Materials Science
Neural Networks as Physics-Consistent Surrogates: An Explainable AI Validation Framework for Learning Constitutive Relations
Chandana Pati and S. M. Mallikarjunaiah
This paper presents a Physics-Explainable AI (XAI) framework to validate and interpret neural networks for the constitutive modeling of solid materials. The study bridges the gap between data-driven models and continuum mechanics by applying a suite of explainability methods to neural networks trained on three distinct material behaviors: hyperelasticity (Mooney-Rivlin), elastoplasticity (Chaboche), and viscoelasticity (Fractional Zener). First, high-fidelity surrogate models, including dense feed-forward networks, LSTMs, and GRUs, are trained on synthetically generated data to accurately capture complex material responses. The core of the work then employs XAI techniques to "open the black box" and confirm that the networks learn physically meaningful principles. For hyperelasticity, gradient-based attributions (Grad Input (GI)) successfully match the analytical tangent modulus, proving the network learned material stiffness. For elastoplasticity, SHapley Additive exPlanations (SHAP) and Principal Component Analysis (PCA) demonstrate the Recurrent Neural Network (RNN) internalizes path-dependent
memory, with SHAP identifying plastic strain as the dominant feature governing the stress prediction. For viscoelasticity, latent-space and wavelet analyses of the Gated Recurrent Unit. GRU layers reveal a clear temporal hierarchy, with different layers encoding instantaneous elastic response, intermediate relaxation, and long-term fractional
memory. Ultimately, the study demonstrates that the XAI framework can verify that the neural networks are not merely curve-fitting but are, in fact, learning the underlying physical mechanisms of stiffness, history-dependence, and temporal damping.
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Superconductivity
Nonlocal Josephson diode effect in minimal Kitaev chains
Jorge Cayao and Masatoshi Sato
We study the emergence of the nonlocal Josephson effect in a system composed of three laterally coupled minimal Kitaev chains and exploit it to realize the nonlocal Josephson diode effect. We find that an imbalance between crossed Andreev reflections and electron cotunneling in the middle Kitaev chain gives rise to an asymmetric $2\pi$-periodic phase-dependent Andreev spectrum, controlled by the superconducting phases across the left and right junctions. We then show that the asymmetric Andreev spectrum, formed by hybridized Andreev bound states at the left and right junctions, enables a supercurrent across one junction via the phase difference at the other junction, thereby signaling the nonlocal Josephson effect. Notably, these nonlocal Josephson supercurrents exhibit distinct positive and negative critical currents, demonstrating the realization of the nonlocal Josephson diode effect with highly tunable polarity and efficiencies exceeding $50\%$. The nonlocal Josephson diode effect requires breaking local time-reversal and local charge-conjugation
symmetries, with the latter being unique to minimal Kitaev chains. Our results establish minimal Kitaev chains as a highly controllable platform for engineering nonlocal Josephson phenomena.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
On-Chip Levitated Neon Particle Arrays for Robust and Scalable Electron Qubits
Sosuke Inui, Yinghe Qi, Yiming Xing et al. (+3 more)
Electron-on-neon (eNe)
qubits have recently emerged as a compelling platform for
quantum computing, which combines the
vacuum isolation advantages of trapped-ion
qubits with the scalability of superconducting
circuits. In this system, electrons are trapped in
vacuum above a solid neon film deposited on superconducting microwave resonators, where they exhibit strong coupling to the resonators, coherence times of ~0.1 ms, and single-
qubit gate fidelities exceeding 99.97%. A central challenge, however, is the spontaneous binding of electrons to neon surface bumps. These bumps, originating from substrate roughness, vary in size: electrons on bumps of suitable sizes within the resonator can couple to microwave
photons and function as
qubits, whereas those on unfavorable bumps remain inactive yet contribute to background charge noise. Moreover, both the bump landscape and the sites where electrons bind differ from run to run, leading to variable
qubit characteristics that hinder scalability. To address this challenging issue, we present an on-chip
magnetic-levitation architecture in which arrays of solid-neon microparticles are suspended above the processor chip to act as electron carriers. This design eliminates substrate effects while retaining strong
qubit-resonator coupling and supporting inter-
qubit connectivity. Our analysis further shows that the
qubit transition frequency can be tuned across the gigahertz range and its anharmonicity can reach ~0.8 GHz by tuning the resonator bias voltage. Together, these features suggest a promising pathway toward robust, reproducible, and scalable eNe-based
quantum computing.
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All authors Sosuke Inui, Yinghe Qi, Yiming Xing, Charles Peretti, Dafei Jin, Wei Guo
Statistical Mechanics
Scaling of a Mutual-Information Distance in One-dimensional Quantum Spin Chains
Beau Leighton-Trudel
We introduce a
geometric scaling relation that characterizes the local scale behavior of correlations using the informational distance $d_E = K_0/\sqrt{I}$, where $I$ is the mutual information. We define a
geometric conversion factor, $G \equiv \partial_r d_E$, which quantifies the local scale. We show that $G$ relates directly to $I$ via $G \propto I^{\kappa}$. For systems with power-law correlations $I(r) \sim r^{-X}$, the metric scaling exponent is $\kappa = 1/X - 1/2$. A key consequence is that the
geometric scale $G$ is uniform (position-independent) if and only if $\kappa = 0$, which occurs precisely at $X = 2$. This identifies $X = 2$ as the unique condition for a uniform and metric informational distance. We validate this relation using DMRG simulations of the 1D XXZ chain and exact results for the XX model. We demonstrate two falsifiable diagnostics: (i) $G(r)$ is flat in the bulk at criticality ($X \approx 2$) but varies strongly when gapped; (ii) a coordinate-agnostic slope test of $\log G$ versus $\log I$ at the XX
benchmark ($X = 2$) yields $\kappa \simeq 0$. This approach provides a coordinate-independent method for identifying scaling regimes that helps to reduce ambiguity from non-universal amplitudes and from the fitting choices in standard power-law analyses, and defines a simple post-processing pipeline that can be applied directly to numerical or experimental mutual-information data.
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Materials Science
Resonant states and nuclear dynamics in solid-state systems: the case of silicon-hydrogen bond dissociation
Woncheol Lee, Mark E. Turiansky, Dominic Waldhör et al. (+3 more)
Bond breaking in the presence of highly energetic carriers is central to many important phenomena in physics and chemistry, including radiation damage, hot-carrier degradation, activation of dopant-hydrogen complexes in
semiconductors, and photocatalysis. Describing these processes from first principles has remained an elusive goal. Here we introduce a comprehensive theoretical framework for the dissociation process, emphasizing the need for a non-adiabatic approach. We
benchmark the results for the case of silicon-hydrogen bond dissocation, a primary process for hot-carrier degradation. Passivation of Si dangling bonds by hydrogen is vital in all Si devices because it eliminates electrically active mid-gap states; understanding the mechanism for dissociation of these bonds is therefore crucial for device technology. While the need for a non-adiabatic approach has been previously recognized, explicitly obtaining diabatic states for solid-state systems has been an outstanding challenge. We demonstrate how to obtain these states by applying a partitioning scheme to the
Hamiltonian obtained from first-principles density functional theory. Our results demonstrate that bond dissociation can occur when electrons temporarily occupy the antibonding states, generating a highly repulsive excited-state potential that causes the hydrogen
nuclear wavepacket to shift and propagate rapidly. Based on the Menzel-Gomer-Redhead (MGR) model, we show that after moving on this excited-state potential on femtosecond timescales, a portion of the
nuclear wavepacket can continue to propagate even after the system relaxes back to the ground state, allowing us to determine the dissociation probability. Our results provide essential insights into the fundamental processes that drive carrier-induced bond breaking in general, and specifically elucidate hydrogen-related degradation in Si devices.
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All authors Woncheol Lee, Mark E. Turiansky, Dominic Waldhör, Byounghak Lee, Tibor Grasser, Chris G. Van de Walle
Materials Science
Ferroic Polarization from Nonpolar Phonons
Seongjoo Jung and Turan Birol
Born effective charge, a fundamental quantity in
lattice dynamics and ferroelectrics, provides a quantitative measure of linear polarization response to ionic displacements. However, it does not account for higher-order effects, which can play a significant role in certain materials, such as fluorite HfO$_2$. In this paper, we use the second-order mode effective charges defined with the second-order atomic dynamical charges as a measure of the dipole moments generated by nonpolar
lattice distortions. Using first-principles calculations, we demonstrate that specific combinations of nonpolar
phonons in many
oxides can induce strongly aligned second-order polarizations, reaching magnitudes comparable to those of intrinsically polar modes even in the zero frequency limit, broadening the understanding of second-order effects, which have historically been emphasized for their dynamical effects at specific frequency ranges. Through a
symmetry-based analysis of the charge density, we elucidate the microscopic origin of these effects, tracing them to variations in bond covalency and local electronic rearrangements. We also demonstrate large second-order mode effective charge in well-studied perovskites, highlighting the generality of these phenomena. Our results offer insights into the design principles of next-generation ferroelectric, piezoelectric and multifunctional materials from the higher-order contribution to polarization in crystalline solids.
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Strongly Correlated Electrons
Spin-resolved Mott crossover and entanglement in the half-filled Hubbard model
Md Fahad Equbal and M. A. H. Ahsan
We investigate the interaction-driven reorganization of
spin and charge correlations in finite Hubbard clusters using exact diagonalization. Focusing on half-filled and lightly doped square
lattices, we analyze
spin-resolved charge-gaps, local observables, two-point correlation functions,
entanglement measures, principal component analysis (PCA) of correlation
matrices and
quantum-geometry-based distance metrics. At half-filling, we observe the emergence of a robust Mott gap whose
spin-dependent component is controlled by the effective exchange energy scale J~4t^2/U at strong coupling, confirming that residual
spin dynamics govern the separation between the lowest-
spin and the next higher-
spin charge excitation channels. Distinct cluster geometries and boundary conditions reveal how
spin-singlet versus finite-
spin ground-state influence charge and
spin responses. Upon one-hole doping, the
spin-resolved charge-gaps collapses, indicating restored compressibility and metallic behavior. PCA and
quantum-geometry-based analysis provide complementary data-driven and wavefunction-based perspectives on correlation-driven Mott crossover phenomena. Our results demonstrate that finite-size Hubbard clusters exhibit clear signatures of the Mott physics,
spin-charge interplay and emergent exchange energy scales, offering a unified microscopic picture of interaction-induced electronic reorganization.
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Mesoscale and Nanoscale Physics
Impact of Electrical Contacts on Transition Metal Dichalcogenides-Based Acoustoelectric and Acousto-Photoelectric Devices
Benjamin Mayer, Felix M. Ehring, Clemens Strobl et al. (+4 more)
We study the impact of electrical contact barriers in hybrid WSe$_2$-LiNbO$_3$-based acoustoelectric and acousto-photoelectric devices using a combination of scanning photocurrent and acousto-electric current spectroscopy. Static scanning photocurrent measurements provide a qualitative measure of the band-bending and spatial distribution of the Schottky barrier between semiconducting WSe$_2$ and gold electrodes whereas the surface acoustic wave-induced acousto-electric current reveals the height of the tunnelling barrier created by the van der Waals gap between the multilayered WSe$_2$ flake and the gold electrodes in addition to the Schottky barrier. The combination of both techniques shows a ten-fold increase in the photocurrent by the acoustic wave. Moreover, the observed spatial redistribution of the current is attributed to the interplay between the contact properties at the source and drain electrodes and the charge carrier dynamics induced by the surface acoustic wave. The ratio of acoustic wavelength to the electrical channel length is found to impact the SAW-induced charge carrier transport. For a channel length shorter than one acoustic wavelength, carriers undergo a seesaw-like motion which changes to charge conveyance for channel lengths comparable or exceeding the acoustic wavelength.
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All authors Benjamin Mayer, Felix M. Ehring, Clemens Strobl, Matthias Weiß, Ursula Wurstbauer, Hubert J. Krenner, Emeline D. S. Nysten
Materials Science
Carrier localization and dynamics in In$_{0.10}$Ga$_{0.90}$N: the impact of alloying and Si doping
Ongeziwe Mpatani, Dominik Muth, Anton Krüger et al. (+4 more)
Alloying and doping are crucial for enhancing the electronic and optical properties of
semiconductors while simultaneously introducing disorder. This report explores the effects of alloying and Si (0.5 at.%) doping on In$_{0.10}$Ga$_{0.90}$N thin films that were grown by metal-organic vapor phase epitaxy. Post-growth X-ray diffraction measurements indicate that Si doping does not affect the
lattice parameters and screw dislocations but significantly increases the edge dislocation density. Temperature-dependent time-resolved photoluminescence spectroscopy shows that Si-doped In$_{0.10}$Ga$_{0.90}$N exhibits higher photoluminescence intensity, blue-shifted peaks, narrower emission linewidths, and quenching of lower energy sidebands when compared to pristine In$_{0.10}$Ga$_{0.90}$N. The peak energies of the most dominant feature, the donor-bound
exciton, for both samples show an $S$-shape behavior indicating the presence of disorder. Although doping improves luminescence, it also introduces deeper localized states. This suggests that
impurity-induced disorder outweighs compositional fluctuations, as confirmed by higher disorder parameters and Stokes shifts. Thus, the Si doping leads to increased localization, reducing nonradiative recombination channels while enhancing radiative processes. The deeper states in the doped sample confirm improved carrier confinement, and their saturation leads to early thermalization, thereby lowering the red-blue shift transition from 165 K to about 50 K. Even though the high doping level makes Si-doped In$_{0.10}$Ga$_{0.90}$N a degenerate system, it exhibits enhanced luminescence properties. These findings shed light on the impact of silicon doping on charge transport in InGaN
alloys for optoelectronic applications.
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All authors Ongeziwe Mpatani, Dominik Muth, Anton Krüger, Rajdeep Adhikari, Alberta Bonanni, Marina Gerhard, Hilary Masenda
Materials Science
Spin-wave emission with current-controlled frequency by a PMA-based spin-Hall oscillator
Moritz Bechberger, David Breitbach, Abbas Koujok et al. (+4 more)
Spin-torque and
spin-
Hall oscillators (SHOs) have emerged as promising candidates for building blocks in neuromorphic computing due to their ability to synchronize mutually, a process that can be mediated by propagating
spin waves. We demonstrate a SHO that takes advantage of a low-damping
magnetic garnet with dominant perpendicular
magnetic anisotropy (PMA), namely gallium-substituted yttrium-iron-garnet (Ga:YIG). In-plane magnetized Ga:YIG allows for the operation at a high efficiency level while also enabling resonant
spin-wave emission. A nonlinear self-localization of the excitation is avoided by exploiting the positive nonlinear frequency shift, which facilitates a current-controlled frequency of the emitted
spin waves. Via micro-focused Brillouin light scattering spectroscopy, we investigate the properties of the local auto-oscillation and its
spin-wave emission. Multiple modes are excited and compete internally, with two propagating modes detected up to distances larger than 10 $\mu$m. Their frequencies combine to an extended frequency bandwidth of approximately 1.6 GHz. The experimentally observed two-mode system and its transition to a single mode at higher currents are reproduced via micromagnetic simulations, which account for spatial variation of the PMA arising due to the microstructures on Ga:YIG. Our results propose a promising platform for hosting SHOs, interconnected via propagating
spin waves with particular relevance to neuromorphic computing.
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All authors Moritz Bechberger, David Breitbach, Abbas Koujok, Björn Heinz, Carsten Dubs, Abbass Hamadeh, Philipp Pirro
Materials Science
Thermomechanical investigation of silicon wafer dynamics within the melting regime driven by picosecond laser pulses for surface structuring
Helen Papadaki, Inam Mirza, Nadezhda M. Bulgakova et al. (+2 more)
Laser-induced periodic surface structures (LIPSS) on silicon, generated by ultrashort pulsed
lasers, provide an efficient means to tailor surface functionality. This work presents a multiphysics finite element study on the thermomechanical dynamics of silicon wafers irradiated by picosecond
laser pulses, focusing on the melting regime where thermomechanical and hydrodynamic effects dominate. To illustrate the sequential nature of
laser scanning, single-pulse irradiation models are developed as thermomechanical analogues of double-pulse interactions. By positioning the
laser focus near reflective boundaries and corners of the target, these models reproduce the stress-wave interference that would occur between successive pulses in scanning. The results show that periodic surface structures originate from mechanical standing wave interference within the molten layer, forming ripples with near-wavelength periodicity. The penetration depth (PD) is identified as a key factor controlling the duration and stability of these ripples: shallow PDs (75-150 nm) yield distinct, persistent patterns, while deeper PDs (app. 2.5 micrometers) lead to extended melting and hydrodynamic smoothing. Simulations of sequential double-pulse irradiation confirm that residual stresses and strains from the first pulse amplify deformation during the second, enhancing ripple amplitude and uniformity. Controlled excitation of mechanical standing waves governed by PD, boundary geometry, and pulse sequencing - thus represents a fundamental mechanism for deterministic LIPSS formation on silicon.
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All authors Helen Papadaki, Inam Mirza, Nadezhda M. Bulgakova, Evaggelos Kaselouris, Vasilis Dimitriou
Statistical Mechanics
Heider balance in square versus triangular lattices under an external field
Zdzisław Burda, Maciej Wołoszyn, Krzysztof Malarz et al. (+1 more)
We discuss the Heider model in the presence of an external social field. This field breaks the possible
symmetry between the probabilities of hostile and friendly relationships. We consider the system in the presence of fluctuations generated by thermal noise and present the results of a comparative study of two-dimensional triangular and square networks with periodic boundary conditions. The results were obtained using three different methods: exact calculations for small systems ($3 \times 3$ square
lattice and $2 \times 2$ triangular
lattice), Monte Carlo simulations of medium-sized systems ($16 \times 16$
lattices), and exact calculations in the thermodynamic limit (corresponding to infinite size) of certain limiting cases for which analytical solutions are possible. In particular, we exploit the recently discovered equivalence between structurally balanced systems and the Ising model to derive an exact form of the edge magnetization susceptibility for systems in Heider
equilibrium.
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All authors Zdzisław Burda, Maciej Wołoszyn, Krzysztof Malarz, Krzysztof Kułakowski
Statistical Mechanics
Universal asymptotic solution of the Fokker-Planck equation with time-dependent periodic potentials
Boxuan Han, Zeyu Rao and Ming Gong
Brownian motion, as one of the most fundamental concepts in statistical physics, has everlasting interests in interdisciplinary fields in the past century. Although this motion with static potentials have been widely explored, its physics in time-dependent periodic potentials are far less well understood. Here we generalize this motion to the realm of time-dependent periodic potentials, showing that the asymptotic solution of the probability distribution function (PDF) can have a universal form, that is, a Boltzmann weight multiplied by a Gaussian envelope function. We derive a partial equation for this Boltzmann weight and demonstrate that many different potentials can give the same Boltzmann weight. We first present an exact solvable model to illustrate the validity of our solution. For the periodic potential with a time-dependent tilt potential, we can determine the Boltzmann weight by numerical solving the partial equation. These results are confirmed by solving the Langevin equation numerically. With this idea, we can determine the asymptotic solution of the Fokker-Planck equation, in which the
entropy satisfies the thermodynamic law. Our results can have wide applications, including quasi-periodic potentials, two-dimensional potentials and even with models with inertia, which should greatly broaden our perspective of Brownian motion.
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Strongly Correlated Electrons
Dressing composite fermions with artificial intelligence
Mytraya Gattu
Recent variational studies have demonstrated that the strongly correlated ground states of the fractional
quantum Hall (FQH) effect can be captured using machine learning approaches starting from no prior knowledge of the underlying physics. We introduce a complementary framework that instead starts from Jain's composite-
fermion (CF) wavefunctions, which accurately describe FQH states as weakly interacting states of CFs at fillings $\nu = n/(2pn+1)$ in an idealized limit. As we move away from this idealized limit to one more in line with experimental reality, we expect CFs to become dressed much like the electrons of a noninteracting system, which are dressed by neutral excitations as interaction is turned on adiabatically, as in Landau's
Fermi-
liquid theory. We model this dressing using a Feynman-Cohen-style backflow approach, implemented through
symmetry-preserving neural networks-a framework we refer to as CF-Flow. CF-Flow achieves competitive accuracy with substantially greater computational efficiency and scales to systems of $\gtrsim 26$ electrons. At fillings $\nu = 1/3$ and $2/5$, as a function of Landau-level mixing strength, CF-Flow produces ground-state energies with low local-energy variance that are nearly indistinguishable from those obtained using the fixed-phase
diffusion Monte Carlo (fp-DMC) method, even though the latter constrains the wavefunction phase to that of the lowest Landau level-thereby providing insight into why fp-DMC has been successful in giving an accurate quantitative account of several experiments. Finally, the
symmetry-preserving architecture of CF-Flow enables access to excited states and computation of the transport gap at $\nu = 1/3$, where we find, unexpectedly, that it decays exponentially toward a finite value in the limit of large Landau-level mixing, suggesting a first-order transition from the FQH
liquid to a non-FQH state.
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Soft Condensed Matter
Avalanches in active glasses with finite persistence
Roland Wiese, Ezequiel Ferrero and Demian Levis
We numerically investigate the statistics of avalanches in glassy systems of active particles with finite persistence, with and without an externally applied shear. In departing from the infinite-persistence limit and exploring the interplay of internal activity and external driving, we uncover when and why active and passive systems display similar avalanche statistics and where these analogies fail. We find that power-law distributed stress drops emerge only when activity builds long enough correlations, controlled by the persistence length, with exponents that vary from the purely strain-driven case, to the purely activity-driven case, in a smooth fashion. The local structure and scaling of avalanches of plastic rearrangements remains universal across both limit cases, supporting an interpretation of activity as increasing the typical size of the regions involved in a given avalanche. Our results bridge quasistatic shear strain and finite-persistence active yielding, showing that avalanches driven by self-propulsion retain the characteristic fingerprints of long-range stress propagation.
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Materials Science
Dual Role of Nb in Defect-Mediated Strength and Ductility of {\gamma}-TiAl Alloys
Zhiqiang Zhao, Siyao Shuang, Kepeng Ouyang et al. (+8 more)
The origin of the superior high-temperature strength of {\gamma}-TiAl with high Nb addition remains highly controversial, largely due to the unclear role of Nb atoms. Using large-scale hybrid Monte Carlo and molecular dynamics simulations with a self-developed neural network potential,we show that Nb atoms predominantly occupy Ti sites and form short-range order with neighboring Al atoms, but a non-negligible fraction also occupies Al sites (NbAl) and promotes the formation of antisite defects (TiAl). Both the NbAl and TiAl antisites exceptionally reduce stacking fault energies and facilitate deformation twinning, thereby enhancing plasticity. Meanwhile, these substitutional and antisite defects also increase the Peierls stress of both screw and edge dislocations, which hinders dislocation motion to cause pronounced solid-solution strengthening. This work provides mechanistic insights into the dual role of Nb in enhancing both strength and ductility in {\gamma}-TiAl and further offers guidance for defect and composition engineering in advanced
alloy systems.
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All authors Zhiqiang Zhao, Siyao Shuang, Kepeng Ouyang, Maolin Yu, Junping Du, Liangli Chu, Xiaokai Chen, Shigenobu Ogata, Wanlin Guo, Zhuhua Zhang, Yong-Wei Zhang
Strongly Correlated Electrons
Near-flat-band-driven violation of Pauli limit in heavy fermion superconductors
Yan-Xiao Wang and Yin Zhong
Heavy-
fermion superconductors often display upper critical fields that exceed the conventional Pauli paramagnetic limit, indicating that strong correlations and hybridized quasiparticle bands play an essential role in the paramagnetic pair-breaking process. Within the two-dimensional Kondo-Heisenberg model, we perform a self-consistent mean-field analysis of
spin-singlet s-, extended-s-, and d-wave pairing under Zeeman fields, and compute the critical field Bc, the transition temperature Tc, and the Clogston-Chandrasekhar ratio rCC. We find that rCC increases sharply as the conduction filling approaches half filling. This enhancement arises from the weakly dispersive region of the lower hybridized band, where the strongly reduced
Fermi velocity diminishes the normal-state paramagnetic energy and stabilizes superconductivity. At fixed filling, the distinct JH dependences among the three pairing channels reflect the sensitivity of Pauli limiting to both band
curvature and the structure of the order parameter. These results provide microscopic evidence that proximity to a near-flat hybridized band offers a robust route to enhanced Pauli-limiting fields in heavy-
fermion superconductors.
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Mesoscale and Nanoscale Physics
Characterizing topology at nonzero temperature: Topological invariants and indicators in the extended SSH model
Julia D. Hannukainen and Nigel R. Cooper
We compare three complementary diagnostics for mixed Gaussian states at nonzero temperature, focusing on the Su-Schrieffer-Heeger (SSH) chain and its inversion-symmetric extension. Whilst the ensemble
geometric phase, a mixed-state generalization of the Zak phase, remains well defined at nonzero temperature, the modulus of the corresponding expectation value vanishes in the thermodynamic limit, limiting its practical use. To develop diagnostics suitable for large systems, we introduce local twist operators acting on neighboring sites, whose expectation values provide local indicators of the underlying topological phase. The topological phase is identified from the relative magnitude of these expectation values, which only requires measuring two local expectation values at nonzero temperature, together with one additional nonlocal expectation value when next-nearest-neighbor hopping is included. In addition, we generalize the local
chiral marker to mixed Gaussian states, fully determined by its single-particle correlation
matrix, with a nonzero purity gap in their effective single-particle
Hamiltonian. The presence of a purity gap ensures that the correlation
matrix can be flattened to an effective projector. Evaluating the
chiral marker with respect to the band-flattened correlation
matrix yields a real-space topological invariant that coincides with the winding number in the zero-temperature limit. The ensemble
geometric phase, the local twist operators, and the local
chiral marker provide complementary methods to characterize
topology in the SSH chain beyond pure states.
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Materials Science
A Rapid Thermal Chemical Vapor Deposition System for Fast Synthesis of Epitaxial Graphene Under Ambient Pressure
Shikhar Kumar Gupta, Meet Ghelani, Pragna Datta et al. (+10 more)
Graphene has emerged as a promising material for next-generation electronic and thermal devices owing to its exceptional charge transport and thermal conductivity. However, high-quality samples are predominantly obtained via mechanical exfoliation from graphite
crystals, a process that inherently lacks scalability. Despite extensive efforts toward large-area synthesis, cost-effective approaches for producing high-quality, large-area, single-crystalline
graphene with fast turnaround time remain limited. Here, we report the design, fabrication, and performance benchmarking of a rapid thermal chemical vapor deposition (RTCVD) system capable of synthesizing epitaxial monolayer
graphene under atmospheric pressure. The entire growth process, from sample loading to unloading, is achieved within $25$ minutes with a temperature ramp rate exceeding $23^\circ\mathrm{C}/s$. Growth at atmospheric pressure eliminates the need for
vacuum components, thereby reducing both system complexity and operational costs. The structural and electronic quality of epitaxial
graphene is comprehensively characterized using Raman spectroscopy, selected area electron diffraction (SAED), and magnetotransport measurements, which reveal signatures of
quantum Hall effect in synthesized
graphene samples. Furthermore, we demonstrate van der Waals epitaxial growth of palladium (Pd) thin films on
graphene transferred to Si/SiO$_{2}$ substrates, establishing its single-crystalline nature over a large area and its potential as a versatile platform for subsequent heteroepitaxial growth.
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All authors Shikhar Kumar Gupta, Meet Ghelani, Pragna Datta, Subhalakshmi Guha, Shivesh Yadav, Nilesh Kulkarni, Maheshwar Gokhale, Bhagyashree Chalke, Devendra Buddhikot, Naveen Paneri, Lavudya Devendar, Arnab Bhattacharya, Shouvik Chatterjee
Statistical Mechanics
First Passage Resetting Gas
Marco Biroli, Satya N. Majumdar and Gregory Schehr
We study a one-dimensional gas of $N$ Brownian particles that diffuse independently but are simultaneously reset whenever any of them reaches a fixed threshold located at $L > 0$. For any $N > 2$, the system reaches a non-
equilibrium stationary state (NESS) at long-times with strong long-range correlations. These correlations emerge purely from the dynamics, and not from built-in interactions. Despite being strongly correlated, the NESS has a solvable structure that allows for an exact computation of several physical observables, both global and local. These include the average density profile, the distribution of the position of the $k$-th ordered particles, the distribution of the gap between two consecutive particles and the full counting statistics, i.e., the distribution of the number of particles in a finite interval around the origin.
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Soft Condensed Matter
Flow of a colloidal solution in an orthogonal rheometer
Krishna Kaushik Yanamundra, Chandler C. Benjamin and Kumbakonam Ramamani Rajagopal
The flow of a colloidal solution between two parallel disks rotating with the same angular velocity about two non-coincident axes was studied. The problem has been approached from two perspectives, the first wherein the stress is expressed in terms of a power-law of kinematical quantities, and the second wherein we consider a non-standard model where the symmetric part of the velocity gradient is given by a power-law of the stress. For a range of power-law exponents, the class of models are non-invertible. By varying the material and
geometric parameters, changes in the flow behaviour at different Reynolds numbers were analysed. We find that pronounced boundary layers develop even at low Reynolds numbers based on the power-law exponents. The new class of stress power-law fluids and fluids that exhibit limiting stress also show the ability to develop boundary layers.
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Superconductivity
Theory of planar quasiballistic Josephson junctions
G. A. Bobkov, I. V. Bobkova, A. M. Bobkov et al. (+2 more)
We develop a theoretical framework for planar quasiballistic Josephson junctions, where multiple superconducting leads are coupled through a large, nearly ballistic normal metal
crystal. Our approach, based on quasiclassical Eilenberger equations, accounts for the dominant role of electron reflections from the
crystal surfaces or single
impurities, a mechanism distinct from both purely ballistic and diffusive limits. We calculate the critical current between superconducting leads for various geometries, examining its dependence on temperature and
magnetic field. Crucially, we demonstrate that in multiterminal setups, the junctions are not independent but form a strongly coupled system. The theory successfully explains key experimental observations from a companion work [Polevoy et al., Phys. Rev. Lett. 137, 166001 (2026)], including a non-monotonic dependence of the critical current on the interlayer length, providing a foundation for designing and understanding complex multi-terminal Josephson systems.
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All authors G. A. Bobkov, I. V. Bobkova, A. M. Bobkov, K. B. Polevoy, V. S. Stolyarov
Superconductivity
Multiterminal Quasiballistic Josephson Effect in Monocrystalline Gold
K. B. Polevoy, G. A. Bobkov, D. S. Kalashnikov et al. (+8 more)
We report on the realization of a planar, quasiballistic Josephson junction array using a Au micron-sized single
crystal. The system exhibits a nonlocal, multiterminal Josephson effect, where the supercurrent between any two superconducting leads is governed by the phase coherence across the entire
crystal. Key evidence includes a nonmonotonic dependence of the critical current on junction length and
magnetic interference patterns with periods corresponding to the shared normal-metal area. Nonlocal transport measurements further confirm that the supercurrent between two electrodes depends on the phase configuration of all the others. Our results, supported by a developed theoretical model, establish a platform for exploring complex superconducting phenomena in multiterminal ballistic systems.
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All authors K. B. Polevoy, G. A. Bobkov, D. S. Kalashnikov, A. G. Shishkin, I. V. Trofimov, A. M. Bobkov, E.A. Sedov, E.A. Krivko, M. A. Tarkhov, I.V. Bobkova, V. S. Stolyarov
Soft Condensed Matter
Free Energy and Diffusivity in the Fokker-Planck Theory of Polymer Translocation
Bhavesh R. Sarode and Harshwardhan H. Katkar
We revisit the Fokker-Planck based theory of driven
polymer translocation through a narrow nanopore. A bead-spring model of a uniformly charged polyelectrolyte chain translocating through a semi-implicit model of a nanopore embedded in a membrane are used to gain insights into the underlying free energy landscape and kinetics of translocation. The free energy landscape is predicted using metadynamics simulation, an enhanced sampling method. A direct comparison with the theoretical free energy formulation proposed in the literature allows us to introduce a modification related to the entropic contribution in the theory. Additional classical Langevin dynamics simulation runs are performed to obtain the translocation time distribution for
polymers of lengths $N$ driven by voltages $V$ through nanopores of radii $r_p$. In agreement with earlier reports, a scaling of the mean translocation time $\langle \tau_\text{LD} \rangle \sim N^\alpha/V$ is observed, with $\alpha \sim 1.40 - 1.48$ depending on the nanopore size. Fitting the mean first passage time given by the Fokker-Planck theory, $\langle \tau_\text{FP}\rangle$,to simulation results helps gain insights into the diffusivity $k_\text{FP}$ used in the theory. We report a scaling of $k_\text{FP}\sim N^\beta$. The $r_p-$dependent values of the exponent $\beta$ significantly deviate from the Rouse theory prediction of $\beta = -1$ for center-of-mass diffusivity of a
polymer chain.
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Soft Condensed Matter · Cross-listed from physics.flu-dyn
Linearized instability of Couette flow in stress-power law fluids
Krishna Kaushik Yanamundra and Lorenzo Fusi
This paper examines the linearized stability of plane Couette flow for stress-power law fluids, which exhibit non-monotonic stress-strain rate behavior. The constitutive model is derived from a thermodynamic framework using a non-convex rate of dissipation potential. Under velocity boundary conditions, the system may admit three steady-state solutions. Linearized stability analysis reveals that the two solutions on ascending constitutive branches are unconditionally stable, while the solution on the descending branch is unconditionally unstable. For mixed traction-velocity boundary conditions, the base state is unique. Stability depends solely on whether the prescribed traction lies on an ascending (stable) or descending (unstable) branch of the constitutive curve. The results demonstrate that flow stability in these complex fluids is fundamentally governed by both boundary conditions and constitutive non-monotonicity.
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Mesoscale and Nanoscale Physics
Wafer-Scale Single-Crystalline Monolayer Graphene
Johanna Huhtasaari, Joyal Jain Palakulam, Awse Salha et al. (+11 more)
Producing large-area single-crystalline
graphene is key to realizing its full potential in advanced applications, including twistronics. Yet, controlling
graphene growth kinetics to avoid grain boundaries or multilayer growth remains challenging. Here, we demonstrate single-crystalline
graphene free from multilayer domains via one-step delamination of epitaxial
graphene from silicon carbide (SiC). This is enabled by a specific surface reconstruction of 4H-SiC(0001) achieved in our growth conditions. High crystalline quality is confirmed by the observation of the half-integer
quantum Hall effect – the hallmark of monolayer
graphene – in near cm-sized
crystals. The scalability of our process, explored with 4”-wafers, represents an advance toward large-scale integration of high-performance
graphene applications.
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All authors Johanna Huhtasaari, Joyal Jain Palakulam, Awse Salha, Per Hyldgaard, Elsebeth Schröder, Magnus Hårdensson Berntsen, Oscar Tjernberg, Manasi Shah, Rodrigo Martinez-Duarte, Hans He, Johannes Hofmann, Thilo Bauch, Naveen Shetty, Samuel Lara-Avila
Strongly Correlated Electrons
Altermagnetic boosting of chiral phonons
J. Okamoto, C. Y. Mou, H. Y. Huang et al. (+10 more)
Chirality characterizes the asymmetry between a structure and its mirror image and underlies a wide range of
chiral functionalities. In crystallographically
chiral materials,
phonons with non-zero linear momentum $\textbf{k}$ can acquire a $k$-induced longitudinal magnetization, giving rise to
chiral phonons. Helical
spin order, with its proper screw-type configuration, breaks all mirror
symmetries and therefore carries
magnetic chirality. Such helical
spins also generate non-relativistic
spin splitting for any quasiparticle excitations propagating along the screw axis. To explore the possible connection between
chiral phonons and
magnetic chirality, we investigated the crystallographically polar and
chiral compound (Mn,Ni)$_3$TeO$_6$, which hosts three distinct states: a paramagnetic state, a helical
spin state with
magnetic chirality, and a collinear
spin state without
magnetic chirality. We find an approximately tenfold enhancement of
chiral-
phonon coupling in the helical
spin state along the screw axis, compared with both the paramagnetic and collinear
spin states. These results identify a new route to amplify
chiral phonons through an altermagnetic effect arising from the broken parity-time
symmetry in helical
spins. %from non-relativistic
spin splitting.
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All authors J. Okamoto, C. Y. Mou, H. Y. Huang, G. Channagowdra, C. Won, K. Du, X. Fang, E. V. Komleva, C. T. Chen, S. V. Streltsov, A. Fujimori, S-W. Cheong, D. J. Huang
Strongly Correlated Electrons
Precise computation of universal corner entanglement entropy at 2+1 dimension: From Ising to Gaussian quantum critical points
Ben Lee-Yeung Ngai, Justin Tim-Lok Chau, Junchen Rong et al. (+3 more)
Computing the subleading logarithmic term in the
entanglement entropy (EE) of (2+1)d
quantum many-body systems remains a significant challenge, despite its central role in revealing universal information about
quantum states and
quantum critical points (QCPs). Building on recent algorithmic advances that enable the stable calculation of EE as an exponential observable~\cite{zhouIncremental2024,zhangIntegral2024,liaoExtracting2024}, we develop a bubble basis projector
quantum Monte Carlo (QMC)
algorithm to precisely and efficiently compute the universal corner of EE at QCPs in a (2+1)d square-
lattice transverse-field Ising model augmented with a four-body interaction. Turning on this interaction allows us to trace an Ising critical line, reaching the tricritical point, and then a line of first-order phase transition. In (2+1)d, the tricritical point is described by the Gaussian theory, where a theoretical calculation of the corner logarithmic term in the 2nd Rényi
entropy term is available~\cite{UniversalCasini2007}. Our QMC results are in quantitative agreement with this theoretical value, providing a highly nontrivial
benchmark of the
algorithm. Furthermore, we also study the Rényi EE at the Ising critical line and on the first-order transition line, obtaining results consistent with theoretical expectations. These findings establish the long-sought connection between the universal values of an exactly solvable limit and those of a strongly correlated regime at (2+1)d.
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All authors Ben Lee-Yeung Ngai, Justin Tim-Lok Chau, Junchen Rong, Meng Cheng, Yuan Da Liao, Zi Yang Meng
Materials Science
Anisotropic and isotropic elasticity and thermal transport in monolayer C$_{24}$ networks from machine-learning molecular dynamics
Qing Li, Haikuan Dong, Penghua Ying et al. (+1 more)
Two-dimensional fullerene networks have recently attracted increasing interest due to their diverse bonding
topologies and mechanically robust architectures. In this work, we develop an accurate machine-learned potential NEP-C$_{24}$ for both the quasi-hexagonal phase (qHP) and the quasi-tetragonal phase (qTP) C$_{24}$ monolayers, based on the neuroevolution potential (NEP) framework. Using this NEP-C$_{24}$ model, we systematically investigate the elastic and thermal transport properties. Compared with C$_{60}$ monolayers, both C$_{24}$ phases exhibit markedly enhanced stiffness, arising from the combination of reduced molecular size and increased density of covalent bonds. The qTP C$_{24}$ monolayer shows nearly isotropic elastic properties and thermal conductivities along its two principal axes owing to its four-fold
symmetry, whereas the chain-like, misaligned bonding
topology of the qHP C$_{24}$ monolayer leads to pronounced in-plane anisotropy. Homogeneous nonequilibrium molecular dynamics and spectral decomposition analyses reveal that low-frequency ($<5$ THz) acoustic
phonons dominate heat transport, with directional variations in
phonon group velocity and mean free path governing the anisotropic response in qHP C$_{24}$. Real-space heat flow visualizations further show that, in these fullerene networks,
phonon transport is dominated by strong inter-fullerene covalent bonds rather than weak van der Waals interactions. These findings establish a direct link between intermolecular bonding
topology and
phonon-mediated heat transport, providing guidance for the rational design of fullerene-based two-dimensional materials with tunable mechanical and thermal properties.
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All authors Qing Li, Haikuan Dong, Penghua Ying, Zheyong Fan
Mesoscale and Nanoscale Physics
Quantized nonlinear transport and its breakdown in Fermi gases with Berry curvature
Fan Yang and Xingyu Li
Quantized transport not only exist in gapped topological states but also in metallic states. Recently, Kane proposed a quantized nonlinear conductance in ballistic metals whose value is determined by the Euler characteristic of the
Fermi sea [Phys. Rev. Lett. 128, 076801 (2022)]. In this paper, we consider two-dimensional noninteracting fermionic systems whose
Fermi surface has nonvanishing Berry
curvature. We find that the Berry
curvature at the
Fermi surface does not affect the quantized nonlinear transport for translationally invariant systems. When spatial inhomogeneity is introduced, such quantization breaks down due to the combined effect of Berry
curvature and the gradient of local potential. Such breakdown of quantization can be observed in trapped ultracold atoms with topological bands.
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