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Physics Condensed Matter

cond-mat Watch Condensed Matter

Saturday 21 March

Materials Science

Substrate-Mediated Evaporation and Stochastic Evolution of Supported Au Nanoparticles

Dmitri N. Zakharov, Xiaohui Qu, Hong Wang et al. (+6 more)

We use in situ transmission electron microscopy with automated tracking to study supported gold nanoparticles (NPs) during high-temperature vacuum annealing. \rev{The average mass loss per NP is governed by a flat, nearly size-independent substrate-mediated evaporation profile.} On top of \rev{this mean shrinkage}, individual NPs show significant fluctuations in apparent growth or shrinkage, and NP volume follows a \rev{random-walk-like trajectory. To rationalize both the ensemble-mean behavior and the particle-resolved variability, we develop a self-consistent theory that couples substrate-mediated evaporation to collective 2D Ostwald-type mass exchange through a shared adatom field, described in terms of a renormalized screening length and background concentration. In the experimentally relevant regime, the theory predicts an approximately size-independent mean shrinkage rate and clarifies how net mass loss suppresses classical coarsening.} \rev{Superimposed on this deterministic drift, we quantify stochastic volume trajectories and capture their fluctuation spectrum with a minimal Langevin description consistent with intermittent adatom attachment and detachment events.} In addition, we characterize the lateral diffusive motion of NPs, which is responsible for their coalescence. Altogether, our results highlight that stochasticity is intrinsic at the nanoscale \rev{and that predicting the evolution of supported NPs at early and intermediate times requires a unified framework combining substrate-mediated evaporation, collective mass exchange, and stochastic fluctuations.
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All authors Dmitri N. Zakharov, Xiaohui Qu, Hong Wang, Yuewei Lin, Aaron Stein, James P. Horwath, Shinjae Yoo, Eric A. Stach, Alexei V. Tkachenko

Materials Science · Cross-listed from cs.SE

Evaluating LLM-generated code for domain-specific languages: molecular dynamics with LAMMPS

Ethan Holbrook, Juan C. Verduzco and Alejandro Strachan

Large language models (LLMs) are changing the way researchers interact with code and data in scientific computing. While their ability to generate general-purpose code is well established, their effectiveness in producing scientifically valid scripts for domain-specific language (DSLs) remains largely unexplored. We propose an evaluation procedure that enables domain experts to assess the validity of LLM-generated input files for LAMMPS, a widely used molecular dynamics (MD) code, without requiring deep familiarity with its syntax. The evaluation procedure combines a normalization step that produces canonical input files with an extensible parser for syntax analysis, followed by a reduced-cost execution stage and accuracy checks that isolate common errors before running costly simulations. We apply the pipeline to eight state-of-the-art LLMs across three prompts of increasing complexity. The parser pass rate has improved from 74% to 91% over the past year, but scientific accuracy on coupled multi-step workflows remains limited. Across all 80 scripts evaluated on the most complex prompt, only one was fully correct as generated. We further package the automated stages as a reusable agentic skill that LLMs can invoke during script generation; in a small-scale demonstration, this skill helped two models produce five fully correct scripts out of six across the same three prompts, including the hardest one. The pipeline highlights both the limitations of current LLMs in generating scientific DSLs and a practical path toward integrating them into domain-specific computational ecosystems.
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Strongly Correlated Electrons

Intrinsic Topological Weyl Phase Transition Induced by a Magnetostructural Transformation in a Kagome Magnet

Tsung-Han Yang, Satoshi Okamoto, D. Alan Tennant et al. (+2 more)

Topological phase transitions provide a unique window into the interplay between structure, magnetism, and Weyl physics in magnetic Weyl semimetals. However, realizing an intrinsic Weyl phase transition between two distinct Weyl states near room temperature remains challenging. Here, we demonstrate that a magnetostructural transition effectively induces such a transition in the kagome magnet Mn$_3$Ga. High-resolution neutron diffraction, magnetization characterizations and first-principles calculations reveal that Mn$_3$Ga undergoes a chiral antiferromagnetic transition below 485 K, followed by a magnetostructural transition to a monoclinic structure with highly canted antiferromagnetic order near room temperature. These cooperative changes in lattice and magnetic symmetries reorganize Weyl nodes, driving a transition from a primary type-II Weyl state to a distinct Weyl state, accompanied by dramatic variations in the anomalous Hall effect and appearance of topological Hall effect. Our findings open a new pathway for discovering novel topological Weyl states and potential spintronic applications.
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All authors Tsung-Han Yang, Satoshi Okamoto, D. Alan Tennant, Michael A. McGuire, Qiang Zhang

Statistical Mechanics · Cross-listed from physics.soc-ph

Conflict Avoidance in Pedestrian Merging in Controlled Experiments by Variance Indicator

Jiawei Zhang, Xiaolu Jia, Sakurako Tanida et al. (+3 more)

Pedestrian congestion at corridor intersections often originates from localized fluctuations in motion rather than from a macroscopic collapse of flow. Understanding pedestrian instability at corridor intersections remains challenging because existing studies mainly rely on density, average speed, or flow-based measures and limited datasets, making it difficult to separate geometric turning effects from interaction induced fluctuations in merging flows. In particular, the mechanism underlying the turning angle dependence in T junctions has not been resolved. Here, we analyze more than 300 controlled experiments conducted in L corridors with turning only and T corridors with turning and merging. Using Voronoi-based speed variance $V_s$ and velocity variance $V_v$, we systematically compare geometric and interaction effects. $V_s$ effectively captures interaction driven instability, while $V_v$ reflects directional adjustments due to geometry. The comparison reveals distinct fluctuation mechanisms and identifies a critical transition near $90{\deg}$, demonstrating the advantage of variance-based indicators for diagnosing pedestrian dynamics.
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All authors Jiawei Zhang, Xiaolu Jia, Sakurako Tanida, Claudio Feliciani, Daichi Yanagisawa, Katsuhiro Nishinari

Friday 20 March

Materials Science

Composition dependence of the critical Rayleigh number curve for macrosegregation in multicomponent metal alloys

Owain S. Houghton, Adrian S. Sabau and Gregory B. Olson

Convective instabilities in the semi-solid mushy zone can trigger channel formation that leads to defects known as freckles, channel segregates and A-type segregates. In the present work, Flemings' model is used to determine conditions for the onset of local remelting when buoyancy-driven flow is suddenly triggered in an initially stagnant mushy zone. An expression in the form of a Rayleigh number $Ra$, and its associated critical value $Ra_{\rm crit}$, above which the local remelting condition is satisfied, are derived. Using thermophysical data from CALPHAD, these expressions are evaluated using results from benchmark experimental and numerical studies for the nickel-based superalloy SX-1 and Pb-Sn alloys. The correlation of this local-remelting criterion with previously reported empirical criteria is also tested for various steel compositions. It is found that $Ra_{\rm crit}$ varies with the local average solid fraction and several thermophysical properties. Since these properties can vary substantially within a relatively narrow composition range, it is suggested that $Ra_{\rm crit}$ is a strongly composition-dependent parameter.
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Strongly Correlated Electrons

Unifying Variational and Dynamical Quantum Embedding: From Ghost Gutzwiller Approximation to Dynamical Mean-Field Theory

Samuele Giuli, Tsung-Han Lee, Yong-Xin Yao et al. (+4 more)

Dynamical and variational frameworks have long been viewed as distinct paradigms. In particular, in quantum embedding (QE) frameworks, dynamical mean-field theory (DMFT) captures nonperturbative dynamical correlations through a frequency-dependent self-energy, while the Gutzwiller approximation (GA) is formulated in terms of a variationally optimized ground-state wavefunction. Here we bridge these perspectives, proving that the ghost-Gutzwiller approximation (ghost-GA), which also admits a density-matrix-matching QE formulation known as ghost density matrix embedding theory (ghost-DMET), becomes strictly equivalent to DMFT in the limit of infinitely many auxiliary bath modes. This formal unification has immediate consequences. In particular, it yields a rigorous finite-temperature extension of ghost-GA and shows that the physical Green's function can be determined from static expectation values of the embedding Hamiltonians, providing a route to computational studies of competing phases in strongly correlated matter with DMFT-level accuracy, while bypassing the need to calculate dynamical spectra with conventional impurity solvers. More broadly, it shows that the variational ghost-GA, the density-matrix-matching ghost-DMET formulation, and the dynamical DMFT description are not separate constructions, but complementary formulations of the same QE structure, thereby providing a concrete formal basis for future controlled extensions beyond DMFT.
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All authors Samuele Giuli, Tsung-Han Lee, Yong-Xin Yao, Gabriel Kotliar, Andrei E. Ruckenstein, Olivier Gingras, Nicola Lanatà

Strongly Correlated Electrons

Magnetic and electric properties of the metallic kagome antiferromagnet CrRhAs

Franziska Breitner, Bin Shen, Anton Jesche et al. (+2 more)

CrRhAs is an antiferromagnetic kagome metal predicted to host a nontrivial spin texture with vector spin chirality [Huang et al., npj Quantum Mater. 8, 32 (2023)]. We report the synthesis and basic characterization of CrRhAs single crystals, which exhibit an antiferromagnetic transition with $T_{\rm N}$ = 150~K, evidenced by electrical transport, heat capacity, and magnetization measurements. Hall resistivity varies linearly with magnetic field, i.e., there is no nonlinear Hall contribution. Intriguingly, the Hall coefficient changes sign between the configurations of $j \parallel ab, H \perp ab$ and $j \parallel c, H \perp c$, which is likely connected to a peculiar topology of the Fermi surface. Furthermore, for $j \parallel ab$, the Hall coefficient shows a pronounced and continuous enhancement below $T_{\rm N}$, signaling a significant reconstruction of the Fermi surface or an extra scattering from the magnons. Our results offer guidance for exploring anomalous electric transport phenomena in exotic magnetic systems.
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All authors Franziska Breitner, Bin Shen, Anton Jesche, Alexander A. Tsirlin, Philipp Gegenwart

Statistical Mechanics

Quantum Chaos in Many-Body Systems Without a Classical Analogue

Fotis I. Giasemis

In classical systems, chaos is clearly defined via the behavior of trajectories. In quantum systems with a classical analogue one finds that the transition from regular to chaotic dynamics is signified by a change in the spectral statistics. This has been found to remain true for quantum systems with no classical analogue, including many-body systems. Furthermore, quantum chaotic systems explore all the allowed configurations in the Hilbert space, i.e. they are ergodic, while integrable systems, and systems in the many-body localized phase, are restricted to a certain subspace of the available phase space, and hence strongly break ergodicity. In this dissertation, we study the intermediate behavior between ergodicity and localization, i.e. the weak breaking of ergodicity. The model examined is the PXP spin chain model, where spins are allowed to flip only under certain kinetic constraints. We start by reproducing some already established results. First, we explore the eigenstate thermalization hypothesis (ETH) for this model and demonstrate the existence of a small number of states, throughout the PXP spectrum, that violate the ETH. Then we study the level-spacing statistics of the model, a well-known quantum chaos diagnostic, which turns out to be close to semi-Poisson and approach Wigner–Dyson statistics for large system sizes. Moreover, we examine various aspects of the model that have not been studied before. For example, the eigenvector component statistics, another quantum chaos diagnostic, for the PXP model turn out to be non-Gaussian. Finally, we perform a quench, in order to study how the energy spreads throughout the system, and observe ballistic fronts.
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Mesoscale and Nanoscale Physics

A cellular automaton model for thermal transport in low-dimensional systems

Alejandra León

In this work, we formulate a theoretical model based on a cellular automaton (CA) to study thermal transport in low-dimensional nanostructures across ballistic, diffusive, and transition regimes. Unlike computationally intensive methods such as the Boltzmann Transport Equation (BTE), our model stands out for its geometrical robustness, allowing the seamless integration of substitutional impurities, vacancies, and irregular edges. We validated the model using graphene nanoribbons (AGNRs), successfully replicating the dependence of thermal conductivity on ribbon width and temperature. Results demonstrate that the model captures critical scattering and confinement effects with a linear scalability O(N). Given the increasing pressure to optimize computational resources and reduce the carbon footprint associated with AI infrastructure, this CA model emerges as a highly efficient tool for the parametric exploration and design of next-generation thermal devices.
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Materials Science · Cross-listed from physics.app-ph

Degradation Dynamics of Perovskite Solar Cells Under Fixed Reverse Current Injection

Fangyuan Jiang, Haruka Koizumi, Hannah Contreras et al. (+8 more)

Previous studies of reverse-bias stability in perovskite solar cells have focused primarily on voltage controlled reverse-bias tests. Here we instead present an investigation of perovskite solar cell degradation under well-defined, constant reverse-current stress. We show that the choice of hole-transport layer dictates the dominant degradation pathway: cells using thick poly(triphenylamine) (PTAA) layers with better indium-doped tin oxide (ITO) coverage can tolerate high reverse bias but quickly undergo catastrophic breakdown under fixed reverse current near their one-sun maximum power-point. In contrast, cells modified with the phosphonic-acid interface layer MeO-2PACz, with poorer ITO coverage compared to PTAA, exhibit soft, gradual, and largely recoverable degradation, regardless of the shading conditions. For MeO-2PACz devices, degradation increases with both current magnitude and duration. Importantly, when normalized by injected charge (current times duration), lower currents applied over longer times cause more severe degradation than higher currents over shorter periods. Combining electrical measurements with spatially resolved photoluminescence imaging, we argue against shunt formation and instead support an ion- and charge-mediated interfacial electrochemical degradation mode.
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All authors Fangyuan Jiang, Haruka Koizumi, Hannah Contreras, Rajiv Giridharagopal, Akash Dasgupta, Zixu Huang, Ryan A. DeCrescent, Kell Fremouw, Michael D. McGehee, Neal R. Armstrong, David S. Ginger

Materials Science · Cross-listed from physics.app-ph

Neutralization of the impact of belt speed on screen printed copper metallization by LECO on PERC homogeneous emitter

Abasifreke Ebong, Donald Intal, Sandra Huneycutt et al. (+6 more)

Copper fire-through metallization is a cost-effective alternative to Ag counterpart for industrial high efficiency solar cells. The fire through dielectric metallization relies on belt speed, which dictates the ramp up and ramp down rates for effective contact formation. In this paper three belt speeds (325oC, 360oC, 390oC) at constant peak firing temperature, were used to process PERC (homogeneous emitter) cells. After the contact firing the electrical parameters were dependent on belt speed, but after LECO treatment, they were identical. The SEM/EDS cross sectional analyses showed increased elemental Cu with belt speed, and the series resistance was lowest for the middle belt speed before LECO. However, after the LECO treatment, the series resistance dropped, respectively, to 0.503 ohm-cm-2, 0.428 ohm-cm-2 and 0.500 ohm-cm-2 leading to efficiency of 20.8% on homogeneous PERC emitter.
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All authors Abasifreke Ebong, Donald Intal, Sandra Huneycutt, Ajeet Rohatgi, Vijay Upadhyaya, Sagnik Dasgupta, Ruohan Zhong, Thad Druffel, Ruvini Dharmadasa

Materials Science · Cross-listed from physics.app-ph

Critical look at the atmospheric Cu fire-through dielectric metallization for cost-effective and high efficiency silicon solar cells

Donald Intal, Sandra Huneycutt, Abasifreke Ebong et al. (+6 more)

The formation of stable copper-silicide (Cu3Si) interfaces is crucial for cost-effective, high-efficiency solar cells. However, copper's diffusivity and electromigration issues pose challenges for contact stability. This study employs Laser-Enhanced Contact Optimization (LECO) to induce localized nano-scale Joule heating at the Cu-Si interface in phosphorus-doped p-PERC solar cells. High-resolution STEM and bright field analyses confirm stable Cu3Si formation in LECO-treated samples, with significantly reduced material segregation compared to nonLECO samples. SEM and post-etch EDS mapping demonstrate improved chemical resistance and interface cleanliness. Electrically, LECO treatmenet reduces series resistance by a factor 3, enhancing fill factor and efficiency while preserving diode quality. These results highlight LECO as a scalable method for reliable, silver-free solar cell metallization.
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All authors Donald Intal, Sandra Huneycutt, Abasifreke Ebong, Ajeet Rohatgi, Vijay Upadhyaya, Sagnik Dasgupta, Ruohan Zhong, Thad Druffel, Ruvini Dharmadasa

Materials Science · Cross-listed from physics.chem-ph

A unified machine-learning framework for ab initio multiscale modeling of liquids

Anna T. Bui and Stephen J. Cox

Understanding and predicting the behavior of liquid matter across length scales, using only the microscopic interactions encoded in the Schrödinger equation, remains a central challenge in the physical sciences. Achieving this goal requires not only an accurate and efficient description of intermolecular forces but also a consistent framework that bridges the micro-, meso-, and macroscales. Here, by combining machine-learned interatomic potentials (MLIPs) with neural classical density functional theory (neural cDFT), we present such a framework. The underlying idea is simple: MLIPs trained on quantum-mechanical energies and forces are used to generate inhomogeneous microscopic density profiles, which in turn serve as the training data for neural cDFT. The resulting ab initio neural cDFT is not only significantly more computationally efficient than molecular simulations, but also provides a conceptually transparent route to the thermodynamics of both homogeneous and inhomogeneous systems. We demonstrate the approach for both water and carbon dioxide using several exchange-correlation functionals. Beyond accurately reproducing bulk equations of state and liquid-vapor phase diagrams, ab initio neural cDFT predicts, from first principles, how confinement modifies liquid-vapor coexistence in water. It also captures complex behavior in supercritical carbon dioxide such as the Fisher-Widom and Widom lines. Ab initio neural cDFT establishes a general first-principles route to multiscale modeling of fluids within a single unified conceptual framework.
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Materials Science

Structural Phase Separation Couples to Charge-Density-Wave Formation in Kagome Metal FeGe

Boyang Zhao, Youngjun Ahn, Qinwen Deng et al. (+7 more)

The intertwining of charge, spin, and lattice degrees of freedom underlies the emergent properties of correlated materials. A recent prominent example is the kagome metal FeGe, which hosts coexisting charge density wave (CDW) and antiferromagnetic orders, accompanied by a lattice distortion associated with partial Ge-Ge dimerization. Using temperature-dependent high-resolution X-ray diffraction measurements, we observed a robust splitting of the lattice reflection into two coexisting peaks with distinct lattice constants at the CDW transition temperature TCDW, providing direct evidence for a first-order structural phase transition that is absent in samples with suppressed CDW order. Furthermore, the long-range CDW order was found to be only commensurate with lattice structures with the compressed out-of-plane lattice constant. The Landau free energy analysis shows that strong lattice-charge coupling is a key factor in stabilizing long-range CDW order. Our work clarifies the critical role of structural transformation in the CDW formation and opens opportunities for strain control of electronic phases in FeGe.
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All authors Boyang Zhao, Youngjun Ahn, Qinwen Deng, Yidai Liu, Sijie Xu, Donald A. Walko, Stephan O. Hruszkewycz, Pengcheng Dai, Liang Wu, Haidan Wen

Mesoscale and Nanoscale Physics

Gate-tunable synthetic antiferromagnetism with nonrelativistic spin splitting in a graphene/MnS/graphene heterostructure

Marko Milivojević and Martin Gmitra

We propose encapsulating type-A antiferromagnetic semiconductors between graphene layers to realize a gate-tunable synthetic antiferromagnet with nonrelativistic spin splitting, enabling efficient spintronic transport via graphene. Ab initio calculations and tight-binding models of graphene/MnS/graphene heterostructure reveal that gate-tuning of the heterostructure breaks top/bottom graphene equivalence, inducing opposite ferromagnetic proximity exchange that lifts spin degeneracy to yield nonrelativistic spin splitting at the Fermi level, dominating over relativistic effects. The induced effects manifest as conductance dips in spin-resolved transport through proximitized graphene nanoribbons, observable as giant magnetoresistance within a narrow energy window around the Fermi level. Our graphene/type-A antiferromagnetic heterostructure, a readily synthesizable platform incorporating antiferromagnets with nonrelativistic spin splitting, pave the way for gate-manipulated, low-dimensional antiferromagnetic devices.
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Strongly Correlated Electrons

Spin-reorientation as a switch for electronic topology in van der Waals ferromagnets

Satyabrata Bera, Sudipta Chatterjee, Suman Kalyan Pradhan et al. (+5 more)

The interplay between spin reorientation and topological electronic structure in two-dimensional (2D) van der Waals (vdW) ferromagnets is central to understanding how magnetic anisotropy shapes charge transport. Although spin-reorientation transitions (SRTs) are common in 2D metallic ferromagnets, their impact on electronic-topology-driven thermodynamic and transport properties remains largely unexplored. Here we investigate this issue in Fe$_4$GeTe$_2$ (F4GT), a room-temperature quasi-2D vdW ferromagnet, using temperature-dependent magnetization, specific heat, magnetotransport, and thermoelectric measurements. Magnetization and specific heat establish a reorientation of the magnetic easy axis near $T_{\mathrm{SRT}} \sim 100$~K, in addition to ferromagnetic ordering at $T_C \sim 270$~K. Across the SRT, the Seebeck coefficient and anisotropic magnetoresistance show clear anomalies, indicating Fermi-surface reconstruction. The magnetoresistance exhibits a two-step field dependence: a low-field enhancement near the SRT associated with scattering from canted spins and evolving domains, followed by a higher-field negative response as spin fluctuations are suppressed. The simultaneous sign change of the ordinary Hall coefficient $R_0$ and the sharp anomaly in the anomalous Hall resistivity $\rho^{A}_{yx}$ further point to a temperature-driven modification of the underlying band topology. Analysis of the anomalous Hall conductivity $\sigma^{A}_{xy}$ and the scaling of $\rho^{A}_{yx}$ shows that the Berry-curvature-driven anomalous Hall response below $T_{\mathrm{SRT}}$ is strongly modified above the transition. Our results identify spin reorientation as an internal control parameter for switching between distinct topological transport regimes in a 2D vdW ferromagnet, providing a symmetry-controlled route to engineer spin-polarized electronic states and domain-texture-driven functionalities.
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All authors Satyabrata Bera, Sudipta Chatterjee, Suman Kalyan Pradhan, Subhadip Pradhan, Arnab Bera, Sk Kalimuddin, Ashis K. Nandy, Mintu Mondal

Quantum Gases

Semi-classical evaporative cooling: classical and quantum distributions

A. A. Arvizu-Velazquez, A. del Río-Lima, S. Dondé-Rodríguez et al. (+1 more)

We develop a semiclassical thermodynamic framework for the evaporative cooling of trapped atomic gases that treats Maxwell–Boltzmann, Bose–Einstein, and Fermi–Dirac statistics on equal footing across box, harmonic, mixed, and linear-quadrupole potentials. Using the global thermodynamic variables of inhomogeneous confinement, we show that all geometries are unified by a single parameter $s$, which fixes the polylogarithm order, the density of states exponent, and the number of degrees of freedom $2s$. Modeling evaporation as a recursive sequence of energy truncation and rethermalization, we derive closed-form recurrence relations for the particle number and internal energy that track the full thermodynamic state, with the classical energy budget set by a virial factor $C_{\mathrm{trap}} = 1 + 3/(2s)$. Quantum degeneracy emerges not as a singularity in the global susceptibilities, but as a smooth, geometry-dependent crossover in which bosons and fermions display opposite thermodynamic signatures. The results provide a versatile theoretical tool for modeling evaporative cooling across experimentally relevant geometries and offer quantitative guidance for optimizing the cooling process in ultracold atomic systems.
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All authors A. A. Arvizu-Velazquez, A. del Río-Lima, S. Dondé-Rodríguez, F. J. Poveda-Cuevas

Quantum Gases

Interference of a chain of Bose condensates in the Pitaevskii-Gross approximation

I. N. Mosaki and A. V. Turlapov

A long chain of Bose condensates freely expands and interferes after being released from an optical lattice. The interference fringes are well resolved both in the case of equal phases of the condensates and in the case of fluctuating phases. In the second case the positions of the fringes also fluctuate. The spectrum of the spatial density distribution, however, is reproducible despite the fluctuations. Moreover two types of peaks are distinguishable in the spectrum. The first type arises due to the phase fluctuations, the second type is associated with the coherence between the condensates. In the framework of the Pitaevskii-Gross equation we calculate the interference of the condensates and compare the calculation with experiment [Phys. Rev. Lett. 122, 090403 (2019)]. The calculation reproduces the positions of the spectrum peaks, including the dependence on the interparticle interaction. The calculated heights of the peaks, however, in some cases differ with the experimental ones.
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Quantum Gases

Order in the interference of a long chain of Bose condensates with unrestricted phases

Vasiliy Makhalov and Andrey Turlapov

For a long periodic chain of Bose condensates prepared in the free space, the subsequent evolution and interference dramatically depend on the difference between the phases of the adjacent and more distant condensates. If the phases are equal, the initial periodic density distribution reappears at later times, which is known as the Talbot effect. For randomly-related phases, we have found that a spatial order also appears in the interference, while the evolution of the fringes differs with the Talbot effect qualitatively. Even a small phase disorder is sufficient for qualitatively altering the interference, though maybe at long evolution times. This effect may be used for measuring the amount of coherence between adjacent condensates and the correlation length along the chain.
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Statistical Mechanics

From the Stochastic Embedding Sufficiency Theorem to a Superspace Diffusion Framework

Carolina Garcia, Lucía Perea Durán, Agnese Venezia et al. (+1 more)

A generalisation of Takens' delay-coordinate embedding theorem to stochastic systems, the Stochastic Embedding Sufficiency Theorem, is an inverse methodology enabling non-parametric recovery of both drift and diffusion fields from scalar time series without prior assumptions about the governing physics. A blind protocol using only time series data is applied to nine domains: classical mechanics, statistical mechanics, nuclear physics, quantum mechanics, chemical kinetics, electromagnetism, relativistic quantum mechanics, quantum harmonic oscillator dynamics, and quantum electrodynamics. Fundamental constants (the Boltzmann constant, the Planck constant, the speed of light, the Fano factor, and the Van Kampen scaling exponent) emerge in both drift and diffusion channels without prior specification. The recovered diffusion coefficients, viewed across domains, constitute an empirical pattern, the $\sigma$-continuum, in which $k_B$, $\hbar$, and $c$ play structurally distinct roles. The Gravitational Diffusion Theorem, derived from the fluctuation-dissipation theorem, massless mode structure of linearised gravity, and gravitational self-coupling via the equivalence principle, determines the gravitational diffusion coefficient as one Planck length per square root of Planck time. Four canonical axioms formalise the framework, within which the noise character, drift, covariance operator, and fluctuation amplitude are uniquely determined by theorem, yielding the superspace diffusion hypothesis: $\mathrm{d}g_{ij} = \mathcal{D}_{ij}[g]\,\mathrm{d}\tau + \ell_P\,\mathrm{d}W_{ij}$ where all coefficients are non-parametric, first-principles consequences of the axioms. An implication of the hypothesis is that coarse-graining of the superspace Fokker-Planck equation via Mori-Zwanzig projection yields predictions for galactic-scale gravitational acceleration testable against kinematic data.
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All authors Carolina Garcia, Lucía Perea Durán, Agnese Venezia, Alex Conradie

Statistical Mechanics · Cross-listed from quant-ph

Noise-induced contraction of MPO truncation errors in noisy random circuits and Lindbladian dynamics

Zhi-Yuan Wei, Joel Rajakumar, Jon Nelson et al. (+3 more)

We study how matrix-product-operator (MPO) truncation errors evolve when simulating two setups: (1) 1D Haar-random circuits under either depolarizing noise or amplitude-damping noise, and (2) 1D Lindbladian dynamics of a non-integrable quantum Ising model under either depolarizing or amplitude-damping noise. We first show that the average purity of the system density matrix relaxes to a steady value on a timescale that scales inversely with the noise rate. We then show that truncation errors contract exponentially in both system size $N$ and the evolution time $t$, as the noisy dynamics maps different density matrices toward the same steady state. This yields an empirical bound on the $L_1$ truncation error that is exponentially tighter in $N$ than the existing bound. Together, these results provide empirical evidence that MPO simulation algorithms may efficiently sample from the output of 1D noisy random circuits [setup (1)] at arbitrary circuit depth, and from the steady state of 1D Lindbladian dynamics [setup (2)].
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All authors Zhi-Yuan Wei, Joel Rajakumar, Jon Nelson, Daniel Malz, Michael J. Gullans, Alexey V. Gorshkov

Mesoscale and Nanoscale Physics

Non-Hermitian Disordered Systems

Kohei Kawabata and Shinsei Ryu

Non-Hermitian disordered systems have emerged as a central arena in modern physics, with ramifications spanning condensed matter, quantum, statistical, and high energy contexts. The same principles also underlie phenomena beyond physics, such as network science, complex systems, and biophysics, where dissipation, nonreciprocity, and stochasticity are ubiquitous. Here, we review the physics and mathematics of non-Hermitian disordered systems, with particular emphasis on non-Hermitian random matrix theory. We begin by presenting the 38-fold symmetry classification of non-Hermitian systems, contrasting it with the 10-fold way for Hermitian systems. After introducing the classic Ginibre ensembles of non-Hermitian random matrices, we survey various diagnostics for complex-spectral statistics and distinct universality classes realized by symmetry. As a key application to physics, we discuss how non-Hermitian random matrix theory characterizes chaos and integrability in open quantum systems. We then turn to the criticality due to the interplay of disorder and non-Hermiticity, including Anderson transitions in the Hatano-Nelson model and its higher-dimensional extensions. We also discuss the effective field theory description of non-Hermitian disordered systems in terms of nonlinear sigma models.
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Materials Science

A chemical language model for reticular materials design

Dhruv Menon, Vivek Singh, Xu Chen et al. (+7 more)

Reticular chemistry has enabled the synthesis of tens of thousands of metal-organic frameworks (MOFs), yet the discovery of new materials still relies largely on intuition-driven linker design and iterative experimentation. As a result, researchers explore only a small fraction of the vast chemical space accessible to reticular materials, limiting the systematic discovery of frameworks with targeted properties. Here, we introduce Nexerra-R1, a building-block chemical language model that enables inverse design in reticular chemistry through the targeted generation of organic linkers. Rather than generating complete frameworks directly, Nexerra-R1 operates at the level of molecular building blocks, preserving the modular logic that underpins reticular synthesis. The model supports both unconstrained generation of low-connectivity linkers and scaffold-constrained design of symmetric multidentate motifs compatible with predefined nodes and topologies. We further combine linker generation with flow-guided distributional targeting to steer the generative process toward application-relevant objectives while maintaining chemical validity and assembly feasibility. The generated linkers are subsequently assembled into three-dimensional frameworks and are structurally optimized to produce candidate materials compatible with experimental synthesis. Using Nexerra-R1, we validate this strategy by rediscovering known MOFs and by proposing the experimental synthesis of a previously unreported framework, CU-525, generated entirely in silico. Together, these results establish a general inverse-design paradigm for reticular materials in which controllable chemical language modelling enables the direct translation from computational design to synthesizable frameworks.
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All authors Dhruv Menon, Vivek Singh, Xu Chen, Mohammad Reza Alizadeh Kiapi, Ivan Zyuzin, Hamish W. Macleod, Nakul Rampal, William Shepard, Omar M. Yaghi, David Fairen-Jimenez

Materials Science · Cross-listed from quant-ph

One-to-one quantum simulation of a frustrated magnet with 256 qubits

Lucas Leclerc, Sergi Julià-Farré, Gabriel Silva Freitas et al. (+33 more)

Analog quantum simulators offer a powerful microscopic probe of quantum many-body systems, yet have largely been benchmarked against model Hamiltonians rather than real materials. Here, we use a 256-qubit Rydberg simulator to implement the effective Hamiltonian of the frustrated triangular-lattice magnet TmMgGaO$_4$. Simulated magnetization curves agree quantitatively with susceptibility measurements on single crystals, and both platforms consistently determine the antiferromagnetic phase transition. Snapshot-resolved analysis confirms that quantum fluctuations, rather than disorder, govern the intermediate paramagnetic regime. Having established this correspondence, we access non-equilibrium dynamics following a sudden quench, a regime at picosecond material timescales where entanglement growth places the problem beyond classical reach. The simulator reveals thermalization of local observables, demonstrating that analog quantum simulation can reproduce and extend the physics of a real material.
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All authors Lucas Leclerc, Sergi Julià-Farré, Gabriel Silva Freitas, Guillaume Villaret, Boris Albrecht, Lucas Béguin, Lilian Bourachot, Clémence Briosne-Frejaville, Dorian Claveau, Antoine Cornillot, Julius de Hond, Djibril Diallo, Clément Dupays, Robin Dupont, Thomas Eritzpokhoff, Emmanuel Gottlob, Loïc Henriet, Michael Kaicher, Lucas Lassablière, Arvid Lindberg, Yohann Machu, Hadriel Mamann, Thomas Pansiot, Julien Ripoll, Eun Sang Choi, Adrien Signoles, Joseph Vovrosh, Bruno Ximenez, Vivien Zapf, Shengzhi Zhang, Haidong Zhou, Minseong Lee, Tiagos Mendes-Santos, Constantin Dalyac, Antoine Browaeys, Alexandre Dauphin

Strongly Correlated Electrons

Collective Spin Excitations in Correlated Moiré Chern Ferromagnets

Ming Xie and Sankar Das Sarma

Moiré-induced narrow electronic bands in transition metal dichalcogenide superlattices support many correlated quantum phases characterized by novel charge, flavor, and topological orders. Among these, magnetic ordering emerges as the most ubiquitous, often serving as the parent state for other correlated phases, including quantum anomalous Hall states, as well as chiral superconducting state. Because of electron-electron correlation, the stability of magnetic order is critically influenced by low-energy collective spin fluctuations, or magnon excitations. We investigate the nature of magnon excitations and their impact on the stability and transition temperature of the magnetic state at integer filling factor $\nu = -1$. We find that the magnon spectrum exhibits isolated low-energy bands whose topological character undergoes a transition upon tuning the interlayer displacement field. The magnon gap is found to depend sensitively on the topology of the magnetic ground state, resulting in an order-of-magnitude enhancement of the transition temperature $T_c$ in the quantum anomalous Hall phase compared to the topologically trivial correlated insulator. Our findings provide insight into the interplay between electron and magnon topology and suggest new routes for controlling magnetism and topology via moiré engineering.
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Strongly Correlated Electrons

Evolution of superconductivity from charge clusters to stripes in the $t$-$t'$-$J$ model

Aritra Sinha, Hannes Karlsson, Martin Ulaga et al. (+1 more)

Competition and coexistence of charge orders and superconductivity are hallmarks in many strongly correlated electron systems. Here, we unravel the precise role of charge fluctuations on the superconducting state in the $t$-$t'$-$J$ model of the high-temperature cuprate superconductors. Using finite-temperature tensor network simulations, we investigate thermal snapshots in the underdoped regime where the ground state features a superconducting stripe phase. At intermediate temperatures, where stripes have melted and hole clustering is observed, we find that pairing correlations are tightly localized on the hole clusters. Upon entering the stripe regime at lower temperatures, pairing increasingly delocalizes across different hole clusters to ultimately become coherent across the full system in the ground state. This pair-charge locking gives rise to an intuitive picture of the parent state of the superconducting stripe phase: pairing is localized on hole clusters formed via hole attraction due to the onset of magnetic correlations at intermediate temperature. We discuss how this microscopic picture is consistent with a broad range of experimental observations in cuprate superconductors, including scanning tunneling microscopy (STM) evidence for local pairing above $T_c$ and nuclear magnetic resonance (NMR) signatures of charge clustering in the underdoped regime.
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All authors Aritra Sinha, Hannes Karlsson, Martin Ulaga, Alexander Wietek

Mesoscale and Nanoscale Physics

Competing skin effect and quasiperiodic localization in the non-Hermitian Su-Schrieffer-Heeger chain: Reentrant delocalization, spectral topology destruction, and entanglement suppression

Souvik Ghosh

We investigate the interplay between the non-Hermitian skin effect and Aubry-André-Harper (AAH) quasiperiodic disorder in a one-dimensional Su-Schrieffer-Heeger (SSH) chain with nonreciprocal hopping. By exact diagonalization, transfer-matrix analysis, and an analytical similarity-transformation argument, we map the full ( , $\delta$) phase diagram, where A is the AAH modulation strength and the nonreciprocity parameter. We identify five distinct regimes: ( ) topological with extended bulk, (II) AAH-localized, (III) skin-localized, (IV) fully localized, and a previously unreported (V) competition regime exhibiting reentrant partial delocalization, in which intermediate quasiperiodic disorder disrupts the directional skin accumulation before ultimately Anderson-localizing all states. Using phase-averaged diagnostics and finite-size scaling, we confirm that the reentrant regime is robust, characterized by a non-monotonic inverse participation ratio that sharpens with increasing system size. We derive an analytical expression for the modified localization boundary $\lambda_{c}(\delta)=2\sqrt{v_{eff}w}$ with $v_{vff}=\sqrt{v^{2}-\delta^{2}}$, which agrees with numerical Lyapunov exponent calculations. We further show that quasiperiodic disorder progressively unwinds the complex spectral loops, destroying the point-gap topology at a critical strength distinct from the band-topological transition ; that the skin effect suppresses entanglement entropy to near-zero values while sufficiently strong AAH disorder partially restores it ; and that the SSH sublattice structure absent in the widely studied non-Hermitian AAH chain is essential for producing the five-phase landscape, as demonstrated by direct comparison with the non-dimerized limit.
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Materials Science

When Cubic Is Not Isotropic: Phonon-Exciton Decoupling in CuInSnS$_4$ Single Crystals

Lara Kim Linke, Yvonne Tomm, Xinyun Liu et al. (+9 more)

Atomic-scale disorder can create hidden optical anisotropy even in crystals that are structurally cubic on average. Here, we show that CuInSnS$_4$ single crystals host locally symmetry-broken environments arising from intrinsic In/Sn cation disorder, which affect vibrational and excitonic properties in markedly different ways. Combining polarization- and temperature-dependent Raman spectroscopy, infrared near-field microscopy, steady-state and time-resolved photoluminescence, and first-principles calculations, we find that phonons remain largely symmetry-averaged and locally homogeneous on the nanoscale. In contrast, photoluminescence reveals a lower-energy band-tail emission with pronounced polarization anisotropy following a well-defined angular symmetry, highlighting the strong sensitivity of excitonic states to local symmetry breaking. This phonon-exciton decoupling reveals that intrinsic disorder can localize excitons while preserving vibrational coherence and dielectric homogeneity, thereby opening new opportunities for polarization-sensitive light sources, anisotropic photodetectors, and exciton-based optical functionalities even in nominally cubic multinary semiconductors.
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All authors Lara Kim Linke, Yvonne Tomm, Xinyun Liu, Galina Gurieva, Daniel M. Tobbens, Pardis Adams, Michel Calame, Ryan W. Crisp, Jessica Boland, Sean Kavanagh, Susan Schorr, Mirjana Dimitrievska

Statistical Mechanics

Detecting the 3D Ising model phase transition with a ground-state-trained autoencoder

Ahmed Abuali, David A. Clarke, Morten Hjorth-Jensen et al. (+3 more)

We develop a one-class, deep-learning framework to detect the phase transition and recover critical behavior of the 3D Ising model. A 3D convolutional neural network autoencoder (CAE) is trained on ground-state configurations only, without prior knowledge of the critical temperature, the Hamiltonian, or the order parameter. After training, the model is applied to Monte Carlo configurations across a wide temperature range and different lattice sizes. The mean-square reconstruction error is shown to be sensitive to the transition. Finite-size scaling of the peak location for the reconstruction error susceptibility yields the critical temperature $T_c=4.5128(58)$ and the correlation-length critical exponent $\nu=0.63(27)$, consistent with results from the literature. Our results show that a one-class CAE, trained on zero-temperature configurations only, can recover nontrivial critical behavior of the 3D Ising model.
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All authors Ahmed Abuali, David A. Clarke, Morten Hjorth-Jensen, Ioannis Konstantinidis, Claudia Ratti, Jianyi Yang

Materials Science

Transformer-based prediction of two-dimensional material electronic properties under elastic strain engineering

Haoran Ma, Yuchen Zheng, Leining Zhang et al. (+2 more)

Strain engineering provides a powerful route for tuning the electronic properties of two-dimensional (2D) materials, but exploring the full multidimensional strain space with density functional theory (DFT) is computationally prohibitive due to the nonlinear coupling between normal and shear components. In this work, we introduce a Transformer-based, multi-target surrogate model framework that achieves DFT-level bandgap prediction accuracy, reaching a mean absolute error of 0.0103 eV while retaining full interpretability through attention-weight analysis. The learned self-attention map consistently identifies shear strain as the interaction center that influences both bandgap and phonon stability, an insight not readily captured by classical feature-importance metrics. This work establishes attention-based architectures as physically interpretable surrogate models for multi-property prediction, offering a generalizable strategy for accelerating deep elastic strain engineering in materials informatics.
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All authors Haoran Ma, Yuchen Zheng, Leining Zhang, Xiaofei Chen, Dan Wang