Other Condensed Matter
Time-dependent terahertz dielectric function of ZnTe under two-photon optical excitation at 800 nm wavelength
Farell Keiser, Wentao Zhang, Dominik Johannesmann et al. (+5 more)
ZnTe is arguably the most widely used nonlinear
crystal for the generation and detection of THz radiation, used in conjunction with sub-bandgap optical excitation by femtosecond
lasers operating near 800 nm. The THz dielectric function of ZnTe is the key parameter defining the efficiency and bandwidth of THz generation and detection. Here, we demonstrate that the THz dielectric function of ZnTe undergoes substantial transient modification at 800 nm sub-bandgap excitation under conditions typical for THz generation. These modifications arise from significant free-carrier generation via two-
photon absorption of the 800 nm pump, accompanied by the pump-driven activation of the THz-active
phonon modes. Using optical pump-THz probe spectroscopy, we characterized the THz dielectric function of ZnTe under 800 nm excitation as a function of pump fluence and pump-probe delay. Analysis of the experimental data within the Drude-Lorentz model provided the generated free carrier density and momentum scattering time, and oscillator strength of the pump activated THz
phonon modes, revealing their transient
evolution in dependence on the excitation conditions.
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All authors Farell Keiser, Wentao Zhang, Dominik Johannesmann, Nicolas S. Beermann, Yuhao Meng, Hassan A. Hafez, Savio Fabretti, Dmitry Turchinovich
Strongly Correlated Electrons
Hubbard vs. Emery model: spectra, transport and relevance for cuprates
Jakša Vučičević and Rok Žitko
Understanding the transport properties of cuprate
superconductors is one of the central challenges in the physics of strongly correlated electrons. The most common approach is to define and solve a low-energy
lattice model, but it is still unclear what the minimal model is to capture all relevant mechanisms and provide quantitative predictions. The main uncertainty concerns the choice of the orbital degrees of freedom to be included in the model, as well as the definition of the effective coupling. In this paper, we study the two most commonly considered models, namely the single-orbital Hubbard model and the three-orbital Emery model. We investigate and compare their spectral and transport properties, and find that the two models present a similar, but not the same, physical picture. We identify several strong quantitative differences which might allow one to discriminate between the two models by comparing theory with experiments. We compare our results for several physical quantities with 7 different experiments on 3 different La$_2$CuO$_4$-based cuprates, and in general find excellent agreement. The dc resistivity and the effective mass results suggest that the coupling constant in the effective Hubbard model is larger than expected. We find several more properties that are sensitive to the precise value of the coupling constant, including the critical doping for the Lifshitz transition, and the local spectral weight in the vicinity of the
Fermi level; the latter provides a promising way to estimate the effective coupling constant in future photoemission experiments.
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Materials Science
Oxophilic Silver-Based Nanoparticles with Low Pd-Au Loading for Ethanol and Glycerol Electrooxidation in Alkaline Media
Tuani Carla Gentil, Camilo Andrea Angelucci, Bruno Lemos Batista et al. (+5 more)
The electrocatalytic activity of oxophilic Ag nanoparticles, combined with small amounts of Pd and Au, was investigated for ethanol oxidation reactions (EOR) and glycerol oxidation reactions (GOR) in alkaline media. The EOR and GOR results revealed competitive current densities and less positive onset potentials for the AgPd/C and AgPdAu/C electrocatalysts, both containing 5 wt% Pd, compared to the commercial Pd/C catalyst, which has a significantly higher loading of the costly noble metal (20 wt%). In situ FTIR analyses during EOR confirmed that ethanol is initially adsorbed as acetylated species, which are subsequently oxidized to acetate ions, the main stable product in alkaline medium. However, the incorporation of Pd and Au into the Ag
matrix did not significantly alter the reaction mechanism. During GOR, the in situ FTIR studies demonstrated that catalyst composition influences the oxidation pathways: Pd-rich surfaces favor oxalate formation, while a significant presence of Ag promotes deeper oxidation (up to carbonate), with the AgPdAu ternary catalyst exhibiting intermediate behavior. One key benefit is the lower susceptibility of Ag to irreversible adsorption of reaction byproducts, which enhances electrocatalyst durability. Thus, surface segregation of Ag at high potentials can modify the catalytic surface reactivity, affecting both stability and efficiency.
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All authors Tuani Carla Gentil, Camilo Andrea Angelucci, Bruno Lemos Batista, Camila Neves Lange, Handro S. N. Lourenço, Mauro Coelho dos Santos, Vinicius Del Colle, Germano Tremiliosi-Filho
Materials Science
Emergence of Lissajous trajectories in skyrmion oscillator
Tamali Mukherjee and V Satya Narayana Murthy
Understanding the dynamics of current-driven skyrmion is essential for their practical applications. In this study, we apply an ac pulse (a) in x– direction, and (b) in both x– and y– directions through the free layer of a Co/Pt thin film and investigate the motion of the skyrmion. We show that the skyrmion follows the sinusoidal current pulse and behaves like an oscillator in the range of current amplitude 1 $\times$ 10$^{11}$ A/m$^2$ to 1 $\times$ 10$^{12}$ A/m$^2$ and frequency 5 $\times$ 10$^{8}$ rad/s to 1 $\times$ 10$^{10}$ rad/s. For current pulse of (A$_1$sin$\omega_1$t, A$_2$sin($\omega_2$t+$\phi$), 0), the skyrmion forms Lissajous figures in the x-y plane, same as observed in classical mechanics. The results are compared at T = 0 K and T $>$ 0 K to analyze the effect of temperature. As the skyrmion
Hall angle ($\theta_{SkH}$) and
stochastic thermal fluctuation ($\bm{F}^{Th}$) are functions of temperature, the skyrmion starts deviating from its path at T = 0 K with increasing temperature and eventually generates somewhat deformed Lissajous figures from ideal.
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Statistical Mechanics
Machine Learning the order-disorder Jahn-Teller transition in LaMnO$_3$
Lorenzo Celiberti, Alexander Ehrentraut, Luca Leoni et al. (+1 more)
We investigate the Jahn-Teller structural phase transition in LaMnO$_3$ at $T_{JT} \simeq 750$ K using molecular dynamics simulations based on machine-learning force fields trained on ab initio data. Analysis of the site-site correlation function of the distortions reveals that the transition is driven by the ordering of the $Q_2$ Jahn-Teller distortion of the MnO$_6$ octahedra, which acts as the order parameter and establishes the order-disorder nature of the transition. Dynamical local distortions are found to persist above $T_{JT}$. Our results reproduce the experimental temperature dependence of both structural and
phonon properties and highlight the presence of anharmonic effects at finite temperature. More broadly, the combined use of machine-learning molecular dynamics and velocity autocorrelation function analysis provides a robust framework for uncovering the microscopic mechanisms of structural phase transitions in correlated materials. In particular, this approach enables a clear distinction between order-disorder transitions and alternative mechanisms, such as displacive behavior, through the temperature
evolution of vibrational properties.
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All authors Lorenzo Celiberti, Alexander Ehrentraut, Luca Leoni, Cesare Franchini
Mesoscale and Nanoscale Physics
Optical Hall absorption sum rule and spectral compensation in time-reversal-breaking moiré and Hofstadter systems
Yixin Zhang and H. Huang
Optical spectroscopy provides a powerful, contact-free probe of topological
quantum states, yet exact constraints on antisymmetric
Hall absorption remain much less well developed than their longitudinal counterparts. Motivated by earlier
Hall-conductivity sum rules, we formulate the corresponding first-frequency-moment constraint for the antisymmetric optical conductivity, whose imaginary part governs chirality-dependent absorption. We then demonstrate this sum rule in two classes of time-reversal-breaking topological systems. For a zero-field moiré continuum model hosting topological bands, the moment vanishes exactly, implying that any low-frequency anomalous
Hall absorption must be compensated by higher-frequency spectral weight of the opposite sign. For a Hofstadter model under a uniform
magnetic field, the same moment takes a universal value fixed by the
magnetic flux density, independent of microscopic model details. By linking low- and high-frequency spectral contributions, this optical
Hall absorption sum rule provides a rigorous framework for quantifying circular dichroism constraints and diagnosing Landau-level mixing. Our results show how a known
Hall spectral constraint acquires new and experimentally relevant content in modern interacting topological materials.
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Soft Condensed Matter · Cross-listed from physics.flu-dyn
Porosity and Material Disorder Drive Distinct Channelization Transition
André F. V. Matias, Rodrigo C. V. Coelho, Humberto A. Carmona et al. (+2 more)
Flow through porous media can reshape the medium through erosion and deposition, producing preferential flow channels across a wide range of natural and industrial systems. Yet the mechanisms by which spatial disorder triggers channelization remain unclear. Here we derive a continuum description for the coupled
evolution of flow and porosity by coarse-graining pore-scale dynamics and validating the resulting model with pore-scale simulations. Using this framework, we show that different sources of disorder lead to qualitatively distinct behaviors. Disorder in erosion resistance produces a discontinuous transition to localized flow, with permanent channels appearing only above a finite disorder strength. In contrast, even extremely weak fluctuations in the initial porosity destabilize homogeneous flow and trigger persistent channelization. These results reveal an unexpected sensitivity of evolving porous media to structural heterogeneity, suggesting that channelization can arise generically even in nearly uniform materials.
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All authors André F. V. Matias, Rodrigo C. V. Coelho, Humberto A. Carmona, José S. Andrade Jr., Nuno A. M. Araújo
Materials Science
Tailoring the Optoelectronic, Photocatalytic, Thermoelectric and Thermodynamic Properties of Halides Li2InBiX6 (X = Cl, Br, I) for Energy Conversion: A DFT Study
Huda A. Alburaih, Sikander Azam, N. A. Noor et al. (+2 more)
Double perovskite halides are emerging as promising materials for a wide range of applications, particularly in renewable energy technologies such as
solar cell devices, thereby contributing to addressing global energy demands. In this work, the structural, electronic, optical, dielectric, thermoelectric, and photocatalytic properties of Li2InBiX6 (X = Cl, Br, I) halides are systematically investigated using density functional theory. The calculated formation energies confirm the thermodynamic stability of these compounds in the cubic phase. The studied materials exhibit semiconducting behavior with direct bandgaps of 1.7 eV, 1.3 eV, and 1.1 eV for Li2InBiCl6, Li2InBiBr6, and Li2InBiI6, respectively. The complex dielectric function is analyzed to explore their optical response, revealing strong absorption in the infrared and visible regions, indicating suitability for optoelectronic applications. Thermoelectric properties, including the Seebeck coefficient, electrical conductivity, and figure of merit (ZT), are evaluated over a temperature range of 30 to 800 K. The relatively small bandgaps contribute to enhanced thermoelectric performance, reflected in improved power factors. Furthermore, photocatalytic analysis indicates that Li2InBiX6 compounds are suitable candidates for water oxidation reactions within the pH range of 0 to 7. Overall, the combined thermoelectric and optical performance highlights these double perovskite halides as promising materials for future energy conversion applications.
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All authors Huda A. Alburaih, Sikander Azam, N. A. Noor, A. Laref, Sohail Mumtaz
Materials Science
Differentiable hybrid force fields support scalable autonomous electrolyte discovery
Xintian Wang, Junmin Chen, Zhuoying Zhu et al. (+1 more)
Autonomous electrolyte discovery demands a computational engine that satisfies a critical trilemma: it must be fast enough for high-throughput screening, accurate enough for quantitative property prediction, and calibratable enough for online refinement. Classical empirical force fields (FFs) are fast but rely on error cancellation, while standard machine learning interatomic potentials (MLIPs) are computationally expensive. In this Perspective, we highlight that differentiable hybrid FFs resolve this trilemma by fusing physically motivated functional forms with neural-network short-range corrections. Grounded in Energy Decomposition Analysis (EDA), state-of-the-art models such as PhyNEO-Electrolyte and ByteFF-Pol achieve zero-shot generalization to bulk phases, delivering throughputs on the order of tens of ns/day (up to $\sim$50 ns/day, depending on model complexity) for 10,000-atom systems. Crucially, their physical skeletons provide a well-conditioned parameter space for differentiable molecular dynamics (dMD). This enables a dual-calibration paradigm: bottom-up ab initio parameterization combined with top-down fine-tuning from macroscopic experimental observables. We propose that this architecture meets the requirements of a “ChemRobot-ready” digital twin by integrating physics-grounded simulation with experimentally calibratable refinement, thereby enabling closed-loop autonomous electrolyte discovery.
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All authors Xintian Wang, Junmin Chen, Zhuoying Zhu, Peichen Zhong
Superconductivity
Spectral solution of axisymmetric magnetization problems for thin superconducting shells
Leonid Prigozhin and Vladimir Sokolovsky
Existing numerical methods for modeling magnetization in thin type-II superconducting films have mostly been developed for flat films. This work introduces an efficient spectral method for axisymmetric magnetization problems involving non-flat films. The method is based on the integral thin-shell current-density formulation of the problem, employs Chebyshev
polynomial expansions for spatial discretization, and uses the method of lines for time integration. It applies to both open and closed axisymmetric shells and is so accurate that the solutions obtained can serve as
benchmarks for numerical methods for general, not necessarily axisymmetric, thin-shell magnetization problems. As one of the examples, we consider
magnetic shielding by a superconducting sphere.
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Mesoscale and Nanoscale Physics
Layer-by-layer water filling in molecular-scale capillaries
Mingwei Chen, Jingshan Wang, Artem Mishchenko et al. (+4 more)
Under ambient humidity, water spontaneously condenses in pores only a few nanometers in size, making nanoscale capillarity central to numerous natural phenomena and technological applications. At these dimensions, water may no longer be treated as a continuous fluid, yet the consequences of molecular discreteness for capillary condensation and filling remain poorly understood. Here we study nanocapillaries fabricated by van der Waals assembly and, using atomic force microscopy, monitor their wall deformations during humidity-driven water uptake. We observe two distinct regimes: layer-by-layer filling of flexible capillaries and abrupt filling of rigid ones. Flexible walls deform in steps of ~3 Å, corresponding to the sequential entry of individual water molecular layers. The different filling regimes are explained by the competition between deformation energy and oscillatory wall-water interactions. Our findings show that the molecular discreteness of water can profoundly affect ubiquitous capillary phenomena, with wall compliance selecting between discrete and abrupt filling.
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All authors Mingwei Chen, Jingshan Wang, Artem Mishchenko, Ivan Timokhin, Fengchao Wang, Andre K. Geim, Qian Yang
Statistical Mechanics
Stochastic Thermodynamics for Autoregressive Generative Models: A Non-Markovian Perspective
Takahiro Sagawa
Autoregressive generative models – including
Transformers, recurrent neural networks, classical Kalman filters, state space models, and Mamba – all generate sequences by sampling each output from a deterministic summary of the past, producing genuinely non-Markovian observed processes. We develop a general theoretical framework based on
stochastic thermodynamics for this class of architectures and introduce the
entropy production, which can be efficiently estimated from sampled trajectories without exponential overhead, despite the non-Markovian nature of the observed dynamics. As a proof-of-concept experiment with a large
language model (LLM), we evaluate the
entropy production for a pre-trained
Transformer-based model, GPT-2. We find that the
token-level
entropy production is dominated by a syntactic artifact, while the sentence-level
entropy production tends to be larger for causally ordered than for non-causal text sets. This observation is supported by a re-evaluation with a substantially larger model, Qwen3-4B-Base. We also demonstrate the framework in the linear Gaussian case, where the model reduces to the Kalman innovation representation and the
entropy production admits an analytical expression. We also show that the
entropy production decomposes exactly into non-negative per-step contributions in terms of retrospective inference, and each of those terms further splits into information-theoretically meaningful terms: a compression loss and a model mismatch. Our results establish a bridge between
stochastic thermodynamics and modern generative models, and provide a starting point for using irreversibility as a quantitative probe of the highly non-Markovian processes generated by models such as LLMs.
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Strongly Correlated Electrons
Fluctuation Mechanism of Single-Ion Anisotropy of Topological Insulator MnBi$_2$Te$_4$
V.V. Val'kov, A.O. Zlotnikov and A. Gamov
We demonstrate that charge fluctuations induced by electron hopping, combined with
spin-orbit coupling, lift the sixfold degeneracy of the orbital singlet $^{6}S$ of Mn ions in the topological
insulator MnBi$_2$Te$_4$, resulting in single-ion anisotropy. To solve the problem, a multiplet representation is introduced for the creation operators of atomic-state
fermions in terms of the operators describing transitions between many-body wavefunctions. Using the operator form of perturbation theory up to the second order, we derive expressions for the populations $n_M$ of Mn ion states with
spin projections $M$ of the $^{6}S$ term and determine the single ion anisotropy constants. The calculations reveal that the fluctuation mechanism ensures the possibility of implementing the easy-axis anisotropy observed in MnBi$_2$Te$_4$. Notably, the range of anisotropy constants $D_2$ obtained by varying the model parameters includes the value $D_2 = -0.0095$ meV, required to reproduce the critical field of the
spin-flop transition $H_{\text{sf}}$, known from the experiment. The proposed mechanism has a wide range of applicability for describing the anisotropy in compounds where the ground state of a
magnetic ion in a weak
crystal field is described by an orbital singlet.
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Mesoscale and Nanoscale Physics
Conductivity of charge-neutral multicomponent 2D electron-hole system
Yuping Huang, O. V. Kibis, V. M. Kovalev et al. (+1 more)
The interplay between distinct carrier species in systems with broken Galilean invariance can give rise to a rich landscape of interaction-driven transport phenomena. Here, we develop a comprehensive theory for the electrical conductivity of a two-dimensional mixture of massless Dirac and massive
fermions, a system realized in HgTe
quantum wells tuned to the charge neutrality point. In this regime, all carriers are thermally activated, enabling a self-consistent, temperature-dependent interplay between the two species. Crucially, the charge neutrality condition ensures that the chemical potential is not externally pinned but is determined self-consistently, making the system's transport response an intrinsic probe of inter-species
quantum friction. We demonstrate that the conductivity undergoes a distinct crossover as temperature increases: at low temperatures, transport is dominated by massless Dirac carriers, yielding nearly temperature-independent conductivity reminiscent of pristine
graphene's charge neutrality point. As the temperature rises, massive holes become thermally excited, and their mutual scattering with Dirac carriers induces a specific nonmonotonic temperature behavior of the conductivity both in clean and disordered structures. In particular, in nearly clean structures with strong screening modeled by a short-range interparticle interaction potential, the system conductivity can exhibit an inverse quadratic temperature dependence. Conversely, in disordered structures with a long-range interparticle interaction, it varies quadratically with temperature. Our findings establish HgTe
quantum wells at charge neutrality as a clean, highly tunable platform for isolating and quantitatively studying interaction-driven transport in the absence of Galilean invariance, offering a direct pathway to explore regimes where interparticle collisions dominate over disorder.
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All authors Yuping Huang, O. V. Kibis, V. M. Kovalev, I. G. Savenko
Materials Science
Alkaline-Earth Rare-Earth Fluoride Nanoparticle Superlattices for Ultrafast, Radiation Stable Scintillators
Parivash Moradifar, Tim Brandt van Driel, Masashi Fukuhara et al. (+9 more)
Radioluminescent nanostructures provide a pathway to the fabrication of next-generation scintillators with tunability in composition, size, and morphology, and spectral and temporal properties, as well as scalable processing. Here we create a 3D millimeter-scale solid-state scintillators from SrLuF Ce3+, Pr3+ (SrLuF) core-shell nanostructures, integrating nanoscale building blocks into self-assembled macroscopic
crystals. These scintillators exhibit single-digit nanosecond decay times, linear response, resistance to radiation-induced degradation, and optical emission yields within an order of magnitude of YAG Ce3+. We select a SrLuF host
lattice owing to its high effective atomic number, wide band gap, and low
phonon energy, which together support efficient 4f-5d radiative transitions from Ce3+ and Pr3+ activators while suppressing afterglow. We create a library of core-shell nanoscintillators with undoped SrLuF shells and cores spanning compositions from undoped SrLuF to fully doped SrCeF or SrPrF. Time-resolved and steady-state X-ray excited optical luminescence (XEOL) reveal broadband emission at 310 nm (Ce3+) and 335 nm (Pr3+) with biexponential decays in the sub-nanosecond (100-500 ps) and sub-15 ns (4-13 ns) regimes, demonstrating tunable radiative efficiency and ultrafast dynamics. Ensemble performance of the mm-scale superlattices is characterized under both continuous-wave and femtosecond high-intensity excitation, revealing high light yield, linear response, and radiation hardness under extreme irradiation of ultrafast 50fs X-ray pulses up to 5mJ per mm2 corresponding to a peak intensity of 1013 W per cm2. Together, these results establish a design framework for stable, bright, and tunable scintillation platforms with applications in precision health, space exploration and hard X-ray imaging at next-generation free-electron
laser facilities.
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All authors Parivash Moradifar, Tim Brandt van Driel, Masashi Fukuhara, Cindy Shi, Ariel Stiber, Federico Moretti, Qingyuan Fan, Diana Jeong, Aaron M. Lindenberg, Garry Chinn, Craig S. Levin, Jennifer A. Dionne
Soft Condensed Matter
Mode-coupling theory for aging in active glasses: relaxation dynamics and evolution towards steady state
Soumitra Kolya, Nir S. Gov and Saroj Kumar Nandi
Aging refers to the
evolution of system properties with waiting time $t_w$. It is a key feature of glassy dynamics. Recent experiments have demonstrated aging in biological systems that are inherently active with a magnitude of self-propulsion force $f_0$ and a persistence time $\tau_p$. Thus, what governs the aging dynamics in these active systems has fundamental importance. We formulate a generic mode-coupling theory (MCT) of active glasses to address this question. The aging solutions of the theory show that the two-point correlation function decays more slowly with growing $t_w$, and the relaxation time $t_r$ increases. The activity-modification of the MCT critical point, $\lambda_\text{C}$, has profound significance for active aging: the quench distance from $\lambda_\text{C}$ governs aging and determines $\delta$, where $t_r\sim t_w^\delta$. $\delta$ decreases with increasing $f_0$, in agreement with existing simulations. However, the variation with $\tau_p$ depends on the nature of activity. Our work has fundamental theoretical implications for active glasses and paves the way for a deeper understanding of the aging dynamics in biological systems.
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Superconductivity
Granular Superconductivity in La$_{2}$PrNi$_{2}$O$_{7-\delta}$ Thin Films
Ziao Han, Lifen Xiang, X.J. Zhou et al. (+1 more)
Superconductivity realized in
bilayer nickelate thin films enables direct spectroscopic and transport studies at ambient pressure. However, a persistent two-step resistive transition remains a major barrier to achieving optimal superconducting properties. Here, we show that the two-step transition in La$_2$PrNi$_2$O$_{7-\delta}$ thin films originates from the granular nature of superconductivity, specifically, the coexistence of two distinct superconducting grain phases coupled by a Josephson junction network. A secondary, lower-temperature transition appears in the $R(T)$ curve, even when residual resistance becomes vanishingly small near 30 K. This two-step behavior significantly lowers the zero-resistance transition temperature, $T_{c, zero}$$\approx$ 10 K, and limits advanced spectroscopic studies. Our findings reveal the microscopic mechanism underlying the two-step transition in thin films and underscore the need for improved oxygen homogeneity to achieve bulk superconductivity in this system.
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All authors Ziao Han, Lifen Xiang, X.J. Zhou, Zhihai Zhu
Strongly Correlated Electrons
Directional Criticality and Higher-Order Flatness: Designing Van Hove Singularities in Three Dimensions
Hua-Yu Li, Hengxin Tan, Hao-Yu Zhu et al. (+2 more)
Van Hove singularities (VHSs) play a pivotal role in driving correlated electronic phenomena. Traditional classifications focus only on critical points where the band gradient vanishes in all directions. Here we establish a unified classification of VHSs in three-dimensional systems, characterized by the number of vanishing gradient components and Hessian
eigenvalues: ordinary ($M$-type), higher-order ($T_1$, $T_2$, $T_3$), noncritical ordinary ($N_0$, $N_1$, $N_2$), and noncritical higher-order ($S_1$, $S_2$) types. Noncritical VHSs exhibit directional quenching: the gradient vanishes in a two-dimensional subspace while remaining finite along the orthogonal direction, yielding finite density-of-states enhancements with distinct energy dependencies. Using an $s$-orbital tight-binding model on the pyrochlore
lattice with
spin-orbit coupling, we demonstrate that all singularity classes emerge at distinct high-
symmetry points through controlled tuning of the hopping ratio. This work establishes directional criticality and higher-order flatness as design principles for tailoring density-of-states enhancements in three-dimensional
quantum materials.
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All authors Hua-Yu Li, Hengxin Tan, Hao-Yu Zhu, Hong-Kuan Yuan, Min-Quan Kuang
Mesoscale and Nanoscale Physics
Type-I and Type-II Saddle Points and a Topological Flat Band in a Bi-Pyrochlore Superconductor CsBi2
Yusei Morita, Yongkai Li, Yu-Hao Wei et al. (+12 more)
The divergence of the electron density of states (DOS) plays an important role in enhancing many-body interactions and inducing various
quantum phases in low-dimensional systems. However, such unique electronic structures remain experimentally elusive in three-dimensional (3D) systems, particularly those with strong
spin-orbit coupling (SOC). Using angle-resolved photoemission spectroscopy and first-principles calculations for a Laves-phase
superconductor CsBi$_2$, which features a Bi-pyrochlore 3D network with strong SOC, we identify two characteristic electronic structures with a large DOS. One is a dispersionless topological flat band with p-orbital character, locally formed around the U-K line, which enhances DOS near the
Fermi level. The other involves type-I and type-II saddle points connected by a flat band, which cooperatively produce an enhancement in the DOS. Our findings suggest a novel mechanism for achieving a DOS enhancement and lay a foundation for exploring exotic phenomena driven by the interplay of multiple singularities with a large DOS, nontrivial
topology, and strong SOC in 3D pyrochlores.
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All authors Yusei Morita, Yongkai Li, Yu-Hao Wei, Kosuke Nakayama, Zhiwei Wang, Hua-Yu Li, Takemi Kato, Seigo Souma, Kiyohisa Tanaka, Kenichi Ozawa, Jia-Xin Yin, Takashi Takahashi, Min-Quan Kuang, Yugui Yao, Takafumi Sato
Materials Science · Cross-listed from physics.bio-ph
Biogenic bubbles enable microbial escape from physical confinement
Babak Vajdi Hokmabad, Thomas Appleford, Hao Nghi Luu et al. (+3 more)
Immotile microbes inhabit nearly every environment on Earth, from soils and sediments to food
matrices – yet how they disperse through these physically confining environments is poorly understood. Here, we show that immotile microbial colonies confined in a model transparent yield-stress
matrix can achieve long-range dispersal by harnessing their own metabolism. Using yeast as a model organism, we find that fermentation drives dissolved CO$_2$ to supersaturation, nucleating biogenic bubbles that grow, yield the
matrix, and rise, hydrodynamically entraining
cells vertically in their wake. Sequential bubble nucleation sculpts persistent columnar colonies extending far beyond what growth alone permits. Multiple colonies interact via their fermentation byproducts, merging and mixing genetically as they collectively sculpt self-sustaining conduit networks. Our findings reveal a third mode of microbial dispersal, distinct from the canonical mechanisms of motility and growth, with implications for ecology, environmental science, and biotechnology. More broadly, they exemplify a previously unrecognized class of active behavior – Metabolically Driven Active Matter – in which metabolic byproducts reshape the physical landscape of confinement to drive population-scale motion.
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All authors Babak Vajdi Hokmabad, Thomas Appleford, Hao Nghi Luu, Meera Ramaswamy, Maziyar Jalaal, Sujit S. Datta
Statistical Mechanics
Generative optimal transport via forward-backward HJB matching
Haiqian Yang, Vishaal Krishnan, Sumit Sinha et al. (+1 more)
Controlling the
evolution of a many-body
stochastic system from a disordered reference state to a structured target ensemble, characterized empirically through samples, arises naturally in non-
equilibrium statistical mechanics and
stochastic control. The natural relaxation of such a system - driven by
diffusion - runs from the structured target toward the disordered reference. The natural question is then: what is the minimum-work
stochastic process that reverses this relaxation, given a pathwise cost functional combining spatial penalties and control effort? Computing this optimal process requires knowledge of trajectories that already sample the target ensemble - precisely the object one is trying to construct. We resolve this by establishing a time-reversal duality: the value function governing the hard backward dynamics satisfies an equivalent forward-in-time HJB equation, whose solution can be read off directly from the tractable forward relaxation trajectories. Via the Cole-
Hopf transformation and its associated Feynman-Kac representation, this forward potential is computed as a path-space free energy averaged over these forward trajectories - the same relaxation paths that are easy to simulate - without any backward simulation or knowledge of the target beyond samples. The resulting framework provides a physically interpretable description of
stochastic transport in terms of path-space free energy, risk-sensitive control, and spatial cost geometry. We illustrate the theory with numerical examples that visualize the learned value function and the induced controlled
diffusions, demonstrating how spatial cost fields shape transport geometry analogously to Fermat's Principle in inhomogeneous media. Our results establish a unifying connection between
stochastic optimal control, Schrödinger bridge theory, and non-
equilibrium statistical mechanics.
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All authors Haiqian Yang, Vishaal Krishnan, Sumit Sinha, L. Mahadevan
Other Condensed Matter · Cross-listed from hep-th
Geometric Phases and Persistent Spin Currents from nonminimal couplings
Edilberto O. Silva, João A. A. S. Reis and L. Lisboa-Santos
We investigate a class of nonminimal derivative couplings between
fermions and electromagnetic fields that generate Rashba-like
spin–orbit interactions in one-dimensional
quantum rings. Starting from a generalized Dirac Lagrangian containing two independent axial structures built from the field strength $F_{\mu\nu}$ and its dual $\tilde{F}_{\mu\nu}$, we perform a systematic nonrelativistic expansion and show that both couplings induce effective
Hamiltonians of the form $\boldsymbol{\mathcal{F}}\cdot(\boldsymbol{p}\times\boldsymbol{\sigma})$. This reveals that
magnetic as well as electric background fields may give rise to Rashba-type interactions, in contrast with standard condensed-matter scenarios. Before passing to the nonrelativistic limit, we analyze the relativistic content of the model in detail: the canonical structure of the deformed Dirac operator, the admissible background classes, the effective bilinear current, and the branch splitting of the relativistic dispersion relation, which constitutes the primary relativistic signature of the theory. We derive exact analytical energy levels and normalized eigenspinors for the resulting ring
Hamiltonian, compute Aharonov–Anandan
geometric phases, and analyze persistent
spin currents together with the associated differential
spin response $\mathcal{G}_s = \partial\mathcal{J}_\varphi^z/\partial\xi$. Exploiting the analytical control offered by the model, we derive the first systematic order-of-magnitude bounds on the two Lorentz-invariant couplings $\mathfrak{g}_1$ and $\mathfrak{g}_2$ from both spectroscopic and mesoscopic scenarios, identifying the experimental channels most sensitive to the new physics encoded in these operators. We discuss physical implications, signatures, and possible experimental analogs, and outline several promising directions involving disorder, noise, and nonequilibrium
spin dynamics.
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Disordered Systems and Neural Networks
Localization–non-ergodic transition in controllable-dimension fractal networks from diffusion-limited aggregation
Oleg I. Utesov, Alexei Andreanov, Tomasz Bednarek et al. (+2 more)
Our study connects the physics of disordered integer-dimensional systems and regular self-similar objects by studying spectral properties of fractal agglomerates with tunable dimension. The latter is controlled by parameter $\alpha$ of the
algorithm that generates the agglomerates. We consider the nearest-neighbor tight-binding model on the agglomerates embedded in 2D and 3D, and observe that all eigenstates are localized in the 2D case, whereas in the 3D case, there is a localization–non-ergodic transition upon increasing $\alpha$,i.e., going from sparse to dense fractals: a sub-extensive number of critical states emerge in the spectrum at a certain critical value of $\alpha$. The complex geometry of the agglomerates is also responsible for a peculiar hierarchy of compact localized states and singularities in the density of states, which are typical for ordered fractals.
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All authors Oleg I. Utesov, Alexei Andreanov, Tomasz Bednarek, Alexandra Siklitskaya, Sergei V. Koniakhin
Disordered Systems and Neural Networks
Bilattice-Catastrophe Isomorphism for Four-Valued Logic in Digital Systems
Jiu Hui Wu, Hua Tian, Mengqi Yuan et al. (+1 more)
Belnap's four-valued logic, distinguished by its inherent bilattice structure, provides a natural algebraic bridge between discrete Four-valued logic (4VL) in
circuit and continuous catastrophe theory (CT). Building on the rigorous verification of the bilattice-catastrophe isomorphism
theorem, we establish a categorical correspondence spanning the catastrophe category, interlaced bilattice category, and 4VL category, with the cusp catastrophe emerging as the canonical CT counterpart to 4VL.This unification provides a foundational framework for explaining 4VL's robustness. Crucially, we demonstrate that the four-valued
algebra FOUR is the minimal complete algebraic structure capable of describing continuous-discrete interfaces with involution
symmetry. Unlike the empirical adoption of X and Z in engineering practice, our work reveals their mathematical necessity: X and Z are topological invariants of discretized continuous dynamical systems, encoding fundamental properties of catastrophe-induced discontinuities. The work enables cross-disciplinary extensions to uncertainty propagation, complex system modeling, and fault-tolerant design.
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All authors Jiu Hui Wu, Hua Tian, Mengqi Yuan, Kejiang Zhou
Materials Science
Symmetry-guided and AI-accelerated design of intercalated transition metal dichalcogenides for antiferromagnetic spintronics
Yu Pang, Yue Gu, Runsheng Zhong et al. (+4 more)
The advancement of
antiferromagnetic spintronics depends on
quantum materials with target
symmetry-dictated functionalities, however, their systematic discovery is hindered by the immense configurational complexity of the available material space. Here, we introduce a
symmetry-guided, AI-accelerated framework incorporating graph neural networks with high generalization ability to overcome this bottleneck. Based on fully intercalated transition metal dichalcogenides (iTMDs) and using only 200 relaxed partially intercalated structures for transfer learning, our model effectively explores more than 100,000 partially intercalated configurations and identifies 35 altermagnetic and 20 $T\tau$-
antiferromagnetic ground-state candidates. Interestingly, we show that tuning
spin-group
symmetry through intercalant arrangement or
magnetic ordering realizes a series of d-wave altermagnets in these hexagonal systems with high
spin-charge conversion efficiency. Furthermore, we reveal plentiful $T\tau$-antiferromagnets enabling efficient Néel
spin-orbit torque switching, driven by
giant $T$-odd
spin Edelstein susceptibilities. These results establish iTMDs as a versatile platform for spintronics and provide a general strategy for the accelerated design of
symmetry-enforced
quantum materials.
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All authors Yu Pang, Yue Gu, Runsheng Zhong, Liyang Zou, Xiaobin Chen, Xiaolong Zou, Wenhui Duan