation often at the single percentage level.
Authors: Keita Kishigi, Yasumasa Hasegawa
Two-dimensional massless Dirac fermions exhibit Dirac cones, which are classified into three types: type-I, type-II, and type-III. In both type-I and type-II cones, the energy dispersion is linear in all momentum directions. Type-I cones are characterized by a non-overtilted structure, where the Dirac point serves as a local minimum (maximum) for the upper (lower) band. In contrast, type-II cones exhibit overtilted dispersions, leading to the coexistence of electron and hole pockets. At the critical tilt, the linear energy dispersion vanishes in one momentum direction, corresponding to a type-III Dirac cone. We further define a special case, termed the "narrow-sense" type-III cone, where not only the linear term but also quadratic and higher-order terms vanish, resulting in a completely flat dispersion along one direction. In this work, we numerically investigate the temperature ($T$) -dependence of the electronic specific heat ($C$), as the Dirac cone is continuously tilted from type-I to narrow-sense type-III. A model with particle-hole symmetry is employed to ensure that the chemical potential ($\mu$) remains temperature independent. Our results reveal a notable crossover in $C$ near narrow-sense type-III, where $C$ changes from $C \propto T^{2}$ below the crossover temperature ($T_{\rm co}$) to $C \propto T^{\frac{1}{2}}$ above $T_{\rm co}$. This crossover is attributed to the energy-dependent structure of the density of states. The present findings suggest a feasible approach for experimentally probing the degree of Dirac cone tilting near the narrow-sense type-III limit.
Authors: Jonathan Schirmer, Enrico Rossi
In this work, we obtain the expression, within the linear response approximation, that allows the direct calculation of the superfluid weight for strongly inhomogeneous superconductors. Using this expression, we find that, in general, the correction to the superfluid weight due to the response of the superconductor's pairing potential to the perturbing vector potential is important in superconductors with a strongly inhomogeneous pairing potential. We consider two exemplary cases: the case when strong inhomogeneities in the pairing potential are induced by a periodic potential, and the case when superconducting vortices are induced by an external magnetic field. For both cases we show that the correction to the superfluid weight due to the response of the paring potential to the perturbing vector potential can be significant, it must be included to obtain quantitatively correct results, and that for the case when vortices are present the expression of the superfluid weight that does not include such correction returns qualitatively wrong results.
Authors: Nikolay V. Gnezdilov, Rufus Boyack
Migdal-Eliashberg theory (METh) of boson-mediated superconductivity contains a $\sqrt{\lambda}$ divergence in the critical temperature $T_c$ at strong electron-boson coupling $\lambda$. In conventional METh, the strong-coupling regime can be accessed only in the limit that $\lambda_E = \lambda \, \omega_D/\varepsilon_F\ll1$, where $\omega_D$ is the Debye frequency and $\varepsilon_F$ is the Fermi energy. Here we go beyond this restriction in the context of the two-dimensional Yukawa-SYK (Y-SYK) model, which is solvable for arbitrary values of $\lambda_E$. We find that $T_c\approx 0.18 \,\omega_D \sqrt{\lambda}$ for large $\lambda$, provided $\lambda_E$ remains small, and crosses over to a universal value of $T_c \approx 0.04\, \varepsilon_F$ for large $\lambda_E$. The saturation of $T_c$ is due to a self-consistent account of the boson dynamics for large $\lambda_E$ and is arguably qualitatively valid beyond the Y-SYK framework. In particular, depending on the value of $\lambda$, this self-consistent approach leads to pairing that describes multiple classes of quantum critical electronic systems. These results demonstrate how the $\sqrt{\lambda}$ growth of $T_c$ in METh saturates to a universal value independent of $\lambda$ and $\omega_D$, providing an upper bound on the critical temperature at strong electron-boson coupling.
Authors: Sondre Duna Lundemo, Flavio S. Nogueira, Asle Sudbø
The term altermagnetism has recently been introduced to describe the Néel order of a class of materials whose magnetic sublattices are neither related by translation nor inversion. While these materials arguably have large technological potential, little effort has been devoted to studying the universal distinction of this phase of matter compared to collinear antiferromagnetism. Employing a recently proposed minimal microscopic model, we explicitly derive a nonlinear sigma model describing long-wavelength fluctuations of the staggered magnetization in this system, including quantum effects to leading order. The term that distinguishes the altermagnetic nonlinear sigma model from its antiferromagnetic counterpart is an interaction term that derives directly from the Berry phase of the microscopic spin degrees of freedom. Its effects on the one-loop renormalization group flow in $d=2+1$ dimensions are examined. Extending the theory to describe the fermionic excitations of the metallic altermagnet, we find an effective low-energy model of $d$-wave spin-split Dirac fermions interacting with the magnetic fluctuations. Using a Dyson-Schwinger approach, we derive the many-body effects on the dynamical critical scaling due to the competition between the long-range Coulomb interaction and the fluctuations of the staggered magnetization.
Authors: Huaiyu Wang, Vladimir Stoica, Cheng Dai, Marek Paściak, Sujit Das, Tiannan Yang, Mauro A. P. Gonçalves, Jiri Kulda, Margaret R. McCarter, Anudeep Mangu, Yue Cao, Hari Padma, Utkarsh Saha, Diling Zhu, Takahiro Sato, Sanghoon Song, Mathias Hoffmann, Patrick Kramer, Silke Nelson, Yanwen Sun, Quynh Nguyen, Zhan Zhang, Ramamoorthy Ramesh, Lane Martin, Aaron M. Lindenberg, Long-Qing Chen, John W. Freeland, Jirka Hlinka, Venkatraman Gopalan, Haidan Wen
Unraveling collective modes arising from coupled degrees of freedom is crucial for understanding complex interactions in solids and developing new functionalities. Unique collective behaviors emerge when two degrees of freedom, ordered on distinct length scales, interact. Polar skyrmions, three-dimensional electric polarization textures in ferroelectric superlattices, disrupt the lattice continuity at the nanometer scale with nontrivial topology, leading to previously unexplored collective modes. Here, using terahertz-field excitation and femtosecond x-ray diffraction, we discovered subterahertz collective modes, dubbed 'skyrons', which appear as swirling patterns of atomic displacements functioning as atomic-scale gearsets. Momentum-resolved time-domain measurements of diffuse scattering revealed an avoided crossing in the dispersion relation of skyrons. We further demonstrated that the amplitude and dispersion of skyrons can be controlled by sample temperature and electric-field bias. Atomistic simulations and dynamical phase-field modeling provided microscopic insights into the three-dimensional crystallographic and polarization dynamics. The discovery of skyrons and their coupling with terahertz fields opens avenues for ultrafast control of topological polar structures.
Authors: Milena Horvath, Alvise Bastianello, Sudipta Dhar, Rebekka Koch, Yanliang Guo, Jean-Sébastien Caux, Manuele Landini, Hanns-Christoph Nägerl
Bethe strings are bound states of constituent particles in a variety of interacting many-body one-dimensional (1D) integrable quantum models relevant to magnetism, nanophysics, cold atoms and beyond. As emergent fundamental excitations, they are predicted to collectively reshape observable equilibrium and dynamical properties. Small individual Bethe strings have recently been observed in quantum magnets and superconducting qubits. However, creating states featuring intermixtures of many, including large, strings remains an outstanding experimental challenge. Here, using nearly integrable ultracold Bose gases, we realize such intermixtures of Bethe strings out of equilibrium, by dynamically tuning interactions from repulsive to attractive. We measure the average binding energy of the strings, revealing the presence of bound states of more than six particles. We find further evidence for them in the momentum distribution and in Tan's contact, connected to the correlated density. Our data quantitatively agree with predictions from generalized hydrodynamics (GHD). Manipulating intermixtures of Bethe strings opens new avenues for understanding quantum coherence, nonlinear dynamics and thermalization in strongly-interacting 1D systems.
Authors: Shun-Li Shang, Nigel L. E. Hew, Rushi Gong, Cillian Cockrell, Paul A. Bingham, Xiaofeng Guo, Jingjing Li, Qi-Jun Hong, Zi-Kui Liu
We have recently developed a breakthrough methodology for rapidly computing entropy in both solids and liquids by integrating a multiscale entropy approach (known as zentropy theory) with molecular dynamics (MD) simulations. This approach enables entropy estimation from a single MD trajectory by analyzing the probabilities of local structural configurations and atomic distributions, effectively addressing the long-standing challenge of capturing configurational entropy. Here, we demonstrate the power of this method by predicting entropies, enthalpies, and melting points for 25 binary and ternary chlorite- and fluoride-based molten salts using ab initio MD (AIMD) simulations. The strong agreement between our predictions and experimental data underscores the potential of this approach to transform computational thermodynamics, offering accurate, efficient, and direct predictions of thermodynamic properties across both solid and liquid phases.
Authors: Naohiro Matsumoto, Ryusuke Endo, Mitsuharu Uemoto, Tomoya Ono
Two processes have been proposed to fabricate graphene/NiFe alloy interfaces for tunneling magnetoresistance devices. One is the transfer of graphene and the other is the evaporation of alloys onto graphene. The formation energy of a NiFe alloy substrate and the adsorption energy of graphene on the NiFe alloy substrate are investigated by a density functional theory calculations to reveal the difference in the atomic structure of the interface between the two processes. It is found that Ni-rich surfaces are preferable for the bare substrate, whereas Fe surfaces are stable for the graphene adsorbed on the substrate. This result indicates that the composition ratio of the surface layer depends on the interface fabrication process.
Authors: Arkadiusz Kobus, Xinwei Li, Mariusz Gajda, Li You, Emilia Witkowska
We propose a multisetting protocol for the detection of two-body Bell correlations, and apply it to spin-nematic squeezed states realized in $f$ pairs of SU(2) subsystems within spin-$f$ atomic Bose-Einstein condensates. Experimental data for $f=1$, alongside with numerical simulations using the truncated Wigner method for $f=1,\,2,\,3$, demonstrate the effectiveness of the proposed protocol. Our findings extend the reach of multisetting Bell tests in ultracold atomic system, paving the way for extended quantum information processing in high-spin ensemble platforms.
Authors: Simanta Lahkar, Valeria Bragaglia, Behnaz Bagheri, Donato Francesco Falcone, Matteo Galetta, Marilyne Sousa, Aida Todri-Sanial
Resistive random access memories (ReRAMs) with a bilayer TaOx/HfO2 stack structure have shown unique multi-level resistive switching capabilities. However, the physical processes governing their behavior, and specifically the atomistic mechanisms of forming, remain poorly understood. In this work, we present a detailed analysis of the forming mechanism at the atomic level using molecular dynamics (MD) simulations. An extended charge equilibration scheme, based on a combination of the charge transfer ionic potential (CTIP) formalism and the electrochemical dynamics with implicit degrees of freedom (EChemDID) method, is employed to model the localized effects of applied voltage. Our simulations reveal that tantalum ions exhibit the highest displacement under applied voltage, followed by hafnium ions, while oxygen ions respond only minimally. This results in the formation of a tantalum-depleted, oxygen-rich zone near the positive top electrode (anode), and the clustering of oxygen vacancies near the negative bottom electrode (cathode), where the conductive filament nucleates. This ionic segregation partially shields the bulk dielectric from the applied electric field, hindering further migration of ions in the vertical direction. We find that a minimum threshold voltage is required to initiate vacancy clustering. Filament growth proceeds through a localized mechanism, driven by thermally activated generation of oxygen vacancy defects, which are stabilized near the edge of the nucleated filament at the cathode.
Authors: Axel van de Walle
We propose an extension of Schrödinger's equation that incorporates the macroscopic measurement-induced wavefunction collapse phenomenon. Our approach relies on a hybrid between Bohm-de Broglie pilot-wave and objective collapse theories. The Bohmian particle is guided by the wavefunction and, conversely, the wavefunction gradually localizes towards the particle's position. As long as the particle can visit any state, as in a typical microscopic system, the localization effect does not favor any particular quantum state and, on average, the usual Schrödinger-like time evolution results. However, when the wavefunction develops spatially well-separated lobes, as would happen during a macroscopic measurement, the Bohmian particle can remain trapped in one lobe, and the wavefunction eventually localizes there. The end result, in macroscopic systems, is a wavefunction collapse that is consistent with Born's rule. We illustrate the theory with a simple double-slit experiment simulation.
Authors: Yiming Zhao, Yazhuang Miao, Yihang Xing, Tianhui Qiu, Hongyang Ma, Xiaolong Zhao
Non-Abelian gauge offers a powerful route to engineer novel topological phenomena. Here, we systematically investigate a two-dimensional (2D) non-Hermitian Hatano-Nelson model incorporating SU(2) non-Abelian gauge, demonstrating the emergence of Hopf-link bulk braiding topology in the complex energy spectrum solely with x-direction nearest-neighbor couplings. Because of the limitations of exceptional point (EP) topology in fully capturing the rich non-Hermitian skin effect (NHSE) under non-Abelian influence, we introduce a novel polarization parameter derived from the generalized Brillouin zone (GBZ). This parameter quantitatively discerns left-, right-, and notably, bipolar skin modes, with its accuracy corroborated by directly encoding real-space eigenstate. Our findings reveal that non-Abelian gauge provides unprecedented influence over NHSE, compared with Abelian gauge and without gauge cases. Furthermore, we uncover unique characteristics of zero-imaginary-energy eigenstates at these topological boundaries, including pronounced degeneracy and bipolar localization which is unaffected by size effects, investigated via dynamical evolution and Inverse Participation Ratio (IPR). This work establishes a new paradigm for synthesizing and manipulating non-Hermitian topological phases driven by non-Abelian structures, opening avenues for topological engineering and holding promise for experimental realization in synthetic dimensional platforms.
Authors: Alessio Zaccone
The thermal properties of solids under nanoscale confinement are currently not understood at the atomic level. Recent numerical studies have highlighted the presence of a minimum in the thermal conductivity as a function of thickness for ultrathin films at a thickness about 1-2 nm, which cannot be described by existing theories. We develop a theoretical description of thin films which predicts a new physical law for heat transfer at the nanoscale. In particular, due to the strong redistribution of phonon momentum states in reciprocal space (with a transition from a spherical Debye surface to a different homotopy group $\mathbb{Z}$ at strong confinement), the low-energy phonon density of states no longer follows Debye's law but rather a cubic law with frequency, which then crosses over to Debye's law at a crossover frequency proportional to the average speed of sound of the material and inversely proportional to the film thickness. Concomitantly, this implies that the phonon population becomes dominated by low-energy phonons as confinement increases, which then leads to a higher thermal conductivity under extreme confinement. The theory is able to reproduce the thermal conductivity minimum in recent molecular simulations data for ultrathin silicon and provides useful guidelines as to tune the minimum position based on the mechanical properties of the material.
Authors: Tzu-chen Liu, Adolfo Salgado-Casanova, So Yubuchi, Bianca Baldassarri, Muratahan Aykol, Jun Yoshida, Hisatsugu Yamasaki, Yizhou Zhu, Steven B. Torrisi, Christopher Wolverton
Newly designed Li-ion battery cathode materials with high capacity and greater flexibility in chemical composition will be critical for the growing electric vehicles market. Cathode structures with cation disorder were once considered suboptimal, but recent demonstrations have highlighted their potential in Li$_{1+x}$M$_{1-x}$O$_{2}$ chemistries with a wide range of metal combinations M. By relaxing the strict requirements of maintaining ordered Li diffusion pathways, countless multi-metal compositions in LiMO$_2$ may become viable, aiding the quest for high-capacity cobalt-free cathodes. A challenge presented by this freedom in composition space is designing compositions which possess specific, tailored types of both long- and short-range orderings, which can ensure both phase stability and Li diffusion. However, the combinatorial complexity associated with local cation environments impedes the development of general design guidelines for favorable orderings. Here we propose ordering design frameworks from computational ordering descriptors, which in tandem with low-cost heuristics and elemental statistics can be used to simultaneously achieve compositions that possess favorable phase stability as well as configurations amenable to Li diffusion. Utilizing this computational framework, validated through multiple successful synthesis and characterization experiments, we not only demonstrate the design of LiCr$_{0.75}$Fe$_{0.25}$O$_2$, showcasing initial charge capacity of 234 mAhg$^{-1}$ and 320 mAhg$^{-1}$ in its 20% Li-excess variant Li$_{1.2}$Cr$_{0.6}$Fe$_{0.2}$O$_2$, but also present the elemental ordering statistics for 32 elements, informed by one of the most extensive first-principles studies of ordering tendencies known to us.
Authors: Tao Liu, Juhao Wu, Mark Ying
By utilizing a unitary transformation, we derive the necessary and sufficient conditions for the degeneracy between the even- and odd-parity energy states of the spin-boson model (SBM). Employing the Rayleigh quotient of matrix algebra, we rigorously prove that the ground state energy of the SBM is lower than the systems lowest possible degenerate energy and possesses a definite parity. Based on the necessary and sufficient conditions for parity breaking, we provide an analytical expression for the parity-breaking critical value, which is closely related to the expansion order and computational accuracy. This expression reproduces the SBM phase diagram obtained by quantum Monte Carlo (QMC) and logarithmic discretization numerical renormalization group (NRG) methods. However, this phase diagram does not characterize the ground state of the system.
Authors: Vittorio Erba, Nathan Malo Kupferschmid, Rodrigo Pérez Ortiz, Lenka Zdeborová
In this paper we introduce and study the Maximum-Average Subtensor ($p$-MAS) problem, in which one wants to find a subtensor of size $k$ of a given random tensor of size $N$, both of order $p$, with maximum sum of entries. We are motivated by recent work on the matrix case of the problem in which several equilibrium and non-equilibrium properties have been characterized analytically in the asymptotic regime $1 \ll k \ll N$, and a puzzling phenomenon was observed involving the coexistence of a clustered equilibrium phase and an efficient algorithm which produces submatrices in this phase. Here we extend previous results on equilibrium and algorithmic properties for the matrix case to the tensor case. We show that the tensor case has a similar equilibrium phase diagram as the matrix case, and an overall similar phenomenology for the considered algorithms. Additionally, we consider out-of-equilibrium landscape properties using Overlap Gap Properties and Franz-Parisi analysis, and discuss the implications or lack-thereof for average-case algorithmic hardness.
Authors: Pablo San-Jose, Elsa Prada
We propose a novel type of superconducting spin qubit, dubbed solitonic Andreev spin qubit (SASQ), that combines features of Andreev spin qubits and geometric spin qubits. The two SASQ states are the degenerate spin orientations of an Andreev bound state trapped in a circular Josephson junction with a Corbino disk geometry, created on a 2DEG. The junction is subjected to a weak magnetic flux that induces a fluxoid mismatch between the inner disk and outer ring superconductors. The fluxoid mismatch produces a cancellation of the induced pairing that traps unconventional spin-degenerate Andreev bound states analogous to Jackiw-Rebbi soliton states. They are localized at a position around the junction that can be controlled by changing the superconducting phase difference. Moving a soliton state with a phase bias induces a holonomic rotation of its spin, by virtue of the spin-orbit coupling in the 2DEG. The holonomic qubit trajectories can densely cover the full Bloch sphere as the soliton state revolves around the junction. Effects of non-holonomic (dynamic) qubit drift are also analyzed.
Authors: Jiaju Zhang, Arash Jafarizadeh, M. A. Rajabpour
In this paper, we employ the bootstrap method, a technique that relies on consistency relations instead of direct diagonalization, to determine the expectation values in quantum many-body systems. We then use these values to assess the entanglement content of the system. Our work extends the bootstrap approach to quantum many-body systems, rather than single-body or few-body systems, concentrating on the well-known Lipkin-Meshkov-Glick (LMG) model with both transverse and longitudinal external magnetic fields. In the bootstrap method we solve the LMG model with up to 16 sites. Unlike previous studies that have focused mainly on ground-state properties, our methodology allows for the calculation of a broad range of properties, including energy spectrum, angular momentum, concurrence, tangle, residual tangle, and quantum Fisher information (QFI), for all eigenstates or a particular sector of the eigenstates, without referring to the explicit wavefunctions of these states. We show that this approach offers not only a new computational methodology but also a comprehensive view of both bipartite and multipartite entanglement properties across the entire spectrum of eigenstates. Specifically, we demonstrate that states typically found in the central region of the spectrum exhibit greater multipartite entanglement, as indicated by larger QFI values, compared to states at the edges of the spectrum. In contrast, concurrence displays the opposite trend. This observed behavior is in line with the monogamy principle governing quantum entanglement.
Authors: Meng-Lin Du, Feng-Kun Guo, Bing Wu
The validity range of the time-honored effective range expansion can be very limited due to the presence of a left-hand cut close to the two-particle threshold. Such a left-hand cut arises in the two-particle interaction involving a light particle exchange with a mass small or slightly heavier than the mass difference of the two particles, identified as a long-range force, a scenario encountered in a broad range of systems. This can hinder a precise extraction of low-energy scattering observables and resonance poles. To address this issue, we propose a new parameterization for the low-energy scattering amplitude that accounts for the left-hand cut. The parameterization is like a Padé approximation but with nonanalytic terms from the left-hand cut and can be regarded as an extension of the effective range expansion. This parameterization is versatile and applicable to a broad range of systems with Yukawa-type interactions -- including particle, hadronic, nuclear, cold atom and quantum gas systems. In particular, it should be invaluable in understanding various near-threshold hadron resonances. As byproducts, we also show that the parameterization can be used to extract the couplings of the exchanged particle to the scattering particles, and derive expressions for amplitude zeros caused by the interplay between the short- and long-range interactions.
Authors: Diego Sier, Lucas Valente, Tiago A. Freitas, Marcelo F. Santos, Carlos H. Monken, Raul Corrêa, Ado Jorio
Recently [PRA 108, L051501 (2023)], it has been shown that in a centrosymmetric cubic system, two-photons from a broadband intense laser field can be converted into a pair of Stokes and anti-Stokes (SaS) entangled photons. While the previous work was based on symmetry arguments, here we present a fully quantum theory for the SaS scattering that properly explains, quantitatively describes, and provides a means to predict its spectral and polarization properties (for diamond). We also explore the possibilities offered by such system, designing an entanglement map based on changes in the light-matter system. In particular, we show how the broadband polarization entanglement, that emerges from the interference between electronic and phononic degrees of freedom in the SaS scattering, depends on parameters such as Stokes-anti-Stokes Raman shift, scattering geometry and laser bandwidth, opening the avenue of exploration of such phenomenon in information processing.
Authors: A. M. Begun, M. N. Chernodub, V. A. Goy, A. V. Molochkov
The XY-plaquette model is the most straightforward lattice realization of a broad class of fractonic field theories that host quasiparticles with restricted mobility. The plaquette interaction appears naturally as a ring-exchange term in the low-energy description of exciton Bose liquids, cold atomic gases, and quantum dimer models. Using first-principle Monte Carlo simulations, we study the phase diagram and the vortex dynamics in the XY-plaquette model on a square lattice in two spatial dimensions. In its minimal formulation, the model contains a ring-exchange plaquette term in two spatial dimensions and a standard XY-link term in the (imaginary) time direction. We show that the phase diagram of the minimal XY-plaquette model possesses two phases: (i) a disordered vortex-dominated phase in which a single percolating vortex trajectory occupies the whole 3d spacetime; (ii) a partially disordered phase in which the vortices become partially immobile, with their worldlines strictly confined to one or several infinite two-dimensional planes. The spatial positions and spatial orientations (along $x$ or $y$ axis) of these vortex domain walls appear to be spontaneous. Individual vortices form a disordered system within each vortex domain wall, so the fractal spacetime dimension of vortex trajectories approaches $D_f = 2$. We argue that the appearance of the vortex walls could be interpreted as a consequence of the spontaneous breaking of a global internal symmetry in the compact XY-plaquette model.
Authors: Christoph Hotter, Arkadiusz Kosior, Helmut Ritsch, Karol Gietka
Due to the inherently probabilistic nature of quantum mechanics, each experimental realization of a dynamical quantum system may yield a different measurement outcome, especially when the system is coupled to an environment that causes dissipation. Although it is in principle possible that some quantum trajectories lead to exotic highly entangled quantum states, the probability of observing these trajectories is usually extremely low. In this work, we show how to maximize the probability of generating highly entangled states, including maximally entangled cat states, in an ensemble of atoms experiencing superradiant decay. To this end, we analyze an effective non-Hermitian Hamiltonian which governs the dynamics between the quantum jumps associated with photon emission. A key result of our study is that, in order to maximally enhance the probability of cat state generation, the initial state needs to be non-classical. This can be achieved e.g. with one-axis twisting in a cavity-QED system.
Authors: Zhuo-Ting Cai, Hai-Dong Li, Wei Chen
Real-to-complex spectral transitions and the associated spontaneous symmetry breaking of eigenstates are central to non-Hermitian physics, yet a comprehensive and universal theory that precisely describes the underlying physical mechanisms for each individual state remains elusive. Here, we resolve the mystery by employing the complex path integral formalism and developing a generalized Gutzwiller trace formula. These methodologies enable us to establish a universal quantum-classical correspondence that precisely links the real or complex nature of individual energy levels to the symmetry properties of their corresponding semiclassical orbits. Specifically, in systems with a general $\eta$-pseudo-Hermitian symmetry, real energy levels are quantized along periodic orbits that preserve the corresponding classical $S_\eta$ symmetry. In contrast, complex conjugate energy levels arise from semiclassical orbits that individually break the $S_\eta$ symmetry but together form $S_\eta$-symmetric pairs. This framework provides a unified explanation for the spectral behaviors in various continuous non-Hermitian models and for the $\mathcal{PT}$ transition in two-level systems. Besides, we demonstrate that the exceptional point is inherently a quantum phenomenon, as it cannot be described by a single classical orbit. Our work uncovers the physical mechanism of non-Hermitian symmetry breaking and introduces a new perspective with broad implications for the control and application of non-Hermitian phenomena.
Authors: Husain Ahmed, Andrea Litvinov, Pauline Guesdon, Etienne Maréchal, John H. Huckans, Benjamin Pasquiou, Bruno Laburthe-Tolra, Martin Robert-de-Saint-Vincent
We demonstrate coherent manipulation of the nuclear degrees of freedom of ultracold ground-state strontium 87 atoms, thus providing a toolkit for fully exploiting the corresponding large Hilbert space as a quantum resource and for quantum simulation experiments with SU(N)-symmetric matter. By controlling the resonance conditions of Raman transitions with a tensor light shift, we can perform rotations within a restricted Hilbert space of two isolated spin states among the 2F+1 = 10 possible states. These manipulations correspond to engineering unitary operations deriving from generators of the SU(N) algebra beyond what can be done by simple spin precession. We present Ramsey interferometers involving an isolated pair of Zeeman states with no measurable decoherence after 3 seconds. We also demonstrate that one can harvest the large spin degrees of freedom as a qudit resource by implementing two interferometer schemes over four states. The first scheme senses in parallel multiple external fields acting on the atoms, and the second scheme simultaneously measures multiple observables of a collective atomic state - including non-commuting ones. Engineering unitary transformations of the large spin driven by other generators than the usual spin-F representation of the SU(2) group offers new possibilities from the point of view of quantum metrology and quantum many-body physics, notably for the quantum simulation of large-spin SU(N)-symmetric quantum magnetism with fermionic alkaline-earth atoms.
Authors: Anne Virkki, Maxim Yurkin
The electromagnetic (EM) scattering by non-symmetric wavelength-scale particles on a planar surface has numerous applications in the remote sensing of planetary bodies, both in planetary and geo-sciences. We conduct numerical simulations of EM scattering by rough polyhedral particles (with 12 or 20 faces) using the discrete-dipole approximation and contrast the results to that of spheres. The particles have permittivities corresponding to common minerals in the microwave regime ($\epsilon_r=4.7 + 0.016$i and $7.8 + 0.09$i), and a size-frequency distribution (SFD) consistent with the observed scattering properties (power-law distribution of size parameters between 0.5 and 8 with an index from $-2.5$ to $-3.5$). The assumed substrate permittivity $2.4 + 0.012$i corresponds to a powdered regolith. We present what roles the particle roundness, permittivity, and SFD for a realistic range of parameters play in the EM scattering properties as a function of incidence angle with a focus on backscattering in microwave-remote-sensing applications. The particle roundness and SFD have a clearly observable effect on the polarimetric properties, while the role of permittivity is relatively minor (in the studied range). Among various backscattering observables, the circular polarization ratio is the least sensitive to the decrease of the upper boundary (down to a size parameter of 3) and the index of the SFD.
Authors: Yuta Suzuki, Tatsunori Taniai, Ryo Igarashi, Kotaro Saito, Naoya Chiba, Yoshitaka Ushiku, Kanta Ono
Understanding structure-property relationships is an essential yet challenging aspect of materials discovery and development. To facilitate this process, recent studies in materials informatics have sought latent embedding spaces of crystal structures to capture their similarities based on properties and functionalities. However, abstract feature-based embedding spaces are human-unfriendly and prevent intuitive and efficient exploration of the vast materials space. Here we introduce Contrastive Language--Structure Pre-training (CLaSP), a learning paradigm for constructing crossmodal embedding spaces between crystal structures and texts. CLaSP aims to achieve material embeddings that 1) capture property- and functionality-related similarities between crystal structures and 2) allow intuitive retrieval of materials via user-provided description texts as queries. To compensate for the lack of sufficient datasets linking crystal structures with textual descriptions, CLaSP leverages a dataset of over 400,000 published crystal structures and corresponding publication records, including paper titles and abstracts, for training. We demonstrate the effectiveness of CLaSP through text-based crystal structure screening and embedding space visualization.
Authors: Alessio Zaccone, Kostya Trachenko
There is currently no consensus on how the global population will evolve in the next decades and in the next century. The reason for this uncertainty is the absence of reliable population dynamic models. In this paper, we remedy to this situation by reporting on a population dynamic model, a single nonlinear differential equation adapted from the physics of disordered systems, which is able to mathematically describe all the various regimes encountered in the global population recorded as a function of time, over the past 12000 years until now. Regimes of simple exponential growth (Malthus), logistic (Verhulst) plateaus as well as stretched-exponential and compressed-exponential growth regimes are all reliably described by this mathematical equation in its various limits. Besides showing that this is, indeed, the most general population dynamic model, we use it to explore its solutions projected into the future. In particular, two different scenarios are predicted. In one of them, which assumes that the future evolution would continue along a similar pattern as the past decades (hence without any major global ecological crisis affecting the resource exploitation), a von Foerster-type doomsday scenario with a sudden rise of the global population to unsustainable levels could appear as early as 2078. In the opposite scenario, if a global ecological crisis were to set in today, affecting the ability to exploit resources, given the current estimates of the Earth's carrying capacity, the global population is forecasted to reduce by half by 2064. Furthermore, the proposed dynamic model provides with a new aggregated parameter (K, in the model) that can be monitored and controlled so as to avoid the doomsday scenarios.
Authors: Dennis P. Clougherty, Nam H. Dinh
H. Lamb considered the classical dynamics of a vibrating particle embedded in an elastic medium before the development of quantum theory. Lamb was interested in how the back-action of the elastic waves generated can damp the vibrations of the particle. We propose a quantum version of Lamb's model. We show that this model is exactly solvable by using a multimode Bogoliubov transformation. We find that the exact system ground state is a multimode squeezed vacuum state, and we obtain the exact Bogoliubov frequencies by numerically solving a nonlinear integral equation. A closed-form expression for the damping rate of the particle is obtained, and it agrees with the result obtained by perturbation theory. The model provides a solvable example of the damped quantum harmonic oscillator.
Authors: A. Bhowmik, D. Blume
Trapped Rydberg atoms are highly promising candidates for quantum science experiments. While several approaches have been put forward to exert (trapping) forces on isolated Rydberg atoms, a widely applicable lossless technique is lacking. This paper proposes a robust versatile alternative technique that avoids lifetime compromising losses. Our proposal leverages the vector polarizability, which is induced by non-linearly polarized light and is shown to be several orders of magnitude larger than the usual scalar and tensor polarizabilities for commonly used alkali Rydberg series such as the $nS$, $nP$, and $nD$ series with principal quantum number $n$ as low as 30. The resulting force can be used to trap isolated Rydberg atoms over long times, which constitutes a key advance that is expected to impact quantum simulation applications, as well as to generate large light--Rydberg-atom hybrid states, which possess non-trivial position-dependent forces.
Authors: Gauthameshwar S., Noufal Jaseem, Dario Poletti
Autonomous quantum thermal machines are particularly suited to understand how correlations between thermal baths, a load, and a thermal machine affect the overall thermodynamic functioning of the setup. Here, we show that by tuning the operating temperatures and the magnitude of the coupling between machine and load, the thermal machine can operate in four modes: engine, accelerator, heater, or refrigerator. In particular, we show that as we increase the coupling strength, the engine mode is suppressed, and the refrigerator mode is no longer attainable, leaving the heater as the most pronounced functioning modality, followed by the accelerator. This regime switching can be amplified by quantum effects, such as the bosonic enhancement factor for a harmonic oscillator load, which modifies the effective machine-load coupling, making the thermodynamic functioning sensitive to the initial preparation of the load.
Authors: Michael Stone
Motivated by recent work on the Sachdev-Ye-Kitaev (SYK) model, we consider the effect of Radon or X-ray transformations, on the Laplace eigenfunctions in hyperbolic Bolyai-Lobachevsky space. We show that the Radon map from this space to Lorentzian-signature Anti-de Sitter or de Sitter space is easier to interpret if we use the Poincare disc model and eigenfunctions rather than the upper-half-plane model. In particular, this version of the transform reveals the geometric origin of the boundary conditions imposed on the eigenfunctions that are involved in calculating the SYK four-point function.
Authors: Naoki Matsumura, Yuta Yoshimoto, Yuto Iwasaki, Meguru Yamazaki, Yasufumi Sakai
Neural network potentials (NNPs) offer a powerful alternative to traditional force fields for molecular dynamics (MD) simulations. Accurate and stable MD simulations, crucial for evaluating material properties, require training data encompassing both low-energy stable structures and high-energy structures. Conventional knowledge distillation (KD) methods fine-tune a pre-trained NNP as a teacher model to generate training data for a student model. However, in material-specific models, this fine-tuning process increases energy barriers, making it difficult to create training data containing high-energy structures. To address this, we propose a novel KD framework that leverages a non-fine-tuned, off-the-shelf pre-trained NNP as a teacher. Its gentler energy landscape facilitates the exploration of a wider range of structures, including the high-energy structures crucial for stable MD simulations. Our framework employs a two-stage training process: first, the student NNP is trained with a dataset generated by the off-the-shelf teacher; then, it is fine-tuned with a smaller, high-accuracy density functional theory (DFT) dataset. We demonstrate the effectiveness of our framework by applying it to both organic (polyethylene glycol) and inorganic (L$_{10}$GeP$_{2}$S$_{12}$) materials, achieving comparable or superior accuracy in reproducing physical properties compared to existing methods. Importantly, our method reduces the number of expensive DFT calculations by 10x compared to existing NNP generation methods, without sacrificing accuracy. Furthermore, the resulting student NNP achieves up to 106x speedup in inference compared to the teacher NNP, enabling significantly faster and more efficient MD simulations.
Authors: Tao Liu, Juhao Wu, Mark Ying
By utilizing a unitary transformation, we derive the necessary and sufficient conditions for the degeneracy between the even- and odd-parity energy states of the spin-boson model (SBM). Employing the Rayleigh quotient of matrix algebra, we rigorously prove that the ground state energy of the SBM is lower than the systems lowest possible degenerate energy and possesses a definite parity. Based on the necessary and sufficient conditions for parity breaking, we provide an analytical expression for the parity-breaking critical value, which is closely related to the expansion order and computational accuracy. This expression reproduces the SBM phase diagram obtained by quantum Monte Carlo (QMC) and logarithmic discretization numerical renormalization group (NRG) methods. However, this phase diagram does not characterize the ground state of the system.
Authors: Griffith Rufo, Sabrina Rufo, Pedro Ribeiro, Stefano Chesi
We investigate the quantum-classical correspondence in open quantum many-body systems using the SU(3) Bose-Hubbard trimer as a minimal model. Combining exact diagonalization with semiclassical Langevin dynamics, we establish a direct connection between classical trajectories characterized by fixed-point attractors, limit cycles, or chaos and the spectral and structural properties of the quantum steady state. We show that classical dynamical behavior, as quantified by the sign of the Lyapunov exponent, governs the level statistics of the steady-state density matrix: non-positive exponents associated with regular dynamics yield Poissonian statistics, while positive exponents arising from chaotic dynamics lead to Wigner-Dyson statistics. Strong symmetries constrain the system to lower-dimensional manifolds, suppressing chaos and enforcing localization, while weak symmetries preserve the global structure of the phase space and allow chaotic behavior to persist. To characterize phase-space localization, we introduce the phase-space inverse participation ratio IPR, which defines an effective dimension D of the Husimi distribution's support. We find that the entropy scales as $S \propto \ln N^D$, consistently capturing the classical nature of the underlying dynamics. This semiclassical framework, based on stochastic mixtures of coherent states, successfully reproduces not only observable averages but also finer features such as spectral correlations and localization properties. Our results demonstrate that dissipative quantum chaos is imprinted in the steady-state density matrix, much like in closed systems, and that the interplay between dynamical regimes and symmetry constraints can be systematically probed using spectral and phase-space diagnostics. These tools offer a robust foundation for studying ergodicity, localization, and non-equilibrium phases of open quantum systems.
Authors: Moroni Santiago-García, Shunashi G. Castillo-López, David A. Ruiz-Tijerina, Arturo Camacho-Guardian
Quantum mixtures of moiré excitons have arisen as a platform for realizing novel phases of light and matter. Here, we study moiré polaritons coupled to a Bose-Einstein condensate of dark-state excitons confined to a moiré superlattice. We develop a variational approach to analyze the optical response of the system and demonstrate that strong exciton-exciton interactions significantly modify the character of moiré polaritons, leading to sizable energy shifts of the avoided crossing between the principal polariton branches, and the emergence of an additional, stable repulsive-polariton bound state.
Authors: Jun-Jie Zhang, Shuai Dong
The interplay of Rashba and quantum spin Hall effects in non-centrosymmetric systems presents both challenges and opportunities for spintronic applications. While Rashba spin-orbit coupling can disrupt the quantum spin Hall phase, their coexistence may enable additional spintronic functionalities by coupling spin-momentum locking in the bulk with topologically protected edge states. Using the ZnIn$_2$Te$_4$ monolayer as a case study-a predicted polar two-dimensional topological insulator-we investigate how intrinsic and Rashba spin-orbit coupling compete within a single material. Our results identify key conditions under which sizable Rashba spin splitting can coexist with a stable quantum spin Hall phase, offering guidance for engineering quantum spin Hall insulators with enhanced spintronic capabilities.
Authors: Marko Milivojević, Juraj Mnich, Paulina Jureczko, Marcin Kurpas, Martin Gmitra
By utilizing the proximity effect, we introduce a platform that exploits ferroelectric switching to modulate spin currents in graphene proximitized by ferroelectric In$_2$Se$_3$ monolayer. Through first-principles calculations and tight-binding modeling, we studied the electronic structure of graphene/In$_2$Se$_3$ heterostructure for twist angles of 0$^{\circ}$ and 17.5$^{\circ}$, considering both ferroelectric polarizations. We discover that switching the ferroelectric polarization reverses the sign of the charge-to-spin conversion coefficients, acting as a chirality switch of the in-plane spin texture in graphene. For the twisted heterostructure, we observed emergence of unconventional radial Rashba field for one ferroelectric polarization direction. Additionally, we demonstrated that the Rashba phase can be directly extracted from the ratio of conversion efficiency coefficients, providing a straightforward approach to characterize the in-plane spin texture in graphene. All the unique features of the studied graphene/In$_2$Se$_3$ heterostructure can be experimentally detected, offering a promising approach for developing advanced spintronic devices with enhanced performance and efficiency.
Authors: S. M. Thomas, A. E. Llacsahuanga, W. Simeth, C. S. Kengle, F. Orlandi, D. Khalyavin, P. Manuel, F. Ronning, E. D. Bauer, J. D. Thompson, Jian-Xin Zhu, A. O. Scheie, Yong P. Chen, P. F. S. Rosa
The discovery of local-moment magnetism in van der Waals (vdW) semiconductors down to the single-layer limit has led to a paradigm shift in the understanding of two-dimensional (2D) magnets and unleashed their potential for applications in microelectronic and optoelectronic devices. The incorporation of strong electronic and magnetic correlations in 2D vdW metals remains a sought-after platform not only to enable control of emergent quantum phases, such as superconductivity, but also to achieve more theoretically tractable microscopic models of complex materials. To date, however, there is limited success in the discovery of such metallic vdW platforms, and $f$-electron monolayers remain out of reach. Here we demonstrate that the actinide $\beta$-UTe$_3$ can be exfoliated to the monolayer limit. A sizable electronic specific heat coefficient provides the hallmark of strong correlations. Remarkably, $\beta$-UTe$_3$ remains ferromagnetic in the half-unit-cell limit with an enhanced ordering temperature of 35 K, a factor of two larger than its bulk counterpart. Our work establishes $\beta$-UTe$_3$ as a novel materials platform for investigating and modeling correlated behavior in the monolayer limit and opens numerous avenues for quantum control with, e.g., strain engineering.
Authors: Zhiming Pan, Chen Lu, Fan Yang, Congjun Wu
Unconventional superconductivity arising from electron-electron interaction can manifest exotic symmetry and topological properties. We investigate the superconducting pairing symmetry problem based on the 3D cubic $O_h$ symmetry with both weak- and strong-coupling approaches. The dominant pairing symmetries belong to the two-dimensional $E_g$ representation at low and intermediate doping levels, and the complex mixing gap function of the $d_{3z^2-r^2}+id_{x^2-y^2}$-type is energetically favored in the ground state. Cooper pairs with such a symmetry do not possess orbital angular momentum (OAM) moments, which is different from other time-reversal symmetry breaking pairings such as $p_x+ip_y$ (e.g $^3$He-A) and $d_{x^2-y^2}+id_{xy}$ under the planar hexagonal symmetry. Instead, they develop the octupolar $O_{xyz}$ component of OAM, which results in 8 nodal points along the body diagonal directions exhibiting an alternating distribution of monopole charges $\pm 1$. This leads to an intriguing 3D Weyl topological SC, which accommodates nontrivial surface states of Majorana arcs. Our results appeal for material realizations and experimental tests in optical lattices.
Authors: Alexei V. Tkachenko
While Landauer's principle sets a fundamental energy limit for irreversible digital computation, we show that Deep Neural Networks (DNNs) implemented on analog physical substrates can operate under markedly different thermodynamic constraints. We distinguish between two classes of analog systems: dynamic and quasi-static. In dynamic systems, energy dissipation arises from neuron resets, with a lower bound governed by Landauer's principle. To analyse a quasi-static analog platform, we construct an explicit mapping of a generic feedforward DNN onto a physical system described by a model Hamiltonian. In this framework, inference can proceed reversibly, with no minimum free energy cost imposed by thermodynamics. We further analyze the training process in quasi-static analog networks and derive a fundamental lower bound on its energy cost, rooted in the interplay between thermal and statistical noise. Our results suggest that while analog implementations can outperform digital ones during inference, the thermodynamic cost of training scales similarly in both paradigms.
Authors: Paulin de Schoulepnikoff, Gorka Muñoz-Gil, Hendrik Poulsen Nautrup, Hans J. Briegel
Interpretable machine learning is rapidly becoming a crucial tool for scientific discovery. Among existing approaches, variational autoencoders (VAEs) have shown promise in extracting the hidden physical features of some input data, with no supervision nor prior knowledge of the system at study. Yet, the ability of VAEs to create meaningful, interpretable representations relies on their accurate approximation of the underlying probability distribution of their input. When dealing with quantum data, VAEs must hence account for its intrinsic randomness and complex correlations. While VAEs have been previously applied to quantum data, they have often neglected its probabilistic nature, hindering the extraction of meaningful physical descriptors. Here, we demonstrate that two key modifications enable VAEs to learn physically meaningful latent representations: a decoder capable of faithfully reproduce quantum states and a probabilistic loss tailored to this task. Using benchmark quantum spin models, we identify regimes where standard methods fail while the representations learned by our approach remain meaningful and interpretable. Applied to experimental data from Rydberg atom arrays, the model autonomously uncovers the phase structure without access to prior labels, Hamiltonian details, or knowledge of relevant order parameters, highlighting its potential as an unsupervised and interpretable tool for the study of quantum systems.
Authors: Tao Liu, Juhao Wu, Mark Ying
By utilizing a unitary transformation, we derive the necessary and sufficient conditions for the degeneracy between the even- and odd-parity energy states of the spin-boson model (SBM). Employing the Rayleigh quotient of matrix algebra, we rigorously prove that the ground state energy of the SBM is lower than the systems lowest possible degenerate energy and possesses a definite parity. Based on the necessary and sufficient conditions for parity breaking, we provide an analytical expression for the parity-breaking critical value, which is closely related to the expansion order and computational accuracy. This expression reproduces the SBM phase diagram obtained by quantum Monte Carlo (QMC) and logarithmic discretization numerical renormalization group (NRG) methods. However, this phase diagram does not characterize the ground state of the system.
Authors: Griffith Rufo, Sabrina Rufo, Pedro Ribeiro, Stefano Chesi
We investigate the quantum-classical correspondence in open quantum many-body systems using the SU(3) Bose-Hubbard trimer as a minimal model. Combining exact diagonalization with semiclassical Langevin dynamics, we establish a direct connection between classical trajectories characterized by fixed-point attractors, limit cycles, or chaos and the spectral and structural properties of the quantum steady state. We show that classical dynamical behavior, as quantified by the sign of the Lyapunov exponent, governs the level statistics of the steady-state density matrix: non-positive exponents associated with regular dynamics yield Poissonian statistics, while positive exponents arising from chaotic dynamics lead to Wigner-Dyson statistics. Strong symmetries constrain the system to lower-dimensional manifolds, suppressing chaos and enforcing localization, while weak symmetries preserve the global structure of the phase space and allow chaotic behavior to persist. To characterize phase-space localization, we introduce the phase-space inverse participation ratio IPR, which defines an effective dimension D of the Husimi distribution's support. We find that the entropy scales as $S \propto \ln N^D$, consistently capturing the classical nature of the underlying dynamics. This semiclassical framework, based on stochastic mixtures of coherent states, successfully reproduces not only observable averages but also finer features such as spectral correlations and localization properties. Our results demonstrate that dissipative quantum chaos is imprinted in the steady-state density matrix, much like in closed systems, and that the interplay between dynamical regimes and symmetry constraints can be systematically probed using spectral and phase-space diagnostics. These tools offer a robust foundation for studying ergodicity, localization, and non-equilibrium phases of open quantum systems.
Authors: Moroni Santiago-García, Shunashi G. Castillo-López, David A. Ruiz-Tijerina, Arturo Camacho-Guardian
Quantum mixtures of moiré excitons have arisen as a platform for realizing novel phases of light and matter. Here, we study moiré polaritons coupled to a Bose-Einstein condensate of dark-state excitons confined to a moiré superlattice. We develop a variational approach to analyze the optical response of the system and demonstrate that strong exciton-exciton interactions significantly modify the character of moiré polaritons, leading to sizable energy shifts of the avoided crossing between the principal polariton branches, and the emergence of an additional, stable repulsive-polariton bound state.
Authors: Jun-Jie Zhang, Shuai Dong
The interplay of Rashba and quantum spin Hall effects in non-centrosymmetric systems presents both challenges and opportunities for spintronic applications. While Rashba spin-orbit coupling can disrupt the quantum spin Hall phase, their coexistence may enable additional spintronic functionalities by coupling spin-momentum locking in the bulk with topologically protected edge states. Using the ZnIn$_2$Te$_4$ monolayer as a case study-a predicted polar two-dimensional topological insulator-we investigate how intrinsic and Rashba spin-orbit coupling compete within a single material. Our results identify key conditions under which sizable Rashba spin splitting can coexist with a stable quantum spin Hall phase, offering guidance for engineering quantum spin Hall insulators with enhanced spintronic capabilities.
Authors: Marko Milivojević, Juraj Mnich, Paulina Jureczko, Marcin Kurpas, Martin Gmitra
By utilizing the proximity effect, we introduce a platform that exploits ferroelectric switching to modulate spin currents in graphene proximitized by ferroelectric In$_2$Se$_3$ monolayer. Through first-principles calculations and tight-binding modeling, we studied the electronic structure of graphene/In$_2$Se$_3$ heterostructure for twist angles of 0$^{\circ}$ and 17.5$^{\circ}$, considering both ferroelectric polarizations. We discover that switching the ferroelectric polarization reverses the sign of the charge-to-spin conversion coefficients, acting as a chirality switch of the in-plane spin texture in graphene. For the twisted heterostructure, we observed emergence of unconventional radial Rashba field for one ferroelectric polarization direction. Additionally, we demonstrated that the Rashba phase can be directly extracted from the ratio of conversion efficiency coefficients, providing a straightforward approach to characterize the in-plane spin texture in graphene. All the unique features of the studied graphene/In$_2$Se$_3$ heterostructure can be experimentally detected, offering a promising approach for developing advanced spintronic devices with enhanced performance and efficiency.
Authors: S. M. Thomas, A. E. Llacsahuanga, W. Simeth, C. S. Kengle, F. Orlandi, D. Khalyavin, P. Manuel, F. Ronning, E. D. Bauer, J. D. Thompson, Jian-Xin Zhu, A. O. Scheie, Yong P. Chen, P. F. S. Rosa
The discovery of local-moment magnetism in van der Waals (vdW) semiconductors down to the single-layer limit has led to a paradigm shift in the understanding of two-dimensional (2D) magnets and unleashed their potential for applications in microelectronic and optoelectronic devices. The incorporation of strong electronic and magnetic correlations in 2D vdW metals remains a sought-after platform not only to enable control of emergent quantum phases, such as superconductivity, but also to achieve more theoretically tractable microscopic models of complex materials. To date, however, there is limited success in the discovery of such metallic vdW platforms, and $f$-electron monolayers remain out of reach. Here we demonstrate that the actinide $\beta$-UTe$_3$ can be exfoliated to the monolayer limit. A sizable electronic specific heat coefficient provides the hallmark of strong correlations. Remarkably, $\beta$-UTe$_3$ remains ferromagnetic in the half-unit-cell limit with an enhanced ordering temperature of 35 K, a factor of two larger than its bulk counterpart. Our work establishes $\beta$-UTe$_3$ as a novel materials platform for investigating and modeling correlated behavior in the monolayer limit and opens numerous avenues for quantum control with, e.g., strain engineering.
Authors: Zhiming Pan, Chen Lu, Fan Yang, Congjun Wu
Unconventional superconductivity arising from electron-electron interaction can manifest exotic symmetry and topological properties. We investigate the superconducting pairing symmetry problem based on the 3D cubic $O_h$ symmetry with both weak- and strong-coupling approaches. The dominant pairing symmetries belong to the two-dimensional $E_g$ representation at low and intermediate doping levels, and the complex mixing gap function of the $d_{3z^2-r^2}+id_{x^2-y^2}$-type is energetically favored in the ground state. Cooper pairs with such a symmetry do not possess orbital angular momentum (OAM) moments, which is different from other time-reversal symmetry breaking pairings such as $p_x+ip_y$ (e.g $^3$He-A) and $d_{x^2-y^2}+id_{xy}$ under the planar hexagonal symmetry. Instead, they develop the octupolar $O_{xyz}$ component of OAM, which results in 8 nodal points along the body diagonal directions exhibiting an alternating distribution of monopole charges $\pm 1$. This leads to an intriguing 3D Weyl topological SC, which accommodates nontrivial surface states of Majorana arcs. Our results appeal for material realizations and experimental tests in optical lattices.
Authors: Alexei V. Tkachenko
While Landauer's principle sets a fundamental energy limit for irreversible digital computation, we show that Deep Neural Networks (DNNs) implemented on analog physical substrates can operate under markedly different thermodynamic constraints. We distinguish between two classes of analog systems: dynamic and quasi-static. In dynamic systems, energy dissipation arises from neuron resets, with a lower bound governed by Landauer's principle. To analyse a quasi-static analog platform, we construct an explicit mapping of a generic feedforward DNN onto a physical system described by a model Hamiltonian. In this framework, inference can proceed reversibly, with no minimum free energy cost imposed by thermodynamics. We further analyze the training process in quasi-static analog networks and derive a fundamental lower bound on its energy cost, rooted in the interplay between thermal and statistical noise. Our results suggest that while analog implementations can outperform digital ones during inference, the thermodynamic cost of training scales similarly in both paradigms.
Authors: Paulin de Schoulepnikoff, Gorka Muñoz-Gil, Hendrik Poulsen Nautrup, Hans J. Briegel
Interpretable machine learning is rapidly becoming a crucial tool for scientific discovery. Among existing approaches, variational autoencoders (VAEs) have shown promise in extracting the hidden physical features of some input data, with no supervision nor prior knowledge of the system at study. Yet, the ability of VAEs to create meaningful, interpretable representations relies on their accurate approximation of the underlying probability distribution of their input. When dealing with quantum data, VAEs must hence account for its intrinsic randomness and complex correlations. While VAEs have been previously applied to quantum data, they have often neglected its probabilistic nature, hindering the extraction of meaningful physical descriptors. Here, we demonstrate that two key modifications enable VAEs to learn physically meaningful latent representations: a decoder capable of faithfully reproduce quantum states and a probabilistic loss tailored to this task. Using benchmark quantum spin models, we identify regimes where standard methods fail while the representations learned by our approach remain meaningful and interpretable. Applied to experimental data from Rydberg atom arrays, the model autonomously uncovers the phase structure without access to prior labels, Hamiltonian details, or knowledge of relevant order parameters, highlighting its potential as an unsupervised and interpretable tool for the study of quantum systems.
Authors: Nick P. Proukakis
Bose-Einstein Condensation is a phenomenon at the heart of many of the past century's most intriguing and fundamental manifestations, such as superfluidity and superconductivity. It was discovered theoretically some 100 years ago, and unequivocally experimentally demonstrated in the context of weakly interacting gases 30 years ago. Since then, it has spawned a revolution in our understanding of fundamental phases of matter and collective quantum dynamics extending across all physical scales and energies, with unforeseen implications and the potential for envisaged quantum technological applications.
Authors: Silas Hoffman, Charles Tahan
Andreev spin qubits (ASQs) are a promising platform for quantum information processing which benefit from both the small footprint of semiconducting spin qubits and the long range connectivity of superconducting qubits. While state-of-the-art experiments have developed ASQs in InAs nanowires, these realizations are coherence-time limited by nuclear magnetic noise which cannot be removed by isotopic purification. In Ge-based Josephson junctions, which can be isotopically purified, Andreev states have been experimentally observed but spin-resolved Andreev states remain elusive. Here, we theoretically demonstrate that the geometry of the Josephson junction can limit the qubit frequency to values below typical experimental temperatures and render the ASQ effectively invisible. ASQs could be experimentally resolved by judiciously choosing the geometry of the junction and filling of the underlying Ge. Our comprehensive study of ASQ frequency on in situ and ex situ experimentally controllable parameters provides design guidance of Ge-based Josephson junctions and paves the way towards realization of high-coherence ASQs.
Authors: Wenjin Zhao, Zui Tao, Yichi Zhang, Bowen Shen, Zhongdong Han, Patrick Knüppel, Yihang Zeng, Zhengchao Xia, Kenji Watanabe, Takashi Taniguchi, Jie Shan, Kin Fai Mak
A Chern metal is a two-dimensional metallic state of matter carrying chiral edge states. It can emerge as a doped Chern insulator, but theoretical studies have also predicted its emergence near a Kondo breakdown separating a metallic chiral spin liquid and a heavy Fermi liquid in a frustrated lattice. To date, the latter exotic scenario has not been realized. Here, we report the observation of a Chern metal at the onset of the magnetic Kondo breakdown in a frustrated moiré Kondo lattice--angle-aligned MoTe2/WSe2 bilayers. The state is compressible and is manifested by a nearly quantized Hall resistance but a finite longitudinal resistance that arises from a bad metallic bulk. The state also separates an itinerant and a heavy Fermi liquid and appears far away from the band inversion critical point of the material, thus ruling out its origin from simply doping a Chern insulator. We demonstrate the presence of a chiral edge state by nonlocal transport measurements and current-induced quantum anomalous Hall breakdown. Magnetic circular dichroism measurements further reveal a magnetization plateau for the Chern metal before a metamagnetic transition at the Kondo breakdown. Our results open an opportunity for moiré engineering of exotic quantum phases of matter through the close interplay between band topology and Kondo interactions.
Authors: Ke Huang, Ajit C. Balram, Hailong Fu, Chengqi Guo, Kenji Watanabe, Takashi Taniguchi, Jainendra K. Jain, Jun Zhu
A two-dimensional electron system exposed to a strong magnetic field produces a plethora of strongly interacting fractional quantum Hall (FQH) states, the complex topological orders of which are revealed through exotic emergent particles, such as composite fermions, fractionally charged Abelian and non-Abelian anyons. Much insight has been gained by the study of multi-component FQH states, where spin and pseudospin indices of the electron contribute additional correlation. Traditional multi-component FQH states develop in situations where the components share the same orbital states and the resulting interactions are pseudospin independent; this homo-orbital nature was also crucial to their theoretical understanding. Here, we study "hetero-orbital" two-component FQH states, in which the orbital index is part of the pseudospin, rendering the multi-component interactions strongly SU(2) anisotropic in the pseudospin space. Such states, obtained in bilayer graphene at the isospin transition between N = 0 and N = 1 electron Landau levels, are markedly different from previous homo-orbital two-component FQH states. In particular, we observe strikingly different behaviors for the parallel-flux and reverse-flux composite fermion states, and an anomalously strong two-component 2/5 state over a wide range of magnetic field before it abruptly disappears at a high field. Our findings, combined with detailed theoretical calculations, reveal the surprising robustness of the hetero-orbital FQH effects, significantly enriching our understanding of FQH physics in this novel regime.
Authors: Hu Zhang
Multiferroics with $d^9$ electronic configurations, such as $SnCuO_2$, $PbCuO_2$, and $BiNiO_2$, exhibit coexisting antiferromagnetic order and ferroelectricity. Motivated by the fundamental link between symmetry breaking, strong electron correlations, and unconventional superconductivity, we propose a materials design strategy targeting noncentrosymmetric high-temperature superconductors through chemical doping of engineered $d^9$ multiferroics. This approach bridges two phenomena: (i) the coexistence of antiferromagnetism and ferroelectricity in correlated insulators, and (ii) the emergence of superconductivity in doped Mott/charge-transfer systems.
Authors: Yongtao Liu, Anton V. Ievlev, Eugene A. Eliseev, Nana Sun, Kazuki Okamoto, Hiroshi Funakubo, Anna N. Morozovska, Sergei Kalinin
Binary ferroelectric nitrides are promising materials for information technologies and power electronics. However, polarization switching in these materials is highly unusual. From the structural perspective, polarization reversal is associated with the change of the effective polarity at the surfaces and interfaces from N-to-M terminated, suggesting strong coupling between ferroelectric and chemical phenomena. Phenomenologically, macroscopic studies demonstrate the presence of complex time dependent phenomena including wake-up. Here, we explore the polarization switching using the multidimensional high-resolution piezoresponse force microscopy (PFM) and spectroscopy, detecting both the evolution of induced ferroelectric domain, electromechanical response, and surface deformation during first-order reversal curve measurements. We demonstrate the presence of two weakly coupled ferroelectric subsystems and the bias-induced electrochemical reactivity. The observed behaviors are very similar to the recent studies of other wurtzite system but additionally include electrochemical reactivity, suggesting the universality of these behaviors for the wurtzite binary ferroelectrics. These studies suggest potential of high-resolution multimodal PFM spectroscopies to resolve complex coupled polarization dynamics in materials. Furthermore, these PFM based studies are fully consistent with the recent electron microscopy observations of the shark-teeth like ferroelectric domains in nitrides. Hence, we believe that these studies establish the universal phenomenological picture of polarization switching in binary wurtzite.
Authors: Petar Bojović, Timon Hilker, Si Wang, Johannes Obermeyer, Marnix Barendregt, Dorothee Tell, Thomas Chalopin, Philipp M. Preiss, Immanuel Bloch, Titus Franz
Quantum simulations of electronic structure and strongly correlated quantum phases are widely regarded as among the most promising applications of quantum computing. These simulations require the accurate implementation of motion and entanglement of fermionic particles. Instead of the commonly applied costly mapping to qubits, fermionic quantum computers offer the prospect of directly implementing electronic structure problems. Ultracold neutral atoms have emerged as a powerful platform for spin-based quantum computing, but quantum information can also be processed via the motion of bosonic or fermionic atoms offering a distinct advantage by intrinsically conserving crucial symmetries like electron number. Here we demonstrate collisional entangling gates with fidelities up to 99.75(6)% and lifetimes of Bell states beyond $10\,s$ via the control of fermionic atoms in an optical superlattice. Using quantum gas microscopy, we characterize both spin-exchange and pair-tunneling gates locally, and realize a robust, composite pair-exchange gate, a key building block for quantum chemistry simulations. Our results enable the preparation of complex quantum states and advanced readout protocols for a new class of scalable analog-digital hybrid quantum simulators. Once combined with local addressing, they mark a key step towards a fully digital fermionic quantum computer based on the controlled motion and entanglement of fermionic neutral atoms.
Authors: Fang Xie, Yuan Fang, Ying Li, Yuefei Huang, Lei Chen, Chandan Setty, Shouvik Sur, Boris Yakobson, Roser Valentí, Qimiao Si
Kagome metals offer a unique platform for investigating robust electron-correlation effects because of their lattice geometry, flat bands and multi-orbital nature. In the cases with active flat bands, recent theoretical studies have pointed to a rich phase diagram that contains not only electronic orders but also quantum criticality. Very recently, $\rm CsCr_3Sb_5$ has emerged as a strong candidate for exploring such new physics. Here, using effective tight-binding models obtained from ab initio calculations, we study the effects of electronic correlations and symmetries on the electronic structure of $\rm CsCr_3 Sb_5$. The effective tight-binding model and Fermi surface comprise multiple Cr-$d$ orbitals and Sb-$p$ orbitals. The introduction of Hubbard-Kanamori interactions leads to orbital-selective band renormalization dominated by the $d_{xz}$ band, concurrently producing emergent flat bands very close to the Fermi level. Our analysis sets the stage for further investigations into the electronic properties of $\rm CsCr_3Sb_5$, including electronic orders, quantum criticality and unconventional superconductivity, which promise to shed much new light into the electronic materials with frustrated lattices and bring about new connections with the correlation physics of a variety of strongly correlated systems.
Authors: Shantonu Mukherjee, Amitabha Lahiri
The coexistence of Ferromagnetism and superconductivity in so called ferromagnetic superconductors is an intriguing phenomenon which may lead to novel physical effects as well as applications. Here in this work we have explored the interplay of topological excitations, namely vortices and skyrmions, in ferromagnetic superconductors using a field theoretic description of such systems. In particular, numerical solutions for the continuous spin field compatible to a given vortex profile are determined in absence and presence of a Dzyaloshinskii-Moriya interaction (DMI) term. The solutions show that the spin configuration is like a skyrmion but intertwined with the vortex structure -- the radius of the the skyrmion-like solution depends on the penetration depth and also the polarity of the skyrmion depends on the sign of the winding number. Thus our solution describes a topological structure: namely a skyrmion-vortex composite. We have also determined the spin wave solutions in such systems in presence and absence of a vortex. In absence of vortex frequency and wave vector satisfy a cubic equation which leads to various interesting features. In particular, we have shown that in the low frequency regime the minimum in dispersion relation shifts from $k=0$ to a non zero $k$ value depending on the parameters. We also discuss the nature of spin wave dispersion in the $\omega \sim \Tilde{m}$ regime which shows a similar pattern in the dispersion curve. The group velocity of the spin wave would change it's sign across such a minimum which is unique to FMSC. Also, the spin wave modes around the local minimum looks like roton mode in superfluid and hence called a magnetic roton. In presence of a vortex, the spin wave amplitude is shown to vary spatially such that the profile looks like that of a Néel Skyrmion. Possible experimental signature of both solutions are also discussed.
Authors: M. Umar Farooq, Arqum Hashmi, Mizuki Tani, Kazuhiro Yabana, Kenichi L. Ishikawa, Li Huang, Tomohito Otobe
The study of interplay between the geometric nature of Bloch electrons and transverse responses under strong field offers new opportunities for optoelectronic applications. Here, we present a comprehensive study of the strong-field response of Weyl Dirac nodes in bilayer T'-WTe2 using time-dependent first-principles formalism. The electron dynamics is explored focusing on the mid-infrared frequency, ranging from the perturbative to nonperturbative regime. In the nonperturbative regime, the high-harmonic generation (HHG) spectra under a strong field clearly exhibit a plateau and energy cutoffs for both longitudinal and anomalous Hall (transverse) currents, with the latter being due to the large interband Berry curvature of the Weyl-Dirac semimetal. For the longitudinal harmonics, the intraband contributions increase with intensity, resulting in a complex interplay between interband polarization and intraband motions. Remarkably, if we take a comprehensive all-band perspective enabled by time-dependent density functional calculations, the anomalous Hall responses are purely attributed to the interband processes, even in the nonperturbative regime, thus Hall HHG can be crucial to understand the carrier dynamics. Our findings suggest that HHG associated with the ultrafast strong-field driven electron dynamics holds immense potential for exploring the nonlinear high Hall responses in Weyl semimetal.
Authors: James H. Cullen, Hong Liu, Dimitrie Culcer
The highly efficient torques generated by 3D topological insulators make them a favourable platform for faster and more efficient magnetic memory devices. Recently, research into harnessing orbital angular momentum in orbital torques has received significant attention. Here we study the orbital Hall effect in topological insulators. We find that the bulk states give rise to a sizeable orbital Hall effect that is up to 3 orders of magnitude larger than the spin Hall effect in topological insulators. This is partially because the orbital angular momentum that each conduction electron carries is up to an order of magnitude larger than the $\hbar/2$ carried by its spin. Our results imply that the large torques measured in topological insulator/ferromagnet devices can be further enhanced through careful engineering of the heterostructure to optimise orbital-to-spin conversion.
Authors: Zhan Wang, Keyu Zeng, Ziqiang Wang
Motivated by the evidence for time-reversal symmetry (TRS) breaking in nonmagnetic kagome metals AV3Sb5, a novel electronic order of persistent orbital loop-current (LC) has been proposed for the observed charge density wave (CDW) state. The LC order and its impact on the succeeding superconducting (SC) state are central to the new physics of the kagome materials. We show that the LC order fundamentally changes the pairing instability and the SC state, leading to an extraordinary topological superconductor, dubbed as a roton superconductor. In the single-orbital model on the kagome lattice, the LC-CDW state is a Chern metal near van Hove filling with a partially filled Chern band hosting 3 Chern Fermi pockets (CFPs). Cooper pairing of quasiparticles on the CFPs generates 3 SC components coupled by complex Josephson couplings induced by the TRS breaking LC. Due to the discrete quantum geometry associated with the 3-fold rotation and sublattice permutation, a small LC produces a large Josephson phase that drives the leading SC instability to the roton superconductor where the relative phases of the 3 SC components are locked at 120°, forming an emergent vortex-antivortex lattice with pair density modulations. Properties of the roton superconductor include topological chiral edge states carrying nonzero electric currents, fractional 1/3 vortex excitations and charge-6e Cooper pair triplets that are immune to the internal chiral phase fluctuations. We discuss these SC properties in connection to recent experimental evidence for TRS breaking chiral SC state in kagome superconductors, exhibiting pair density modulations, zero-field SC diode effect, and charge-6e flux quantization. These findings are also relevant for the interplay between the orbital-driven quantum anomalous Hall and SC states in other systems, e.g. the graphene and transition metal dichalcogenide based quantum materials.
Authors: Giovanni Citeroni, Marco Polini, Michael Dapolito, D. N. Basov, Giacomo Mazza
We study the dynamics of quantum matter interacting with time-energy entangled photons. We consider the stimulation of a collective mode of a two-dimensional material by means of one of the two partners of a time-energy entangled pair of photons. Using an exactly solvable model, we analyze the out-of-equilibrium properties of both light and matter degrees of freedom, and show how entanglement in the incident photons deeply modifies relevant time scales of the light-matter interaction process. We find that entanglement strongly suppresses the delay between the transmission and absorption events, which become synchronous in the limit of strongly entangled wave packets. By comparing numerical simulations with analytic modeling, we trace back this behavior to the representation of entangled wave packets in terms of a superposition of multiple train pulses containing an increasing number of ultrashort non-entangled packets. As a result, we show that the entangled driving allows the creation of a matter excitation on a time scale shorter than the temporal width of the pulse. Eventually, by analyzing temporal correlations of the excited matter degrees of freedom, we show that driving with entangled photons imprints characteristic temporal correlations of time-energy entangled modes in the matter degree of freedom.
Authors: Jonathan Stepp, Eduardo Ibarra-García-Padilla, Richard T. Scalettar, Kaden R. A. Hazzard
Recent advances in microwave shielding have increased the stability and control of large numbers of polar molecules, allowing for the first realization of a molecular Bose-Einstein condensate. Remarkably, it was also recently realized that shielded polar molecules exhibit an SU(N) symmetry among their hyperfine states, opening the door to SU(N) systems with larger N, bosonic particle statistics, and tunable interactions -- both repulsive and attractive. Motivated by these results, we have studied the SU(3) attractive Fermi-Hubbard model (FHM) on a square lattice. Using the Determinant Quantum Monte Carlo (DQMC) method, we explore the finite-temperature phase diagram and provide evidence for three distinct regions -- a three-component Fermi liquid (FL) region, a "trion" liquid (TL) region, and an ordered Charge Density Wave (CDW) phase. The CDW phase is stable at finite temperature (in contrast to the SU(2) CDW), while the FL to TL crossover appears to point to a quantum phase transition at zero temperature. Our method extends straightforwardly to larger N and is sign-problem free for even values of N. With these results, we demonstrate the potential physics enabled by using polar molecules as a quantum simulation platform for the attractive SU(N) FHM.
Authors: Ipsita Mandal
The band-degeneracy points in the Brillouin zones of chiral crystals exist in multiple avatars, with the high-symmetry points being able to host multifold nodes of distinct characters. A class of such crystals, assisted by the spin-orbit coupling, harbours fourfold degeneracy in the form of Rarita-Schwinger-Weyl node (RSWN) at the $\Gamma$-point. Our aim is to explore the nature of longitudinal magnetoconductivity, arising from applying collinear electric and magnetic fields, for such systems. Adjusting the chemical potential to lie near the intrinsic energy-location of the RSWN, the multifold nature of the RSWN is revealed by an interplay of intraband and interband scatterings, which would not arise in twofold degeneracies like the conventional Weyl nodes. The current study fills up the much-needed gap in obtaining the linear response from an exact computation, rather than the insufficient relaxation-time approximation employed earlier.
Authors: R. K. Kushwaha, Arushi, S. Jangid, P. K. Meena, R. Stewart, A. D. Hillier, R. P. Singh
Non-centrosymmetric superconductors have emerged as a fascinating avenue for exploring unconventional superconductivity. Their broken inversion and time-reversal symmetries make them prime candidates for realizing the intrinsic superconducting diode effect (SDE). In this work, we synthesize the ternary non-centrosymmetric $\alpha$-Mn alloy NbTaOs$_{2}$ and conduct a comprehensive investigation of its superconducting properties through resistivity, magnetization, specific heat and muon spin rotation/relaxation ($\mu$SR) techniques. Our transverse field-$\mu$SR and specific heat results provide evidence of a moderately coupled, fully-gaped superconducting state. Zero field-$\mu$SR measurements reveal a subtle increase in the relaxation rate below the transition temperature, suggesting time reversal symmetry breaking in the superconducting ground state of NbTaOs$_{2}$.
Authors: Vincent Pouthier, Saad Yalouz
We study the quantum dynamics of a strongly correlated electron pair in a one-dimensional lattice, focusing on the occurrence of local dissociation/pairing mechanisms induced by a site energy defect. To this end, we simulate the time evolution of two interacting electrons on a finite-size chain governed by an extended Hubbard Hamiltonian including on-site Coulomb repulsion $ U $ and nearest-neighbor interaction $V$, along with single-electron hopping $J$. By introducing a local site energy defect with amplitude $ \Delta $, we show that a transition between spatially paired/dissociated electrons can occur in the vicinity of this site. Such mechanisms arise in a strongly correlated regime with non-zero nearest neighbor Coulomb interactions and under the conditions $ (U \sim V \sim \Delta) \gg J$. To rationalize these phenomena, we reformulate the two-electron dynamics of the original Hubbard chain as an effective single-particle problem on a two-dimensional network. Within this framework, we show that the pairing/dissociation dynamics are driven by resonances between two distinct families of two-electron eigenstates: $(i)$ states with two spatially well-separated electrons with one located at the site defect, and $(ii)$ states with locally bound electron located away from the defect. At resonance, these states hybridize, allowing transitions from locally paired to dissociated electrons (and vice versa) in the vicinity of the defect. These results provide new insights into exotic pairing phenomena in strongly correlated electronic systems and may have implications for the design of tunable many-body states in low-dimensional quantum materials.
Authors: Xiang-Jian Hou, Lei Wang, Ying-Hai Wu
We study fractional quantum Hall states in double layer systems that can be interpreted as exciton condensates of composite fermions. An electron in one layer is dressed by two fluxes from the same layer and two fluxes from the other layer to become composite fermions that form effective Landau levels. It is found that two types of composite fermion exciton condensates could occur. In the first type ones, all effective levels are partially occupied and excitonic correlations are present between composite fermions in the same effective level. In the second type ones, composite fermions in the topmost effective levels of the two layers form exciton condensate whereas those in lower effective levels are independent. The electric transport signatures of these states are analyzed. We demonstrate using numerical calculations that some composite fermion exciton condensates can be realized in microscopic models that are relevant for graphene and transition metal dichalcogenides. For a fixed total filling factor, an exciton condensate may only be realized when the electron densities in the two layers belong to a certain range. It is possible that two types of states appear at the same total filling factor in different ranges. These results shed light on recent experimental observations and also suggest some promising future directions.
Authors: Jin-Xin Hu, Akito Daido, Zi-Ting Sun, Ying-Ming Xie, K. T. Law
Recent experiments have observed signatures of spin-valley-polarized unconventional superconductivity in twisted bilayer MoTe$_2$ (tMoTe$_2$). Here, we explore the rich physics of superconducting tMoTe$_2$, enabled by its unique layer-pseudospin structure. Within a minimal two-orbital layer-pseudospin model framework, both interlayer and intralayer Cooper pairings can be effectively visualized using a layer-space Bloch sphere representation. Remarkably, we find that interlayer pairing prevails in the spin-valley-polarized state, whereas intralayer pairing dominates in the spin-valley-unpolarized state. Strikingly, we further predict that for spin-valley-polarized intravalley superconducting state, experimentally feasible weak displacement fields can stabilize finite-momentum pairings at low temperatures. Additionally, in-plane magnetic fields, which break three-fold rotational symmetry, induce field-direction-dependent finite-momentum pairing states, leading to a versatile momentum-selection phase diagram. Our work highlights the crucial role of layer pseudospin in tMoTe$_2$'s unconventional superconductivity and demonstrates its unique tunability via external fields.
Authors: Mohit Sharma, Srikanth Sastry, Sarika Maitra Bhattacharyya
Understanding the connection between structure, dynamics, and fragility (the rate at which relaxation times grow with decreasing temperature) is central to unraveling the glass transition. Fragility is often linked to dynamic heterogeneity, and thus it is commonly assumed that if structure influences dynamics, more fragile systems should exhibit stronger structure--dynamics correlations. In this study, we test the generality of this assumption using three model systems: Lennard-Jones (LJ) and Weeks--Chandler--Andersen, where fragility is tuned via density, and a modified LJ (q, p) system, where potential softness is changed to vary fragility. We employ a structural order parameter derived from the mean--field caging potential and analyze energy barriers at both macroscopic and microscopic levels. While the macroscopic slope of the energy barrier, suitably defined, correlates with fragility, no consistent correlation is found for the microscopic energy barriers. Instead, the latter shows a strong correlation with an independently computed structure--dynamics measure obtained from isoconfigurational ensemble. Surprisingly, the two systems with the highest structure--dynamics correlation, LJ at rho = 1.1 and the (8, 5) model, are respectively the least and most fragile within their classes. These systems exhibit broad mobility distributions, bimodal displacement profiles, and high non-Gaussian parameters, all indicative of dynamic heterogeneity. However, their dynamic susceptibilities remain low, suggesting a decoupling between spatial correlation and temporal heterogeneity. Both systems lie in the enthalpy-dominated regime and are near the spinodal, suggesting mechanical instability as a source of heterogeneity. These findings challenge the conventional linkage among fragility, heterogeneity, and structure--dynamics correlation.
Authors: Yunlin Lei, Xinyu Yang, Shouyu Wang, Daliang Zhang, Zitao Wang, Jiayou Zhang, Yihao Yang, Chuanshou Wang, Tianqi Xiao, Yinxin Bai, Junjiang Tian, Congcong Chen, Yu Han, Shuai Dong, Junling Wang
Materials possessing long range ordering of magnetic spins or electric dipoles have been the focus of condensed matter research. Among them, ferri-systems with two sublattices of unequal/noncollinear spins or electric dipoles are expected to combine the properties of ferro- and antiferro-systems, but lack experimental observations in single phase materials. This is particularly true for the ferrielectric system, since the electric dipoles usually can be redefined to incorporate the two sublattices into one, making it indistinguishable from ferroelectric. This raises doubts about whether or not ferrielectricity can be considered as an independent ferroic order. Here we report the observation of true ferrielectric behaviors in a hybrid single crystal (MV)[SbBr5] (MV2+ = N,N'-dimethyl-4,4'-bipyridinium or methylviologen), where the two electric dipole sublattices switch asynchronously, thus cannot be reduced to ferroelectric by redefining the unit cell. Furthermore, the complex dipole configuration imparts circularly polarized light sensitivity to the system. An electric field can modulate the non-collinear dipole sublattices and even induce a transition from ferrielectric to ferroelectric state, thereby tuning the helicity-dependent photocurrent. This study opens a new paradigm for the study of true irreducible ferrielectricity (a new class of polar system) and provides an effective approach to the electric field control of spin-orbit coupling and circular photogalvanic effect.
Authors: Ziwei Jeffrey Yang, Zhuangnan Li, James Moloney, Leyi Loh, John Walmsley, Jiahang Li, Lixin Liu, Han Zang, Han Yan, Soumya Sarkar, Yan Wang, Manish Chhowalla
Metallic monolayered [or two - dimensional (2D)] MoS2 nanosheets show tremendous promise for energy storage and catalysis applications. However, state-of-the-art chemical exfoliation methods require > 48 hours to produce milligrams of metallic 2D MoS2. Further, chemically exfoliated MoS2 nanosheets are a mixture of metallic (1T or 1T prime 50% to 70%) and semiconducting (2H 30% to 50%) phases. Here, we demonstrate large-scale and rapid (>600 grams per hour) production of purely metallic phase 2D MoS2 (and WS2, MoSe2) nanosheets using microwave irradiation. Atomic resolution imaging shows 1T or 1T prime metallic phase in basal plane - consistent with close to 100% metallic phase concentration measured by X-ray photoelectron spectroscopy. The high 1T phase concentration results in the highest exchange current density of 0.175 plus-minus 0.03 mA cm-2 and among the lowest Tafel slopes (39 - 43 mV dec-1) measured to date for the hydrogen evolution reaction. In supercapacitors and lithium-sulfur pouch cell batteries, record-high volumetric capacitance of 753 plus-minus 3.6 F cm-3 and specific capacity of 1245 plus-minus 16 mAh g-1 (at exceptionally low electrolyte to sulfur ratio = 2 microlitre g-1), respectively, are obtained. Our method provides a practical pathway for producing high quality purely metallic phase 2D materials for high performance energy devices.
Authors: Zhengtao Huang, Ben Xu
Accurate atomic-scale simulations of magnetic materials require precise handling of coupled spin-lattice degrees of freedom. Traditional spin-lattice dynamics (SLD), employing Newtonian equation for lattice evolution and the Landau-Lifshitz-Gilbert (LLG) equation for spins, encounters severe limitations with machine-learning potentials, including poor energy conservation and excessive computational costs due to non-symplectic integration. In this work, we propose TSPIN, a unified Nosé-Hoover Chain-based method overcoming these issues. By extending the classical Lagrangian with explicit spin kinetic terms and thermostat variables, we derive symplectic Hamiltonian formulations suitable for NVE, NVT, and NPT ensembles. The method integrates spin and lattice dynamics simultaneously, ensuring robust energy conservation and significantly reducing computational cost. Benchmarks against analytical harmonic spin-lattice models confirm its accuracy, and application to FCC iron using a DeepSPIN MLP demonstrates superior numerical stability and near-linear computational scaling compared to the conventional LLG method. Thus, TSPIN provides a powerful, broadly applicable framework for efficiently simulating complex spin-lattice phenomena and multi-degree-of-freedom systems at large scales.
Authors: Yoshishige Suzuki, Hiroki Mori, Soma Miki, Kota Emoto, Ryo Ishikawa, Eiiti Tamura, Hikaru Nomura, Minori Goto
The probabilistic information flow and natural computational capability of a system with two magnetic skyrmions at room temperature have been experimentally evaluated. Based on this evaluation, an all-solid-state built-in Maxwell's demon operating at room temperature is also proposed. Probabilistic behavior has gained attention for its potential to enable unconventional computing paradigms. However, information propagation and computation in such systems are more complex than in conventional computers, making their visualization essential. In this study, a two-skyrmion system confined within a square potential well at thermal equilibrium was analyzed using information thermodynamics. Transfer entropy and the time derivative of mutual information were employed to investigate the information propagation speed, the absence of a Maxwell's demon in thermal equilibrium, and the system's non-Markovian properties. Furthermore, it was demonstrated that the system exhibits a small but finite computational capability for the nonlinear XOR operation, potentially linked to hidden information in the non-Markovian system. Based on these experiments and analyses, an all-solid-state built-in Maxwell's demon utilizing the two-skyrmion system and operating at room temperature is proposed.
Authors: John P. Barber, William J. Deary, Andrew N. Titus, Gerald R. Bejger, Saeed S.I. Almishal, Christina M. Rost
High entropy oxides (HEOs) are a rapidly growing class of compositionally complex ceramics in which configurational disorder is engineered to unlock novel functionality. While average crystallographic symmetry is often retained, local structural and chemical disorder, including cation size and valence mismatch, oxygen sublattice distortions, and site-specific bonding, strongly governs ionic transport, redox behavior, magnetic ordering, and dielectric response. This review outlines how these modes of disorder manifest across key oxide families such as rock salt, spinel, fluorite, and perovskite. We highlight recent advances in spectroscopy, total scattering, and high-resolution microscopy enable multi-scale insight into short- and intermediate-range order. By integrating experimental observations with theoretical modeling of entropy and local energetics, we establish a framework linking structural heterogeneity to emergent properties. These insights not only deepen our fundamental understanding of disorder-property relationships but also offer a path toward rational design of tunable materials for catalysis, energy storage, electronics, and much more.
Authors: Alexander Contreras-Payares, Pablo G. Lustemberg, M. Verónica Ganduglia-Pirovano
The vibrational frequency of carbon monoxide (CO) adsorbed on ceria-based catalysts serves as a sensitive probe for identifying exposed surface facets, provided that experimental reference data on well-defined single-crystal surfaces and reliable theoretical assignments are available. Previous studies have shown that the hybrid DFT approach using the HSE06 functional yields good agreement with experimental observations, whereas the generalized gradient approximation (GGA) with PBE+U does not. In this work, we assess the performance of different exchange-correlation functionals by comparing the meta-GGA functionals SCAN and r2SCAN meta-GGA functionals with HSE06 in predicting CO vibrational frequencies on cerium oxide surfaces. The meta-GGA functionals offer no significant improvement for oxidized CeO2(111) and CeO2(110) surfaces and fail to localize excess charge on the reduced surfaces. Adding a Hubbard U term improves charge localization, but the predicted vibrational frequencies still fall short of HSE06 accuracy. These limitations are attributed to the meta-GGA's inability to adequately capture facet- and configuration-specific donation and back-donation effects, which influence the C-O bond length and CO force constant upon adsorption. Despite the higher computational cost when used with plane-wave basis sets, hybrid DFT remains essential for accurate interpretation of experimental results.
Authors: Ramon Skane, Franca Jones, Arie van Riessen, Evan Jamieson, Xiao Sun, William D.A. Rickard
Geopolymers present a sustainable alternative to conventional binders, however, their commercial viability is hindered by a lack of standardised methods for preparing stabile activator solutions; alkaline feedstocks critical to geopolymer synthesis. This study presents a combined experimental and modelling approach to evaluate the thermochemical stability, solubility constraints, and silica speciation behaviour of sodium silicate-based activators. Using quantitative 29Si NMR analysis, thermodynamic stability and three-dimensional solubility modelling, this research identifies optimal preparation conditions that minimise irreversible precipitation risks and optimises mixing periods. Key findings indicate that higher solution temperatures associated with optimised activator solution preparation were found to enhance thermochemical stability and reactivity, while cooling increased viscosity and the likelihood of unstable solution behaviour, which may necessitate discarding. The order in which feedstocks are combined directly affects whether the solution becomes unstable, with an optimal sequence of water, alkali-hydroxide, soluble silicate found to ensure greater process reliability. A predictive model and accompanying visual tools enable practitioners to assess solution viability and define stability windows by quantifying initial and final/unstable periods and temperatures based on feedstock composition and solution temperature. These results contribute to improved reproducibility and quality control in geopolymer research and represent a step toward developing standard operating procedures for activator solution synthesis.
Authors: O. E. Alon, L. S. Cederbaum
We consider a multiple-species mixture of interacting bosons, $N_1$ bosons of mass $m_1$, $N_2$ bosons of mass $m_2$, and $N_3$ bosons of mass $m_3$ in a harmonic trap of frequency $\omega$. The corresponding intraspecies interaction strengths are $\lambda_{11}$, $\lambda_{22}$, and $\lambda_{33}$, and the interspecies interaction strengths are $\lambda_{12}$, $\lambda_{13}$, and $\lambda_{23}$. When the shape of all interactions are harmonic, this is the generic multiple-species harmonic-interaction model which is exactly solvable. We start by solving the many-particle Hamiltonian and concisely discussing the ground-state wavefunction and energy in explicit forms as functions of all parameters, the masses, numbers of particles, and the intraspecies and interspecies interaction strengths. We then move to compute explicitly the reduced one-particle density matrices for all the species and diagonalize them, thus generalizing the treatment in [J. Chem. Phys. {\bf 161}, 184307 (2024)]. The respective eigenvalues determine the degree of fragmentation of each species. As applications, we focus on aspects that do not appear for the respective single-species and two-species systems. For instance, placing a mixture of two kinds of bosons in a bath made by a third kind, and controlling the fragmentation of the former by coupling to the latter. Another example exploits the possibility of different connectivities (i.e., which species interacts with which species) in the mixture, and demonstrates how the fragmentation of species $3$ can be manipulated by the interaction between species $1$ and species $2$, when species $3$ and $1$ do not interact with each other. We thereby highlight properties of fragmentation that only appear in the multiple-species mixture. Further applications are briefly discussed.
Authors: Alexandra J. Hardy, Samuel Cameron, Steven McDonald, Abdallah Daddi-Moussa-Ider, Elsen Tjhung
We derive a self-consistent hydrodynamic theory of coupled binary-fluid-surfactant systems from the underlying microscopic physics using Rayleigh's variational principle. At the microscopic level, surfactant molecules are modelled as dumbbells that exert forces and torques on the fluid and interface while undergoing Brownian motion. We obtain the overdamped stochastic dynamics of these particles from a Rayleighian dissipation functional, which we then coarse-grain to derive a set of continuum equations governing the surfactant concentration, orientation, and the fluid density and velocity. This approach introduces a polarization field, representing the average orientation of surfactants, and yields a mesoscopic free energy functional from which all governing equations are consistently derived. The resulting model accurately captures key surfactant phenomena, including surface tension reduction and droplet stabilization, as confirmed by both perturbation theory and numerical simulations.
Authors: Marco Musacchio, Alexander P. Antonov, Hartmut Löwen, Lorenzo Caprini
We study a two-dimensional crystal composed of active units governed by self-alignment. This mechanism induces a torque that aligns a particle's orientation with its velocity and leads to a phase transition from a disordered to a flocking crystal. Here, we provide the first microscopic theory that analytically maps the crystal dynamics onto a Landau-Ginzburg model, in which the velocity-dependent effective free energy undergoes a transition from a single-well shape to a Mexican-hat profile. As confirmed by simulations, our theory quantitatively predicts the transition point and characteristic spatial velocity correlations. The continuous change of the order parameter and the diverging behavior of the analytically predicted correlation length imply that flocking in self-aligning active crystals is a second-order phase transition. These findings provide a theoretical foundation for the flocking phenomenon observed experimentally in active granular particles and migrating cells.
Authors: T. Alper Yoğurt, Matthew T. Eiles
An impurity immersed in a Bose condensate can form a quasiparticle known as a Bose polaron. When the impurity-boson interaction is short-ranged, the quasiparticle's properties are universal, characterized - independent of the bath density $n_0$ - by the impurity-boson scattering length $a_{IB}$. Long-ranged interactions - such as provided by Rydberg or ionic impurities - introduce an effective interaction range $r_{\mathrm{eff}}$, and boson-boson interactions provide a third length scale, the condensate coherence length $\xi $. These competing length scales raise the question of whether a universal description remains valid across different bath densities. In this study, we discuss the quasiparticle nature of long-range impurities and its dependence on the length scales $ n_0^{-1/3} $, $ r_{\mathrm{eff}} $, and $ \xi $. We employ two complementary theories - the coherent state Ansatz and the perturbative Gross-Pitaevskii theory - which incorporate beyond-Fröhlich interactions. We derive an analytical expression for the beyond-Fröhlich effective mass for a contact interaction and numerically compute the effective mass for long-range impurities. We argue that the coupling parameter $ |a_{IB}| n_0^{1/3} $ remains the principal parameter governing the properties of the polaron. For weak $ (|a_{IB}| n_0^{1/3} \ll 1) $ and intermediate $ (|a_{IB}| n_0^{1/3} \simeq 1) $ values of the coupling parameter, long-range impurities in a BEC are well-described as quasiparticles with a finite quasiparticle weight and a well-defined effective mass. However, the quasiparticle weight becomes significantly suppressed as the effective impurity volume is occupied by an increasing number of bath particles $ (r_{\mathrm{eff}} n_0^{1/3} \gg 1) $.
Authors: Guanghong Wen, Yi Zhu, Yingxiang Zheng, Shuhe Cui, Ji Wang, Yanyun Ren, Hao Li, Guofeng Zhang, Lixing You
Quantum metrology based on Josephson junction array reproduces the most accurate desired voltage by far, therefore being introduced to provide voltage standards worldwide. In this work, we quantitatively analyzed the dependence of the first Shapiro step height of the junction array at 50 GHz on the parameter spread of 10,000 Josephson junctions by numerical simulation with resistively shunted junction model. The results indicate an upper limit spread of the critical current and resistance of the Josephson junctions. Specifically, to keep the maximum first Shapiro step above 0.88 mA, the critical current standard deviation, $\sigma$, should not exceed 25%, and for it to stay above 0.6 mA, the resistance standard deviation should not exceed 1.5%.
Authors: W. P. Lima, T. F. O. Lara, J. P. G. Nascimento, J. Milton Pereira Jr., D. R. da Costa
Lieb and Kagome lattices exhibit two-dimensional topological insulator behavior with $\mathbb{Z}_2$ topological classification when considering spin-orbit coupling. In this study, we used a general tight-binding Hamiltonian with a morphological control parameter $\theta$ to describe the Lieb ($\theta=\pi/2$), Kagome ($\theta=2\pi/3$), and transition lattices ($\pi/2<\theta<2\pi/3$) while considering intrinsic spin-orbit (ISO) coupling. We systematically investigated the effects of shear and uniaxial strains, applied along different crystallographic directions, on the electronic spectrum of these structures. Our findings reveal that these deformations can induce topological phase transitions by modifying the structural lattice angle associated with the interconversibility process between Lieb and Kagome, the amplitude of the strain, and the magnitude of the ISO coupling. These transitions are confirmed by the evolution of Berry curvature and by changes in the Chern number when the gap closes. Additionally, by analyzing hypothetical strain scenarios in which the hopping and ISO coupling parameters remain intentionally unchanged, our results demonstrated that the strain-induced phase transitions arise from changes in the hopping and ISO coupling parameters.
Authors: Dominik Krengel, Jian Chen, Zhipeng Yu, Hans-Georg Matuttis, Takashi Matsushima
Clay minerals are non-spherical nano-scale particles that usually form flocculated, house-of-card like structures under the influence of inter-molecular forces. Numerical modeling of clays is still in its infancy as the required inter-particle forces are available only for spherical particles. A polytope approach would allow shape-accurate forces and torques while simultaneously being more performant. The Anandarajah solution provides an analytical formulation for van der Waals forces for cuboid particles but in its original form is not suitable for implementation in DEM simulations. In this work, we discuss the necessary changes for a functional implementation of the Anandarajah solution in a DEM simulation of rectangular particles and their extension to cuboid particles.
Authors: Chao Xu, Yunlong Zang, Yixin Ma, Yingfei Gu, Shenghan Jiang
Symmetry-protected topological (SPT) phases are short-range entangled quantum states characterized by anomalous edge behavior, a manifestation of the bulk-boundary correspondence for topological phases. Moreover, the Li-Haldane conjecture posits that the entanglement spectrum exhibits the same anomaly as the physical edge spectrum, thereby serving as an entanglement-based fingerprint for identifying topological phases. In this work, we extend the entanglement-based diagnostic tools by demonstrating that the edge anomaly is manifested not only in the entanglement spectrum but also in the reduced density matrix itself, a phenomenon we refer to as the mixed state anomaly. Focusing on the two-dimensional $\mathbb{Z}_2$ SPT phase, we show that this anomaly is subtly encoded in symmetry-twisted mixed states, leading to a topological contribution to the disorder parameter beyond the area law, as well as a spontaneous-symmetry-breaking type long-range order when time reversal symmetry is present.
Authors: Feng Huang, Hanshuang Chen
We investigate the first-passage properties and extreme-value statistics of an overdamped Brownian particle confined by an external linear potential $V(x)=\mu |x-x_0|$, where $\mu>0$ is the strength of the potential and $x_0>0$ is the position of the lowest point of the potential, which coincides with the starting position of the particle. The Brownian motion terminates whenever the particle passes through the origin at a random time $t_f$. Our study reveals that the mean first-passage time $\langle t_f \rangle$ exhibits a nonmonotonic behavior with respect to $\mu$, with a unique minimum occurring at an optimal value of $\mu \simeq 1.24468D/x_0$, where $D$ is the diffusion constant of the Brownian particle. Moreover, we examine the distribution $P(M|x_0)$ of the maximum displacement $M$ during the first-passage process, as well as the statistics of the time $t_m$ at which $M$ is reached. Intriguingly, there exists another optimal $\mu \simeq 1.24011 D/x_0$ that minimizes the mean time $\langle t_m \rangle$. All our analytical findings are corroborated through numerical simulations.
Authors: Toranosuke Umemura, Issei Sakai, Takuma Akimoto
We investigate the nonequilibrium dynamics of active matter using a two-dimensional active Brownian particles model. In these systems, self-propelled particles undergo motility-induced phase separation (MIPS), spontaneously segregating into dense and dilute phases. We find that in the high-density phase, local particle mobility exhibits glassy behavior, with diffusivity remaining unchanged despite variations in the global system density. As global density increases further, the system undergoes a transition to a solid-like state through this glassy phase. These findings provide insights into nonequilibrium phase transitions in active matter, revealing a robust glassy phase en route to solidification, and may guide future studies in both synthetic and biological active systems.
Authors: Jiali Zhang, Shaoliang Zhang
Recently, tensor gauge fields and their coupling to fracton phases of matter have attracted more and more research interest, and a series of novel quantum phenomena arising from the coupling has been predicted. In this article, we propose a theoretical scheme to construct a time-dependent rank-2 tensor electric field by introducing a periodically driving quadratic potential in a dipole-conserving Bose-Hubbard model, and investigate the dynamics of dipole and fracton excitations when the drive frequency is resonant with the on-site interaction. We find that the dynamics are dominated by the splitting of large dipoles with the photon-assisted correlated tunneling and the movement of small dipoles, both of which can be well controlled by the drive amplitude. Our work provides a possible approach for engineering the dynamics of dipole-conserving quantum systems via tensor gauge fields.
Authors: Lorenzo Monacelli, Maria Rescigno, Alasdair Nicholls, Umbertoluca Ranieri, Simone Di Cataldo, Livia Eleonora Bove
Hydrogen bond symmetrization is a fundamental pressure-induced transformation in which the distinction between donor and acceptor sites vanishes, resulting in a symmetric hydrogen-bond network. While extensively studied in pure ice, most notably during the ice VII to ice X transition, this phenomenon remains less well characterized in hydrogen hydrates. In this work, we investigate hydrogen bond symmetrization in the high-pressure phases of hydrogen hydrate (H2-H2O and H2-D2O) through a combined approach of Raman spectroscopy and first-principles quantum atomistic simulations. We focus on the C2 and C3 filled-ice phases, using both hydrogenated and deuterated water frameworks. Our results reveal that quantum fluctuations and the interaction between the encaged H2 molecules and the host lattice play a crucial role in driving the symmetrization process. Remarkably, we find that in both C2 and C3 phases, hydrogen bond symmetrization occurs via a continuous crossover at significantly lower pressures than in pure ice, without any change in the overall crystal symmetry. These findings provide new insight into the quantum-driven mechanisms of bond symmetrization in complex hydrogen-bonded systems under extreme conditions.
Authors: Virginie de Mestral, Lorenzo Bastonero, Michele Kotiuga, Marko Mladenovic, Nicola Marzari, Mathieu Luisier
We present an ab initio method to calculate the clamped Pockels tensor of ferroelectric materials from density-functional theory, the modern theory of polarization exploiting the electric-enthalpy functional, and automated first- and second-order finite-difference derivatives of the polarizations and the Hellmann-Feynman forces. Thanks to the functional-independent capabilities of our approach, we can determine the Pockels tensor of tetragonal barium titanate (BTO) beyond the local density approximation (LDA), with arbitrary exchange-correlation (XC) functionals, for example, PBEsol. The latter, together with RRKJ ultra-soft pseudo-potentials (PP) and a supercell exhibiting local titanium off-centering, enables us to stabilize the negative optical phonon modes encountered in tetragonal BTO when LDA and norm-conserving PP are combined. As a result, the correct value range of $r_{51}$, the largest experimental Pockels coefficient of BTO, is recovered. We also reveal that $r_{51}$ increases with decreasing titanium off-centering for this material. The lessons learned from the structural, dielectric, and vibrational investigations of BTO will be essential to design next-generation electro-optical modulators based on the Pockels effect.
Authors: Marusa Mur, Aljaz Kavcic, Uros Jagodic, Rok Podlipec, Matjaz Humar
3D printing has revolutionized numerous scientific fields and industries, with printing in biological systems emerging as a rapidly advancing area of research. However, its application to the subcellular level remains largely unexplored. Here, we demonstrate for the first time the fabrication of custom-shaped polymeric microstructures directly inside living cells using two-photon polymerization. A biocompatible photoresist is injected into live cells and selectively polymerized with a femtosecond laser. The unpolymerized photoresist is dissolved naturally within the cytoplasm, leaving behind stable intracellular structures with submicron resolution within live cells. We printed various shapes, including a $10 \mu m$ elephant, barcodes for cell tracking, diffraction gratings for remote readout, and microlasers. Our top-down intracellular biofabrication approach, combined with existing functional photoresists, could open new avenues for various applications, including intracellular sensing, biomechanical manipulation, bioelectronics, and targeted intracellular drug delivery. Moreover, these embedded structures could offer unprecedented control over the intracellular environment, enabling the engineering of cellular properties beyond those found in nature.
Authors: Camino Martín-Sáncheza, Ana Sánchez-Iglesias, José Antonio Barreda-Argüeso, Jean-Paul Itié, Paul Chauvigne, Luis M. Liz-Marzán, Fernando Rodríguez
We report on the high-pressure optical and mechanical properties of penta-twinned gold nanoparticles (PT-AuNPs) of different geometries: decahedra, rods and bipyramids. Our results show that, unlike single-crystal (SC-AuNPs), PT-AuNPs preserve both their non-cubic crystal structures and their overall morphology up to 30 GPa. This structural integrity under compression is related to an enhanced mechanical resilience of PT-AuNPs, despite exhibiting bulk moduli comparable to those of SC-AuNPs. Notwithstanding, comparable pressure-induced localized surface plasmon resonance redshifts - for all nanoparticle geometries - were observed. Our analysis indicates that these shifts are primarily caused by changes in the refractive index of the surrounding medium, with electron density compression playing a minor role, contrasting with the behavior in SC-AuNPs, where electron density compression has a greater influence.
Authors: Simon Brunner, Christian F. Schmidt, Stefan Floerchinger
We consider excitations of a spin-1 Bose-Einstein-condensate (BEC) in the vicinity of different mean-field configurations and derive mappings to emergent relativistic scalar field theories minimally coupled to curved acoustic spacetimes. The quantum fields are typically identified with Nambu-Goldstone bosons, such that the structure of the analogue quantum field theories on curved spacetimes depends on the (spontaneous) symmetry breaking pattern of the respective ground-state. The emergent spacetime geometries are independent of each other and exhibit bi-metricity in the polar and antiferromagnetic phase, whereas one has tri-metricity in the ferromagnetic phase. Compared to scalar BECs, the spinor degrees of freedom allow to investigate massive vector and scalar fields where the former is a spin-nematic rotation mode in the polar phase which can be cast into a Proca field that is minimally coupled to a curved spacetime that emerges on length scales larger than the spin-healing length. Finally, we specify the Zeeman couplings and the condensate trap to be spacetime-dependent such that a cosmological FLRW-metric can be achieved. This work enables a pathway towards quantum-simulating cosmological particle production of Proca quanta via quenching the quadratic Zeeman-coefficient or via magnetic field ramps, which both result in the creation of spin-nematic squeezed states.