Statistical Mechanics
Efficient protocol for the Markovian Mpemba effect in $N$-level systems
David Gelbwaser-Klimovsky
The Mpemba effect is an anomalous phenomenon in which the time to thermalize does not depend monotonically on the distance from
equilibrium, allowing systems with an initially larger temperature difference to thermalize before those with a smaller one. The rarity of the effect makes it hard to find parameters that produce it, complicating the design of experiments and the development of applications. Here, we find necessary and sufficient conditions for the Markovian Mpemba effect in three-level systems and explain its underlying physical mechanisms. Based on our understanding of the three-level case, we develop an efficient
algorithm to determine the parameters for the effect in $N$-level systems. This protocol could open the door for the realization of Mpemba experiments and related applications in large systems.
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Statistical Mechanics · Cross-listed from q-bio.MN
Thermodynamic and Statistical Signatures of Modality Changes in Concentration Distributions Driven by Stochastic Switching Between Two Activity States
Aindrila Deb and Pintu Patra
Stochastic switching between gene expression states, coupled with production and degradation dynamics, governs the accumulation of mRNA and
proteins in
cells. The concentrations of these accumulated entities dictate the phenotypic distribution of genetically identical
cells. The underlying accumulation dynamics are well-captured by a two-state promoter switching model, with statistical and thermodynamic properties quantified via the Fano factor and
entropy production rates. However, how these measures correlate with concentration distributions and their shifts under varying kinetic parameters remains largely unexplored. To this end, we use chemical master equations to study a generalized model of mRNA accumulation dynamics in the presence of
stochastic switching between two activity states and state-dependent production and degradation rates. We derive exact expressions for the steady-state probability distribution and analytically compute the mean concentration, Fano factor, and
entropy production rate (EPR). Simplifying these expressions, we identify contributions arising from
stochastic switching rates and relaxation dynamics toward
equilibrium in each activity state. Next, using our theoretical results, we characterize the variation in the Fano factor and EPR as a function of mean expression during modality changes of the distributions mediated by the variation of switching rates. We also identify the conditions in kinetic parameters that achieve the highest Fano factor and
entropy production rates. Our findings establish a generalized framework for examining
stochastic accumulation dynamics, clarifying how kinetic parameters dictate molecular distributions, noise, and dissipation. These insights extend readily to broader contexts coupling
stochastic switching with accumulation, including
protein burst dynamics, phenotype-switching-mediated drug intake, and queuing theory.
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Materials Science
Strong Impact of Halide Ordering on Structural Phase Transitions in Mixed Perovskites
Felix Uddén, Erik Fransson, Julia Wiktor et al. (+3 more)
Mixed halide perovskites are highly versatile
semiconductors with applications in photovoltaics, light-emitting diodes, and photodetectors. Understanding their thermodynamic phase behavior is central to guiding compositional design and improving device stability. Here, we train machine-learned interatomic potentials (MLIPs) on density functional theory reference data for CsxRb1-xPbBr3yI3-3y, CsxRb1-xPbBr3yCl3-3y, and CsxRb1-xPbCl3yI3-3y halide perovskites, enabling large-scale hybrid Monte Carlo-molecular dynamics simulations that sample both configurational and vibrational degrees of freedom. All three binary halide systems exhibit a miscibility gap, the extent of which correlates with halide ion size mismatch. The gaps in Br-Cl and Br-I close at low temperatures, while the Cl-I gap extends above room temperature. At temperatures above the miscibility gap (200 K to 500 K), all systems show a tendency toward layered halide ordering, with halide species preferentially occupying apical or equatorial octahedral sites. In CsPbBr3yI3-3y, this ordering occurs in a device-relevant temperature regime and is linked to the structural phase transitions, shifting transition temperatures by up to 100 K relative to randomly mixed structures. We attribute the strongly non-linear composition dependence of the orthorhombic-tetragonal phase boundary observed experimentally (a linear decrease followed by a plateau) to halide ordering. Introducing Rb on the A-site weakens halide ordering and eliminates the non-linear behavior, while narrowing the miscibility gap in both the Br-I and Br-Cl systems. These results establish halide ordering as a key determinant of structural phase stability in mixed-halide perovskites.
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All authors Felix Uddén, Erik Fransson, Julia Wiktor, Benjamin M. Gallant, Dominik J. Kubicki, Paul Erhart
Disordered Systems and Neural Networks · Cross-listed from physics.optics
Image recognition based on optical spike processing with exciton-polaritons
Olgierd Jeziorski, Jakub Rogala and Krzysztof Tyszka
Exciton-polariton condensates combine ultrafast dynamics with strong optical nonlinearities, making them promising for optical neuromorphic computing. Here, we numerically demonstrate image recognition using the transient response of an
exciton-polariton condensate. Downscaled MNIST images are encoded as optical pulse sequences, and the resulting condensate dynamics are sampled and processed by a linear classifier. For ten-class classification, condensate features achieve 92.2% accuracy, compared with 91.4% for raw-pixel linear classification. Combining both feature sets increases the accuracy to 93.2%. For the challenging binary classification of digits 7 and 9, the combined model reaches 97.3%, exceeding both the linear (95.5%) and feed-forward neural-network (96.6%) baselines. These results demonstrate that polariton dynamics can extract useful nonlinear features for ultrafast optical information processing.
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Soft Condensed Matter
Configurational-space separation and structure selection in three hard squares
Yuheng Yang, Meng Xiao and Duanduan Wan
Self-assembly of hard particles with diverse shapes gives rise to a rich variety of structures through excluded-volume constraints alone. Here we show that even a minimal system of three hard squares confined in a two-dimensional periodic box exhibits nontrivial configurational behavior relevant to structure selection. As the packing fraction increases, radial distribution functions obtained from Markov-chain Monte Carlo and uniform non-overlapping insertion sampling agree at low densities, deviate markedly over an intermediate range, and converge again at higher densities. Pressure measurements provide strong numerical evidence that the discrepancy originates from the separation of the allowed configurational space into two disconnected regions above a characteristic density. We identify the separation density as $\phi_{\rm sep}=3/5$, construct explicit overlap-free transition pathways connecting the two regions immediately below it, and quantify their relative configurational-space volumes. At higher packing fractions, an approximately L-shaped arrangement of the particle centers becomes strongly favored over a staggered one, revealing a structural motif characteristic of tetratic and square-
lattice ordering in larger hard-square systems. These results show that excluded-volume geometry can govern both configurational connectivity and local structure selection even in a three-particle system, revealing how signatures of many-particle self-assembly can already emerge in the few-particle limit.
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Materials Science
Dimensional Control of Excitonic Interactions in Exfoliated 2D Molecular Crystals
Jonghyun Son, Seonghyun Koo, Daniel Yim et al. (+17 more)
Two-dimensional (2D) materials provide unique opportunities to tailor excited-state properties through reduced dimensionality, altered dielectric screening and layer-dependent structural reconstruction. While such effects have been widely explored in norganic systems, their realization in molecular
crystals has been limited by the difficulty of controlling thickness at the atomic scale while preserving crystalline order. Here we show that tetracene and three other molecular
crystals can be mechanically exfoliated into mono-, few- or multilayer flakes, while retaining crystalline order. This capability enables new studies of molecular
crystals across a well defined thickness range within the same structural organization. Thickness-dependent spectra of these samples reveal how out-of-plane confinement modifies the excited-state energy landscape of tetracene: With decreasing thickness, the Davydov splitting diminishes, the Stokes shift increases, and signatures of more delocalized
excitons emerge. Electron diffraction and
exciton model-based analyses correlate these trends to changes in molecular packing, intermolecular coupling and dielectric screening. Our results also demonstrate that key features of molecular
excitons can be systematically tuned by layer number, extending dimensional control from inorganic 2D materials to molecular
crystals.
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All authors Jonghyun Son, Seonghyun Koo, Daniel Yim, Sangjin Han, Dong-Hwan Yang, Gi-Yeop Kim, Kihyun Lee, Jieun Yeon, Hye Soo Kim, Eunbeen Jeon, Minji Ko, Minhee Choe, Kenji Watanabe, Takashi Taniguchi, Hee Cheul Choi, Kwanpyo Kim, Si-Young Choi, Seogjoo J. Jang, Hyungjun Kim, Sunmin Ryu
Mesoscale and Nanoscale Physics
Apparent Zero-Momentum Signals from Magnon–Magnon Interference in Near-Field Spin-Wave Imaging
Julien Berthomier, Romain Lebrun, Vincent Cros et al. (+3 more)
Spatially resolved measurements of coherent waves are commonly read as direct maps of the underlying eigenmode spectrum. We show that this interpretation fails in near-field imaging of multimode
spin-wave transport. Scanning nitrogen-vacancy magnetometry of yttrium iron garnet reveals pronounced apparent low-wave-vector signals at frequencies for which no propagating
spin-wave mode exists. By tuning the probe-sample distance and modeling the anisotropic near-field response, we identify their origin as coherent mixing between directly excited Damon-Eshbach waves and defect- or transducer-scattered
spin waves: the measured signal acquires spatial
Fourier components at the difference wave vector $\mathbf{k}_{\mathrm{exc}}-\mathbf{k}_{\mathrm{scat}}$, which can vanish even though both constituent waves carry finite momentum. These results establish that near-field spectra of coherent excitations are interferometric field spectra rather than eigenmode maps, providing both a caution and a framework for identifying scattering processes in nanoscale magnonic devices.
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All authors Julien Berthomier, Romain Lebrun, Vincent Cros, Jamal Ben Youssef, Karim Bouzehouane, Abdelmadjid Anane
Statistical Mechanics
Quantifying cell shape and density fluctuations in epithelial tissue in vivo
Jake Turley, Helen Weavers, Paul Martin et al. (+2 more)
Controlling changes in
cell shape are crucial for many biological processes, such as tissue development and wound healing. Tissues typically are heterogeneous with a variety of
cell shapes and sizes. Of particular interest are local deviations from an average
cell shape and size. These fluctuations may extend and transmit across tissues, potentially offering valuable insights into tissue characteristics such as variations in effective "stiffness" or rigidity. In this study, we present a theoretical framework that captures the dynamics of epithelial
cell shapes within tissue, incorporating both their average behaviour and fluctuation patterns. We model
cells as interacting soft ellipsoids of varying size and aspect ratio. Coarse-graining our model, we obtain a set of continuum
stochastic differential equations from which we derive spatial-temporal correlation functions. These correlation functions fit with our experimental data from the developmental process of the Drosophila pupal wing. From the correlation functions, critical parameters representing active
cell shape changes and effective tissue "stiffness" can be determined.
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All authors Jake Turley, Helen Weavers, Paul Martin, Isaac V. Chenchiah, Tanniemola B. Liverpool
Mesoscale and Nanoscale Physics
Photo-induced Wavelength-tuning of Telecom-band Quantum Dot Nanowires Embedded in a Phase Change Material
Evangelos Sotiropoulos, Philippe Regreny, Matthieu Bugnet et al. (+4 more)
Scalable
quantum-photonic technologies require spatially separated emitters to emit at the same wavelength, yet epitaxially grown
quantum dots naturally exhibit emitter-to-emitter variations in their emission energies. Here, we demonstrate a contact-free post-growth tuning approach for InAs
quantum dots embedded in InP nanowires using the photo-induced transformation of an amorphous Sb2S3 shell. This photoinduced effect leads to a progressive relaxation of the strain imposed on the InP core, enabling controlled spectral tuning of the
quantum-dot emission. The effect is observed both at room temperature and under cryogenic conditions for
quantum dots emitting in the O-band of the telecommunications spectrum. Strain-induced
redshifts of approximately 7 meV at room temperature and 28 meV under cryogenic conditions are observed, respectively. The use of an amorphous chalcogenide shell therefore provides a route to achieve local wavelength tuning at the single
quantum-dot-in-a-nanowire level after growth. This approach could enable spectrally matched emitters for scalable
quantum-photonic architectures.
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All authors Evangelos Sotiropoulos, Philippe Regreny, Matthieu Bugnet, Nicholas P. Blanchard, Sébastien Cueff, José Penuelas, Nicolas Chauvin
Soft Condensed Matter · Cross-listed from physics.chem-ph
Comprehensive Study of L-Menthol and Octanoic Acid as a Hydrophobic Eutectic Solvent
Bernarda Lovrinčević, Martina Požar, Romana Cerc Korošec et al. (+4 more)
Hydrophobic eutectic solvents (HES) based on natural compounds represent promising green alternatives to conventional solvents. In this work, we investigate the physicochemical, structural, and dynamical properties of an ES formed by L-menthol and octanoic acid using a combined experimental and molecular dynamics simulation approach. Five compositions with molar ratios from 1:3 to 3:1 were studied with molecular dynamics simulation in the temperature range 15 degrees C to 35 degrees C. Experimental measurements of density and viscosity in the temperature range from 5 degrees C to 35 degrees C were complemented with results obtained from MD simulations employing the OPLS force field. Structural analyses based on radial distribution functions and Kirkwood-Buff integrals reveal that the dominant interactions in the mixture are hydrogen bonds between L-menthol and octanoic acid molecules. Dynamic properties, including self-
diffusion coefficients and hydrogen-bond lifetimes, indicate that intermolecular hydrogen bonds between the two components are stronger and longer-lived than bonds between identical species. These findings provide molecular-level insight into the structure and transport properties of menthol-based ESs relevant for green solvent applications.
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All authors Bernarda Lovrinčević, Martina Požar, Romana Cerc Korošec, Klara Švegelj, Peter Ogrin, Marija Bešter-Rogač, Tomaž Urbič
Materials Science
uFlowCSP: Crystal Structure Prediction using Mean flow generative models
Sourin Dey, Dipannoy Das Gupta, Lai Wei et al. (+2 more)
Crystal structure prediction (CSP) is fundamental to computational materials discovery. Generative models including CDVAE, DiffCSP, FlowMM, and CrystalFlow learn stable-
crystal distributions directly, but
diffusion and flow-matching inference requires tens to thousands of sequential network evaluations per candidate. We introduce uFlowCSP, a MeanFlow-based CSP model that learns the average, rather than instantaneous, probability-flow velocity. It generates a complete structure in one to five evaluations, delivering 5x-58x faster inference with equal or better performance. A chemistry- and
symmetry-aware
Transformer uses canonical atom ordering, global composition, and per-
token chemistry
embeddings. A coarse
crystal-system
token is used only during training; it provides additive gains, particularly improving space-group agreement despite being absent at inference, which remains formula-only. On MP-20 with 20 candidates per target, one step matches CrystalFlow (78.38% vs. 78.34%) with 100x fewer evaluations and about 10x lower wall-clock time. Five steps reach 83.64%, exceeding CrystalFlow (78.34% at 2,000 evaluations) and DiffCSP (77.93% at about 20,000), while using 20x fewer evaluations. uFlowCSP generates 10,000 structures in 0.39-1.31 minutes, versus 6.5 for CrystalFlow and 76.1 for DiffCSP. Under CSPBench's energy-ranked top-five structure-and-space-group criterion, five-step uFlowCSP reaches 72%/72%/65% structure, space-group, and consensus match rates. CrystalFlow reaches 78%/73%/68% at 100 steps but falls to 49%/32%/31% at five. Thus, uFlowCSP improves accuracy per network evaluation, not merely peak accuracy.
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All authors Sourin Dey, Dipannoy Das Gupta, Lai Wei, Sadman Sadeed Omee, Jianjun Hu
Strongly Correlated Electrons
Semi-Dirac States and Quantum Linear Magnetoresistance in Helimagnetic Pnictide MnP
Prasanta Chowdhury, Jyotirmoy Sau, Sanat Kumar Adhikari et al. (+7 more)
Large linear positive magnetoresistance (LPMR) in topological and
magnetic materials remains a subject of intense debate, particularly in noncollinear
spin systems where
spin-dependent scattering complicates charge transport. Manganese phosphide (MnP), a helimagnetic binary pnictide with multiple field-induced
magnetic transitions, provides a useful platform to investigate the interplay between complex magnetism and electronic
topology. Here, we present a comprehensive experimental and theoretical investigation of phase-dependent magnetotransport in high-quality MnP single
crystals. Hall measurements reveal an anomalous Hall effect dominated by skew scattering at high temperatures and a finite topological Hall effect in the noncollinear fan (FAN) and low-temperature screw (SCR) phases. At low temperatures, we observe a large, non-saturating LPMR reaching nearly 800 percent at 4 K and 15 T, with a pronounced linear field dependence in the field-polarized ferromagnetic (FM2) state. First-principles calculations reveal a strongly anisotropic semi-Dirac-like band at the Y point that progressively approaches the Fermi level from the SCR to FAN and FM2 states. Our analysis indicates that the resulting small Fermi pocket can access the extreme
quantum-limit regime at experimentally accessible fields, providing a microscopic framework for the observed LPMR within Abrikosov's
quantum magnetoresistance theory.
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All authors Prasanta Chowdhury, Jyotirmoy Sau, Sanat Kumar Adhikari, Sourav Chowdhury, Peter Bencok, Matthias Gutmann, Souvik Chatterjee, Saurav Giri, Manoranjan Kumar, Subham Majumdar
Materials Science
Facile hBN-hBN Interfacial Overlap Engineering for Enhanced Quantum Emitter Formation
Nhat Minh Nguyen, Trung Vuong Doan, Md Shakhawath Hossain et al. (+12 more)
Quantum emitters in two-dimensional materials, particularly hBN, are promising platforms for
quantum technologies. However, achieving high-density emitters at predetermined locations while preserving optical quality remains challenging. Here, we introduce a facile, cost-effective double-layer all-dry transfer approach to deterministically create overlap regions between hBN flakes. These pre-defined capped regions exhibit a significantly enhanced emitter density, with up to a 15-fold increase compared to uncapped areas. Importantly, this method does not compromise emitter quality: emitters within overlap regions demonstrate excellent optical performance, including high signal-to-background and signal-to-noise ratios, large Debye-Waller factors, high brightness, and strong spectral stability. Possible defect configurations are also discussed to contextualize the observed emission characteristics. This scalable strategy enables preferential formation of
quantum emitters in targeted regions, achieving higher densities than simple treatments such as
plasma irradiation while avoiding the complexity of advanced fabrication techniques. The approach provides a practical pathway for integrating high-quality
quantum emitters into scalable
quantum photonic platforms.
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All authors Nhat Minh Nguyen, Trung Vuong Doan, Md Shakhawath Hossain, Akila Elangasinghe, Duc Anh Ngo, Ha Ngoc Duy Huynh, Thi Ngoc Anh Mai, Yongliang Chen, Kenji Watanabe, Takashi Taniguchi, Michael G. Ruppert, Chaohao Chen, Xiaoxue Xu, Toan Dinh, Toan Trong Tran
Materials Science
Morphology and depletion force-based large-scale self-assembly of nanocubes on surface
Yeonhee Lee, Seungsang Cha, Yuna Kwak et al. (+3 more)
Self-assembling nanoparticles is a highly efficient and facile way to form functional nano-, micro- and macrostructures. However, currently available methods lack precision and controllability in size, shape and composition, suffer from poor reproducibility and scalability, and require complex steps and expensive materials. Here, we present the uniform morphology-induced and depletion force-directed nanoparticle assembly on surface (MIDAS) method with gold nanocubes (AuNCs). Using this approach, morphology-sensitive depletion forces trigger shape-selective flocculation and assembly of the AuNCs with uniform size and shape. Importantly, the surface roughness-controlled substrate drives the large-scale formation of AuNC-assembled monolayers (2D AuNAMs) or three-dimensional AuNC-assembled multilayers (3D AuNAMs) in a highly specific manner without any complex ligand modification or preparation steps.
Lattice-gas modeling and kinetic Monte Carlo simulations show the depletion force is the key parameter determining supercrystal morphology and corroborate the experimental findings. This work establishes a generalizable nanoparticle assembly mechanism and demonstrates the broad applicability of the MIDAS strategy for scalable fabrication and patterning of 2D and 3D nanoparticle architectures.
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All authors Yeonhee Lee, Seungsang Cha, Yuna Kwak, Nicholas Juntunen, Grant M. Rotskoff, Jwa-Min Nam
Strongly Correlated Electrons
Orbital-selective electronic modes induced by doping and originating from distinct spin excitations: an essential feature of orbital-selective Mott transition
Masanori Kohno
The nature of the orbital-selective Mott transition (OSMT) remains elusive. This study shows that, by doping an orbitally degenerate
spin-1 antiferromagnetic
insulator in the Kanamori-Hubbard model, electronic modes emerge in the band gap in an orbital-selective manner, exhibiting momentum-shifted
spin-mode dispersion relations. Electronic modes originating from conventional
spin excitations, including the low-energy one, appear in the doped orbital, while those from inter-orbital
spin excitations appear in the undoped orbital. These emergent modes constitute an essential feature of the OSMT.
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Statistical Mechanics
Intermittent continuous-time random walks under renewal reset mechanism
Guohua Li, Hong Zhang and Yuexiong Liu
Stochastic resetting as a practical and efficient search strategy in complex and disordered environments has long been a topic of interest to researchers. Based on the competition between jumping and resetting, this article proposes and investigates intermittent continuous-time random walks (CTRWs) under
stochastic resetting, using the smaller waiting time for jump and reset as the renewal time, where the waiting times for both jump and reset can have arbitrary distributions. After each renewal event, the system will proceed with new waiting times for jump and reset regardless of their previous histories. We study the governing equation and Montroll-Weiss equation with renewal resetting, as well as the Markovian resetting for intermittent CTRWs. We prove the existence of non-
equilibrium stationary states within the renewal reset mechanism when the jump and reset waiting times follow any exponential and power law distributions. For exponential and Gaussian distributed jump lengths, we examine the mean square displacements (MSDs) of particles to determine their monotonicity and asymptotic stability. Moreover, we calculate the first-arrival time to quantify search efficiency, and validate the intermittent CTRWs under renewal resetting lead to a finite mean first-arrival time (MFAT) to any fixed position for exponential jump and reset waiting time distributions (WTDs), power-law jump and exponential reset WTDs, as well as exponential jump and power-law reset WTDs. However, the MFAT diverges for power-law jump and reset WTDs. The intermittent CTRW model, which is based on the competition mechanism, can be applied to many physical scenarios, such as the foraging strategy of animals that return to their nests after an unsuccessful foraging attempt, or the work planning of intelligent
robots that return to energy replenishment points after prolonged operation.
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Quantum Gases
Fractional Chern Insulators in Twisted Bilayer Optical Lattices
Yan-Bin Yang, Jiong-Hao Wang, Shicheng Ma et al. (+1 more)
Twisted bilayer materials provide a versatile platform for realizing correlated topological states. Motivated by the recent experimental realization of atomic Bose-Einstein condensates in twisted bilayer optical
lattices, we investigate the emergence of fractional topological phases in such systems. For experimentally realistic parameters, the single-particle spectrum hosts a pair of quasi-degenerate nearly flat moiré bands. We show using self-consistent Hartree-Fock calculations that atomic interactions spontaneously break time-reversal
symmetry, lift the quasi-degeneracy, and generate an isolated nearly flat band with a nonzero Chern number. At fractional filling, exact diagonalization of the
Hamiltonian projected to this band reveals a threefold degenerate ground-state
manifold and a characteristic particle
entanglement spectrum, providing strong evidence for a fractional Chern
insulator. The resulting many-body gap is of order \(10^{-3}E_R\), corresponding to a nanokelvin energy scale accessible to state-of-the-art cold-atom experiments. Our scheme requires neither
spin-orbit coupling, as in transition metal dichalcogenides, nor a finite
magnetic field, as in existing twisted-bilayer-
graphene experiments, providing a highly tunable route to strongly correlated topological phases in twisted bilayer optical
lattices.
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All authors Yan-Bin Yang, Jiong-Hao Wang, Shicheng Ma, Yong Xu
Superconductivity
Record-Breaking Elemental Superconductivity in Tetralayer Kagome Borophene
Yingnan Liu, Yan Liu, Renyu Duan et al. (+4 more)
Superconductivity above the
liquid-nitrogen temperature remains rare in two-dimensional elemental
crystals, where strong covalent bonding often yields high
phonon frequencies but insufficient electron-
phonon coupling. Here, using first-principles calculations and fully anisotropic Migdal-Eliashberg theory, we predict tetralayer kagome borophene (TKB) stabilized by ABAB covalent stacking, as a
liquid-nitrogen-temperature elemental
superconductor. With a predicted critical temperature of 102 K, TKB sets a record-high value among previously reported elemental
superconductors. Unlike known high-Tc boron-based
superconductors dominated by in-plane sigma-bonding states and high-frequency in-plane B-B stretching modes, TKB realizes an out-of-plane s-pz-bonding-mediated pairing mechanism, in which interlayer s-pz bonding states at the Fermi level are strongly coupled to low-frequency out-of-plane vibrations of boron atoms. These results reveal a distinct out-of-plane pairing channel in multilayer borophene and establish covalent stacking engineering as a potential route for high-Tc superconductivity in two-dimensional materials.
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All authors Yingnan Liu, Yan Liu, Renyu Duan, Menghui Wang, Meiling Xu, Hanyu Liu, Shoutao Zhang
Mesoscale and Nanoscale Physics
A discrete Stiefel-Whitney invariant with twofold rotation symmetry
Ken Shiozaki
We review Stiefel–Whitney invariants and give a discrete formulation of an additional $\mathbb{Z}_2$ invariant for two-dimensional spinful
insulators with twofold rotation and time-reversal
symmetries (layer group $p1121'$). A singular gauge transformation specifies a real bundle over the quotient of the Brillouin
torus, whose second Stiefel–Whitney number defines the invariant. We derive its dependence on the choice of auxiliary gauge function and prove invariance under changes of Bloch frame and additivity under direct sums. The discrete formula uses overlaps of independently chosen Bloch frames and
symmetry-compatible $\mathrm{Pin}_+$ lifts on the boundary of a half Brillouin zone. Atomic and topological-
insulator models illustrate the formula and distinguish the additional invariant from the Kane–Mele index. Together with three quantized $\mathbb{Z}_2$ partial polarizations and the filling number, it labels the known stable classification $\mathbb{Z}\oplus\mathbb{Z}_2^{\oplus 4}$.
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Materials Science
First-principles investigation of structural, mechanical, vibrational, thermal, electronic and optical properties of Na3Bi: a topological Dirac semimetal
Maisha Fahmida, Syed Shovon Mahbub Mahin, Suptajoy Barua et al. (+1 more)
Exploring the properties of topological materials has remained an active area of research in condensed matter physics for the past few decades. Here, we present a first-principles investigation of the structural, elasto-mechanical, thermal, electronic, and optical properties of Na3Bi, one of the earliest discovered topological Dirac semimetals, using density functional theory. The hexagonal phase of Na3Bi is found to be both mechanically and dynamically stable, exhibiting moderate elastic anisotropy with a universal anisotropy index of 0.832. The compound displays a moderate machinability index of 2.386 alongside a low hardness value of 2.005, consistent with its predominantly brittle, covalently bonded character accompanied by a slight metallic contribution. Its comparatively low Debye temperature of 181.39K points to a mechanically soft
lattice with loosely bound atoms. Electronic structure calculations confirm semimetallic behavior, with well-defined Dirac points pinned at the Fermi level and a Fermi surface composed of point-like pockets. Optical analysis across a wide spectral range reveals non-selective, moderate reflectivity of 40 to 45% and, in the visible region, an unusually high refractive index reaching between 2 and 4.5. Na3Bi is additionally found to be an efficient absorber of ultraviolet radiation. Together, these findings establish a comprehensive baseline for the mechanical, thermal, and optical behavior of hexagonal Na3Bi and point to its potential relevance for acoustic damping, UV-sensing, and optoelectronic applications
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All authors Maisha Fahmida, Syed Shovon Mahbub Mahin, Suptajoy Barua, Ishtiaque M. Syed
Strongly Correlated Electrons
Anomalous Hall Response Induced by Correlated Disorder in the Breathing Kagome Lattice Mn$_{3}$Sn
Tsung-Han Yang, Seng Huat Lee, Hengxin Tan et al. (+10 more)
Macroscopic transport tensors are generally constrained by the average crystallographic and
magnetic symmetries of a material. In the kagome antiferromagnetic Weyl semimetals Mn$_{3+\delta}X$ ($X=$~Sn or Ge), previous studies showed that the anomalous Hall conductivity $\sigma_{yx}$ is forbidden by the average \hexsg{} structure and coplanar inverse-triangular
magnetic order. Here we report that nearly stoichiometric Mn$_3$Sn nevertheless exhibits a finite $\sigma_{yx}$ with large hysteresis, together with enhanced $\sigma_{zx}$ and $\sigma_{yz}$, in the inverse-triangular phase below $T_{\mathrm{N1}}\approx 440~\mathrm{K}$, whereas all AHE components vanish in the amplitude-modulated conical phase below $T_{\mathrm{N2}}\approx 280~\mathrm{K}$. Total scattering and
magnetic pair distribution function analysis reveal correlated orthorhombic distortions and noncoplanar Mn moments. First-principles calculations show that this coupled
lattice-
spin distortion activates the average
symmetry forbidden $\sigma_{yx}$ within the inverse-triangular phase. Its disappearance below $T_{\mathrm{N2}}$ indicates that the correlated disorder must cooperate with a long-range inverse-triangular antiferromagnetic order capable of supporting Berry
curvature. Our results establish correlated disorder as an active
symmetry-breaking degree of freedom that enables topological transport inaccessible from the Bragg-average structure alone.
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All authors Tsung-Han Yang, Seng Huat Lee, Hengxin Tan, Yuanpeng Zhang, Benjamin A. Frandsen, Václav Petříček, Huibo Cao, Daniel Olds, Matthew G. Tucker, Jiaqiang Yan, Binghai Yan, Zhiqiang Mao, Qiang Zhang
Materials Science · Cross-listed from quant-ph
Cascade-induced high-performance nonreciprocal quantum batteries
Niaz Ali Khan and Dahai He
Nonreciprocal
quantum batteries harness reservoir engineering for controlled energy transfer, heralding a paradigm shift for
quantum energy storage. A prior study utilizing the Metelmann-Clerk formalism reported a fourfold enhancement in nonreciprocal energy accumulation over reciprocal counterparts. This fourfold enhancement, however, appears to stem from a Lindblad master equation that exhibits fundamental inconsistencies, which may systematically understate the actual nonreciprocal advantage. Our approach is rooted in the rigorously established cascaded open
quantum systems formalism, which ensures both mathematical consistency and physical fidelity. Remarkably, we surpass the previously reported fourfold
benchmark, attaining a regime-independent sixteenfold steady-state nonreciprocal energy advantage over reciprocal systems. We further uncover a dissipation-dependent battery-to-charger efficiency, fourfold under symmetric damping, surpassing this
benchmark when the battery is less dissipative, and lower otherwise. This work establishes the cascaded formalism as a mathematically rigorous and experimentally viable foundation for high-performance
quantum energy storage.
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Disordered Systems and Neural Networks · Cross-listed from math-ph
Wasserstein Stability, Couplings Across Volumes, and the $1+1/d$ Moment Thresholds in the Edwards–Anderson Model
Mauris Chueng, Hexiang Wang and Keheng Zhu
We study the quenched pressure of the nearest-neighbor Edwards–Anderson Ising model with free and periodic boundary conditions. First, we prove that the infinite-volume pressure is $\beta d$-Lipschitz in the coupling law for the $1$-Wasserstein distance, yielding quantitative thermodynamic limits for spatially inhomogeneous disorder. Second, for periodic volumes, we prove that almost-sure convergence under every joint coupling of the finite-volume disorder arrays is equivalent to complete convergence of the one-volume pressure laws. Third, we prove that $\mathbb{E}\vert{}J\vert{}^{1+1/d}<\infty$ guarantees this universal-coupling conclusion. We further show that this exponent is optimal among uniform power-moment assumptions: for every $1\leq q<1+1/d$, there is a centered symmetric law with finite $q$-th moment for which canonical nested volumes converge almost surely, whereas independently resampled volumes with the same fixed-volume marginals converge in probability but not almost surely. Finally, in dimension one, we prove that the first-moment condition is also necessary for a finite limiting pressure.
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Materials Science
Automated Generation of Commensurate Magnetic Structures based on Spin Space Groups and Graph Theory
Yifan Wang, Boyang Deng, John Robertson et al. (+3 more)
Magnetic structures with
symmetry constraints are candidates for energetically favorable configurations. Enumerating these structures is essential for identifying experimental observations and provides unbiased, linearly stable, and optimally sampled reference configurations for energy fitting when extracting
spin interactions. We present SpinGraph, an automated workflow generating
symmetry-distinct
magnetic configurations. SpinGraph is not only compatible with the more general
spin space groups, but also allows precise control of the prescribed single- or multi-Q states superposition. For finite groups, we enumerate compatible subgroups directly. For
spin space groups with a continuous or special
spin-only part, the finite component is enumerated first and then combined with the compatible exact
spin-only constraints. These actions are translated into graph constraints in real or
Fourier space. The
symmetry of every generated structure is re-evaluated after construction. Finally, we integrate SpinGraph with the
magnetic analysis code AMATIS to perform a thorough calculation for the
spin interactions of the insulating monolayer CrI3. SpinGraph complements the last part of AMATIS and realizes the fully automated workflow for the
spin Hamiltonian construction, which is essential for studying phase transitions,
spin textures,
magnons, and
spin dynamics.
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All authors Yifan Wang, Boyang Deng, John Robertson, Weisheng Zhao, Stefan Blügel, Haichang Lu
Other Condensed Matter
Microscopic Understanding of Thermal-magnon Transport in Low-damping Ferrimagnetic Thin Films
Lerato Takana, Katya Mikhailova, Junwei Tong et al. (+9 more)
Thermally generated
magnons enable heat-driven
spin transport in
magnetic insulators, yet the relative importance of multiple microscopic mechanisms governing their propagation remains incompletely understood. Here, we investigate thermal
magnon transport in low-damping Li$_{0.5}$Al$_{1.0}$Fe$_{1.5}$O$_4$/Pt nanodevices using a nonlocal
spin Seebeck geometry that separates
magnon transport from local thermoelectric effects. Thermal imaging establishes a detector region outside the thermal healing length, enabling intrinsic nonlocal measurements. We find that thermal
magnon transport is strongly suppressed by
magnetic fields far above saturation, and further that thermal
magnon transport decreases with increasing temperature despite an increasing
magnon population. Brillouin light scattering reveals the key microscopic mechanism driving this effect: increasing field reduces the group velocity of backward volume
magnons, directly reducing the
magnon spin diffusion length. Micromagnetic simulations reproduce this behavior only when a temperature-dependent exchange stiffness is included. These results identify
magnon group velocity and exchange stiffness as key parameters governing thermal
magnon transport in ferrimagnetic thin films.
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All authors Lerato Takana, Katya Mikhailova, Junwei Tong, Xiangcheng Liu, Kwangyul Hu, Juan Hofer, Guanxiong Qu, Clare Yu, Ivan Schuller, Michael Flatté, Xiaoqin Li, Yuri Suzuki
Soft Condensed Matter
Geodesic Trapping and Escape of Active Particles on Curved Surfaces
Yuzhu Chen, Vishal P. Patil and David Saintillan
Active particles on curved surfaces can become trapped along closed geodesics even without physical barriers. We show that escape from these
geometric traps exposes a fundamental distinction between continuous and discrete reorientation. At high Péclet numbers, active Brownian particles escape efficiently through rotational
diffusion, whereas run-and-tumble particles remain trapped much longer; at low Péclet numbers, both reduce to passive
diffusion. Gaussian
curvature controls escape by focusing or defocusing neighboring geodesics, producing distinct asymptotic scalings of the mean exit time.
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Statistical Mechanics
Renewal process's guide to fractional Navier-Stokes equations
Hong Zhang
The Navier-Stokes equations, which remain unsolved, are crucial equations in fluid mechanics. Discovering the solutions to the Navier-Stokes equations is one of the challenging Millennium problems. In 1900,
Hilbert proposed a potential approach to tackle this problem by establishing the relationship between microscopic dynamics and the macroscopic continuum equations. The key bridge is the derivation of Boltzmann equation and the theory of probability. In this paper, we shall use the collision renewal process with arbitrarily distributed waiting times to derive the Boltzmann equation for the time
evolution of the probability of the velocity and the displacement of the particle, based on which we prove that the renewal process with exponential collision waiting time is equivalent to the classical Navier-Stokes equations, and that with power-law waiting time is equivalent to the fractional Navier-Stokes equations. Since the collision renewal process with arbitrarily distributed waiting times is a random process and is easy to perform the
stochastic simulations of trajectories to obtain the corresponding solution, we actually find a
stochastic approach to solve the classical and fractional Navier-Stokes equations.
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Superconductivity
Eight-unit-cell electronic modulations in cuprates originating from local molecular orbitals
Zhiheng Yao, Sixuan Chen, Jianfa Zhao et al. (+10 more)
The pair density wave (PDW) state with eight-unit-
cell (8a0) periodicity has been widely regarded as the primary order in cuprates, yet its existence and origin remain subjects of intense debate. Using spectroscopic imaging scanning tunneling microscopy, we observe spatial modulations of the electronic states with approximately 8a0 periodicity in both the superconducting and insulating regimes of hole-doped Ca2CuO2Cl2 cuprate. We find that the 8a0 spatial patterns are generated by the formation of molecular orbitals by doped holes, which organize into 4a0*4a0 plaquettes as the basic unit. Our results identify the 4a0 molecular orbital as the fundamental electronic building block in cuprates, while the 8a0 PDW represents a spatial subharmonic that emerges at sufficiently high doping.
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All authors Zhiheng Yao, Sixuan Chen, Jianfa Zhao, Shusen Ye, Weixiang Qu, Ning Xia, Yuling Dai, Luchuan Shi, Hongrui Zhang, Zhenqi Hao, Changqing Jin, Shuo Yang, Yayu Wang
Materials Science
Twist and strain identification in moiré heterostructures
Zhen Zhan, Federico Escudero, Dong Wang et al. (+4 more)
The geometrical and electronic properties of moiré materials are highly sensitive to the twist and strain in the samples due to the moiré magnifying effect. Accurate identification of twist and strain in moiré materials is therefore essential. In this work, we establish a general framework to extract the twist and strain configurations from moiré images with either atomic or moiré scale resolution. With only moiré-wavelength information, we show that there is a continuous family of possible twist and strain configurations, each one accounting for different orientations of the moiré pattern. To estimate the most likely twist-strain configuration, we discuss additional constraints and methods involving the minimum elastic energy and the electronic spectra. The minimum elastic energy, in particular, reflects that shear configurations become much more favorable as the strain increases. As an example of the developed methodology, we discuss the formation and identification of strained triangular moiré patterns. Our framework provides a comprehensive approach to identify the twist and strain configurations in systems with moiré-scale resolution.
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All authors Zhen Zhan, Federico Escudero, Dong Wang, Yiwen Liu, Ambikesh Gupta, Pierre A. Pantaleón, Francisco Guinea
Strongly Correlated Electrons · Cross-listed from quant-ph
Convex-Gaussianity of fermionic Gibbs states in perturbation theory
Kaifeng Bu and Yuanjie Ren
We study the structure of Gibbs states in weakly perturbed interacting fermionic systems. First, for a sparse
Hamiltonian $H=H_0+V$ with a quadratic term $H_0$ and a non-quadratic perturbation $V$ of scale $\epsilon$, we show that the Gibbs state $\rho_{\beta}$ decomposes into a convex combination of Gaussian states whenever the inverse temperature satisfies $\beta \le O(\log(1/\epsilon))$. Moreover, we prove that this bound is asymptotically tight by establishing that $\beta \le \Theta(\log(1/\epsilon))$ is necessary for certain sparse
Hamiltonians. This general framework applies directly to the weak-coupling (small-$\vert{}U\vert{}$) regime of the Fermi–Hubbard model with hopping $t$ and on-site interaction $U$ on any graph of maximum degree $D$. Complementarily, in the strong-coupling (small-$\vert{}t\vert{}$) regime, we show that the Gibbs state remains convex-Gaussian up to $\beta \le O\big(\vert{}U\vert{}^{-1}\log(\vert{}U\vert{}/(D\vert{}t\vert{}))\big)$, revealing a mechanism for convex-Gaussianity distinct from the weak-coupling setting.
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