Disordered Systems and Neural Networks
Rigorous Asymptotics for First-Order Algorithms Through the Dynamical Cavity Method
Yatin Dandi, David Gamarnik, Francisco Pernice et al. (+1 more)
Dynamical Mean Field Theory (DMFT) provides an asymptotic description of the dynamics of macroscopic observables in certain disordered systems. Originally pioneered in the context of
spin glasses by Sompolinsky and Zippelius (1982), it has since been used to derive asymptotic dynamical equations for a wide range of models in physics, high-dimensional statistics and machine learning. One of the main tools used by physicists to obtain these equations is the dynamical cavity method, which has remained largely non-rigorous. In contrast, existing mathematical formalizations have relied on alternative approaches, including Gaussian conditioning, large deviations over paths, or
Fourier analysis. In this work, we formalize the dynamical cavity method and use it to give a new proof of the DMFT equations for General First Order Methods, a broad class of dynamics encompassing
algorithms such as Gradient Descent and Approximate Message Passing.
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All authors Yatin Dandi, David Gamarnik, Francisco Pernice, Lenka Zdeborová
Strongly Correlated Electrons
Synergistic doping and stabilization of magnetically tunable LnTi$_3$(Sb,Sn)$_4$ (Ln:Ce–Gd) kagome metals
Brenden R. Ortiz, Ramakanta Chapai, German Samolyuk et al. (+9 more)
Here we present our synthesis and characterization of the LnTi$_3$(Sb,Sn)$_4$ (Ln: Ce, Pr, Nd, Sm, Gd) family of cleavable kagome metals. While these materials are isostructural to the LnTi$_3$Bi$_4$ family, they only form as (Sb,Sn) solid-solutions with no corresponding LnTi$_3$Sb$_4$ or LnTi$_3$Sn$_4$ phases. We use a combination of first-principles density functional theory (DFT) and
Crystal Orbital Hamilton Population (COHP) calculations to show that (Sb,Sn) alloying has a stabilizing effect on the structure by adjusting the
Fermi level, filling bonding states, depopulating antibonding states, and adjusting the density-of-states (DOS) towards local minima, an effect we call “synergistic doping.” The tunable
Fermi level also has a profound effect on the magnetism, which we demonstrate through a detailed characterization of the SmTi$_3$(Sb,Sn)$_4$ series. The series hosts multiple
magnetic ground states resulting from competing
magnetic interactions that are tunable by the (Sb,Sn) ratio. While the focus of this work is on SmTi$_3$(Sb,Sn)$_4$, we briefly comment on the (Sb,Sn) solubility range and the conferred
magnetic tunability in the other rare-earths compounds (Ln: Ce, Pr, Nd, Gd) as well. Our work demonstrates how the (Sb,Sn) synergistic pair can be used to stabilize the LnTi$_3$(Sb,Sn)$_4$ structure while simultaneously providing a means to tune the magnetism, ultimately providing a potential route to develop new intermetallics with chemical,
magnetic, and electronic tunability.
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All authors Brenden R. Ortiz, Ramakanta Chapai, German Samolyuk, Milo Sprague, Arun K. Kumay, Hu Miao, Karolina Gornicka, Xiaoping Wang, Qiang Zhang, Madhab Neupane, David Parker, Jiaqiang Yan
Materials Science
Atomistic modeling of the hygromechanical properties of amorphous Polyamide 6,6
Karim Gadelrab, Armin Kech and Camilo Cruz
Polyamide 6,6 (PA66) is a key engineering
polymer, whose unique mechanical properties arise from strong interchain hydrogen bonding. However, its hygroscopic nature makes it highly sensitive to water uptake, which markedly alters its thermomechanical behavior. Contrary to traditional experimental approaches, this study uses atomistic molecular dynamics (MD) simulations to investigate the role of water in modifying the glass transition temperature (Tg) and the viscoelastic response of amorphous PA66. Simulations capture a nonmonotonic dependence of Tg on water content. At low water concentrations, isolated water molecules bind to amide groups and restrict chain mobility, while beyond ~2.5 wt %, water clustering disrupts the hydrogen bond network and causes a pronounced Tg depression. Analysis of amide group fluctuations reveals a master correlation between local segmental dynamics and bulk density, verifying the known temperature humidity equivalence in terms of density variation. The computed Young's modulus exhibits systematic softening with increasing temperature and water content, consistent with experimental trends, albeit a more pronounced impact of water at low temperatures. Time temperature superposition behavior is observed for both dry and hydrated systems. This work provides molecular scale information on the hygromechanical coupling in PA66 and demonstrates the ability of MD simulations to predict water induced transitions that govern the macroscopic behavior of polyamides.
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Mesoscale and Nanoscale Physics
Nanoscale mapping of internal magnetization dynamics reveals how disorder shapes heat generation in magnetic particle hyperthermia
Elizabeth M. Jefremovas, Pauline Rooms, Álvaro Gallo-Córdova et al. (+4 more)
Magnetic particle hyperthermia relies on the efficient conversion of
magnetic field energy into heat in biomedical applications, yet the microscopic mechanisms governing heat generation within individual particles remain poorly understood. In this study, AC magnetometry experiments are combined with dynamic micromagnetic simulations to connect microstructural features, magnetization dynamics, and macroscopic heat dissipation. Beyond macroscopic heating metrics, the heat generation is resolved at the intra-particle level, uncovering a heterogeneous landscape of localized ”hot spots” with nanometer spatial and nanosecond temporal resolution. The results demonstrate that grain size acts as a key experimentally tunable parameter, balancing anisotropy disorder and pinning strength, thereby controlling both the magnitude and spatio-temporal distribution of heat release within the particle. In particular, nanoflower architectures composed by larger grains deliver larger heat generation, while the smaller grains offer a deeper intra-particle pinning landscape, which effectively redistributes the heat generation over extended time windows. Together, our results provide a mechanistic framework linking nanoparticle microstructure to
magnetic heating and establish design principles for optimizing nanoflowers as
magnetic hyperthermia transducers.
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All authors Elizabeth M. Jefremovas, Pauline Rooms, Álvaro Gallo-Córdova, María P. Morales, Frank Wiekhorst, Andreas Michels, Jonathan Leliaert
Strongly Correlated Electrons
Microwave spin resonance in epitaxial thin films of spin liquid candidate TbInO3
Sandesh S. Kalantre, Johanna Nordlander, Margaret A. Anderson et al. (+2 more)
Minimizing the energy of a many body system tends to favor order, but classical frustration and
quantum fluctuations destabilize that order. The tension between these effects can produce exotic
quantum states of matter.
Quantum spin liquid (QSL) states emerge in models of localized
magnetic moments where the
crystal lattice connectivity frustrates ordering, and the exchange interaction of neighboring
spins strengthens
quantum fluctuations. Experimentally identifying a QSL in a real material is challenging from the lack of an order parameter. Piecing together evidence from varied techniques is necessary for diagnosing the nature of the ground state – QSL or otherwise – of a frustrated
spin system. In this work, we use coplanar superconducting resonators to probe
magnetic excitations in epitaxially grown thin films of a
spin liquid candidate TbInO3. Adapting microwave techniques from the field of
circuit quantum electrodynamics, we measure responses of these thin films whose volume is too low for applying conventional bulk techniques. In-plane susceptibility extracted from the
spin resonance signal indicates extreme frustration of
magnetic order down to 20 mK, over two orders of magnitude lower than the Curie-Weiss energy scale. Through a
crystal field analysis, we identify the doublet eigenstates comprising the ground state. As a consequence of improper ferroelectricity, Tb moments split into two
flavors with distinct g-factors reflecting the local
crystal field environment of each site.
Spin-orbit coupling,
crystal fields,
magnetic frustration and improper ferroelectricity distinctively combine to shape the
magnetic ground state of TbInO3. This work establishes a measurement technique using superconducting resonators to probe thin films of frustrated magnets, and applies this technique towards building a coherent understanding of the
magnetic properties of TbInO3.
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All authors Sandesh S. Kalantre, Johanna Nordlander, Margaret A. Anderson, Julia A. Mundy, David Goldhaber-Gordon
Disordered Systems and Neural Networks
Learning Associations in Reconfigurable Particle Packings via Local Cyclic Driving
Wenjing Guo, Vidyesh Rao Anisetti, Kairui Zhang et al. (+7 more)
We investigate associative-
memory behavior in a reconfigurable particle packing programmed by purely local cyclic driving. The system is a two-dimensional bidisperse Lennard–Jones particle assembly with periodic boundaries evolved under athermal quasistatic relaxation. During training, a fixed set of input particles is driven cyclically while output particles are selected on-the-fly by a region-driving rule and driven according to a prescribed flow pattern; during
retrieval, only the inputs are driven. Associative-
memory performance is quantified by the cosine similarity between realized and target output displacement directions. Unlike physical learning systems with fixed architecture, learning here arises through emergent weight updates: localized rearrangements modify the contact network and reshape the effective mechanical couplings between inputs and outputs. Across task difficulty we identify three regimes. In an easy setting, the intrinsic mechanical response already produces coherent motion in the right-hand region under input-only driving, yielding high performance without training. In a hard setting, the desired mapping conflicts with the dominant collective drift, resulting in low baseline performance and only modest training gains; introducing intermittent relaxation cycles reduces train–
retrieval mismatch and improves performance. In an intermediate quadrupolar task, repositioning the input–output geometry stabilizes the desired response and converts initially
stochastic trajectories into reproducible learned motions. Together these results identify minimal physical ingredients for association-based functionality in athermally driven particulate media and motivate an association learning phase diagram for reconfigurable matter.
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All authors Wenjing Guo, Vidyesh Rao Anisetti, Kairui Zhang, Shabeeb Ameen, Ananth Kandala, Menachem Stern, Nidhi Pashine, Joseph D. Paulsen, J. M. Schwarz, Tao Zhang
Soft Condensed Matter
Density-Dependent Transition in Bacterial Self-Organization Driven by Confinement and Aerotaxis
Minjun Kim and Joonwoo Jeong
We experimentally investigate how aerotactic bacteria, confined within a thin
liquid film between two solid substrates, respond to a controlled oxygen gradient. We find that the total bacterial number density dictates which mechanism dominates the steady-state spatial distribution: wall accumulation or aerotaxis. At low densities, despite receiving oxygen only from one substrate, motile bacteria accumulate at both walls, forming a symmetric distribution. In contrast, pronounced aerotactic migration toward the oxygen-supplying wall emerges as the density increases. Analyzing the temporal
evolution of this bacterial distribution reveals that the aerotactic response is driven by a self-generated oxygen gradient induced by collective respiration. Our
diffusion-advection model of bacteria and oxygen, accounting for aerotactic migration, hydrodynamic attraction to the walls, and respiration, quantitatively reproduces our experimental observations and provides valuable insights into bacterial self-organization within complex environments.
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Materials Science
Gas sensing potential of stacked graphene/h-BN structures: a DFT-based investigation
Martin Siebel, Pavel Rubin and Raivo Jaaniso
Using periodic DFT, we examined the adsorption of NO2, NH3, and O3 on the h-BN side of a
graphene/h-BN
heterostructure designed as a model gas sensor material. The h-BN overlayer serves both as an active adsorption surface and as protection that may reduce irreversible processes such as
graphene oxidation. Two model systems were considered: an extended
graphene/h-BN
bilayer (B36N36C72) and a
graphene sheet partially covered by a smaller h-BN island (B11N11C72). Their electronic structures differ strongly near the Dirac point. In the extended
bilayer, the
Fermi level remains aligned with that of pristine
graphene, indicating negligible charge transfer. In the island-covered system, the
Fermi level shifts to lower energies, reflecting electron transfer from
graphene to h-BN. These differences lead to distinct adsorption behavior. NO2 binds much more strongly to B11N11C72, forming a chemical bond, while O3 dissociates on this surface but remains intact on the extended
bilayer. NH3 unusually acts as an electron acceptor in the island system. Overall, NO2 and O3 substantially increase
graphene conductivity, whereas NH3 induces much weaker changes. These results highlight the potential of
graphene/h-BN
heterostructures for gas sensing.
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Strongly Correlated Electrons
Variance reduction for forces and pressure in variational Monte Carlo
David Linteau, Saverio Moroni, Giuseppe Carleo et al. (+1 more)
We present simple and practical strategies to reduce the variance of Monte Carlo
estimators. Our focus is on variational Monte Carlo calculations of atomic forces and pressure in electronic systems, although we show that the underlying ideas apply more broadly to other observables, like pair-correlation and angular-distribution functions, and other methods, including molecular dynamics. For Pulay-type contributions, we show that a minor modification based on the Metropolis acceptance ratio softens the power-law divergence of the variance to a logarithmic one, and that inexpensive regularizations can further suppress outliers at the price of a controlled small bias. For Hellmann-Feynman forces, we derive compact variance-reduced
estimators for periodic systems that are straightforward to implement in standard Monte Carlo codes. The approach is illustrated for high-pressure metallic hydrogen with more than a hundred atoms described by neural
quantum states, including an application to molecular dynamics driven by the improved forces.
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All authors David Linteau, Saverio Moroni, Giuseppe Carleo, Markus Holzmann
Soft Condensed Matter
Air Drag Controls the Finite-Time Singularity of Euler's Disk
Benjamin G. Thorne, Ahmad Zareei, Kausalya Mahadevan et al. (+2 more)
The motion of a disk spinning to rest after being tipped on its side is a classic example of a finite-time singularity, yet the dominant dissipation mechanism governing this process remains debated. Using stereoscopic high-speed imaging, we study the dynamics of disks with varying mass and radius on different surfaces. We show that the late-time motion near the singularity is governed by viscous air-drag arising from shear in the boundary layer beneath the disk, as evidenced by the mass dependence of the dynamics, measurements in a partial
vacuum, and a
geometric control using a steel ring. At earlier times, dissipation is dominated by rolling friction, which on glass exhibits an unexpected sublinear scaling with disk mass, suggesting an adhesion-based rolling resistance. These results clarify the dissipation mechanisms underlying the singularity of Euler's disk and have broader implications for rolling-contact systems operating under low loads on smooth surfaces.
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All authors Benjamin G. Thorne, Ahmad Zareei, Kausalya Mahadevan, Shmuel M. Rubinstein, Ariel Amir
Superconductivity
Filling and Interlayer Superexchange Control Superconductivity in La$_3$Ni$_2$O$_7$
Zeyu Chen, Jia-Heng Ji, Yu-Bo Liu et al. (+2 more)
A central puzzle in
bilayer nickelate
superconductors is why pressure, epitaxial strain, oxygen stoichiometry, and chemical substitution produce systematic but apparently different changes in the superconducting T$_\text{c}$. Here we show that these trends can be organized by a two-parameter control principle based on the $d_{x^2-y^2}$-orbital filling $n_x$ and the effective interlayer
antiferromagnetic superexchange $J_\perp$. Starting from a physical picture in which the nearly half-filled $d_{z^2}$ orbital supplies localized
spin correlations while the nearly quarter-filled $d_{x^2-y^2}$ orbital carries superconductivity, we study an effective
bilayer $t-J_\parallel-J_\perp$ model with parameters constrained by first-principles calculations. Combined slave-
boson mean-field and density-
matrix renormalization group calculations place realistic La$_3$Ni$_2$O$_7$ in an overdoped-cuprate-like regime where T$_\text{c}$ is governed mainly by the pairing scale. In this regime, hole doping reduces $n_x$ and suppresses T$_\text{c}$, whereas tuning routes that enhance $J_\perp$ raise T$_\text{c}$. This framework accounts for the suppression by over-oxidation and Ca/Sr substitution, the half-dome oxygen-stoichiometry response in the film, the enhancement by Nd/Sm substitution in the pressurized bulk, the right-triangle-like pressure dependence in the bulk, and the enhancement by compressive strain in the film. It also separates clean carrier doping from oxygen-vacancy tuning: clean electron doping mainly increases $n_x$, whereas oxygen vacancies weaken the apical-oxygen-mediated exchange path and introduce disorder. This leads to a falsifiable materials-design prediction: clean electron doping should enhance the pairing scale if introduced without oxygen vacancies or strong pair-breaking disorder.
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All authors Zeyu Chen, Jia-Heng Ji, Yu-Bo Liu, Ming Zhang, Fan Yang
Statistical Mechanics
First-return time in fractional kinetics
M. Dahlenburg G. Pagnini
The first-return time is the time that it takes a random walker to go back to the initial position for the first time. We study the first-return time when random walkers perform fractional kinetics, specifically fractional
diffusion, that is modelled within the framework of the continuous-time random walk on homogeneous space in the uncoupled formulation with Mittag-Leffler distributed waiting-times. We consider both Markovian and non-Markovian settings, as well as any kind of symmetric jump-size distributions, namely with finite or infinite variance. We show that the first-return time density is indeed independent of the jump-size distribution when it is symmetric, and therefore it is affected only by the waiting-time distribution that embodies the
memory of the process. We perform our analysis in two cases: first jump then wait and first wait then jump, and we provide several exact results, including the relation between results in the Markovian and non-Markovian settings and the difference between the two cases.
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Materials Science · Cross-listed from cs.LG
Geometric and Topological Deep Learning for Predicting Thermo-mechanical Performance in Cold Spray Deposition Process Modeling
Akshansh Mishra
This study presents a
geometric deep learning framework for predicting cold spray particle impact responses using finite element simulation data. A parametric
dataset was generated through automated Abaqus simulations spanning a systematic range of particle velocity, particle temperature, and friction coefficient, yielding five output targets including maximum equivalent plastic strain, average contact plastic strain, maximum temperature, maximum von Mises stress, and deformation ratio. Four novel
algorithms i.e. a GraphSAGE-style inductive graph neural network, a Chebyshev spectral graph convolution network, a topological data analysis augmented multilayer perceptron, and a
geometric attention network were implemented and evaluated. Each input sample was treated as a node in a k-nearest-neighbour feature-space graph, enabling the models to exploit spatial similarity between process conditions during training. Three-dimensional feature space visualisations and two-dimensional contour projections confirmed the highly non-linear and velocity-dominated nature of the input-output relationships. Quantitative evaluation demonstrated that GraphSAGE and GAT consistently achieved R-square values exceeding 0.93 across most targets, with GAT attaining peak performance of R-square equal to 0.97 for maximum plastic strain. ChebSpectral and TDA-MLP performed considerably worse, yielding negative R-square values for several targets. These findings establish spatial graph-based neighbourhood aggregation as a robust and physically interpretable surrogate modelling strategy for cold spray process optimisation.
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Soft Condensed Matter
Directed Polymer Transfer Matrices as a Unified Generator of Distinct One-Point Fluctuation Laws
Sen Mu, Abbas Ali Saberi, Roderich Moessner et al. (+1 more)
We numerically revisit the transfer-
matrix formulation of directed
polymers in random media and show that a common finite-dimensional framework organizes the canonical one-point fluctuation laws in $(1+1)$ dimensions. For a fixed realization of the bulk disorder, full-space partition functions are obtained from the same time-ordered product $W(t)$ through endpoint contractions or a Brownian-weighted initial vector, while the half-space construction modifies only the transfer rule at the absorbing boundary. These choices yield distributions consistent with the standard KPZ subclasses: Tracy–Widom GUE for point-to-point geometry, Tracy–Widom GOE for point-to-line geometry, Tracy–Widom GSE for half-space point-to-point geometry, and Baik–Rains for the stationary line-to-point construction. In all four cases, the free-energy fluctuations grow as $t^{1/3}$, and the low-order cumulants approach the corresponding universal
benchmarks. The
matrix-product formulation also provides access to intrinsic spectral observables. For the leading
eigenvalue $\lambda_1(t)$, the fluctuations of $\ln\lambda_1(t)$ exhibit an intermediate $t^{1/3}$ regime, while the standardized distribution remains distinct from the canonical
benchmark laws over the studied time range.
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All authors Sen Mu, Abbas Ali Saberi, Roderich Moessner, Mehran Kardar
Other Condensed Matter
Terahertz cavity hybridization of collective proteins vibrations
Elsa Perez-Martin, Laurent Bonnet, Songlin Fang et al. (+8 more)
Hybrid light-matter states have transformed photonics, yet their realization with driven collective vibrations in biological systems remains an open challenge. Here we show that optically pumped R-phycoerythrin
proteins at room temperature support coherent sub-terahertz vibrational modes consistent with Frohlich condensation, and that these modes hybridize with confined terahertz cavity
photons in a microfluidic cavity platform. The resulting spectra exhibit a resolved doublet, power- and concentration-dependent redistribution of spectral weight, and linewidth narrowing indicative of cavity-modified dissipation. Quantitative analysis reveals collective square-root of N-scaling of the coupling strength, with cooperativity and splitting-to-linewidth ratios exceeding unity, consistent with the onset of strong collective coupling driven by the vibrational molecular mode. A microscopic nonequilibrium analysis further indicates that the relaxation timescale toward the Frohlich polariton state is on the order of 1-10 microseconds. These findings identify terahertz cavities as a platform for stabilizing and controlling collective molecular vibration dynamics and open opportunities for cavity-engineered vibrational spectroscopy, label-free biosensing and photonic control of energy transport in complex biomolecular systems.
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All authors Elsa Perez-Martin, Laurent Bonnet, Songlin Fang, Jelle Bannink, Elwin Vrouwe, Cedric Bray, Frederic Teppe, Sandra Ruffenach, Elodie Strupiechonski, Zhedong Zhang, Jeremie Torres
Materials Science
Role of ionic quantum-anharmonic fluctuations on the bond length alternation and giant piezoelectricity of conjugated polymers
Stefano Paolo Villani, Lorenzo Monacelli, Paolo Barone et al. (+1 more)
Functionalized conjugated
polymers are promising materials for electromechanical applications due to predicted
giant piezoelectricity, arising from anomalously large dynamical effective charges and an enhanced response in the proximity of the dimerization phase transition. In this work, we assess the impact of
quantum ionic fluctuations on piezoelectricity using the
stochastic self-consistent harmonic approximation with a Rice-Mele diatomic chain model, parametrized to reproduce hybrid-functional first-principles calculations of prototypical carbyne. The model's accuracy is validated against first-principles calculations both with and without
quantum-anharmonic effects. We find that ionic fluctuations strongly impact the structural properties, with the boundary of the dimerization phase transition shifted by $34\%$. Despite
quantum fluctuations in the bond length reaching magnitudes comparable to the average, the strong piezoelectric response persists. The topological enhancement of the effective charges remains robust and is even enhanced by about $\sim20\%$ thanks to a
quantum-induced shrinking of the electronic gap. The piezoelectric coefficient remains dominated by the internal relaxation and retains a morphotropic-like character, reaching maximum values near the renormalized boundary, with
quantum anharmonicity mainly shifting the optimal enhancement window.
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All authors Stefano Paolo Villani, Lorenzo Monacelli, Paolo Barone, Francesco Mauri
Materials Science
Self-Assembled H2NC Molecular Lattices as a Platform for Tunable Quantum Superlattices
Adrian Bahri, Zhibo Kang, Ziyan Zhu et al. (+3 more)
Compared to van der Waals moiré systems, molecular assembly has emerged as an exciting alternative platform for superlattice engineering via heterointegration. The electronic properties of the self-assembled square
lattice monolayer molecular
crystal of metal-free naphthalocyanine (H$_2$Nc), in particular the electronic band dispersion and their tunability by metal substrates, remain less explored. Using density functional theory, supported by angle-resolved photoemission and scanning tunneling microscopy, we compare the electronic structure of a free-standing H$_2$Nc monolayer with that of H$_2$Nc
lattice assembled on noble metal substrates. In the free-standing film, we identify both nearly flat, molecule-localized states and more dispersive bands, and we show that each can be compactly described by an anisotropic tight-binding
Hamiltonian that yields band-resolved hopping anisotropies. We further show theoretically the wide tunability in the inter-site hopping and Coulomb interaction based on dielectric and screening environment, and show two experimental realizations using Ag(100) and Au(111) substrates. On Ag(100), orbital hybridization between molecular frontier states and the substrate drives finite spectral weight at the
Fermi level and local interfacial polarization. This hybridization enhances the effective intermolecular hopping roughly thirty-fold, drastically reducing $U/t$. Complementary angle-resolved photoemission spectroscopy resolves substantial interfacial charge redistribution and enhanced bandwidth of the HOMO band, consistent with theoretical predictions. These results clarify how metal substrates and gates convert H$_2$Nc from isolated molecules into a tunable 2D
lattice, and highlight molecular superlattices as a promising platform in which the effective interaction parameters can be engineered over a wide range.
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All authors Adrian Bahri, Zhibo Kang, Ziyan Zhu, Eric I. Altman, Yu He, Chunjing Jia
Strongly Correlated Electrons · Cross-listed from hep-th
Flux Quantization on M-Strings
Pinak Banerjee, Hisham Sati and Urs Schreiber
The electric Gauss law in 11D SuGra is famously non-linear, whence its flux quantization must be in nonabelian
cohomology. We have previously shown that the minimal admissible choice is 4-Cohomotopy, which in the presence of magnetized M5-probes takes its relative twistorial form. Here we discuss how this situation is further refined in the presence of M-string probes on the M5-worldvolume. Based on the superspace formulation of 11D SuGra, we find the nested Bianchi identities by iterating the superembedding construction for super p-branes. The resulting probe brane hierarchy (M1 on magnetized M5 in 11D bulk) turns out to admit flux quantization in a doubly-relative form of twisted Cohomotopy, classified by the factorization of the quaternionic
Hopf fibration through the twistor fibration. The further equivariant refinement of this
cohomology theory reduces on A-type singularities to a form of relative 2-Cohomotopy which geometrically engineers Chern-
insulator phases on $\mathrm{M5}\cap \mathrm{A}_n$, with the M-string playing the role of gapped nodal lines.
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Strongly Correlated Electrons
Disentangling Tensor Network States with Deep Neural Network
Chaohui Fan, Bo Zhan, Yuntian Gu et al. (+5 more)
We introduce Neural Tensor Network States ($\nu$TNS), a variational many-body wave-function ansatz that integrates deep neural networks with tensor-network architectures. In the $\nu$TNS framework, a neural network serves as a disentangler of the wave-function, transforming the physical degrees of freedom into renormalized variables with much less
entanglement. The renormalized state is then efficiently encoded by a back-flow tensor network. This construction yields a compact yet highly expressive representation of strongly correlated
quantum states. Using convolutional neural networks combined with
matrix product states as a concrete implementation, we obtain state-of-the-art variational energies for the
spin-$1/2$ $J_1$-$J_2$ Heisenberg model on the square
lattice at the highly frustrated point $J_2/J_1=0.5$, for systems up to $20\times 20$ with periodic boundary conditions. Finite-size scaling of
spin, dimer, and plaquette correlations exhibits power-law decay without
magnetic or valence-bond long-range order, consistent with a gapless
quantum spin-
liquid ground state at that point.This $\nu$TNS framework is flexible and naturally extensible to other neural and tensor-network structures, offering a general platform for investigating strongly correlated
quantum many-body systems.
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All authors Chaohui Fan, Bo Zhan, Yuntian Gu, Tong Liu, Yantao Wu, Mingpu Qin, Dingshun Lv, Tao Xiang
Statistical Mechanics
Nonholonomic constraints at finite temperature
Eduardo A. Jagla, Anthony M. Bloch and Alberto G. Rojo
We investigate the behavior of dynamical systems with nonholonomic constraints when coupled to a thermal bath, focusing on the paradigmatic case of the Chaplygin sleigh. A straightforward Langevin-type approach obtained by naively adding
stochastic and dissipative terms to the equations of motion predicts a regime in which useful work can be extracted, violating the second law of thermodynamics. To resolve this paradox, we resort to a physically motivated implementation of the nonholonomic constraint as the limiting case of a viscous interaction. However, at finite temperature, fluctuation-dissipation relations imply that the viscous force has to be complemented with
stochastic forces acting at the contact. We show that their incorporation restores compliance with the second law. Therefore, our results place fundamental limits on the physical realizability of idealized nonholonomic constraints.
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Superconductivity
Quantum Interference Breaks Bias Symmetry at Extended Superconducting Interfaces
Vishal Tripathi and Goutam Sheet
Particle-hole
symmetry of the Bogoliubov-de~Gennes
Hamiltonian is widely assumed to enforce bias-symmetric transport at superconducting interfaces. We show that this expectation fails generically for interfaces with finite spatial extent due to
quantum interference. Using a tight-binding scattering formalism that preserves exact particle-hole
symmetry, we demonstrate that propagation through an extended interface causes electrons and holes to accumulate unequal phases, leading to intrinsic bias-asymmetric conductance. The interface thereby acts as an effective Andreev interferometer with characteristic damped oscillations arising from coherent multiple reflections within the barrier. While the asymmetry originates from normal-state interference, its bias dependence is governed by the superconducting gap, which emerges as a sharp crossover scale that can be clearly resolved even when conventional coherence peaks are weak or absent. Thus we present bias asymmetry as an interferometric, spectroscopic probe of nonlocal interface physics and superconducting energy scales in hybrid and topological systems where extended interfaces are unavoidable.
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Disordered Systems and Neural Networks · Cross-listed from cs.AI
Autonomous Agents Coordinating Distributed Discovery Through Emergent Artifact Exchange
Fiona Y. Wang, Lee Marom, Subhadeep Pal et al. (+4 more)
We present ScienceClaw + Infinite, a framework for autonomous scientific investigation in which independent
agents conduct research without central coordination, and any contributor can deploy new
agents into a shared ecosystem. The system is built around three components: an extensible registry of over 300 interoperable scientific skills, an artifact layer that preserves full computational lineage as a directed acyclic graph (DAG), and a structured platform for
agent-based scientific discourse with provenance-aware governance.
Agents select and chain tools based on their scientific profiles, produce immutable artifacts with typed metadata and parent lineage, and broadcast unsatisfied information needs to a shared global index. The ArtifactReactor enables plannerless coordination: peer
agents discover and fulfill open needs through pressure-based scoring, while schema-overlap matching triggers multi-parent synthesis across independent analyses. An autonomous mutation layer actively prunes the expanding artifact DAG to resolve conflicting or redundant workflows, while persistent
memory allows
agents to continuously build upon complex epistemic states across multiple cycles. Infinite converts these outputs into auditable scientific records through structured posts, provenance views, and machine-readable discourse relations, with community feedback steering subsequent investigation cycles. Across four autonomous investigations, peptide design for the somatostatin receptor SSTR2, lightweight impact-resistant ceramic screening, cross-domain resonance bridging biology, materials, and music, and formal analogy construction between urban morphology and grain-boundary
evolution, the framework demonstrates heterogeneous tool chaining, emergent convergence among independently operating
agents, and traceable
reasoning from raw computation to published finding.
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All authors Fiona Y. Wang, Lee Marom, Subhadeep Pal, Rachel K. Luu, Wei Lu, Jaime A. Berkovich, Markus J. Buehler
Statistical Mechanics
Discrete time crystal order in spin chains enabled by Floquet flat bands
Mahbub Rahaman and Analabha Roy
We propose a novel protocol to realize discrete time-
crystal (DTC) order in clean, periodically driven
spin-$1/2$ chains. In each drive cycle, a global
spin flip is followed by a two-tone flat-band segment. This flat-band segment engineers a fully degenerate Floquet quasienergy spectrum, suppresses thermalization, and stabilizes a robust period-doubled subharmonic response. Using exact time
evolution, we identify a pronounced subharmonic peak at half the drive frequency in the
Fourier spectrum of the order parameter, thereby providing clear evidence for the emergence of stable DTC. The resulting phase is insensitive to system size, interaction strength, and interaction range; however, it remains sensitive to
spin-rotation errors ($\varepsilon_r$), which can destabilize the subharmonic response. Compared with disorder-induced many-body localized (MBL) and disorder-free dynamically many-body localized (DMBL) DTCs, we find that the exact flat-band protocol offers a broader tunability of drive parameters, whereas MBL and DMBL based DTCs are more resistant to $\varepsilon_r$. In particular, the $\varepsilon_r$ sensitivity can be suppressed by incorporating additional
spin-
spin interactions that have modest deviations from the ideal flat-band protocol. This manifests itself in a robust DTC response over a finite window of
spin-coupling strengths and drive frequencies. Our results establish flat-band driving as a versatile and experimentally relevant route to DTC order in disorder-free
spin systems and motivate further exploration of nonequilibrium phases.
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Statistical Mechanics · Cross-listed from astro-ph.HE
Reconnection-driven State Transitions in Flat Spectrum Radio Quasars
Agniva Roychowdhury
We extend the work of Roychowdhury (2026) on skewness variations of the logarithmic flux, driven by large GeV
flares in FSRQs, to a sample of 18 FSRQs. We find that they can be categorized into three groups, one where the skewness attains a persistent lower value after a large
flare, one where it increases, and those where change in skewness is not significant. To provide a theoretical ground for these results, we use the statistical plasmoid model of Fermo et al. (2010) that self-consistently produces large plasmoids through merging which, when gain energy from the reconnection event and are Doppler aligned, produce large
flares. We find that a downsampling of our simulation of 1500 runs to 18 statistically reproduces the observed distribution in p-values for change in skewness. We further compute the ensemble Shannon
entropy of the system and the skewness, where the
entropy is found to decrease at a $3\sigma$ level in both the groups where skewness either increases or decreases, as a direct evidence of increase in order in the system caused by a
flare. We find that the power spectral densities of the simulated light curves are broken-power-laws, resembling a white noise+red noise broken by the typical cooling timescale in our system, in accordance with known blazar variability. We find that our results are robust to a $200-300\%$ change in several fiducial parameters of the simulation. Our
stochastic simulation of plasmoids inside a blazar jet is consistent with key observable statistical properties of blazar GeV light curves.
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Mesoscale and Nanoscale Physics
Ab Initio Transfer Length Method Simulations of Tunneling Limits in 2D Semiconductors
Tae Hyung Kim, Juho Lee and Yong-Hoon Kim
As
semiconductor devices approach the sub-2 nm technology node, identifying the
quantum-mechanical limits of contact-resistance scaling becomes imperative; however, the transition from thermionic emission to direct tunneling in this deep nanoscale regime remains experimentally inaccessible and theoretically undefined. Herein, we present a systematic first-principles framework to characterize metal/2D-
semiconductor interfaces at the atomic scale and identify their intrinsic contact resistance and tunneling limits. Based on large-scale multi-space density functional theory calculations, we perform ab initio transmission line model (TLM) analyses for monolayer MoS2 contacted by Sc, Ag, Au, and Pd electrodes in both top-contact and edge-contact geometries. This computational procedure reveals a universal transition in resistance scaling from metal-induced gap states-mediated direct tunneling in the sub-10 nm regime to thermionic emission at longer channel lengths. The resulting transition length provides a rigorous first-principles measure of the critical tunneling length, establishing a physically grounded metric for assessing contact quality and the source-to-drain tunneling limit of 2D ballistic transistors. Using the ab initio TLM method, we further identify optimal contact strategies-top contact with low-work-function metals for n-type operation and edge contact with high-work-function metals for p-type operation. Our study introduces a general computational framework for evaluating and comparing 2D
semiconductor contacts and offers practical guidelines for engineering low-resistance, scalable contact technologies for next-generation 2D transistors.
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Statistical Mechanics · Cross-listed from quant-ph
Mixed-State Entanglement in a Minimal Model of Quantum Chaos
Tanay Pathak
Understanding the dynamics of
quantum correlations in many-body systems is a central problem in non-
equilibrium quantum physics. We study the spread of mixed-state
entanglement in a minimal model of
quantum chaos, the kicked field Ising model. By combining the replica trick with the space-time duality of the model, we determine the exact spectrum of the partially transposed reduced density
matrix. The resulting flat spectrum leads to exact relations between
entanglement negativity, odd
entropy and Rényi mutual information at early times. Numerical results further demonstrate that for equal tri-partitions and at late times, all
entanglement measures saturate to the Haar-random values. In contrast, for unequal tri-partitions Rényi mutual information and negativity vanish at late times, implying that the corresponding reduced density
matrix is factorizable. Extensive numerical simulations also show that the relation remains quantitatively valid for generic initial states, leading us to
conjecture it for all initial states and all times.
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Materials Science
Diagonal Curvature in Second Order Jahn Teller Theory Can Be Negative: An Analytic Proof with First-Principles Confirmation in NH3
Zhian Li, Hanxiang Mi, Xiyue Cheng et al. (+2 more)
We demonstrate that the diagonal
curvature in second-order Jahn-Teller theory (SOJTT) can be negative, invalidating its foundational positivity assumption. Using a frozen-
phonon many-body expansion, we show no
quantum-mechanical principle enforces its positivity; recasting into the Kohn-Sham framework further reveals that
phonon-induced eigen-energy changes arise solely from electron-
nuclear, Hartree, and exchange-correlation terms, with kinetic-energy contributions canceling identically. First principles calculations on NH3 place the D3h reference configuration at an A2" saddle point; Schwarz-inequality upper-bound analysis confines the HOMO-LUMO mixing contribution to < 0.2% of the total energy drop,while 99.8% originates from the diagonal electron-
nuclear term driving N (2s-2pz) electron redistribution. These findings overturn a core SOJTT tenet and establish that spontaneous structural
symmetry breaking demands prior verification of a saddle point, not assumed positivity of the diagonal
curvature.
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All authors Zhian Li, Hanxiang Mi, Xiyue Cheng, Jurgen Kohler, Shuiquan Deng
Materials Science
Evolution of Phonon Transport Across Structural Phase Transitions in MgAgSb
Luman Shang, Yu Wu, Yufan Liu et al. (+3 more)
MgAgSb, a promising thermoelectric material, undergoes reversible phase transitions that drastically alter its thermal transport behavior. Using first-principles calculations, we systematically investigate the
lattice thermal conductivity ($\kappa_L$) of its three phases: $\alpha$, $\beta$, and $\gamma$, revealing a progressive increase following $\alpha < \beta < \gamma$. This trend originates from distinct scattering mechanisms. Four-
phonon scattering substantially suppresses the particle-like conductivity ($\kappa_p$) in the $\beta$ and $\gamma$ phases, while electron-
phonon scattering provides a minor additional reduction. In contrast, the wave-like conductivity ($\kappa_c$) from coherent
phonon tunneling is highest in the complex $\alpha$ phase, contributing up to 44% of $\kappa_L$. Notably, the temperature dependence of $\kappa_L$ differs fundamentally between phases: in $\beta$, the weak $\kappa_p$ variation arises from a decreasing Grüneisen parameter with temperature; in $\alpha$, the strong rise in $\kappa_c$ with temperature counteracts the decay of $\kappa_p$. Our findings establish a comprehensive picture of thermal transport in MgAgSb, highlighting the phase-dependent interplay between particle-like and wave-like
phonon contributions.
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All authors Luman Shang, Yu Wu, Yufan Liu, Shuming Zeng, Gang Tang, Chenhan Liu
Materials Science
Millimeter-Scale, Atomically Controlled 2D Topological Insulators Revealed by Multimodal Spectroscopy
Woojoo Lee, Qiang Gao, Yufei Zhao et al. (+20 more)
Quantum spin Hall insulators, or synonymously known as 2D topological
insulators, are crucial 2D systems hosting topologically protected edge states. The working temperature of this topological
quantum phase is dictated by the inverted bandgap. However, the previously identified large-gap 2D topological
insulators are either extremely chemically unstable, or cannot be made with atomistic precision over macroscopic scales. Here, we establish two-quintuple-layer Bi2Te3 and MnBi2Te4/Bi2Te3
heterostructures as atomically controlled, millimeter-scale 2D topological
insulators, enabled by precision layer-by-layer growth that yields a carpet-like morphology extending coherently over macroscopic distances. This carpet-like growth mode renders the films amenable to mechanical exfoliation and subsequent wet or dry transfer.
Multimodal spectroscopies and microscopies reveal the integer-layer tuned electronic structure of (Bi2Te3)n with excellent agreement to theory.
Photon-energy-dependent photoemission and time-resolved photoemission identify band inversion and band dynamics, respectively, while scanning tunneling spectroscopy resolves topological edge states, characteristic of the 2D topological
insulator phase. Thickness- and
photon-energy-dependent photoemission further validates MnBi2Te4/Bi2Te3 as a robust 2D topological
insulator. The large inverted gaps of ~100 meV in (Bi2Te3)2 and ~150 meV in MnBi2Te4/Bi2Te3 suggest operation near ambient temperature. These results define a scalable materials platform for next-generation, low-loss
quantum and energy-efficient devices.
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All authors Woojoo Lee, Qiang Gao, Yufei Zhao, Hui Li, Albert Tsui, Yichao Zhang, Yunhe Bai, Haoran Lin, Khanh Duy Nguyen, Gabriele Berruto, Gangbin Yan, Jianchen Dang, Tongyao Wu, Hossein Rokni, Thomas S. Marchese, Ying Shirley Meng, Chao-Xing Liu, Xiao-Xiao Zhang, Chong Liu, Pinshane Y. Huang, Mark C. Hersam, Binghai Yan, Shuolong Yang
Soft Condensed Matter · Cross-listed from physics.flu-dyn
Non-Reciprocal Capillary Waves
Holly du Plessis, Pedro Cosme, Hugo França et al. (+1 more)
Capillary waves are a classical free-surface phenomenon in fluid mechanics, yet their behavior in
chiral fluids remains largely unexplored. We show that odd viscosity breaks the reciprocity of capillary waves. Using linear theory together with fully nonlinear direct numerical simulations, we find that surface tension creates two inequivalent branches of odd capillary waves: a dispersive branch and a quasi-acoustic branch absent in the capillarity-free limit. Their unequal propagation and attenuation transform standing waves into traveling waves and produce an anomalously deep vortical boundary layer. Above a threshold odd viscosity, nonlinear accumulation of vorticity near the surface reverses the induced shear current and drives bulk particles opposite to the wave motion, giving rise to an anti-Stokes drift with no counterpart in conventional fluids. Our results show how combining capillarity with broken parity can be used to control wave propagation and transport at fluid interfaces, opening a route toward one-way fluidic waveguiding and chirality-programmed interfacial flows.
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All authors Holly du Plessis, Pedro Cosme, Hugo França, Maziyar Jalaal