Statistical Mechanics
Quantum Thermalization beyond Non-Integrability and Quantum Scars in a Multispecies Bose-Josephson Junction
Francesco Di Menna, Sergio Ciuchi and Simone Paganelli
The modern framework for
quantum thermalization is grounded in the Eigenstate Thermalization Hypothesis (ETH), in which non-integrability and chaos are historically assumed as prerequisites. This work investigates this relationship in a three-species Bose-Josephson Junction (BJJ) with mutual interactions, experimentally achievable in current ultracold-atom platforms. After a thorough characterization of
quantum chaos in this system, we examine the occurrence of thermal behavior expected when ETH holds. We identify three distinct regimes: chaotic, integrable, and separable. Remarkably,
quantum thermalization occurs in both the chaotic and integrable regimes, while it breaks down in and near the separable limit - supporting that non-integrability is not a necessary condition for thermalization. Furthermore, since the system exhibits collective phenomena in the semiclassical limit, we identify ergodicity breaking phenomena such as athermal states in the chaotic regime classifiable as
quantum scars, which show no signs of thermalization, consistently with a weak form of ETH.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Metasurface Engineering with Tantalum Pentoxide-Coated Microspheres: Tailoring Optical Resonances and Enhancing Local Density of States
Alexandra Fălamaş, Ana Maria M. Gherman, Renaud Vallée et al. (+1 more)
Hexagonally-packed polystyrene microsphere monolayers coated with tantalum pentoxide (Ta$_2$O$_5$) form scalable dielectric metasurfaces that support tunable photonic resonances and enhanced local density of optical states (LDOS). Here we combine fabrication, optical and fluorescence spectroscopy, and multiscale electromagnetic simulations to quantify how the thickness of the Ta$_2$O$_5$ shells control far-field resonances and Rhodamine 6G (Rh6G) emission. Experimentally, Ta$_2$O$_5$ shells of 10 - 70 nm deposited on microsphere
lattices generate resonances that shift red with the thickness of the shell and systematically enhance the Rh6G fluorescence relative to flat Ta$_2$O$_5$ films. The largest enhancement is obtained for 30 - 50 nm shells, when
lattice resonances overlap the Rh6G excitation and emission bands. Finite-cluster finite-difference time-domain simulations reproduce the measured transmittance and reflectance spectra, confirming the assumed geometry of the Ta$_2$O$_5$ shells covering the sphere
lattice. Periodic-
cell simulations of single electric dipoles yield wavelength-dependent Purcell factors $Fp(\lambda)$ and directional $\beta$-factors $\beta_{top}(\lambda)$, from which we construct emission-weighted figures of merit that link LDOS modulation to the experimentally accessible top-side fluorescence enhancement. As a complementary test of our emitter-environment model, we compare simulated and measured Purcell factors for PS/Ta$_2$O$_5$ microsphere
lattices. A physically motivated averaging that accounts for emitter position, orientation and ensemble spectral smoothing yields very good agreement across all shells. Overall, our results establish Ta$_2$O$_5$-coated microsphere
lattices as robust dielectric substrates for surface-enhanced fluorescence and clarify how shell thickness and emitter placement jointly control photonic resonances, LDOS and fluorescence response.
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All authors Alexandra Fălamaş, Ana Maria M. Gherman, Renaud Vallée, Cosmin Farcău
Materials Science
Electrical and thermal magnetotransport in altermagnetic CrSb
Sajal Naduvile Thadathil, Christoph Müller, Reza Firouzmandi et al. (+20 more)
Chromium antimonide has emerged as a key material platform for studying altermagnetism because of its simple binary composition, high Néel temperature, and semimetallic electronic structure. Here, we investigate electrical and thermal magnetotransport in single-crystalline CrSb using steady-and pulsed-
magnetic fields up to 65 T, and complement these measurements with
neutron diffraction and magnetization data. We confirm the compensated
magnetic structure and observe a large nonsaturating magnetoresistance together with a pronounced nonlinear
Hall response at low temperatures. Multicarrier modeling, supported by mobility-spectrum analysis, reveals coexisting electron- and hole-like charge carriers with mobilities up to ~3000 cm2/Vs and shows that the number of transport channels that can be resolved strongly depends on the accessible
magnetic-field range. Thermal-transport measurements further reveal a nonlinear thermal
Hall response and a thermal conductivity substantially exceeding a simple Wiedemann-Franz law. The broadly similar field and temperature
evolution of electrical and thermal transport point to a dominant electronic contribution, while the remaining deviations indicate additional heat-carrying channels.
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All authors Sajal Naduvile Thadathil, Christoph Müller, Reza Firouzmandi, Lorenz Farin, Srikanta Goswami, Antonin Badura, Pascal Manuel, Fabio Orlandi, Philipp Ritzinger, Václav Petříček, Marc Uhlarz, Tommy Kotte, Michal Baj, Marein C. Rahn, Thanassis Speliotis, Markéta Žáčková, Jiří Pospíšil, Bernd Büchner, Jochen Wosnitza, Helena Reichlová, Vilmos Kocsis, Toni Helm, Dominik Kriegner
Strongly Correlated Electrons
Magnetism and magnetoelastic effect in 2D van der Waals multiferroic CuCrP2S6
Jiasen Guo, Ryan P. Siebenaller, Michael A. Susner et al. (+3 more)
We report a
magnetic and
neutron diffraction study on the ground state magnetism and field
evolution of single
crystal van der Waals multiferroic CuCrP2S6. The ordered moments align along the b axis in the A-type
antiferromagnetic configuration with a
spin-flop transition along the same direction. Field application along a introduces a smooth transition to a fully-polarized
ferromagnetic state via in-plane
spin rotation. These findings resolve the ambiguity of the ground state magnetization direction in CuCrP2S6 and uncover its field responses, providing a firm basis for future magnetoelectric study. A magnetoelastic coupling effect connecting the interlayer spacing and the
magnetic order was further revealed, highlighting the out-of-plane strain as an effective control knob for tuning magnetism both in this system and in related van der Waals magnets.
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All authors Jiasen Guo, Ryan P. Siebenaller, Michael A. Susner, Jiaqiang Yan, Zachary Morgan, Feng Ye
Materials Science
Suppressed excitonic effects enable high mobility, high-yield photoconductivity in a two-dimensional polymer crystal with axial pyridine coordination
Shuai Fu, Ye Yang, Guoquan Gao et al. (+8 more)
Two-dimensional
polymers (2DPs) and their layer-stacked covalent organic frameworks (2D COFs) offer modular, atomically precise platforms for organic optoelectronics, yet their photoconductive responses remain fundamentally constrained by strong excitonic effects and localized charge transport. Here, we demonstrate that a diyne-linked 2DP
crystal with axial pyridine coordination overcomes this limitation, enabling simultaneous efficient free-carrier generation and band-like transport. Introducing pyridine ligands that axially coordinate to Cu-porphyrin nodes transforms weak van der Waals stacking into a pyridine-bridged architecture with pronounced interlayer band dispersion and substantially reduced carrier effective masses. The resulting strong interlayer electronic coupling suppresses the
exciton binding energy to well below thermal energy, such that optical excitation directly populates delocalized electronic states. Time-resolved terahertz spectroscopy reveals Drude-type photoconductivity with room-temperature mobilities approaching 500 cm^2 V^-1 s^-1 and a
photon-to-free-carrier conversion ratio of ~0.4, yielding a photoconductive response that exceeds that of state-of-the-art organic and many inorganic photoactive materials. These results establish interlayer coordination as a powerful strategy for mitigating excitonic effects and accessing inorganic-like charge transport in organic 2D
crystals, opening a pathway toward highly efficient photo-to-electricity conversion in organic-based systems.
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All authors Shuai Fu, Ye Yang, Guoquan Gao, Shuangjie Zhao, Miroslav Položij, Tong Zhu, Lei Gao, Thomas Heine, Zhiyong Wang, Mischa Bonn, Xinliang Feng
Superconductivity
Imaging the Meissner effect and local superfluid stiffness in a graphene superconductor
Ruoxi Zhang, Benjamin A. Foutty, Owen Sheekey et al. (+15 more)
We report the observation of the Meissner effect in a rhombohedral
graphene superconductor, realized via direct imaging of the static fringe
magnetic field. In our few-micron sample, the onset of superconductivity manifests as a diamagnetic response that screens only $\sim 100$ ppm of the applied
magnetic field. Tracking the
evolution of the resulting nanotesla-scale fields in real space allows us to observe the entry of superconducting
vortices and map the local superfluid stiffness, $\rho_s$. Correlating fringe field signals from both Meissner screening and magnetically ordered states, we show that superconductivity onsets in the midst of a continuous
quantum phase transition to a canted
spin ferromagnet. Within the superconducting state, we find the temperature dependence of $\rho_s$ to be incompatible with isotropic Bardeen-Cooper-Schrieffer theory and the zero-temperature stiffness $\rho_s^0$ to be linearly proportional to $T_c$, constraining future theoretical models of superconductivity in this system.
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All authors Ruoxi Zhang, Benjamin A. Foutty, Owen Sheekey, Trevor Arp, Siyuan Xu, Tian Xie, Yi Guo, Hari Stoyanov, Sherlock Gu, Aidan Keough, Evgeny Redekop, Canxun Zhang, Takashi Taniguchi, Kenji Watanabe, Martin E. Huber, Chenhao Jin, Erez Berg, Andrea F. Young
Statistical Mechanics · Cross-listed from quant-ph
Typical entanglement in anyon chains: Page curves beyond Lie group symmetries
Yale Yauk, Lucas Hackl and Alexander Hahn
We study bipartite
entanglement statistics in one-dimensional anyon chains, whose
Hilbert spaces are constrained by fusion rules of
unitary pre-modular categories. Our setup generalizes previous frameworks on
symmetry-resolved
entanglement entropy for non-abelian Lie group
symmetries to the setting of
quantum groups. We derive analytical expressions for the average anyonic
entanglement entropy and its variance. Surprisingly, despite the constrained
Hilbert space structure, the large $L$ expansion has no universal $O(\sqrt{L})$ or $O(1)$
symmetry-type corrections except for a subleading topological correction term that produces a Page curve asymmetry. We further show that the variance decays exponentially with system size, establishing the typicality. Numerical simulations of the integrable and
quantum-chaotic golden chain
Hamiltonian show that chaotic mid-spectrum eigenstates match the Haar-random predictions, supporting the use of eigenstate
entanglement as a diagnostic of
quantum chaos. Our results establish the anyonic Page curve as an appropriate chaotic
benchmark in topological many-body systems and connect anyonic
entanglement to Page-type universality in
quantum many-body physics.
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Quantum Gases
Francisco Machado, Sabrina Chern, Michael P. Zaletel et al. (+1 more)
Continuous control over
lattice geometry, when combined with long-range interactions, offers a powerful yet underexplored tool to generate highly frustrated
quantum spin systems. By considering long-range dipolar
antiferromagnetic interactions on a breathed Kagome
lattice, we demonstrate how these tools can be leveraged to stabilize a
chiral spin liquid. We support this prediction with large-scale density-
matrix renormalization group calculations and explore the surrounding phase diagram, identifying a route to adiabatic preparation via a locally varying
magnetic field. At the same time, we identify the relevant low-energy degrees of freedom in each unit
cell, providing a complementary
language to study the
chiral spin liquid. Finally, we carefully analyze its stability and signatures in finite-sized clusters, proposing direct, experimentally viable measurements of the
chiral edge mode in both Rydberg atom and ultracold polar molecule arrays.
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All authors Francisco Machado, Sabrina Chern, Michael P. Zaletel, Norman Y. Yao
Quantum Gases
Detecting Complex-Energy Braiding Topology in a Dissipative Atomic Simulator with Transformer-Based Geometric Tomography
Yang Yue, Nan Li, Xin Zhang et al. (+8 more)
Machine learning (ML) is shaping our exploration of topological matter, whose existence is inherently tied to the geometry of
quantum states or energy spectra. In non-Hermitian systems, distinctive spectral geometry can lead to topological braiding of complex-energy bands, yet directly probing this
topology-geometry interplay remains challenging. Here, we introduce a
Transformer-based ML framework to capture this interplay and experimentally demonstrate it in a dissipative cold-atom simulator. Using a Bose-Einstein condensate, we engineer tunable dissipative two-level systems whose complex eigenenergies form braids. Owing to the density-dependent dissipation, the instantaneous energy braids exhibit topologically distinct structures at short and long times. The
Transformer not only accurately predicts topological invariants for diverse energy braids but also, through its self-
attention mechanism, autonomously highlights band crossings as the governing underlying
geometric feature. Our work paves the way for ML-guided exploration of non-Hermitian topological phases in cold atoms and beyond.
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All authors Yang Yue, Nan Li, Xin Zhang, Chenhao Wang, Zeming Fang, Zhonghua Ji, Liantuan Xiao, Suotang Jia, Yanting Zhao, Liang Bai, Ying Hu
Materials Science · Cross-listed from cs.CV
Evaluating Synthetic Images as Effective Substitutes for Experimental Data in Surface Roughness Classification
Binwei Chen, Huachao Leng, Chi Yeung Mang et al. (+5 more)
Hard coatings play a critical role in industry, with ceramic materials offering outstanding hardness and thermal stability for applications that demand superior mechanical performance. However, deploying artificial intelligence (AI) for surface roughness classification is often constrained by the need for large labeled
datasets and costly high-resolution imaging equipment. In this study, we explore the use of synthetic images, generated with Stable
Diffusion XL, as an efficient alternative or supplement to experimentally acquired data for classifying ceramic surface roughness. We show that augmenting authentic
datasets with generative images yields test accuracies comparable to those obtained using exclusively experimental images, demonstrating that synthetic images effectively reproduce the structural features necessary for classification. We further assess method robustness by systematically varying key training hyperparameters (epoch count, batch size, and learning rate), and identify configurations that preserve performance while reducing data requirements. Our results indicate that generative AI can substantially improve data efficiency and reliability in materials-image classification workflows, offering a practical route to lower experimental cost, accelerate model development, and expand AI applicability in materials engineering.
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All authors Binwei Chen, Huachao Leng, Chi Yeung Mang, Tsz Wai Cheung, Yanhua Chen, Wai Keung Anthony Loh, Chi Ho Wong, Chak Yin Tang
Strongly Correlated Electrons
Pseudogap and Non-Fermi-liquid criticality in double Kondo model for bilayer nickelates
Jing-Yu Zhao and Ya-Hui Zhang
Motivated by recent experimental progress on high-temperature superconductivity in
bilayer nickelates, we investigate the phase diagram of the normal state in a
bilayer Kondo
lattice model using single-site dynamical mean-field theory (DMFT). When the interlayer tunneling $t_\perp$ is absent, we identify a non-
Fermi-
liquid (NFL) critical point tuned by the interlayer
spin coupling $J_\perp$ or hole doping $x$, which separates a standard
Fermi liquid in the overdoped region from a distinct pseudogap (PG) metal in the underdoped regime. This PG phase, which we term the `second
Fermi liquid' (sFL), exhibits small hole pockets and violates the perturbative Luttinger
theorem despite the absence of
symmetry breaking or fractionalization. The PG metal behaves like a heavy
Fermi liquid, with small quasi-particle residue and large effective mass. We also provide an intuitive analytical description of the pseudogap and the ground-state wave function based on an ancilla-
fermion framework. Inside the PG phase, we interpret the ancilla
fermion as a
spin-polaron and demonstrate a Kondo-like resonance peak in the spectral function of this composite
fermion directly in DMFT calculation. Extending the analysis to finite $t_\perp$, we apply this framework to the
bilayer nickelate $\mathrm{La}_3\mathrm{Ni}_2\mathrm{O}_7$. We propose that current experimental samples ($x \approx 0.5$) reside in the overdoped FL regime, suggesting that the pseudogap phase and the NFL criticality may be accessed via electron doping.
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Disordered Systems and Neural Networks
Krylov-space anatomy and spread complexity of a disordered quantum spin chain
Bikram Pain, David E. Logan and Sthitadhi Roy
We investigate the anatomy and complexity of
quantum states in Krylov space, in the ergodic and many-body localised (MBL) phases of a disordered, interacting
spin chain. The Krylov basis generated by the
Hamiltonian from an initial state provides a representation in which the spread of the time-evolving state constitutes a basis-optimised measure of complexity. We show that the long-time Krylov spread complexity sharply distinguishes the two phases. In the ergodic regime, the infinite-time complexity scales linearly with the Fock-space dimension, indicating that the state spreads over a finite fraction of the Krylov chain. By contrast, it grows sublinearly in the MBL regime, implying that the long-time state occupies only a vanishing fraction of the chain. Further, the profile of the infinite-time state along the Krylov chain exhibits a stretched-exponential decay in the MBL regime. This behaviour reflects a broad distribution of decay lengthscales, associated with different eigenstates contributing to the long-time state. Consistently, a large-deviation analysis of the statistics of eigenstate spread complexities shows that while the ergodic regime receives contributions from almost all eigenstates, the complexity in the MBL regime is dominated by a vanishing fraction of eigenstates, which have anomalously large complexity relative to the typical ones.
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Materials Science
Electrostatic Photoluminescence Tuning in All-Solid-State Perovskite Transistors
Vladimir Bruevich, Dmitry Maslennikov, Beier Hu et al. (+2 more)
We demonstrate an all solid state
semiconductor device, based on epitaxial single crystalline metal halide perovskites, enabling reversible control of a perovskite photoluminescence with a gate voltage. Fundamentally distinct from electroluminescent diodes, such a photoluminescence field effect transistor uses the gate electric field to electrostatically modulate the interfacial density of mobile charges, thereby affecting the radiative and nonradiative recombination channels of photocarriers. Varying the gate voltage in such transistors efficiently changes the rate of nonradiative interfacial recombination and modulates the photoluminescence intensity by 65 to 98 percent (depending on temperature). At favorable gating, nearly complete elimination of non-radiative losses can be achieved. This functionality, coupled with the strong visible-range absorption and emission, possible due to the high absorption coefficient, as well as controllable thickness and macroscopically homogeneous morphology of epitaxial perovskite films, leads to high external photoluminescence
quantum efficiencies realized in large-area, thin-film devices. Such high-efficiency, scalable, electrostatically tunable optoelectronic switches broaden the potential applications of metal-halide perovskites in photonics and optoelectronics.
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All authors Vladimir Bruevich, Dmitry Maslennikov, Beier Hu, Artem A. Bakulin, Vitaly Podzorov
Strongly Correlated Electrons · Cross-listed from quant-ph
Provably Efficient Long-Time Exponential Decompositions of Non-Markovian Gaussian Baths
Zhen Huang, Zhiyan Ding, Ke Wang et al. (+3 more)
Gaussian baths are widely used to model non-Markovian environments, yet the cost of accurate simulation at long times remains poorly understood, especially when spectral densities exhibit nonanalytic behavior as in a range of realistic models. We rigorously bound the complexity of representing bath correlation functions on a time interval $[0,T]$ by sums of complex exponentials, as employed in recent variants of pseudomode and hierarchical equations of motion methods. These bounds make explicit the dependence on the maximal simulation time $T$, inverse temperature $\beta$, and the type and strength of singularities in an effective spectral density. For a broad class of spectral densities, the required number of exponentials is bounded independently of $T$, achieving time-uniform complexity. The $T$-dependence emerges only as polylogarithmic factors for spectral densities with strong singularities, such as step discontinuities and inverse power-law divergences. The temperature dependence is mild for bosonic environments and disappears entirely for fermionic environments. Thus, the true bottleneck for long-time simulation is not the simulation duration itself, but rather the presence of sharp nonanalytic features in the bath spectrum. Our results are instructive both for long-time simulation of non-Markovian open
quantum systems, as well as for Markovian
embeddings of classical generalized Langevin equations with
memory kernels.
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All authors Zhen Huang, Zhiyan Ding, Ke Wang, Jason Kaye, Xiantao Li, Lin Lin
Mesoscale and Nanoscale Physics
Anomalous thermoelectric Hall response of interacting 2D Dirac fermions
A. Daria Dumitriu-I., Feng Liu, Alexander E. Kazantsev et al. (+1 more)
We study the anomalous thermoelectric
Hall response of two-dimensional massive Dirac
fermions to first order in the electron-electron interaction. We compute both the Nernst response to a Luttinger-type gravitational potential and the particle magnetization, the latter being required to remove spurious non-transport contributions. We show that, for arbitrary interactions, the magnetization is described by a remarkably simple formula. Surprisingly, and contrary to expectations, subtracting the magnetization currents does not make the thermoelectric
Hall coefficient vanish in the zero-temperature limit. We attribute this to violation of locality on the smallest length scales, which is inevitable in a quantized field theory, that happens to manifest itself in infrared physics.
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All authors A. Daria Dumitriu-I., Feng Liu, Alexander E. Kazantsev, Alessandro Principi
Mesoscale and Nanoscale Physics
Magnetic field Controlled Anderson Delocalization in a Spinful Non-Hermitian Chain
Moirangthem Sanahal, Subhasis Panda and Snehasish Nandy
Anderson localization (AL) and the non-Hermitian skin effect (NHSE) represent two paradigmatic localization phenomena driven, respectively, by disorder and non-Hermiticity. In one-dimensional (1D) non-Hermitian systems, these factors are known to compete and provide a smooth crossover between AL and NHSE upon parameter tuning. Here, we show that this interplay is fundamentally enriched in spinful systems, where an external
magnetic field acts as an additional degree to manipulate the localization behavior. By investigating a disordered 1D spinful non-Hermitian chain, we demonstrate that under appropriately correlated disorder configurations across
spin sectors, the
magnetic field enhances the AL $\rightarrow$ NHSE crossover. Interestingly, this facilitates the Anderson delocalization transition even in strongly disordered systems where states would otherwise be Anderson localized. By analyzing the inverse participation ratio and the mean center of mass, we map the resulting triple interplay between disorder, non-Hermiticity, and the
magnetic field strength, identifying regimes of Anderson localization and skin accumulation. We further reveal that this
magnetic field driven delocalization phenomenon originates from an effective suppression of disorder strength via Zeeman-induced inter-chain coupling across the
spin sectors.
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Materials Science · Cross-listed from math.NA
A Quasicontinuum Method with Optimized Local Maximum-Entropy Interpolation and Heaviside Enrichment for Heterogeneous Lattices
Benjamin Werner, Ondřej Rokoš and Jan Zeman
Lattice systems are effective for modeling heterogeneous materials, but their computational cost is often prohibitive. The QuasiContinuum (QC) method reduces this cost by interpolating the
lattice response over a coarse finite-element mesh, yet material interfaces in heterogeneous systems still require fine discretizations. Enrichment strategies from the eXtended Finite Element Method (XFEM) address this by representing interfaces on nonconforming meshes. In this work, we combine Heaviside enrichment with meshless Local Maximum
Entropy (LME) interpolation in the QC framework for heterogeneous
lattice systems. We systematically investigate the role of the LME locality parameter and its optimization. The results show that optimized LME interpolation improves displacement accuracy by about one order of magnitude over QC with linear interpolation at the same number of degrees of freedom. In addition, the optimal locality-parameter fields are nonuniform near interfaces and exhibit systematic spatial structure. Based on these observations, we derive simple pattern-based rules that retain much of the benefit of full optimization at a fraction of the computational cost. The approach is demonstrated on three numerical examples.
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Statistical Mechanics
Non-linear Sigma Model for the Surface Code with Coherent Errors
Stephen W. Yan, Yimu Bao and Sagar Vijay
The surface code is a promising platform for a
quantum memory, but its threshold under coherent errors remains incompletely understood. We study maximum-likelihood decoding of the square-
lattice surface code in the presence of single-
qubit unitary rotations that create electric anyon excitations. We microscopically derive a non-linear sigma model with target space $\mathrm{SO}(2n)/\mathrm{U}(n)$ as the effective long-distance theory of this decoding problem, with distinct replica limits: $n\to1$ for optimal decoding, which assumes knowledge of the coherent rotation angle, and $n\to0$ for suboptimal decoding with imperfect angle information. This exposes a sharp distinction between the two decoders. The suboptimal decoder supports a "thermal-metal" phase, a non-decodable regime that is qualitatively distinct from the conventional non-decodable phase of the surface code under incoherent Pauli errors. By contrast, the metal phase cannot arise in optimal decoding, since the metallic fixed-point becomes unstable in the $n\to 1$ replica limit. We argue that optimal decoding may be possible up to the maximally-coherent rotation angle. Within the sigma model description, we show that the decoding fidelity is related to twist defects of the order-parameter field, yielding quantitative predictions for its system-size dependence near the metallic fixed point for both decoders. We examine our analytic predictions for the decoding fidelity as well as other physical observables with extensive numerical simulations. We discuss how the
symmetries and the target space for the sigma model rely on the
lattice of the surface code, and how a stable thermal metal phase can arise in optimal decoding when the syndromes reside on a non-bipartite
lattice.
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Quantum Gases
Diffusion in interacting two-dimensional systems under a uniform magnetic field
Łukasz Iwanek, Marcin Mierzejewski and Adam S. Sajna
The dynamics of interacting particles in orbital
magnetic fields are notoriously difficult to study, as this physics is inherently connected to electronic correlations in two-dimensional systems, for which no straightforward theoretical methods are available. Here, we report on the diffusive relaxation dynamics of two-dimensional interacting fermionic systems under a uniform
magnetic field in the infinite temperature regime. We first show that the fermionic truncated Wigner approximation captures the equilibration dynamics unexpectedly well for intermediate interaction strengths when going beyond one dimension. This high accuracy holds at least for relatively small ladder systems, which are accessible to the Lanczos method that we use to
benchmark the reliability of the Wigner approximation. We find that strong interactions, which exceed the hopping energy, suppress
magnetic-field effects on diffusive transport. However, when the interactions are comparable to the kinetic energy, the
diffusion is significantly reduced by the
magnetic flux. This is observed for sufficiently large systems (above approximately 400
lattice sites), where finite-size effects weakly affect particle transport. We suggest that our results should be directly accessible on current optical
lattice platforms.
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Materials Science
Interfacial Polytype Engineering of Polymer-Derived SiC via Compositionally Complex MXene Templating
Yuxiang Gan, Jianyu Dai, Laxmi Sai Viswanadha et al. (+5 more)
Controlling polytype selection in
polymer-derived silicon carbide (SiC) remains challenging since stacking sequences are determined locally at the nucleation front. Here, we demonstrate an interface-driven strategy to bias SiC polytype
evolution by introducing compositionally complex TiVCrMoC3 MXene nanosheets at the preceramic stage. Under spark
plasma sintering (1900 C, 70 MPa), which typically stabilizes cubic beta-SiC, the MXene partially transforms into multicomponent carbide structures and generates two distinct heterogeneous interfacial states: reconstructed carbide/SiC interfaces that locally disrupt stacking sequences and promote hexagonal ordering, driving the emergence of alpha-SiC; and coherent MXene/SiC interfaces that preserve cubic stacking. Mechanical testing further reveals peak performance at an optimal MXene loading where interfacial reconstruction is most pronounced, with an around 82% increase in Young's modulus and 42% improvement in fracture toughness. These findings highlight interfacial polytype engineering via two-dimensional carbide templates as a promising route for directing
crystal structure
evolution in
polymer-derived ceramics.
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All authors Yuxiang Gan, Jianyu Dai, Laxmi Sai Viswanadha, Congjie Wei, Kelvin Y. Xie, Jeremy Watts, Mohammad Naraghi, Chenglin Wu
Superconductivity
Prediction of new superconducting bilayers heterostructures using quantum confinement and proximity effects
Giovanni A. Ummarino and Alessio Zaccone
A central challenge in nanoscale superconductivity is to understand and exploit the combined action of
quantum confinement and proximity effects in experimentally realistic metallic
heterostructures. We theoretically investigate superconducting
bilayer heterostructures in which these two effects coexist. Using a generalized Eliashberg framework that incorporates both
quantum confinement and proximity coupling, we show that their interplay can substantially enhance the superconducting critical temperature. In particular, the theory predicts superconductivity in selected
bilayers whose constituent materials are nonsuperconducting or only weakly superconducting in the bulk. These results identify
quantum-confined
bilayers as a promising route to engineering emergent superconductivity in metallic
heterostructures.
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Strongly Correlated Electrons
Majorana-assisted nonlocal spin correlation in quasi-one-dimensional Kitaev spin liquids
Yuki Yamazaki, Shingo Kobayashi and Akira Furusaki
We propose Majorana-assisted nonlocal
spin correlation as a manifestation of Majorana nonlocality in quasi-one-dimensional (1D) Kitaev
spin liquids. Focusing on the flux-free sector of the Kitaev honeycomb model in a quasi-1D geometry, we uncover its topological nature and show that it hosts Majorana zero modes localized at both ends, which are stabilized by finite-size-induced
topology. We further show that the nonlocal Majorana
fermion parity operator, $P_{\text{MF}}=i\gamma_{\text{L}}\gamma_{\text{R}}$, is mapped to a nonlocal
spin-string operator, producing an end-to-end
spin correlation proportional to the product of $P_{\text{MF}}$ and total
fermion parity operators when local perturbations remove redundant ground-state degeneracies while preserving the Majorana and total
fermion parities in the flux-free sector. Numerical calculations confirm a finite nonlocal
spin correlation generated by these Majorana zero modes without any local magnetization. Our results establish a concrete signature of intrinsic Majorana nonlocality in
quantum spin liquids.
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Materials Science · Cross-listed from physics.flu-dyn
Converting vertical heat supply into horizontal motion for microtechnological pumping and autonomous waste heat recovery
Jan-Niklas Schäfer, Tillmann Carl, Kristin Kühl et al. (+4 more)
The rapid advancement of high-performance computing infrastructure and its extended application produce an increasing amount of waste heat. This heat constitutes an unsustainable loss of energy as well as requires cooling solutions that transcend conventional thermal management. Here, we demonstrate a novel mechanism that converts vertical waste heat supply directly into horizontal fluid motion, enabling autonomous, self-powered pumping in microenvironments. Our approach is based on a concept that combines
geometric symmetry breaking with heterogeneous thermal conductivities to induce local thermocapillary Marangoni flows. We provide an implementation of the concept as well as an experimental and numerical proof-of-concept, showing good agreement between the respective flow fields. The approach is scalable and operates under realistic areal heating conditions. It enables versatile pumping designs for microtechnological applications, lab-on-a-chip architectures, passive thermal management and heat-driven microfluidic systems.
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All authors Jan-Niklas Schäfer, Tillmann Carl, Kristin Kühl, Sonja Kiehren-Ehses, Jan Aurich, Georg von Freymann, Clarissa Schönecker
Materials Science
Growth and Kerr magnetometry of Mn2Au on a gold-capped Nb(001) substrate
Jendrik Gördes, Christian Janzen, Arne J. Vereijken et al. (+4 more)
We report on the epitaxial growth of
antiferromagnetic Mn2Au on a Nb(001) substrate capped with a pseudomorphic layer of gold. We observe a layer-by-layer growth by means of medium-energy electron diffraction and confirm stoichiometry and surface structure by Auger electron spectroscopy and low-energy electron diffraction. Evaporation of 15 ML of
ferromagnetic Fe on 12–17 ML of Mn2Au results in an exchange-coupled
bilayer system with an exchange-bias shift that can be set by field-cooling from 400 K. Areas with and without exchange bias, with domain sizes in the range of tens of {\mu}m, are identified by Kerr microscopy. Postannealing the sample at or above 450 K after Mn2Au layer growth decreases the amount of areas where Fe magnetically couples to Mn2Au. We conclude that exchange coupling to an interfacial Fe layer depends on the interface termination of Mn2Au. Our findings provide insight into the growth process of Mn2Au and the coupling to an Fe layer. Our results point out the importance of growth, interface quality and termination on the
magnetic properties of a Mn2Au/Fe
bilayer which may help to improve material properties for spintronic applications.
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All authors Jendrik Gördes, Christian Janzen, Arne J. Vereijken, Tingwei Li, Tauqir Shinwari, Arno Ehresmann, Wolfgang Kuch
Materials Science
Molecular dynamics study of the role of anisotropy in radiation-driven embrittlement
Hojjat Mousavi, Stanisław Stupkiewicz and Aneta Ustrzycka
This study investigates the influence of crystallographic orientation on fracture behavior and the resulting mechanical anisotropy in a Fe55Ni19Cr26
alloy crystal containing radiation-induced defects, using molecular dynamics (MD) simulations. Crack propagation is analyzed in irradiated samples with three selected high-
symmetry crystallographic orientations to show how radiation-induced defects modify local deformation mechanisms and amplify mechanical anisotropy. The investigation focuses on the anisotropic nature of the ductile-to-brittle transition (DBT) driven by radiation-induced defects by simulating fracture behavior under tensile loading. Fracture resistance is quantitatively evaluated using a traction-separation (T-S) approach to extract the atomic-scale fracture energy under realistic defect conditions. The results reveal a strong crystallographic orientation dependence in the
evolution of deformation and fracture behavior during DBT. The
crystal lattice orientation governs dislocation activity and defect interactions, which in turn regulate local plasticity mechanisms, strain localization, slip system activation, and fracture resistance, thereby driving the development and enhancement of mechanical anisotropy in irradiated materials. It is further shown that radiation-induced embrittlement cannot be explained solely by defect accumulation, but rather by orientation-sensitive interactions among dislocations, defects, and fracture process zones. A key novelty of this work lies in integrating radiation-induced defect
evolution with orientation-dependent fracture within an atomistic T-S analysis, enabling quantitative assessment of atomic-scale fracture resistance under realistic defect conditions.
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Materials Science
General-Purpose Machine-Learned Potential for CrCoNi Alloys Enabling Large-Scale Atomistic Simulations with First-Principles Accuracy
Yong-Chao Wu, Tero Mäkinen, Mikko Alava et al. (+1 more)
CrCoNi medium-
entropy alloys exhibit exceptional mechanical properties arising from pronounced chemical complexity, including short-range order (SRO), and low stacking fault energy, posing challenges for large-scale atomistic simulations. While most models focus on equimolar compositions, deviations from equimolarity provide an effective route to tuning properties, requiring transferable interatomic potentials that capture composition-dependent behavior. Here we develop a general-purpose machine-learned interatomic potential for the CrCoNi system within the neuroevolution potential (NEP) framework, achieving near first-principles accuracy with high computational efficiency. Trained on a comprehensive
dataset spanning pure elements, binary and ternary
alloys across a wide compositional range, diverse
crystal structures and thermodynamic conditions, and based on
spin-polarized ab initio data, the model accurately reproduces equations of state,
phonons, elastic constants, dislocation dissociation, surface and defect energies, melting temperatures and strain-induced phase transformations. It further captures SRO and its effect on stacking fault energies across both equimolar and non-equimolar compositions, in agreement with first-principles and experiments. In contrast to existing potentials, typically limited to equimolar
alloys and less accurate for pure elements, the present model delivers consistent accuracy across the full compositional space while retaining superior efficiency. These results enable reliable atomistic simulations of composition-dependent behaviour and provide a framework for the design of non-equimolar CrCoNi
alloys.
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All authors Yong-Chao Wu, Tero Mäkinen, Mikko Alava, Amin Esfandiarpour
Materials Science
Single Atom Magnets on Thermally Stable Adsorption Sites: Dy on NaCl(100)
M. Pivetta, M. Blanco-Rey, S. Reynaud et al. (+14 more)
We report
magnetic bistability in single Dy atoms on NaCl(100) thin films. Individual Dy atoms substituting Na at the surface of the NaCl layer are thermally stable up to at least 300 K, display $4f^{9}$ occupancy, out-of-plane easy magnetization axis, and long
spin relaxation time $T_1$ of about 10 s at 2.5 K; thereby they are the first single atom magnet on a thermally stable adsorption site. Dy atoms adsorbed onto the Cl and bridge sites display $4f^{10}$ occupancy. Dy on top-Cl exhibit
magnetic hysteresis and a $T_1$ of 550 s at 0.3 T and 2.5 K. The observed slow
magnetic relaxation of Dy on both adsorption sites introduces NaCl as an effective platform for single atom magnets.
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All authors M. Pivetta, M. Blanco-Rey, S. Reynaud, R. Baltic, A. Rary-Zinque, S. Toda Cosi, F. Patthey, B. V. Sorokin, A. Singha, F. Donati, A. Barla, L. Persichetti, P. Gambardella, A. Arnau, F. Delgado, S. Rusponi, H. Brune
Mesoscale and Nanoscale Physics
Puiseux series about exceptional singularities dictated by symmetry-allowed Hessenberg forms of perturbation matrices
Ipsita Mandal
We develop a systematic framework for determining the nature of exceptional points of $n^{\rm th}$ order (EP$_n$s) in non-Hermitian (NH) systems, represented by complex square
matrices. By expressing
symmetry-preserving perturbations ($\propto \epsilon$) in the Jordan-normal basis of the defective
matrix at an EP$_n$, we show that the upper-$\ell$ Hessenberg structure of the perturbation
matrix directly dictates the leading-order
eigenvalue- and eigenvector-splitting to be $\propto \epsilon^{1/\ell}$, when expanded in a Puiseux series. Applying this to three-band NH models invariant under parity (P), charge-conjugation (C), or parity-time-reversal (PT), we find that EP$_3$s in P- and C-symmetric systems are restricted to at most $\sim \epsilon^{1/2}$ branch points, while PT-symmetric systems generically support EP$_3$s with the strongest possible singularities (viz. $\sim \epsilon^{1/3}$). We illustrate these results with concrete three-dimensional models in which exceptional curves and surfaces emerge. We further show that fine-tuned perturbations can suppress the leading-order branch point to a less-singular splitting, which have implications for designing direction-dependent EP-based sensors. The appendix extends the analysis to four-band P- and C-symmetric models, establishing the existence of EP$_4$s with $\sim \epsilon^{1/4}$ and $\sim \epsilon^{1/2}$ singularities, respectively.
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Soft Condensed Matter
Dissolution of a two-component drop onto macrophase due to surface tension effect
Alexey Kabalnov
Additives of sparingly soluble components are known to slow down or completely inhibit Ostwald ripening in dispersed systems. In this paper series, our earlier model of the stabilization against Ostwald ripening is revisited and extended over the whole range of compositions, molar volumes of components, and their activity coefficients. In the first paper, a simpler problem, the dissolution of a two-component drop under the action of excess Laplace pressure inside is analyzed. Three stages of dissolution are identified. In the first stage, called pre-lock-in, the concentration of the poorly soluble component undergoes a quick increase, and the system enters the lock-in state, in which the Laplace pressure effect on the chemical potential of the more soluble component is nearly completely counterbalanced by the Raoult effect. After this, the dissolution kinetics slows down and enters a steady state. In the process, the concentration of the sparingly soluble component continues to increase, first slowly and then more rapidly in the very end of the particle lifetime; this latter stage is called the 'late lock-in'. Despite all those variations, if the initial concentration of the poorly soluble component is above a certain threshold, the dissolution kinetics nearly follows the classical cubic law. An improved equation for the rate of dissolution is proposed that covers the whole formulation range and represents an extension over our previous formula.
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Disordered Systems and Neural Networks · Cross-listed from stat.ML
The Rules-and-Facts Model for Simultaneous Generalization and Memorization in Neural Networks
Gabriele Farné, Fabrizio Boncoraglio and Lenka Zdeborová
A key capability of modern neural networks is their capacity to simultaneously learn underlying rules and memorize specific facts or exceptions. Yet, theoretical understanding of this dual capability remains limited. We introduce the Rules-and-Facts (RAF) model, a minimal solvable setting that enables precise characterization of this phenomenon by bridging two classical lines of work in the statistical physics of learning: the teacher-student framework for generalization and Gardner-style capacity analysis for memorization. In the RAF model, a fraction $1 - \varepsilon$ of training labels is generated by a structured teacher rule, while a fraction $\varepsilon$ consists of unstructured facts with random labels. We characterize when the learner can simultaneously recover the underlying rule - allowing generalization to new data - and memorize the unstructured examples. Our results quantify how overparameterization enables the simultaneous realization of these two objectives: sufficient excess capacity supports memorization, while regularization and the choice of kernel or nonlinearity control the allocation of capacity between rule learning and memorization. Experiments on a CIFAR10-based RAF task show that the qualitative trade-off persists for fixed kernels, whereas representations learned by deeper neural networks substantially mitigate it, preserving factual recall while improving generalization. The RAF model provides a theoretical foundation for understanding how modern neural networks can infer structure while storing rare or non-compressible information.
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