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Physics Condensed Matter

cond-mat Watch Condensed Matter

Tuesday 6 January

Statistical Mechanics

Propulsion dispersion mediated ordering transition in active particles

Debraj Dutta and Urna Basu

We show that dispersion in propulsion strength qualitatively alters collective behavior of active multi-particle systems interacting via short-range attractive potential, giving rise to novel ordered phases that combine spatial and orientational ordering. Considering a binary mixture of active Brownian particles with two distinct self-propulsion strengths, we find that, the interplay between interaction range, self-propulsion strengths and the relative numbers of the particles with different propulsion strengths can lead to three different phases, namely, a disordered one, and two ordered ones with partial and complete spatial and orientational ordering. The partially ordered phase is characterized by formation of a ring-like assembly of the slower particles while the faster particles diffuse randomly. Two concentric rings, comprising faster and slower particles, form in the fully ordered phase. Using the example of a truncated harmonic potential, we analytically characterize the phase boundaries and identify the associated order parameters. Our results demonstrate that propulsion dispersion provides a robust and novel route to collective ordering in attractive active matter.
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Materials Science

Interface-induced band bending and charge separation in all-organic ZnPc/F$_x$ZnPc heterostructures

Stephanie Amos, Neno Fuller, Wai-Lun Chan et al. (+1 more)

Organic semiconductors are attractive building blocks for electronic devices due to their low cost and flexibility. Furthermore, heterostructures with type-II band alignments can efficiently separate photogenerated charges via a charge transfer and separation process. Here, we use density functional theory (DFT) to investigate model interfaces formed by zinc phthalocyanine (ZnPc) and its fluorinated derivatives (F$_8$ZnPc and F$_{16}$ZnPc). We demonstrate that these interfaces not only exhibit a type-II band offset, but also band bending. The band bending causes both the LUMO and HOMO states to localize away from the interface. Therefore, the band bending creates a strong driving force for charge separation. We used ultraviolet photoemission spectroscopy (UPS) to experimentally confirm this predicted band bending. The wavefunction envelopes of vertically-stacked molecules resemble particle-in-a-box states, but this shape is lost when the molecules are staggered. These results elucidate how interface-induced band bending facilitates charge separation in all-organic heterostructures and suggest a design pathway toward improved performance in organic photovoltaic devices.
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All authors Stephanie Amos, Neno Fuller, Wai-Lun Chan, Hartwin Peelaers

Materials Science

Novel fast Li-ion conductors for solid-state electrolytes from first-principles

Tushar Singh Thakur, Loris Ercole and Nicola Marzari

We present a high-throughput computational screening for fast lithium-ion conductors to identify promising materials for application in all solid-state electrolytes. Starting from more than 30,000 Li-containing experimental structures sourced from Crystallography Open Database, Inorganic Crystal Structure Database and Materials Platform for Data Science, we perform highly automated calculations to identify electronic insulators. On these ~1000 structures, we use molecular dynamics simulations to estimate Li-ion diffusivities using the pinball model, which describes the potential energy landscape of diffusing lithium with accuracy similar to density functional theory while being 200-500 times faster. Then we study the ~60 most promising and previously unknown fast conductors with full first-principles molecular dynamics simulations at several temperatures to estimate their activation barriers. The results are discussed in detail for the 9 fastest conductors, including $Li_7NbO_6$ which shows a remarkable ionic conductivity of ~5 mS/cm at room temperature. We further present the entire screening protocol, including the workflows where the accuracy of the pinball model is improved self-consistently, necessary to automatically running the required calculations and analysing their results.
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Strongly Correlated Electrons

Higher-Dimensional Anyons via Higher Cohomotopy

Sadok Kallel, Hisham Sati and Urs Schreiber

We highlight that integer Heisenberg groups at level 2 underlie topological quantum phenomena: their group algebras coincide with the algebras of quantum observables of abelian anyons in fractional quantum Hall (FQH) systems on closed surfaces. Decades ago, these groups were shown to arise as the fundamental groups of the space of maps from the surface to the 2-sphere – which has recently been understood as reflecting an effective FQH flux quantization in 2-Cohomotopy. Here we streamline and generalize this theorem using the homotopy theory of H-groups, showing that for $k \in \{1,2,4\}$, the non-torsion part of $\pi_1 \mathrm{Map}\big({(S^{2k-1})^2, S^{2k}}\big)$ is an integer Heisenberg group of level 2, where we identify this level with 2 divided by the Hopf invariant of the generator of $\pi_{4k-1}(S^{2k})$. This result implies the existence of higher-dimensional analogs of FQH anyons in the cohomotopical completion of 11D supergravity ("Hypothesis H").
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Strongly Correlated Electrons

Phase diagram and macroscopic ground state degeneracy of frustrated spin-1/2 anisotropic Heisenberg model on diamond-decorated lattices

D. V. Dmitriev, V. Ya. Krivnov and O. A. Vasilyev

We study the ground state properties of the anisotropic spin-1/2 Heisenberg model on lattices built from ideal diamond units with competing ferro- and antiferromagnetic interactions. The study covers the one-dimensional diamond chain and its two- and three-dimensional generalizations. The ground-state phase diagram contains four distinct phases: ferromagnetic (F), critical (C), monomer-dimer (MD), and tetramer-dimer (TD), which converge at a quadruple point. We demonstrate the presence of macroscopic ground-state degeneracy and corresponding residual entropy, which is maximal at the quadruple point and also extends throughout the MD phase and its boundaries with TD and F phases. For the diamond chain, we derive exact degeneracies, while for higher-dimensional lattices, we map the problem onto a bond percolation model or used transfer-matrix approach, enabling the numerical computation of the ground state degeneracy.
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Soft Condensed Matter

An O(N) quasi-Ewald splitting method for nanoconfined electrostatics

Zecheng Gan, Xuanzhao Gao and Yuqing Li

Simulating the dynamics of charged particles in quasi-two-dimensional (quasi-2D) nanoconfined systems presents a significant computational challenge due to the long-range nature of electrostatic interactions and the geometric anisotropy. To address this, we introduce a novel quasi-Ewald splitting strategy tailored for particle-based simulations in such geometry. Our splitting strategy seamlessly integrates a collection of advanced numerical techniques, including optimal quadrature rules [L. N. Trefethen, SIAM Rev. 64(1)(2022), pp.132-150], fast pairwise kernel summation methods [S. Jiang and L. Greengard, Commun. Comput. Phys. 31(1)(2022), pp.1-26], and the random batch method with importance sampling in k-space [S. Jin, L. Li, Z. Xu et al., SIAM J. Sci. Comput. 43(4)(2021), pp.B937-B960]. The resulting algorithm achieves an O(N) overall computational complexity, where N denotes the total number of confined particles. Simulations of several prototype systems validate the accuracy and efficiency of our method. Furthermore, we present numerical observations specifically related to nanoconfined charged many-body systems, highlighting phenomena such as dielectric boundary effects, anisotropic diffusion, and the structure of the electrical double layer (EDL) under conditions of charge asymmetry.
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Mesoscale and Nanoscale Physics

Thermal conductance across bonded SiOx-SiOx interfaces in hybrid bonding process

Xingqiang Zhang, Liu Chang, Liyi Li et al. (+1 more)

Hybrid bonding is a pivotal technology for enabling three dimensional integrated circuits. Among the foremost challenges facing 3D IC implementation is thermal management, where a deep understanding of heat conduction across bonded interfaces is essential for addressing heat dissipation and reliability issues. Nevertheless, the thermal conductance of bonded dielectric-dielectric interfaces remains poorly understood. In this study, we employ the low-temperature bonding technique integral to hybrid bonding to fabricate SiO-SiO interfaces and investigate their thermal boundary conductance using time domain thermoreflectance. Structural characterizations show high quality bonded interfaces. By fitting the data with an equivalent multilayer thermal model, we establish a lower limit TBC of 150 MW/m2-K for the SiO-SiO interfaces, which corresponds to a thermal resistance lower than that of a 9.2-nm-thick dielectric layer. These findings offer valuable insights into thermal transport in hybrid-bonded structures and provide critical guidance for the thermal design of advanced packaging solutions.
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All authors Xingqiang Zhang, Liu Chang, Liyi Li, Zhe Cheng

Strongly Correlated Electrons

Intervalley Band Crossing and Transition of Fractional Chern Insulators in Floquet Twisted Bilayer MoTe$_2$

Yuhao Shi and Zhao Liu

We study the twisted MoTe$_2$ homobilayer coupled to periodic driving of a circularly polarized light (CPL). Using Floquet theory in the high-frequency limit, we start from the Dirac model including both the valence and conduction bands of monolayer MoTe$_2$ to derive an effective time-independent Floquet Hamiltonian. The photon processes coupling the valence and conduction bands are captured in this Floquet analysis, and the resulting Floquet Hamiltonian contains explicit time-reversal symmetry breaking terms that are absent if conduction bands are integrated out from the beginning of the derivation. Based on the Floquet Hamiltonian, we find the increase of CPL driving intensity can cause the crossing of Floquet bands and redistribution of holes between the two valleys. When interactions are included, a transition between Floquet Laughlin-type FCIs with different behaviors of valley polarization is identified at total hole filling $5/3$.
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Materials Science

Charge Transport in Thin-Film Transistors Based on Liquid-Crystalline Phthalocyanines

L. B. Avila, Zuchong Yang, Ilknur Hatice Eryilmaz et al. (+6 more)

We investigate a series of liquid-crystalline phthalocyanines (metal-free and Cu, Zn, Ni, Co complexes) by correlating their vibrational signatures with their electronic performance in organic thin-film transistors (OTFTs). Raman spectroscopy reveals metal-dependent distortions of the phthalocyanine macrocycle, reflected in systematic shifts of the C-N-C and M-N vibrational modes. When integrated into OTFTs, all compounds exhibit markedly enhanced current response under ultrahigh vacuum compared to an N2-rich environment, demonstrating that intrinsic charge transport is strongly suppressed by atmospheric species. Temperature-dependent measurements (100-300 K) show clear threshold-voltage shifts driven by deep interface and bulk traps, while all devices display thermally activated mobility with low activation energies (14-20 meV). These results highlight how mesomorphic order, metal coordination, and environmental conditions collectively govern charge transport in liquid-crystalline phthalocyanines, offering design guidelines for their use as orientable semiconducting materials in organic electronics.
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All authors L. B. Avila, Zuchong Yang, Ilknur Hatice Eryilmaz, Lilian Skokan, Leonardo N Furini, Andreas Ruediger, H. Bock, I.H. Bechtold, E. Orgiu

Mesoscale and Nanoscale Physics

Signatures of moiré intralayer biexcitons and exciton-phason coupling in WSe2/WS2 heterostructures

Ranju Dalal, Harsimran Singh, Rwik Dutta et al. (+6 more)

Interactions among electronic and lattice degrees-of-freedom are foundational to various phases in condensed-matter physics, yet the dynamic interplay between excitonic and phononic quasiparticles represents an equivalent, underexplored frontier. Moiré superlattices provide an ideal platform for realizing these interactions by offering localized intralayer excitons (IALX) and ultralow-energy collective lattice modes, such as phasons. Here, by optically suppressing ultrafast charge-transfer (CT) to interlayer excitons in WSe2/WS2 heterostructures, we uncover dynamics of moiré IALX revealing long lifetimes ({\tau} > 1000 ps) arising from localized Wannier and in-plane CT nature. We then observe moiré intralayer intervalley biexcitons with binding energy ~ 16 meV, with long lifetimes due to moiré confinement. Furthermore, we find time-domain signatures of strong coupling between moiré-IALX and ~ 10 micro-eV phasons, evidenced as twist-angle-dependent GHz oscillations in IALX dynamics. Our findings establish moiré superlattices as interacting hybrid quantum systems and for engineering non-equilibrium phenomena, as well as for GHz-scale optoelectronics.
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All authors Ranju Dalal, Harsimran Singh, Rwik Dutta, Hariharan Swaminathan, Kenji Watanabe, Takashi Taniguchi, Mit H Naik, Manish Jain, Akshay Singh

Strongly Correlated Electrons · Cross-listed from quant-ph

Who can compete with quantum computers? Lecture notes on quantum inspired tensor networks computational techniques

Xavier Waintal, Chen-How Huang and Christoph W. Groth

This is a set of lectures on tensor networks with a strong emphasis on the core algorithms involving Matrix Product States (MPS) and Matrix Product Operators (MPO). Compared to other presentations, particular care has been given to disentangle aspects of tensor networks from the quantum many-body problem: MPO/MPS algorithms are presented as a way to deal with linear algebra on extremely (exponentially) large matrices and vectors, regardless of any particular application. The lectures include well-known algorithms to find eigenvectors of MPOs (the celebrated DMRG), solve linear problems, and recent learning algorithms that allow one to map a known function into an MPS (the Tensor Cross Interpolation, or TCI, algorithm). The lectures end with a discussion of how to represent functions and perform calculus with tensor networks using the "quantics" representation. They include the detailed analytical construction of important MPOs such as those for differentiation, indefinite integration, convolution, and the quantum Fourier transform. Three concrete applications are discussed in detail: the simulation of a quantum computer (either exactly or with compression), the simulation of a quantum annealer, and techniques to solve partial differential equations (e.g. Poisson, diffusion, or Gross-Pitaevskii) within the "quantics" representation. The lectures have been designed to be accessible to a first-year PhD student and include detailed proofs of all statements.
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Mesoscale and Nanoscale Physics

Shubnikov-de Haas oscillations of two-dimensional electron gases in AlYN/GaN and AlScN/GaN heterostructures

Yu-Hsin Chen, Thai-Son Nguyen, Isabel Streicher et al. (+4 more)

AlYN and AlScN have recently emerged as promising nitride materials that can be integrated with GaN to form two-dimensional electron gases (2DEGs) at heterojunctions. Electron transport properties in these heterostructures have been enhanced through careful design and optimization of epitaxial growth conditions. In this work, we report for the first time Shubnikov-de Haas (SdH) oscillations of 2DEGs in AlYN/GaN and AlScN/GaN heterostructures, grown by metal-organic chemical vapor deposition. SdH oscillations provide direct access to key 2DEG parameters at the Fermi level: (1) carrier density, (2) electron effective mass (m* ~ 0.24 me for AlYN/GaN and m* ~ 0.25 me for AlScN/GaN), and (3) quantum scattering time (~ 68 fs for AlYN/GaN and ~ 70 fs for AlScN/GaN). These measurements of fundamental transport properties provide critical insights for advancing emerging nitride semiconductors for future high-frequency and power electronics.
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All authors Yu-Hsin Chen, Thai-Son Nguyen, Isabel Streicher, Jimy Encomendero, Stefano Leone, Huili Grace Xing, Debdeep Jena

Materials Science

Multiscale Experimental Evidence of a Transitory State in the HDA-LDA Transition in Alumino-sodo-silicate Glasses

Antoine Cornet, Thierry Deschamps, Sylvie Le Floch et al. (+2 more)

The structural evolution with temperature of pure silica (SiO2), sodium-silicate (5Na2O-95SiO2, 10Na2O-90SiO2 and 25Na2O-75SiO2) and albite (15Na2O-15Al2O3-75SiO2) glasses previously densified from hot compression is monitored with a combination of small and wide angle x-ray scattering. Transient scattering maxima in the length scales associated with both techniques indicate the presence of a transitory state, suggesting the classification of the initial and final states as distinct glass states in the context of polyamorphism. In all glasses, a transient intensity peak in the small angle scattering is observed, consistent with the nucleation of a new amorphous state. Based on a comparison with the phenomenology observed in supercooled and glassy water, we propose that this structural evolution provide a strong evidence of the glass polyamorphism as the consequence of the existence of an underlying but thermodynamically defined liquid-liquid transition, independent on the polymerization degree of the system.
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All authors Antoine Cornet, Thierry Deschamps, Sylvie Le Floch, Dominique de Ligny, Christine Martinet

Materials Science

Many-electron systems with fractional electron number and spin: exact properties above and below the equilibrium total spin value

Yuli Goshen and Eli Kraisler

In this work, we analyze the fundamental question of what is the ensemble ground state of a general, finite, many-electron system at zero temperature, with a given, possibly fractional, electron number $N_{tot}$ and a given $z$-projection of the spin, $M_{tot}$, distinguishing between low- and high-spin cases. For the low-spin case, the general form of the ensemble ground state has been rigorously derived in J. Phys. Chem. Lett. 15, 2337 (2024), finding the presence of an ambiguity in the ground state. Here we further discuss this ambiguity, and show that it can be removed via maximization of the entropy. For the high-spin case, we find that the form of the ensemble ground state strongly depends on the system in question. Furthermore, we prove three general properties which characterize the ensemble, and narrow the list of pure states it may consist of. We relate the frontier Kohn-Sham orbital energies to total energy differences, providing a generalization of the ionization potential theorem to systems with arbitrary fractional $M_{tot}$. Furthermore, we derive expressions for new derivative discontinuities, which appear as jumps in the KS potentials when crossing a boundary in the $N_{\uparrow}$-$N_{\downarrow}$ plane. Our analytical results are supported by an extensive numerical analysis of the Atomic Spectra Database of the National Institute of Standards. The new exact conditions for many-electron systems derived in this work are instrumental for development of advanced approximations in density functional theory and other many-electron methods.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Entanglement signatures of quantum criticality in Floquet non-Hermitian topological systems

Siyuan Cheng, Rui Xie, Xiaosen Yang et al. (+2 more)

The entanglement entropy can be an effective diagnostic tool for probing topological phase transitions. In one-dimensional single particle systems, the periodic driving generates a variety of topological phases and edge modes. In this work, we investigate the topological phase transition of the one-dimensional Floquet Su-Schrieffer-Heeger model using entanglement entropy, and construct the phase diagram based on entanglement entropy. The entanglement entropy exhibits pronounced peaks and follows the logarithmic scaling law at the phase transition points, from which we extract the central charge $c=1$. We further investigate the entanglement spectrum to accurately distinguish the different topological phases. In addition, the coupling between zero and $\pi$ modes leads to characteristic splittings in the entanglement spectrum, signaling their hybridization under periodic driving. These results remain robust in non-Hermitian regimes and in the presence of next-nearest-neighbor hopping, demonstrating the reliability and universality of entanglement entropy as a diagnostic for topological phase transitions.
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All authors Siyuan Cheng, Rui Xie, Xiaosen Yang, Yuee Xie, Yuanping Chen

Strongly Correlated Electrons

Electron pairing in model with two overlapping bands

Igor N. Karnaukhov

We consider the two-band Hubbard model, where electrons from different bands interact through an on-site one- and two-particle hybridization. The proposed Hamiltonian makes it possible to construct an effective theory and answer the question of the nature of pairing: conduction electrons form pairs due to two-particle hybridization of electrons from different bands, compensating for the direct Hubbard repulsion between conduction electrons. It is shown that an effective attraction between conduction electrons leads to $\eta$-pairing. The electron-electron pairing mechanism explains the presence of superconductivity at high temperatures experimentally observed in hydrogen-rich materials at high pressure.
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Superconductivity

Enhanced Electron-Phonon Coupling and Superconductivity in Ba-Alloyed A15 LaH5.75

Jakkapat Seeyangnok, Udomsilp Pinsook and Graeme J Ackland

Recent experiments have established rare earth A15 type hydrides as a distinct family of high temperature superconductors that can be stabilized at significantly lower pressures compared to other superconducting hydrides. In particular, A15 type LaH5.75 was recently shown to be a high Tc superconductor. We have investigated a range of ternary substitutions and demonstrate that partial substitution of La by Ba stabilizes the A15 hydride lattice, with La0.75Ba0.25H5.75 identified as a stable compound. We calculate a superconducting transition temperature of approximately 183 K, almost double that of LaH5.75 at similar pressures. Ba typically acts as a 2 plus ion, while La is 3 plus. The reduced electron count disrupts the formation of H2 units and shifts the Fermi surface, leading to strongly enhanced electron phonon coupling. By contrast, substitution with Hf fails to produce any stable compounds. This work extends emerging alloy design principles in A15 hydride superconductors, demonstrating that doping can shift the Fermi level and tune the strength of the electron phonon coupling. These results provide concrete guidance for the experimental realization of new high Tc phases.
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Strongly Correlated Electrons

Soliton Pumping in the Rice-Mele Model with On-Cell Kerr Nonlinearity

Zhe Wang, Xi-Wang Luo, Bo-Ye Sun et al. (+1 more)

We investigate the Rice-Mele model with on-cell Kerr-type nonlinearities, where the interaction depends on the total particle number within each unit cell rather than on individual sites. This interaction enables a nontrivial interplay between topology and nonlinear dynamics in soliton pumping. In the weakly interacting regime, the ground-state soliton undergoes quantized Thouless pumping. At intermediate interaction strengths, soliton creation and annihilation break adiabaticity and disrupt quantized transport. In the strong-coupling regime, the coexistence of ground- and excited-state solitons leads to negligible coupling at energy crossings, giving rise to discrete time-translation symmetry breaking (DTTSB) in the soliton dynamics. Comparison of mean-field results with exact diagonalization along closed circular pumping paths confirms both the validity of the mean-field description and the robustness of DTTSB across different pumping trajectories. Our findings reveal how interaction-induced effects can fundamentally modify topological transport and suggest that these phenomena may be explored in cold-atom, photonic, and superconducting-circuit platforms.
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All authors Zhe Wang, Xi-Wang Luo, Bo-Ye Sun, Zheng-Wei Zhou

Superconductivity

Charge Density Wave Order and Superconductivity in Janus MoXH Monolayers

Jakkapat Seeyangnok, Udomsilp Pinsook and Graeme J Ackland

Two-dimensional Janus hydrogenated transition metal chalcogenides provide an unusual platform where lattice instabilities, electron-phonon coupling, and superconductivity are strongly intertwined. Using first-principles calculations, we demonstrate that Janus 2H and 1T MoXH (X = S, Se) monolayers host an intrinsic, commensurate charge density wave (CDW) ground state originating from soft phonon modes at the Brillouin zone M point. Real-space supercell optimizations confirm that the CDW reconstruction lowers the total energy and fully stabilizes the lattice, eliminating the imaginary phonon modes present in the high-symmetry metallic structures. Analysis of the electronic susceptibility shows that the CDW instability is not driven by Fermi surface nesting, but instead arises from strong electron-phonon coupling. We further reveal a material-dependent interplay between CDW order and superconductivity. In 1T MoSH, CDW formation enhances low-energy phonon contributions and strengthens electron-phonon coupling, leading to an increased superconducting transition temperature. In contrast, for 1T MoSeH and 2H MoSeH, the CDW phase suppresses electron-phonon coupling and reduces superconductivity. Finally, we show that thermal fluctuations, compressive strain, and carrier doping can selectively suppress CDW order and restore superconductivity. These results establish Janus MoXH monolayers as a tunable two-dimensional system for exploring lattice-driven charge ordering and its competition with superconductivity.
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Materials Science

DeepH-pack: A general-purpose neural network package for deep-learning electronic structure calculations

Yang Li, Yanzhen Wang, Boheng Zhao et al. (+15 more)

In computational physics and materials science, first-principles methods, particularly density functional theory, have become central tools for electronic structure prediction and materials design. Recently, rapid advances in artificial intelligence (AI) have begun to reshape the research landscape, giving rise to the emerging field of deep-learning electronic structure calculations. Despite numerous pioneering studies, the field remains in its early stages; existing software implementations are often fragmented, lacking unified frameworks and standardized interfaces required for broad community adoption. Here we present DeepH-pack, a comprehensive and unified software package that integrates first-principles calculations with deep learning. By incorporating fundamental physical principles into neural-network design, such as the nearsightedness principle and the equivariance principle, DeepH-pack achieves robust cross-scale and cross-material generalizability. This allows models trained on small-scale structures to generalize to large-scale and previously unseen materials. The toolkit preserves first-principles accuracy while accelerating electronic structure calculations by several orders of magnitude, establishing an efficient and intelligent computational paradigm for large-scale materials simulation, high-throughput materials database construction, and AI-driven materials discovery.
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All authors Yang Li, Yanzhen Wang, Boheng Zhao, Xiaoxun Gong, Yuxiang Wang, Zechen Tang, Zixu Wang, Zilong Yuan, Jialin Li, Minghui Sun, Zezhou Chen, Honggeng Tao, Baochun Wu, Yuhang Yu, He Li, Felipe H. da Jornada, Wenhui Duan, Yong Xu

Strongly Correlated Electrons

ESR Investigations of the Magnetic Anisotropy in $\kappa$-(BETS)$_2$Mn[N(CN)$_{2}$]$_3$

Zhijie Huang, Marvin Schmidt, Savita Priya et al. (+3 more)

The two-dimensional molecular conductor $\kappa$-(BETS)$_2$Mn[N(CN)$_2$]$_3$ has been studied because of the intriguing magnetic coupling of the molecular $\pi$-electrons to the Mn$^{2+}$ ions. Utilizing X-band electron spin resonance spectroscopy we have performed comprehensive investigations of the magnetic properties, in particular on the temperature and angular dependences of the spin susceptibility, the $g$-factor and the linewidth. Due to the $\pi$-$d$-coupling, a rearrangement of the $\pi$-spins occurs: At low temperatures the $g$-factor shifts enormously with a pronounced in-plane anisotropy that flips as the temperature decreases; the lines broaden significantly; and the spin susceptibility increases upon cooling with a kink at the phase transition. By carefully analyzing the angular dependence of $g(\theta)$ and $\Delta H(\theta)$ we reveal the influence of anisotropic Zeeman interaction in addition to spin-phonon coupling. We conclude the presence of two magnetically distinct BETS chains and discuss the possibility of altermagnetic order.
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All authors Zhijie Huang, Marvin Schmidt, Savita Priya, Mark Kartsovnik, Natalia Kushch, Martin Dressel

Statistical Mechanics · Cross-listed from math.PR

Dimension-decaying diffusion processes as the scaling limit of condensing zero-range processes

Johel Beltrán, Kyuhyeon Choi and Claudio Landim

In this article, we prove that, on the diffusive time scale, condensing zero-range processes converge to a dimension-decaying diffusion process on the simplex \[ \Sigma = \{(x_1,\dots,x_S) : x_i \ge 0,\; \sum_{i\in S} x_i = 1\}, \] where $S$ is a finite set. This limiting diffusion has the distinctive feature of being absorbed at the boundary of the simplex. More precisely, once the process reaches a face \[ \Sigma_A = \{(x_1,\dots,x_S) : x_i \ge 0,\; \sum_{i\in A} x_i = 1\}, \qquad A \subset S, \] it remains confined to this set and evolves in the corresponding lower-dimensional simplex according to a new diffusion whose parameters depend on the subset $A$. This mechanism repeats itself, leading to successive reductions of the dimension, until one of the vertices of the simplex is reached in finite time. At that point, the process becomes permanently trapped. The proof relies on a method to extend the domain of the associated martingale problem, which may be of independent interest and useful in other contexts.
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Statistical Mechanics

Data-driven Reduction of Transfer Operators for Particle Clustering Dynamics

Nathalie Wehlitz, Grigorios A. Pavliotis, Christof Schütte et al. (+1 more)

We develop an operator-based framework to coarse-grain interacting particle systems that exhibit clustering dynamics. Starting from the particle-based transfer operator, we first construct a sequence of reduced representations: the operator is projected onto concentrations and then further reduced by representing the concentration dynamics on a geometric low-dimensional manifold and an adapted finite-state discretization. The resulting coarse-grained transfer operator is finally estimated from dynamical simulation data by inferring the transition probabilities between the Markov states. Applied to systems with multichromatic and Morse interaction potentials, the reduced model reproduces key features of the clustering process, including transitions between cluster configurations and the emergence of metastable states. Spectral analysis and transition-path analysis of the estimated operator reveal implied time scales and dominant transition pathways, providing an interpretable and efficient description of particle-clustering dynamics.
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All authors Nathalie Wehlitz, Grigorios A. Pavliotis, Christof Schütte, Stefanie Winkelmann

Materials Science

Surface reconstruction-driven band folding and spin-orbit enhancement at the $\alpha$-antimonene/Au(111) interface

Thomas Pierron, José de Jesùs Villalobos Castro, Etienne Barre et al. (+9 more)

The electronic properties of the two-dimensional (2D) $\alpha$ phase of antimonene are unique, featuring unpinned Dirac cones that can be moved with strain. Here we investigate the structural and electronic properties of an epitaxial 2D $\alpha$-antimonene, grown on Au(111). Using angle-resolved photoemission spectroscopy and density-functional theory, we reveal a strong hybridization at the Sb/Au interface, which imprints a rectangular reconstruction in the Au states, producing a band folding and hybrid bands exhibiting trigonal pockets. Additionally, hybridization displaces part of the Au wavefunction in regions of large electrostatic potential gradient, thereby enhancing spin-orbit splitting. Our work underscores that the pristine electronic properties of $\alpha$-antimonene may be deeply modified by its substrate, and even overwhelmed by the bands of the latter, and also shows that spin-orbit interaction in a heavy metal (Au) can be substantially enhanced by a lighter element (Sb).
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All authors Thomas Pierron, José de Jesùs Villalobos Castro, Etienne Barre, Dan Wang, Stephane Pons, Dimitri Roditchev, Azzedine Bendounan, Valerie Guisset, Philippe David, Johann Coraux, Lorenzo Sponza, Sergio Vlaic

Materials Science

Strain Engineering of Intrinsic Anomalous Hall and Nernst Effects in Altermagnetic MnTe at Realistic Doping Levels

Weiwei Chen, Ziyu Zhou, Jie Meng et al. (+3 more)

Hexagonal MnTe has emerged as a prototypical g-wave altermagnet, hosting time-reversal symmetry breaking in momentum space despite a vanishing net magnetization. While this symmetry breaking theoretically allows for an intrinsic anomalous Hall effect, experimentally observed signals have remained weak. In this work, we investigate the origin of this suppression and demonstrate a strategy to amplify anomalous transport responses within the experimentally accessible doping regime. Using a $\bm{k}\cdot\bm{p}$ effective model, we reveal that near the valence band maximum, which corresponds to the energy window relevant for typical hole doping ($\sim10^{19}cm^{-3}$), the intrinsic Hall effect is suppressed due to a symmetry-enforced cancellation of opposing Berry curvature contributions. We propose that breaking the crystalline symmetry via volume-conserving biaxial strain lifts this cancellation, resulting in a significant enhancement of the anomalous Hall conductivity by orders of magnitude. This strain-induced Fermi surface distortion also amplifies the anomalous Nernst effect. Furthermore, the analysis of the spin texture confirms that these strain-enabled anomalous transport signatures emerge while preserving the zero net magnetization.
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All authors Weiwei Chen, Ziyu Zhou, Jie Meng, Weiyi Wang, Ye Yang, Zhongjun Li

Materials Science

Observation of spin-valley locked nodal lines in a quasi-2D altermagnet

Quanxin Hu, Xingkai Cheng, Qingchen Duan et al. (+19 more)

The interplay among quantum degrees of freedom-spin, orbital and momentum-has emerged as a fertile ground for realizing magnetic quantum states with transformative potential for electronic and spintronic technologies. Prominent examples include ferromagnetic Weyl semimetals and antiferromagnetic axion insulators. Recently, altermagnets(AMs) have been identified as a distinct spin-splitting class of collinear antiferromagnets(AFMs), characterized by crystal symmetry that connects magnetic sublattices in real space and enforces C-paired spin-momentum locking in reciprocal space. These materials combine the advantages of nonrelativistic spin-polarization akin to FMs and vanished net-magnetization as AFMs, making them highly promising for spintronic applications. Furthermore, they introduce nontrivial spin-momentum locking spin texture as an additional degree of freedom for realizing novel quantum phases. In this work, we report the discovery of a new type of spin-valley-locked nodal line phase in the layered AM Rb-intercalated V{_2}Te{_2}O. By combining high-resolution spin and angle-resolved photoemission spectroscopy with first-principles calculations, we observe the coexistence of both spinless and spinful nodal lines near the Fermi level. Remarkably, the spinful nodal lines exhibit uniform spin polarization within each valley, while displaying opposite spin polarizations across symmetry-paired valleys-a unique feature we term spin-valley-locked nodal lines, which is exclusive to AMs. Direct measurements of out-of-plane band dispersion using a side-cleaving technique reveal the two-dimensional nature of these nodal lines. Our findings not only unveil a previously unexplored topological phase in AMs where valley-locked spin as an additional quantum character but also establish RbV{_2}Te{_2}O as a promising platform for spintronics, valleytronics, and moire-engineered quantum devices.
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All authors Quanxin Hu, Xingkai Cheng, Qingchen Duan, Yudong Hu, Bei Jiang, Yusen Xiao, Yaqi Li, Mojun Pan, Liwei Deng, Changchao Liu, Guanghan Cao, Zhengtai Liu, Mao Ye, Shan Qiao, Zhanfeng Liu, Zhe Sun, Anyuan Gao, Yaobo Huang, Ruidan Zhong, Junwei Liu, Baiqing Lv, Hong Ding

Materials Science

Finite Element Simulation of NMC Particle Fracture during Calendering: a Route to Optimize Electrode Microstructures

Pierrick Guichard, Benoit Mathieu and Eric Woillez

Beyond active material intrinsic properties, the electrode manufacturing process is a crucial step to reach high energy density and long-life of Li-ion batteries. In particular, very high pressures are applied to the electrode during the calendering step, that directly influence the microstructure and the electrochemical performances. This article reports the first calendering simulation of a NMC cathode using a finite element method (FEM), including the post-fracturation behaviour of the secondary NMC particles. Calibrated with nano-indentation experiments, the mechanical model provides stress-strain predictions fully consistent with experimental data. On assemblies up to 100 particles, simulations reveal three calendering regimes along compression: particle rearrangement, moderatepressure fracturing, and complete crushing. The model shows the strong sensitivity of the electrode microstructure to the calendering pressure level, and can thus be used as a guidance in the multi-criteria optimization of the manufacturing process.
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Soft Condensed Matter

Interplay of Structure and Dynamics in Solid Polymer Electrolytes: a Molecular Dynamics Study of LiPF6/polypropylene carbonate

Amaury Coste, Thomas Meyer, Claire Villevielle et al. (+3 more)

Solid-state batteries (SSB) are emerging as next-generation electrochemical energy storage devices. Achieving high energy density in SSB relies on solid polymer electrolytes (SPE) that are electrochemically stable against both lithium metal and high-potential positive electrodes, two conditions that are difficult to satisfy without chemical degradation. In this work, molecular dynamics simulations are employed to investigate the relationship between structure and dynamics in carbonate-based SPE composed of polypropylene carbonate and lithium hexafluorophosphate (LiPF$_6$), at salt concentrations ranging from 0.32 to 1.21 mol$/$kg. Structural properties are analyzed under ambient pressure at the experimentally relevant temperature $T = 353$ K. Since the slow dynamical processes governing ion transport in these systems are inaccessible to direct molecular dynamics, transport properties are simulated at elevated temperatures up to 900 K and extrapolated to $T = 353$ K using Arrhenius behavior. The results reveal strong ionic correlations, a limited fraction of free ions, and a predominance of negatively charged clusters, especially at high salt concentration. At high temperature, the self-diffusion coefficient of Li$^+$ exceeds that of PF$_6^-$ due to weaker Li$^+$-carbonate and ion-ion interactions. However, at $T = 353$ K, Li$^+$ mobility becomes lower than that of the anion, consistent with typical experimental observations in SPE. As expected, the ionic conductivity $\sigma$ increases with temperature, while at $T = 353$ K it exhibits a maximum for salt concentrations between 1.0 and 1.1 mol$/$kg. Overall, the estimated physico-chemical parameters highlight the key role of ion correlations in SPE and suggest strategies to optimize electrolyte performance. The Arrhenius extrapolation approach used here provides valuable insight into ion transport mechanisms in solid polymer electrolytes.
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All authors Amaury Coste, Thomas Meyer, Claire Villevielle, Fannie Alloin, Stefano Mossa, Benoit Coasne

Materials Science

Hybrid Disclination Skin-topological Effects in Non-Hermitian Circuits

Boyuan Li, Zekun Huang, Wenao Wang et al. (+6 more)

The bulk-disclination correspondence (BDC) is a fundamental concept in Hermitian systems that has been widely applied to predict disclination states. Recently, disclination states have also been observed and experimentally verified in non-Hermitian systems with C6 lattice symmetry, where gain and loss are introduced to induce non-Hermiticity. In this Letter, we propose a non-Hermitian two-dimensional (2D) Su-Schrieffer-Heeger (SSH) disclination model with skin-topological (ST) disclination states, and calculate its biorthogonal Zak phase. Together with the real-space disclination index, we predict the emergence of disclination states in a C4-symmetric non-Hermitian lattice and the corresponding fractional charge. We also generalize the symmetry indicator within the biorthogonal framework to predict the anomalous filling near the disclination core. Experimentally, the model is implemented on a nonreciprocal circuit platform, where we analyze the impedance matrix characterized by complex eigenfrequencies and directly observe the ST disclination states. Our work further extends the bulk-disclination correspondence to the non-Hermitian realm.
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All authors Boyuan Li, Zekun Huang, Wenao Wang, Jiaxi Wang, Yu Chen, Shaojie Ma, Ce Shang, Tie Jun Cui, Shuo Liu

Materials Science

Anomalous Hall transport in Mn$_{3}$Sn$_{0.5}$X$_{0.5}$C (X = Ge and Zn)

Sunil Gangwar and C. S. Yadav

Mn-based antiperovskites that exhibit topological surface states show potential applications in spintronics, magnetoelectronics, and quantum devices owing to the interplay between magnetism and topology. In this family of compounds, Mn$3$SnC exhibits a concurrent ferromagnetic and antiferromagnetic ground state below $T \sim 285$ K, along with a Berry curvature driven anomalous Hall effect. Here, we report the anomalous Hall effect in Ge- and Zn-doped Mn$3$SnC compounds, namely Mn$3$Sn${0.5}$Ge${0.5}$C (MSGC) and Mn$3$Sn${0.5}$Zn${0.5}$C (MSZC). MSGC undergoes a paramagnetic to concurrent antiferromagnetic and ferromagnetic transition at $T_C \sim 300$ K, whereas MSZC exhibits a paramagnetic to ferromagnetic transition at $T_C \sim 240$ K, followed by a ferromagnetic to ferrimagnetic transition at $T_N \sim 170$ K. The electronic transport in these compounds is governed by electron-phonon and electron-magnon scattering and shows anomalous Hall resistivity $\rho^A_{xy}$. Our analysis indicates that the anomalous Hall effect arises from contributions of skew scattering and intrinsic Berry curvature mechanisms, with electron-phonon and electron-magnon scattering playing an important role in skew scattering at high temperatures. Ge and Zn doping in Mn$_3$SnC significantly enhances the anomalous Hall conductivity.
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