Statistical Mechanics
Finding the Edge of Chaos in a Ferromagnet: Quantifying the "Complexity" of 2D Ising Phase Transitions with Image Compression
Cooper Jacobus
The data-driven characterization of the “complexity” present in dynamical systems remains an open problem with broad applications across the physical sciences. We investigate the “structural complexity” of the 2D
ferromagnetic Ising model, a paradigmatic system exhibiting a second-order phase transition at a certain critical temperature which is often cited as a canonical example of complex morphology. We define a quantitative metric for this structural complexity, $\mathcal C_s$, through the lens of algorithmic information theory by approximating the Kolmogorov complexity of
lattice configurations via standard lossless image compression
algorithms. We regularize our proposed metric, $\mathcal C_s$, by comparing the compressibility of a configuration to that of its pixel-wise sorted and randomly shuffled counterparts. We arrive at a definition of $\mathcal C_s$ as a product of two components representing the systems departure from perfect order and disorder respectively which we then plot as a function of temperature. Our numerical simulations reveal a distinct peak in $\mathcal C_s$ at the known critical temperature $T_c$. This result demonstrates that such information-theoretic measures can act as sensitive, model-agnostic indicators of criticality, directly quantifying the emergence of complex structure at the boundary between order and chaos, opening the door to data-driven applications in domains where analytic solutions are unavailable.
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Superconductivity
Deciphering Majorana Zero Modes in Topological Superconductor FeTe0.55Se0.45 with Machine-Learning-Assisted Spectral Deconvolution
Jewook Park, Hoyeon Jeon, Dongwon Shin et al. (+4 more)
Unambiguous identification of Majorana zero modes (MZMs) in topological
superconductors (TSCs) remains a challenge due to complex in-gap states that can also produce zero-bias conductance peaks (ZBPs). Here we demonstrate a data-driven workflow that integrates pixel-wise spectral deconvolution with machine-learning (ML) to analyze tunneling spectroscopy from FeTe0.55Se0.45, an intrinsic TSC. Based on the local density of states (LDOS) spectra acquired with a millikelvin scanning tunneling microscope under
magnetic fields, each spectrum was decomposed into multiple Lorentzian peaks. The extracted peak parameters were assembled into a structured feature set and subsequently embedded and clustered with unsupervised ML
algorithms. ML-based clustering identified distinct classes of LDOS spectra, separating
superconductor vortices exhibiting ZBPs consistent with established characteristics of MZMs from
vortices displaying ZBP-mimicking features of trivial origin. Furthermore, spatially resolved ZBP distributions differentiate isotropic
vortex cores with well-defined ZBPs from
vortices that exhibit locally distorted ZBPs. By comparing the ZBP distributions to defect locations measured without
magnetic field, we found a correlation between local heterogeneity and the ZBP formation, necessitating the systematic, data-driven analysis to disentangle genuine MZM signatures in TSC. This objective and reproducible workflow advances reliable MZM detection in TSCs, providing a foundation for MZM manipulation towards
quantum computation.
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All authors Jewook Park, Hoyeon Jeon, Dongwon Shin, Guannan Zhang, Michael A McGuire, Brian C. Sales, An-Ping Li
Statistical Mechanics
Bond percolation in distorted simple cubic and body-centered cubic lattices
Bishnu Bhowmik, Sayantan Mitra, Robert M. Ziff et al. (+1 more)
We investigate the effect of structural distortion on bond percolation in simple cubic and body-centered cubic
lattices using extensive Monte Carlo simulations. Distortion is introduced through controlled random displacements of
lattice sites, thereby modifying nearest-neighbor distances. Bond occupation is permitted only when the bond length is smaller than a prescribed connection threshold, directly coupling
geometric disorder to connectivity. Finite-size scaling analysis is employed to determine percolation thresholds for finite systems and in the thermodynamic limit. We find that when the connection threshold exceeds the nearest-neighbor distance of the undistorted
lattice, the percolation threshold increases monotonically with distortion strength, indicating a systematic suppression of spanning. In contrast, this monotonic behavior breaks down when the connection threshold is below the nearest-neighbor distance of the undistorted
lattice, highlighting a nontrivial interplay between
geometric distortion and connectivity. We further identify critical values of the connection threshold and the distortion amplitude required for global spanning when all the allowed bonds are occupied. All qualitative behaviors remain robust across both
lattice geometries. These results clarify how
geometric disorder reshapes percolation in three-dimensional crystalline networks.
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All authors Bishnu Bhowmik, Sayantan Mitra, Robert M. Ziff, Ankur Sensharma
Strongly Correlated Electrons
Band splitting in the altermagnet CrSb
Vladimir P.Mineev
Altermagnets are a class of metallic magnets characterized by
spin-split electron bands. Like antiferromagnets they lack spontaneous bulk magnetisation. The initial description of the momentum dependent
spin splitting of electron bands in altermagnets was based on the
spin groups approach, which is valid when relativistic interactions are neglected. Then the
spin-orbit coupling has been taken into account according with time-reversal-odd, even-parity irreducible representations of centrosymmetric point groups considered by R.M.Fernandes et al, Phys.Rev.B 109, 024404 (2024). Here we show inadequacy of this formal approach. The problem of electron band splitting should be discussed based on
crystal symmetry of concrete altermagnet material. The band
spin-splitting in hexagonal altermagnet CrSb is established using
magnetic groups formalism that allows to find the additional
spin splitting missed in frame of exchange approximation. Another type of
spin splitting takes place in so called hidden altermagnets. This type materials do not possess
symmetry in respect of space and time inversion but are symmetric in respect of the product of these operations known as toroid
symmetry. There is demonstrated the real space
spin splitting in materials with toroid
symmetry.
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Statistical Mechanics · Cross-listed from physics.bio-ph
Bringing calorimetry (back) to life
Faezeh Khodabandehlou, Christian Maes and Édgar Roldán
Micro-calorimetry offers significant potential as a quantitative method for studying the structure and function of biological systems, for instance, by probing the excess heat released by cellular or sub-cellular structures, isothermal or not, when external parameters change. We present the conceptual framework of nonequilibrium calorimetry, and as illustrations, we compute the heat capacity of biophysical models with few degrees of freedom related to ciliar motion (rowing model) and molecular motor motion (flashing ratchets). Our quantitative predictions reveal intriguing dependencies of the (nonequilibrium) heat capacity as a function of relevant biophysical parameters, which can even take negative values as a result of biological activity.
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Materials Science
Complex Magnetic Behavior in RuO$_2$ Thin Films Driven by Strain and Substrate Effects
Mojtaba Alaei, Nafise Rezaei, Ilia Mikhailov et al. (+2 more)
Ruthenium dioxide (RuO$_2$) has been proposed as a prototypical metallic $d$-wave altermagnet, a Néel-ordered compensated
antiferromagnetic state exhibiting nonrelativistic momentum-dependent
spin splitting; yet, its
magnetic ground state remains controversial both theoretically and experimentally. Using comprehensive first-principles calculations, we investigate RuO$_2$ thin films with (110), (100), and (001) orientations, both (un)strained freestanding and supported on a TiO$_2$ substrate. We show that emergent
magnetic moments in RuO$_2$ thin films are highly fragile, strongly influenced by strain, surface orientation, and atomic relaxation, while also being highly sensitive to the choice of the Brillouin-zone integration scheme. We find that none of the thin film structures considered can stabilize a compensated
antiferromagnetic order; therefore, an altermagnetic ground state cannot be realized. Instead, substrate-supported RuO$_2$ films on TiO$_2$ exhibit pronounced layer- and site-dependent
magnetic moment variations and incomplete compensation between the two antiferromagnetically coupled Ru moments, yielding a ferrimagnetic-like behavior. On the other hand, freestanding RuO$_2$ films display complex
magnetic structures depending on their orientation and applied strain, with distinct behavior at the surfaces and in the inner layers. Our results reconcile conflicting theoretical and experimental reports and underscore the sensitivity of RuO$_2$ magnetism to structural and methodological details.
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All authors Mojtaba Alaei, Nafise Rezaei, Ilia Mikhailov, Artem R. Oganov, Alireza Qaiumzadeh
Statistical Mechanics
Inhomogeneous quenches and GHD in the $\nu = 1$ QSSEP model
Angelo Russotto, Filiberto Ares, Pasquale Calabrese et al. (+1 more)
We investigate the dynamics of the $\nu=1$
Quantum Symmetric Simple Exclusion Process starting from spatially inhomogeneous initial states. This one-dimensional system of free
fermions has time-dependent
stochastic hopping amplitudes that are uniform in space. We focus on two paradigmatic setups: domain-wall melting and the expansion of a trapped gas. Both are investigated by extending the framework of
quantum generalized hydrodynamics to account for the underlying
stochastic dynamics. We derive the
evolution of the local quasiparticle occupation function, which characterizes the system at large space-time scales, and analyze the resulting
entanglement spreading. By incorporating
quantum fluctuations of the occupation function and employing conformal field theory techniques, we obtain the exact contribution to the
entanglement entropy for each individual noise realization. Averaging over these realizations then yields the full
entanglement statistics in the hydrodynamic regime. Our theoretical predictions are confirmed by exact numerical calculations. The results presented here constitute the first application of
quantum generalized hydrodynamics to
stochastic quantum systems, demonstrating that this framework can be successfully extended beyond purely
unitary dynamics to include
stochastic effects.
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All authors Angelo Russotto, Filiberto Ares, Pasquale Calabrese, Vincenzo Alba
Superconductivity
Topological superconductivity with emergent vortex lattice in twisted semiconductors
Daniele Guerci, Ahmed Abouelkomsan and Liang Fu
The coexistence of superconductivity and fractional
quantum anomalous
Hall (FQAH) effect has recently been observed in twisted MoTe$_2$ and theoretically demonstrated in a model of repulsively interacting electrons under an emergent
magnetic field arising from the layer pseudospin texture in moiré superlattice. Here, we show that this superconducting state is a
chiral $f$-wave
superconductor hosting an array of $double$
vortices, which are induced by the emergent
magnetic field with $h/e$ flux quanta per moiré unit
cell. This superconducting
vortex lattice state is topological and features Chern number $-1/2$, giving rise to a half-integer thermal
Hall conductance. Our theory provides a common mechanism and unified understanding of FQAH and topological superconductivity, with a rich phase diagram controlled by the spatial modulation of the emergent
magnetic field.
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Statistical Mechanics · Cross-listed from hep-th
Exact Solutions to Matrix Models and String Theories: The Local Construction
Jasper Kager, João Rodrigues, Ricardo Schiappa et al. (+2 more)
Exact nonperturbative solutions to hermitian one-
matrix models, their topological string duals, as well as their double-scaling limits to multicritical and minimal string theories, may be obtained via the use of resurgent transseries. These solutions are generically resonant, entailing both
eigenvalues and anti-
eigenvalues, or, equivalently, both D-branes and negative-tension D-branes – but are otherwise intricate to write down, having been previously addressed on a case-by-case approach. This work shows how there is a general and rather compact way to write down all these exact and fully nonperturbative transseries solutions in closed-form, immediately starting from the spectral geometry of the
matrix model or string theory at hand, in the form of a discrete
Fourier or Zak transform for their partition functions. This structure is inherently associated to the existence of anti-
eigenvalues or negative-tension D-branes. The validity of these solutions is testable across all values of the parameters – from weak to strong 't Hooft coupling, from small to large N; equivalently, from semi-classical to deeply
quantum regimes – and many such nonperturbative tests are performed against diverse examples ranging from
matrix models to non-critical strings, fully validating our analytical and exact expressions. In particular, anti-
eigenvalues or negative-tension D-branes are absolutely required to find sharp numerical matches. In order to study these solutions globally across their phase diagrams, however, complete non-linear Stokes data is still needed – which will be addressed in a complementary follow-up paper.
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All authors Jasper Kager, João Rodrigues, Ricardo Schiappa, Maximilian Schwick, Noam Tamarin
Statistical Mechanics
Hidden Twisted Sectors and Exponential Degeneracy in Root-of-Unity XXZ Heisenberg Chains
Yongao Hu, Felix Gerken and Thore Posske
Recently, product states have been identified as simple-structured eigenstates of XXZ Heisenberg
spin models in arbitrary dimensions, occurring at anisotropy values corresponding to certain roots of unity. Yet, the product states typically only span parts of a larger degenerate eigenspace. Here, we classify this eigenspace in the one-dimensional periodic XXZ chain at all roots of unity $q$, where $q^2$ is an $\ell$-th primitive root of unity. For commensurate chain lengths $N$ with $q^N=1$, we prove that the minimal degeneracy is $2^{N/\ell}\ell$ using the representation theory of the affine Temperley-Lieb (aTL)
algebra. For the incommensurate case, we derive analogous exponential lower bounds of $2^{2\lfloor\frac{N}{2\ell}\rfloor+1}$ if $N$ is even and $2^{2\lfloor \frac{N}{2\ell}+\frac{1}{2}\rfloor}$ if $N$ is odd and $q^\ell=1$. Our proof employs the morphisms between aTL modules discovered by Pinet and Saint-Aubin and emphasizes the importance of exact sequences and hidden twisted boundary condition sectors that mediate the degeneracy. In the case of commensurate chain lengths, we connect to the Fabricius-McCoy string construction of all Bethe roots of the degenerate subspace, which previously uncovered parts of our results. We corroborate our results numerically and demonstrate that the lower bound is saturated for chain lengths $N\leq20$. Our work demonstrates for a concrete system how the interplay of the Bethe ansatz, aTL representation theory, and twisted boundary conditions explains degeneracy connected to long-lived product states, stimulating research towards generalization to higher dimensions. Exponential degeneracy could boost applications of
spin chains as
quantum sensors.
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Disordered Systems and Neural Networks · Cross-listed from cs.LG
Symmetry in language statistics shapes the geometry of model representations
Dhruva Karkada, Daniel J. Korchinski, Andres Nava et al. (+2 more)
The internal representations learned by
language models consistently exhibit striking
geometric structure: calendar months organize into a circle, historical years form a smooth one-dimensional
manifold, and cities' latitudes and longitudes can be decoded using a linear probe. To explain this neural code, we first show that
language statistics exhibit translation
symmetry (for example, the frequency with which any two months co-occur in text depends only on the time interval between them). We prove that this
symmetry governs these
geometric structures in high-dimensional word
embedding models, and we analytically derive the
manifold geometry of word representations. These predictions empirically match large text
embedding models and large
language models. Moreover, the representational geometry persists at moderate
embedding dimension even when the relevant statistics are perturbed (e.g., by removing all sentences in which two months co-occur). We prove that this robustness emerges naturally when the co-occurrence statistics are controlled by an underlying latent variable. Our results indicate that these representational
manifolds originate in the statistical
symmetries of natural
language.
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All authors Dhruva Karkada, Daniel J. Korchinski, Andres Nava, Matthieu Wyart, Yasaman Bahri
Strongly Correlated Electrons
3d Conformal Field Theories via Fuzzy Sphere Algebra
Luisa Eck and Zhenghan Wang
Fuzzy sphere models conjecturally realize 3d CFTs in small systems of spinful
fermions, but why they work so well is still not fully understood. Their
Hamiltonians are built from electron density operators projected to the lowest Landau level. We analyze the Lie
algebra generated by these density modes and its large-$s$ limits. Depending on how the limit is taken, the
algebra approaches either the Girvin-MacDonald-Platzman
algebra in a local planar limit or a semiclassical
algebra for low-angular-momentum modes in a global commutative limit. With an additional restriction to a low-excitation sector above the paramagnetic state, the density modes become approximate harmonic oscillators. We also test whether the conformal
algebra $so(3,2)$ can be realized directly by density modes. Such a representation exists only in the minimal two-electron system; its natural coproduct extension does not match the physical thermodynamic limit of a single growing fuzzy sphere.
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Strongly Correlated Electrons
Majorana Signatures in Planar Tunneling through a Kitaev Spin Liquid
Weiyao Li, Vitor Dantas, Wen-Han Kao et al. (+1 more)
We propose a planar tunneling setup to probe vacancy-bound Majorana modes in the
chiral Kitaev
spin liquid. In this geometry, the inelastic tunneling conductance can be expressed directly in terms of real-space
spin correlations, establishing a link between measurable spectra and the underlying fractionalized excitations. We show that
spin vacancies host localized Majorana states that generate sharp near-zero-bias features, well separated from the continuum of bulk
spin excitations. Compared to local STM measurements, the planar configuration naturally enhances the signal by coherently summing over multiple vacancies, reducing spatial resolution requirements. Our results demonstrate a realistic and scalable route to detect Majorana excitations in Kitaev materials.
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All authors Weiyao Li, Vitor Dantas, Wen-Han Kao, Natalia B. Perkins
Strongly Correlated Electrons
Controlled Theory of Skyrmion Chern Bands in Moiré Quantum Materials: Quantum Geometry and Collective Dynamics
Yi-Hsien Du
Recent experiments in moiré
quantum materials exhibit quantized
Hall states without an external
magnetic field, motivating continuum mechanisms based on smooth moiré-periodic pseudospin textures. We present a controlled theory of skyrmion Chern bands generated by such textures. An exact local $SU(2)$ transformation reveals an emergent non-Abelian gauge field; for large branch splitting we perform an operator-level Schrieffer-Wolff expansion, yielding a single-branch
Hamiltonian together with systematically dressed physical operators that define the projected interacting theory beyond strict adiabaticity. The leading dynamics is governed by a $U(1)$ Berry connection whose flux is set by the skyrmion density, while controlled non-adiabatic corrections are fixed by the texture's real-space
quantum geometric tensor. In a Landau-level representation built from the averaged emergent field, moiré-periodic modulations induce Umklapp-resolved deformations of Girvin-MacDonald-Platzman kinematics and microscopic sources of excess optical
quantum weight above the topological lower bound. Assuming a gapped
Hall phase, we further derive a skyrmion-
crystal effective field theory with a universal Berry-phase term and a noncommutative magnetophonon. Our results provide experimentally accessible signatures for twisted transition-metal dichalcogenide homobilayers and rhombohedral
graphene aligned with hexagonal boron nitride.
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Superconductivity
Signatures of Dynes superconductivity in the THz response of ALD-grown NbN thin films
Frederik Bolle, Yayi Lin, Ozan Saritas et al. (+6 more)
The frequency-dependent complex optical conductivity reflects key properties of
superconductors, such as the energy gap in the density of states (DOS) and the superfluid density. For disordered
superconductors, the optical conductivity often can be described within Bardeen-Cooper-Schrieffer (BCS) theory, while in corresponding tunneling experiments, deviations in the observed DOS typically require modelling by the phenomenological Dynes formula. The implications of such Dynes DOS for optics were rarely discussed so far. Here we probe the terahertz conductivity of superconducting NbN thin films with thicknesses ranging from 4.5 to 20nm, which were grown by atomic layer deposition (ALD). Our frequency range from 0.3 to 2.1 THz covers energies below and above the spectral gap. For 20nm thick NbN, we find in the optical conductivity distinct deviations from the BCS model, including a step-like characteristic in the absorption at half the zero-temperature spectral gap. These observations can be fully captured by Dynes electrodynamics with a small and temperature-independent pair-breaking rate. For the other films, we also observe signs of Dynes electrodynamics, and we discuss the
evolution of the energy gap, the superfluid density, and the pair-breaking rate as function of film thickness.
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All authors Frederik Bolle, Yayi Lin, Ozan Saritas, Martin Dressel, Ciprian Padurariu, Sahitya Varma Vegesna, Nitesh Yerra, Heidemarie Krüger, Marc Scheffler
Materials Science
Stacking-Engineered Thermal Transport and Phonon Filtering in Rhenium Disulfide
Yongjian Zhou, Haoran Cui, Zefang Ye et al. (+3 more)
Cross-plane heat transport is a critical bottleneck for van der Waals (vdW) electronics, yet its microscopic governing principles remain elusive. We demonstrate that stacking order is an effective control knob for cross-plane
phonon transport in multilayer Rhenium Disulfide (ReS2). Thickness-dependent thermal conductivity measurements reveal remarkably long cross-plane
phonon mean free paths (MFPs) (>= 200-300 nm) and provide a direct experimental observation of the transition from quasi-ballistic transport to a thickness-independent ballistic limit. AA stacking exhibits nearly double the cross-plane thermal conductivity of AB stacking, driven by longer acoustic
phonon lifetimes from a more "coherent" interlayer registry. Integrated deep neural-network molecular dynamics reveals that
phonon filtering in ReS2 is fundamentally frequency-selective: weak vdW coupling acts as a low-pass filter, whereas stronger coupling broadens the transmission passband. These results establish ReS2 as a model system where stacking order and interlayer coupling can be engineered to tune heat conduction across diffusive, quasi-ballistic, and ballistic regimes, offering a new framework for thermal management in 2D electronics.
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All authors Yongjian Zhou, Haoran Cui, Zefang Ye, Jung-Fu Lin, Yan Wang, Yaguo Wang
Strongly Correlated Electrons
Nematostriction in frustrated two-dimensional Heisenberg models
Olav F. Syljuåsen and Jens Paaske
We investigate the nematic phase transition in the Heisenberg $J_1$-$J_2$-model on square and triangular
lattices, accounting for finite
lattice compressibility and bond-length-dependent
magnetic exchange. Using Nematic Bond Theory, a diagrammatic self-consistent method, we study the nematostriction that happens when the onset of nematic order in the
spin-system drives a concomitant structural phase transition. We analyze the mechanisms by which the magnetoelastic couplings renormalize the critical temperature and modify the
phonon spectrum. The magnetoelastic feedback can also alter fundamentally the nature of the phase transition. Specifically, on the square
lattice, the transition shifts from continuous to weakly first-order (discontinuous) beyond a critical magnetoelastic coupling threshold. Conversely, on the triangular
lattice, the transition remains discontinuous regardless of coupling strength.
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Materials Science
Practical and accurate density functionals for transition-metal heterogeneous catalysis
Benjamin X. Shi and Timothy C. Berkelbach
Density functional theory (DFT) underpins modern atomistic simulations of transition-metal surfaces. It can predict key properties linked to catalytic performance, such as adsorption energies and barrier heights, enabling new paradigms in rational catalyst design. These applications require reliable density functionals, however achieving transition-metal chemical accuracy (13 kJ/mol) on these properties remains challenging. We introduce a framework for designing new functionals tailored to catalytic processes on transition-metal surfaces, building on recent non-self-consistent approaches. Within this framework, we develop a hybrid and a double-hybrid functional that achieve unprecedented accuracy, with the latter reaching transition-metal chemical accuracy on average across 39 experimental adsorption reactions. In addition, both functionals demonstrate balanced performance for 17 barrier heights and correct qualitative failures of standard functionals, including CO adsorption on Pt(111) and
graphene on Ni(111). They are computationally efficient, readily integrated into existing DFT codes, and supported by open-source workflows to facilitate adoption. More broadly, this framework provides a systematic route towards improved functionals for heterogeneous catalysis and complex materials.
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Materials Science
Large Transverse Thermoelectric Effect in Weyl Semimetal TaIrTe$_4$ Engineered for Photodetection
Morgan G. Blevins, Xianglin Ji, Vivian J. Santamaria-Garcia et al. (+4 more)
Anomalous local photocurrent generation via second-order nonlinear and thermoelectric responses is a signature of many topological semimetals. The emergence of these photocurrents is inherently linked to
symmetry breaking and anisotropy of their
crystal lattices. Studies of type-II Weyl semimetals of group C$_{2v}$ (WTe$_2$, MoTe$_2$, TaIrTe$_4$) have reported anomalous, nonlocal photocurrents localized to
crystals edges or far from electrodes, which are highly dependent on the geometry of the material sample. While originally attributed to a nonlinear charge current response, it was recently shown that these currents could instead be attributed to the anisotropic Seebeck coefficients of the materials. Here, we confirm that anomalous photocurrents observed in TaIrTe$_4$ under either visible or far-infrared far-field illumination originate from the large transverse thermoelectric effect. We engineer the mutual orientation of
crystal edges and electrodes as well as the thermal environment of TaIrTe$_4$ to control and amplify its spatial photocurrent response. We show that substrate engineering can locally enhance photocurrent. This framework of thermal device engineering can enable broadband photo detection schemes by leveraging spectral and spatial dependence of photocurrents for applications like wavefront sensing, beam positioning, and edge detection.
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All authors Morgan G. Blevins, Xianglin Ji, Vivian J. Santamaria-Garcia, Abhishek Mukherjee, Thanh Nguyen, Mingda Li, Svetlana V. Boriskina
Mesoscale and Nanoscale Physics
Emergent Gauge Fields and Linear Dichroism in Spin-Textured Altermagnets
Andrea Maiani
Spin textures are ubiquitous in antiferromagnets, yet their consequences for altermagnets remain largely unexplored. We show that smooth spatial variations of the Néel order act on itinerant electrons as emergent gauge fields that couple to the altermagnetic sublattice-odd channel. For a coplanar
spin helix, this channel generates two responses that vanish when it is removed: a momentum-resolved sublattice-odd spectral structure and a net interband linear dichroism whose principal axes are controlled by the helix wave vector, so the optical response can be steered by the
magnetic texture. The dichroism exhibits two distinct regimes separated by a crossover: at low frequencies the absorption axis is locked to the
crystal axes, while at high frequencies it tracks the helix. Anisotropic dc transport provides a complementary quantitative signature, and all signatures are robust to weak intrinsic
spin-orbit coupling. Our results identify polarization-resolved optics and sublattice-sensitive spectroscopy as direct probes of textured altermagnetic states and suggest a route to direction-selective electronic and optical functionality in altermagnets.
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Soft Condensed Matter
Stick-slip dynamics in an interleaved system with self-amplified friction
A. Plati, F. Restagno and C. Poulard
Understanding how stick-slip dynamics manifests in diverse physical conditions is a crucial topic in tribology. Although it has been extensively studied in simple frictional configurations, the characterization of stick-slip behavior in complex assemblies is challenging. This work presents the first systematic investigation of stick-slip dynamics in a system with multiple contact surfaces undergoing friction amplification through conversion of traction forces into normal compression. Using interleaved paper blocks as a model system, we combine force measurements and image processing to characterize stick-slip events occurring when the two blocks are pulled apart at different detachment velocities. We find that both the peak force and the amplitude of the stick-slip events decrease along with the system's detachment. By combining a previously designed model for friction amplification and the stick-slip dynamics predicted by a simple frictional spring-block system, we link the observed behavior to the evolving normal compression within the assembly. Through force measurements and imaging, we extract the effective stiffness of the system from stick-slip events at low velocities and relate it to the system's normal compression. We then predict the observed decrease of the global stiffness as a function of the detachment by considering the spatial distribution of normal forces within the assembly, which determines an effective number of sheets contributing to the system's mechanical response. Our findings reveal a non-trivial interplay between internal stress distribution and mechanical response mediated by frictional forces, with implications for granular materials, textiles, fibrous systems, and mechanical metamaterials.
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Materials Science
Anisotropy-driven interfacial magnetism in Ru-deficient SrRuO$_3$ thin films
Vítor A. de Oliveira Lima, Michael I. Faley, Asmaa Qdemat et al. (+9 more)
While stoichiometric SrRuO$_3$ (SRO) is a metallic itinerant ferromagnet with relatively homogeneous magnetization, Ru deficiency provides a powerful route to alter its electronic transport and depth-dependent
magnetic properties. Ru-deficient SRO thin films grown by
radio-frequency high oxygen pressure sputtering were investigated using a combination of X-ray reflectivity, polarized
neutron reflectometry, off-specular
neutron scattering, scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy, electrical transport, and magnetometry. Structural and compositional analyses reveal that Ru deficiency is intrinsic to the films, with an enhanced deficiency at the interfaces. As a result, coherent electronic transport is suppressed and the saturation magnetization is reduced, while the Curie temperature remains largely unaffected, placing Ru-deficient SRO in a regime consistent with
ferromagnetic insulator-like behavior. Depth- and lateral-resolved
magnetic measurements further show that the interfacial regions remain
ferromagnetic but exhibit enhanced perpendicular
magnetic anisotropy, which constrains the local magnetization to remain predominantly out-of-plane and strongly reduces its in-plane projection. Our results establish Ru deficiency as a key control parameter governing transport, magnetization, and anisotropy in SRO thin films and highlight defect and interface engineering as powerful routes to tailor interfacial magnetism in correlated
oxide heterostructures.
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All authors Vítor A. de Oliveira Lima, Michael I. Faley, Asmaa Qdemat, Valeria Lauter, Haile Ambaye, Omar Concepción, Ankita Singh, Emmanuel Kentzinger, Milan Radovic, Shibrabata Nandi, Thomas Brückel, Connie Bednarski-Meinke
Disordered Systems and Neural Networks
From Classical to Quantum: Extending Prometheus for Unsupervised Discovery of Phase Transitions in Three Dimensions and Quantum Systems
Brandon Yee, Wilson Collins, Pairie Koh et al. (+1 more)
We extend the Prometheus framework for unsupervised phase transition discovery from two-dimensional classical systems to three-dimensional classical systems and
quantum many-body systems. Building upon preliminary observations from a 2D Ising model student abstract [Yee et al., 2026], we address two fundamental questions: (1) Does the framework scale to higher dimensions where exact solutions are unavailable? (2) Can it generalize to
quantum phase transitions driven by
quantum fluctuations rather than thermal fluctuations? For the 3D Ising model on
lattices up to $L{=}32$, we achieve critical temperature detection within 0.01% of literature values ($\Tc/J = 4.511 \pm 0.005$) and extract critical exponents with ${\geq}70\%$ accuracy, with statistical analysis correctly identifying the 3D Ising universality class ($p = 0.72$). For
quantum systems, we develop
quantum-aware VAE (Q-VAE) architectures operating on complex-valued wavefunctions with fidelity-based loss functions, achieving 2% accuracy in
quantum critical point detection for the transverse field Ising model. For the disordered TFIM, we perform a consistency check of activated dynamical scaling $\ln \xi \sim |h - \hc|^{-\psi}$, extracting tunneling exponent $\psi = 0.48 \pm 0.08$ consistent with theoretical predictions ($\psi = 0.5$, $\Delta\chi^2 = 12.3$, $p < 0.001$). This demonstrates that unsupervised learning can identify qualitatively different types of critical behavior, serving as a consistency check on known IRFP physics.
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All authors Brandon Yee, Wilson Collins, Pairie Koh, Maximilian Rutkowski
Materials Science
Ferrocene-functionalized covalent organic framework exceeding the ultimate hydrogen storage targets: a first-principles multiscale computational study
Marcus Djokic and Jose L. Mendoza-Cortes
The development of efficient hydrogen storage materials is crucial for advancing the hydrogen economy and meeting the U.S. Department of Energy's targets of 6.5 wt% and 50 g H<sub>2</sub>/L for automotive applications. We present a computational study of ferrocene-functionalized covalent organic frameworks (COFs) for hydrogen storage. Following the <b>M</b>ulti-binding <b>S</b>ites <b>U</b>nited in <b>C</b>ovalent-<b>O</b>rganic <b>F</b>ramework (MSUCOF) approach, we introduce MSUCOF-4-FeCp, designed by incorporating ferrocene (FeCp<sub>2</sub>) moieties into IRCOF-102. Notably, it achieves exceptional performance with gravimetric and volumetric uptakes of 18.0 wt% and 72.6 g H<sub>2</sub>/L at 298 K and 700 bar. The material exhibits optimal binding energies (15-20 kJ/mol) ensuring both high storage capacity and deliverable hydrogen under practical conditions. This work establishes ferrocene functionalization as a cost-effective alternative to precious metal incorporation in COFs.
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Materials Science
Sub-1-Angstrom-Resolution Imaging Reveals Phase Contrast Transition in Ice Ih Caused by Basal Stacking Faults
Jingshan S. Du, Suvo Banik, Lehan Yao et al. (+3 more)
Phase-contrast transmission electron microscopy (TEM) of hexagonal ice (Ih) along [0001] sometimes shows a honeycomb-like pattern, often interpreted as individual oxygen columns in single
crystals. Here, we show that this pattern commonly arises from intrinsic basal stacking faults instead. A translational boundary separating domains of comparable thickness, with an in-plane offset of $(\frac{2}{3} a_{1} + \frac{1}{3} a_{2})$, produces this honeycomb-like contrast. Stacking domains translated in nonequivalent directions yields patterns resembling cubic ice (Ic) along [111] but with a 3-fold
symmetry. We imaged this structure at a record-breaking line resolution of 89 picometers, finer than the O-H covalent bond length. These findings highlight the defect tolerance of ice's molecular packing and clarify the structural relationships among hexagonal, stacking-disordered, and cubic ice phases. This resolution milestone opens new avenues for characterizing subtle structural perturbations of water in the solid state.
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All authors Jingshan S. Du, Suvo Banik, Lehan Yao, Shuai Zhang, Subramanian K. R. S. Sankaranarayanan, James J. De Yoreo
Materials Science
Low-Temperature Sputtering and Polarity Determination of Vertically Aligned ZnO Nanocolumns
A. Hamzi, L. Ouardas, M. Saleh et al. (+10 more)
We report the low temperature growth of vertically aligned ZnO nanocolumns on Si substrates by using reactive
radio frequency magnetron sputtering.High sputtering pressure combined with low substrate temperatures induce a pronounced self shadowing effect,leading to the formation of isolated nanocolumns. In contrast, lower sputtering pressure promotes void filling in deposited films, favouring the growth of dense, low roughness columnar films. Modification of native SiOx on Si surfaces via substrate preheating prior to deposition, alters the initial nucleation stage, thereby determining dominant polarity and morphology of ZnO nanostructures. O polar columnar films and nanocolumns exhibit higher effective piezoelectric coefficient, corresponding to their higher differential resistance and reduced dielectric loss, suggesting suppressed carrier induced screening of piezoelectric charges. This low thermal budget, scalable sputtering approach provides an alternative route for integrating ZnO nanostructures onto thermal constrained substrates, including those used in flexible and wearable electronics.
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All authors A. Hamzi, L. Ouardas, M. Saleh, P. Leuasoongnoen, T. Sonklin, P. David, S. le Denmat, O. Leynaud, E. Mossang, B. Fernandez, S. Pojprapai, D. Mornex, R. Songmuang
Strongly Correlated Electrons
Competing states in the $S=1/2$ triangular-lattice $J_1$-$J_2$ Heisenberg model: a dynamical density-matrix renormalization group study
Shengtao Jiang, Steven R. White, Steven A. Kivelson et al. (+1 more)
Previous studies of the $S=1/2$ triangular-
lattice $J_1$–$J_2$ Heisenberg antiferromagnet have inferred the existence of a non-
magnetic ground-state phase for an intermediate range of $J_2$, but disagree concerning whether it is a gapped $\mathbb{Z}_2$
quantum spin liquid (QSL), a gapless (Dirac) QSL, or a weakly
symmetry-broken phase. Using an improved dynamical density-
matrix renormalization group method, we investigate the relevant intermediate $J_2$ regime for cylinders with circumferences from 6 to 9. Depending on the initial state and boundary conditions, we find two distinct variational states. The higher energy state is consistent with a Dirac QSL. In the lower-energy state, both the static and dynamical properties are qualitatively similar to the magnetically ordered state at $J_2=0$, suggestive of either a weakly magnetically ordered non-QSL or a gapped QSL proximate to a continuous transition to such an ordered state.
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All authors Shengtao Jiang, Steven R. White, Steven A. Kivelson, Hong-Chen Jiang
Materials Science
Identifying open-orbit topological surface states in dual topological semimetal TaSb$_2$
Susmita Changdar, Heike Schlörb, Oleksandr Suvorov et al. (+8 more)
TaSb$_2$, a member of the transition metal dipnictide family of materials, hosts the very rare dual topological phase - weak topological insulating state and topological crystalline insulating state along different crystallographic orientations. So far, studies on the electronic structure of transition metal dipnictides have focused on their overall electronic structure and the bulk open-orbit
Fermi surfaces. Using angle-resolved photoemission spectroscopy, density functional theory calculations, and transport measurements, we distinguish the intertwined bulk and surface states on the weakly topological $(20\bar{1})$ plane of TaSb$_2$. We identify multiple electron- and hole-like bulk bands, yielding a near-perfect carrier compensation. Crucially, we observe open-orbit FSs parallel to $\bar{L}$-$\bar{Y}$ direction that are entirely of surface origin. Circular-dichroism ARPES reveals $k \rightarrow -k$ spectral reversal, indicating
spin-momentum locking and the topological nature of these surface states. Consistent with this, magnetotransport measurements display weak antilocalization, establishing TaSb$_2$ as a platform for
spin-polarized topological transport on a weakly topological surface.
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All authors Susmita Changdar, Heike Schlörb, Oleksandr Suvorov, Dimitry Efremov, Alexander Yaresko, Rui Lou, Alexander Fedorov, Bernd Büchner, Andy Thomas, Sergey Borisenko, Setti Thirupathaiah
Disordered Systems and Neural Networks
Drift-Diffusion Matching: Embedding dynamics in latent manifolds of asymmetric neural networks
Ramón Nartallo-Kaluarachchi, Renaud Lambiotte and Alain Goriely
Recurrent neural networks (RNNs) provide a theoretical framework for understanding computation in biological neural
circuits, yet classical results, such as Hopfield's model of associative
memory, rely on symmetric connectivity that restricts network dynamics to gradient-like flows. In contrast, biological networks support rich time-dependent behaviour facilitated by their asymmetry. Here we introduce a general framework, which we term drift-
diffusion matching, for training continuous-time RNNs to represent arbitrary, nonlinear
stochastic differential equations (SDEs), with given drift and
diffusion coefficients, within a low-dimensional latent subspace. Allowing asymmetric connectivity, we show that RNNs can faithfully embed the drift and
diffusion of a given SDE, including nonlinear and nonequilibrium dynamics such as chaotic attractors. As an application, we construct RNN realisations of
stochastic systems that transiently explore various attractors through both input-driven switching and autonomous transitions driven by nonequilibrium currents, which we interpret as models of associative and sequential (episodic)
memory. To elucidate how these dynamics are encoded in the network, we introduce decompositions of the RNN based on its asymmetric connectivity and its time-irreversibility. Our results extend attractor neural network theory beyond
equilibrium, showing that asymmetric neural populations can implement a broad class of dynamical computations within low-dimensional
manifolds, unifying ideas from associative
memory, nonequilibrium statistical mechanics, and neural computation.
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Strongly Correlated Electrons
Electron-phonon coupling in EuAl4 under hydrostatic pressure
A. S. Sukhanov, S. Gebel, A.N. Korshunov et al. (+7 more)
In the intermetallid rare-earth tetragonal EuAl4 system, competing itinerant exchange mechanisms lead to a complex
magnetic phase diagram, featuring a centrosymmetric skyrmion
lattice. Previous inelastic x-ray scattering (IXS) experiments revealed that the incommensurate charge-density wave (CDW) transition in EuAl4 (TCDW = 142 K) is driven by momentum-dependent electron-
phonon coupling (EPC). We present the results of IXS under high hydrostatic pressure induced by diaond anvils and show how the EPC in EuAl4 is renormalized and suppressed in the material's temperature-pressure phase diagram. Our findings highlight the crucial role of momentum-dependent EPC in the formation of the CDW in EuAl4 and provide further insights into how external pressure can be used to tune charge ordering in
quantum materials.
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All authors A. S. Sukhanov, S. Gebel, A.N. Korshunov, N. D. Andriushin, M.S. Pavlovskii, Y. Gao, K.M. Moya, K. Allen, E. Morosan, M. C. Rahn