CMP Journal 2025-08-16
Statistics
Physical Review Letters: 6
arXiv: 53
Physical Review Letters
Novel Approach to Cosmological Nonlinearities as an Effective Fluid
Research article | Cosmology | 2025-08-15 06:00 EDT
Leonardo Giani, Rodrigo von Marttens, and Ryan Camilleri
We propose a two parameters extension of the flat $\mathrm{\Lambda }\mathrm{CDM}$ model to capture the impact of matter inhomogeneities on our cosmological inference. Non virialized but nonlinearly evolving overdense and underdense regions, whose abundance is quantified using the Press-Schechter formalism, are collectively described by two effective perfect fluids ${\rho }{\mathrm{c}}$, ${\rho }{\mathrm{v}}$ with nonvanishing equation of state parameters ${w}{\mathrm{c},\mathrm{v}}\ne 0$. These fluids are coupled to the pressureless dust, akin to an interacting DM-DE scenario. The resulting phenomenology is very rich, and could potentially address a number of inconsistencies of the standard model, including a simultaneous resolution of the Hubble and ${\sigma }{8}$ tensions. To assess the viability of the model, we set initial conditions compatible to the Planck 2018 best fit $\mathrm{\Lambda }\mathrm{CDM}$ cosmology and fit its additional parameters using SN Ia observations from DESY5, BAO distances from DESI DR2 and a sample of uncorrelated $f{\sigma }_{8}$ measurements. Our findings show that backreaction effects from the cosmic web could restore the concordance between early and late Universe cosmological probes.
Phys. Rev. Lett. 135, 071004 (2025)
Cosmology, Evolution of the Universe, Large scale structure of the Universe, Relativistic aspects of cosmology
Energy Transfer by Feebly Interacting Particles in Supernovae: The Trapping Regime
Research article | Novae & supernovae | 2025-08-15 06:00 EDT
Damiano F. G. Fiorillo, Tetyana Pitik, and Edoardo Vitagliano
Feebly interacting particles, such as sterile neutrinos, dark photons, and axions, can be abundantly produced in the proto-neutron star (PNS) formed in core-collapse supernovae (CCSNe). These particles can decay into photons or charged leptons, depositing energy outside the PNS. Strong bounds on new particles can thus be derived from the observed luminosity of CCSNe, with even tighter bounds obtained from low-energy SNe observations. For the first time we highlight that, at sufficiently large couplings, particle production outside the PNS must also be considered. Using the prototypical case of axions coupling to two photons, we show that at large couplings the energy transfer from PNS to its surroundings is diffusive rather than ballistic, substantially reducing the deposited energy. Our findings have implications for the parameter space of particles probed in beam dump experiments and for dark matter models involving a sub-GeV mediator.
Phys. Rev. Lett. 135, 071005 (2025)
Novae & supernovae, Particle astrophysics, Particle decays, Axion-like particles, Axions
Nonlinear Transverse Conductivity in Antiferroic Types of Magnetic Toroidal Metal
Research article | Electrical conductivity | 2025-08-15 06:00 EDT
T. Miyamoto, M. Shimozawa, S. Hosoi, M. Yatsushiro, K. Izawa, Y. Ōnuki, D. Aoki, and S. Hayami
We have performed careful measurements of nonlinear transverse conductivity (NLTC) at zero field in the intermetallic compound HoAgGe with two distinct magnetic toroidal (MT) structures. Below 7 K (MT1 phase), the NLTC signal becomes observable and significantly increases with decreasing temperature, whereas between 7 and 11.6 K (MT2 phase), it remains nearly zero. However, this result is incompatible with the previous research, which assigned the former and latter MT phases as antiferro- and ferro-MT structures, respectively. This discrepancy stems from an inappropriate assignment of MT structures in prior studies. Our analysis, based on multipole theory, redefines the MT1 and MT2 phases as ferri- and antiferro-MT structures, respectively, providing a coherent framework to explain the observed NLTC in HoAgGe. These findings not only establish NLTC as a robust diagnostic tool for identifying MT metals but also highlight its potential for exploring phenomena driven by the antiferroic interactions of MT dipoles.
Phys. Rev. Lett. 135, 076502 (2025)
Electrical conductivity, Hall effect, Transport phenomena, Intermetallic compounds, Kagome metal, Noncollinear magnets, Rare-earth magnetic materials, Strongly correlated systems, Hall bar, Liquid helium cooling, Resistivity measurements
Direct Evidence of Intrinsic Mott State and Its Layer-Parity Oscillation in a Breathing Kagome Crystal Down to Monolayer
Research article | Electronic structure | 2025-08-15 06:00 EDT
Huanyu Liu, Wenhui Li, Zishu Zhou, Hongbin Qu, Jiaqi Zhang, Weixiong Hu, Chenhaoping Wen, Ning Wang, Hao Deng, Gang Li, and Shichao Yan
We report direct spectroscopic evidence of correlation-driven Mott states in layered ${\mathrm{Nb}}{3}{\text{Cl}}{8}$ through combining scanning tunneling microscopy (STM) and dynamical mean-field theory. The Hubbard bands persist down to monolayer, providing the definitive evidence for the Mottness in ${\mathrm{Nb}}{3}{\text{Cl}}{8}$. While the size of the Mott gap remains almost constant across all layers, a striking layer-parity-dependent oscillation emerges in the local density of states (LDOS) between even ($n=2$, 4, 6) and odd layers ($n=1$, 3, 5), which arises from the dimerization and correlation modulation of the obstructed atomic states, respectively. Our conclusions are supported by a critical technical advance in atomic-scale LDOS mapping for highly insulating systems. This Letter provides the definitive experimental verification of correlation-driven Mott ground states in ${\mathrm{Nb}}{3}{\text{Cl}}{8}$, while establishing a general protocol for investigating the interplay of electronic correlation and interlayer coupling in layered insulators by using a low-temperature STM technique.
Phys. Rev. Lett. 135, 076503 (2025)
Electronic structure, Mott insulators, Dynamical mean field theory, Scanning tunneling spectroscopy
Hyperbolic Spin Liquids
Research article | Quantum error correction | 2025-08-15 06:00 EDT
Patrick M. Lenggenhager, Santanu Dey, Tomáš Bzdušek, and Joseph Maciejko
Hyperbolic lattices present a unique opportunity to venture beyond the conventional paradigm of crystalline many-body physics and explore correlated phenomena in negatively curved space. As a theoretical benchmark for such investigations, we extend Kitaev’s spin-$1/2$ honeycomb model to hyperbolic lattices and exploit their non-Euclidean space-group symmetries to solve the model exactly. We elucidate the ground-state phase diagram on the ${8,3}$ lattice and find a gapped ${\mathbb{Z}}_{2}$ spin liquid with Abelian anyons, a gapped chiral spin liquid with non-Abelian anyons and chiral edge states, and a Majorana metal whose finite low-energy density of states is dominated by non-Abelian Bloch states.
Phys. Rev. Lett. 135, 076604 (2025)
Quantum error correction, Quantum spin liquid, Crystalline systems, Quantum many-body systems, Topological materials, Bloch wave theory, Symmetries in condensed matter
Coherent Dynamics of Molecular Vibrations in Single Plasmonic Nanogaps
Research article | Frequency conversion | 2025-08-15 06:00 EDT
Fiona Bell, Lukas Jakob, Caleb Todd, Ishaan Lohia, Yeeun Roh, Rakesh Arul, and Jeremy J. Baumberg
Dipolar interactions among molecules in a plasmonic nanocavity extend vibrational coherence by counteracting dephasing from cavity coupling.
Phys. Rev. Lett. 135, 076901 (2025)
Frequency conversion, Nanoantennas, Nanophotonics, Phonons, Plasmonics, Quantum coherence & coherence measures, Ultrafast phenomena, Vibrational states
arXiv
Structural transition and possible pressure-induced superconductivity in a suboxide La$_5$Pb$_3$O
New Submission | Superconductivity (cond-mat.supr-con) | 2025-08-15 20:00 EDT
Jiaqiang Yan, David Singh, Bayram Saparov, Huibo Cao, Yejun Feng, Jinguang Cheng, Yoshia Uwatoko, David Mandrus
Here we report a structural phase transition and its possible competition with superconductivity in the suboxide La$ _5$ Pb$ _3$ O. Upon cooling through $ T_t$ = 225 K, La$ _5$ Pb$ _3$ O transforms from a high-temperature I4/mcm to a low-temperature P4/ncc structure in which La - Pb dimerization along the c-axis occurs. This transition is accompanied by anomalies in the temperature dependence of electrical resistivity and specific heat. High-pressure electrical transport measurements reveal that hydrostatic pressure suppresses the structural transition and possibly induces superconductivity with a maximum superconducting temperature of 10 K. Density functional theory calculations show minimal changes in the electronic density of states and no gap opening at $ E_F$ across $ T_t$ , suggesting that the transition is driven by bonding effects rather than Fermi surface instability. These findings establish La$ _5$ Pb$ _3$ O as a promising platform for exploring the interplay between weak structural transitions and superconductivity.
Superconductivity (cond-mat.supr-con), Materials Science (cond-mat.mtrl-sci)
9 figures, 9 pages
Emergent Interacting Phases in the Strong Coupling Limit of Twisted M-Valley Moiré Systems: Application to SnSe${}_2$
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-08-15 20:00 EDT
Ming-Rui Li, Dumitru Calugaru, Yi Jiang, Hanqi Pi, Ammon Fischer, Henning Schlömer, Lennart Klebl, Maia G. Vergniory, Dante M. Kennes, Siddharth A. Parameswaran, Hong Yao, B. Andrei Bernevig, Haoyu Hu
We construct an interacting Wannier model for both AA-stacked and AB-stacked twisted SnSe2, revealing a rich landscape of correlated quantum phases. For the AA-stacked case, the system is effectively described by a three-orbital triangular lattice model, where each orbital corresponds to a valley and exhibits an approximate one-dimensional hopping structure due to a new momentum-space non-symmorphic symmetry. By exploring the interacting phase diagram using a combination of theoretical methods, including Hartree-Fock mean-field theory and exact solutions of the spin model in certain limits, we identify several exotic quantum phases. These include a dimerized phase with finite residual entropy, valence bond solids, and quantum paramagnetism. In the AB-stacked case, the system realizes an interacting kagome lattice model, where the Wannier orbitals associated with the three valleys form three sublattices. In the strong coupling regime, we use cluster mean-field methods to demonstrate the emergence of a classical spin liquid phase due to the frustrated lattice structure. The high tunability of the moiré system, which allows control over both the filling and interaction strength (via twist angle), renders twisted SnSe2 a versatile platform for realizing a wide range of exotic correlated quantum phases.
Strongly Correlated Electrons (cond-mat.str-el), Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Materials Science (cond-mat.mtrl-sci)
72 pages, 42 figures
Physical Principles of Size and Frequency Scaling of Active Cytoskeletal Spirals
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-08-15 20:00 EDT
Aman Soni, Shivani A. Yadav, Chaitanya A. Athale
Cytoskeletal filaments transported by surface immobilized molecular motors with one end pinned to the surface have been observed to spiral in a myosin-driven actin ‘gliding assay’. The radius of the spiral was shown to scale with motor density with an exponent of -1/3, while the frequency was theoretically predicted to scale with an exponent of 4/3. While both the spiraling radius and frequency depend on motor density, the theory assumed independence of filament length, and remained to be tested on cytoskeletal systems other than actin-myosin. Here, we reconstitute dynein-driven microtubule spiraling and compare experiments to theory and numerical simulations. We characterize the scaling laws of spiraling MTs and find the radius dependence on force density to be consistent with previous results. Frequency on the other hand scales with force density with an exponent of ~1/3, contrary to previous predictions. We also predict that the spiral radius scales proportionally and the frequency scales inversely with filament length, both with an exponent of ~1/3. A model of variable persistence length best explains the length dependence observed in experiments. Our findings that reconcile theory, simulations, and experiments improve our understanding of the role of cytoskeletal filament elasticity, mechanics of microtubule buckling and motor transport and the physical principles of active filaments.
Soft Condensed Matter (cond-mat.soft), Biological Physics (physics.bio-ph), Biomolecules (q-bio.BM)
5 figures
Predicting First-Passage Dynamics in Disordered Systems Exactly: Application to Sparse Networks
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-08-15 20:00 EDT
Daniel Marris, Chittaranjan Hens, Subrata Ghosh, Luca Giuggioli
Quantifying how spatial disorder affects the movement of a diffusing particle or agent is fundamental to target search studies. When diffusion occurs on a network, that is on a highly disordered environment, we lack the mathematical tools to calculate exactly the temporal characteristics of search processes, instead relying on estimates provided by stochastic simulations. To close this knowledge gap we devise a general methodology to represent analytically the movement and search dynamics of a diffusing random walk on sparse graphs. We show its utility by uncovering the existence of a bi-modality regime in the time-dependence of the first-passage probability to hit a target node in a small-world network. By identifying the network features that give rise to the bi-modal regime, we challenge long-held beliefs on how the statistics of the so-called direct, intermediate, and indirect trajectories influence the shape of the resulting first-passage and first-absorption probabilities and the interpretation of their mean values. Overall these findings show that temporal features in first-passage studies can be utilised to unearth novel transport paradigms in spatially heterogeneous environments.
Statistical Mechanics (cond-mat.stat-mech)
19 pages inc. 12 sup. mat. with 6 figures
Group theory method for extracting order parameters from scanning tunneling microscopy data
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-08-15 20:00 EDT
Julian Ingham, Yu-Xiao Jiang, M. Zahid Hasan, Harley D. Scammell
Scanning tunneling microscopy (STM) is a powerful local probe of correlated electronic states. Here we present a group theoretical framework for the analysis of STM data, filtering STM images into components which provide a real space mapping of the local symmetry properties of the underlying density of states. Using this formalism, we show that certain kinds of symmetry breaking are impossible to resolve in the first Brillouin zone, due to symmetry restrictions we term ``Bragg peak extinctions’’ in analogy with related ideas in x-ray crystallography. We show extinct patterns of symmetry breaking can be resolved using sub-unit cell structure, and develop methodological details for the accurate extraction of this symmetry information. We illustrate our results on synthetic STM data for $ 2\times 2$ charge density waves on the kagome lattice, and on topographic data for kagome metal ScV$ _6$ Sn$ _6$ . Our results provide a powerful method for extracting symmetry insights from STM data, and provide constraints on when and how certain ground states are experimentally observable.
Strongly Correlated Electrons (cond-mat.str-el), Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Materials Science (cond-mat.mtrl-sci)
6+29 pages; 4+11 figures
Run-and-tumble dynamics with non-reciprocal transitions between three velocity states
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-08-15 20:00 EDT
Julio C. R. Romo-Cruz, Francisco J. Sevilla
We investigate the transport properties of active particles undergoing a three-state run-and-tumble dynamics in one dimension, induced by non-reciprocal transition rates between self-propelling velocity states $ {-v, 0, +v}$ that explicitly break microscopic reversibility. Departing from conventional reciprocal models, our formulation introduces a minimal yet rich framework for studying non-equilibrium transport driven by internal state asymmetries. Using kinetic Monte Carlo simulations and analytical methods, we characterize the particle’s transport properties across the transition-rates space. The model exhibits a variety of non-equilibrium behaviors, including ballistic transport, giant diffusion, and Gaussian or non-Gaussian transients, depending on the degree of asymmetry in the transition rates. We identify a manifold in transition-rate space where long-time diffusive behavior emerges despite the absence of microscopic reversibility. Exact expressions are obtained for the drift, effective diffusion coefficient, and moments of the position distribution. Our results establish how internal-state irreversibility governs macroscopic transport, providing a tractable framework to study non-equilibrium active motion beyond reciprocal dynamics.
Statistical Mechanics (cond-mat.stat-mech)
FreeBird.jl: An Extensible Toolbox for Simulating Interfacial Phase Equilibria
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-08-15 20:00 EDT
Ray Yang, Junchi Chen, Douglas Thibodeaux, Robert B. Wexler
We present this http URL, an extensible Julia-based platform for computational studies of phase equilibria at generic interfaces. The package supports a range of system configurations, from atomistic solid surfaces to coarse-grained lattice$ -$ gas models, with energies evaluated using classical interatomic potentials or lattice Hamiltonians. Both atomistic and lattice systems accommodate single- or multi-component mixtures with flexibly definable surface and lattice geometries. Implemented sampling algorithms include nested sampling, Wang$ -$ Landau sampling, Metropolis Monte Carlo, and, for tractable lattice systems, exact enumeration. Leveraging Julia’s type hierarchies and multiple dispatch, this http URL provides a modular interface that allows seamless integration of system definitions, energy evaluators, and sampling schemes. Designed for flexibility, extensibility, and performance, this http URL offers a versatile framework for exploring the thermodynamics of interfacial phenomena.
Statistical Mechanics (cond-mat.stat-mech), Materials Science (cond-mat.mtrl-sci), Chemical Physics (physics.chem-ph), Computational Physics (physics.comp-ph)
17 pages, 5 figures
Spin and thermal current scaling at a $Y$-junction of XX spin chains
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-08-15 20:00 EDT
Domenico Giuliano, Francesco Buccheri
We study the boundary phase diagram and the low-temperature heat and magnetization transport at a $ Y$ -junction of XX spin chains.
Depending on the magnetization axis anisotropy between the magnetic exchange interactions at the junction, the system exhibits two different strong-coupling regimes at low energies/temperatures, similar to the overscreened (topological) four- and to the two-channel Kondo fixed points. Using renormalization group arguments combined with boundary conformal field theory methods, we show the instability of the former under any XY-type anisotropy at the junction. We analyze the low-temperature spin and the heat conductances. We find evidence of spin fractionalization of the elementary excitations at the four-channel Kondo fixed point by means of the magnetic Wiedemann-Franz law. We caution that the instability under XY anisotropy may hinder the detection of the phenomenology related to the four-channel Kondo effect, therefore requiring careful control in experimental realizations.
Strongly Correlated Electrons (cond-mat.str-el)
20 pages, 4 .eps figures
Data-Driven Topological Analysis of Polymorphic Crystal Structures
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-08-15 20:00 EDT
Sourin Dey, Nicholas Miklaucic, Sadman Sadeed Omee, Rongzhi Dong, Lai Wei, Qinyang Li, Nihang Fu, Jianjun Hu
Polymorphism, the ability of a compound to crystallize in multiple distinct structures, plays a vital role in determining the physical, chemical, and functional properties of materials. Accurate identification and prediction of polymorphic structures are critical for materials design, drug development, and device optimization, as unknown or overlooked polymorphs may lead to unexpected performance or stability issues. Despite its significance, predicting polymorphism directly from a chemical composition remains a challenging problem due to the complex interplay between molecular conformations, crystal packing, and symmetry constraints. In this study, we conduct a comprehensive data-driven analysis of polymorphic materials from the Materials Project database, uncovering key statistical patterns in their composition, space group distributions, and polyhedral building blocks. We discover that frequent polymorph pairs across space groups, such as (71, 225), display recurring topological motifs that persist across different compounds, highlighting topology not symmetry alone as a key factor in polymorphic recurrence. We reveal that many polymorphs exhibit consistent local polyhedral environments despite differences in their symmetry or packing. Additionally, by constructing polyhedron connectivity graphs and embedding their topology, we successfully cluster polymorphs and structurally similar materials even across different space groups, demonstrating that topological similarity serves as a powerful descriptor for polymorphic behavior. Our findings provide new insights into the structural characteristics of polymorphic materials and demonstrate the potential of data mining and machine learning for accelerating polymorph discovery and design.
Materials Science (cond-mat.mtrl-sci)
Atomistic Description of Spin Crossover Under Pressure and its Giant Barocaloric Effect
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-08-15 20:00 EDT
S. Vela, J. Ribas-Ariño, S.P. Vallone, A.M. dos Santos, M.A. Halcrow, K.G. Sandeman
The pressure-dependent evolution of the spin crossover (SCO) transition has garnered significant interest due to its connection to the giant barocaloric effect (BCE) near room temperature. Pressure alters both the molecular and solid-state structures of SCO materials, affecting the relative stability of low- and high-spin states and, consequently, the transition temperature ($ T_{1/2}$ ). Crucially, the shape of the $ T_{1/2}$ vs. pressure curve dictates the magnitude of the BCE, making its accurate characterization essential for identifying high-performance materials. In this work, we investigate the nonlinear $ T_{1/2}$ vs. pressure behavior of the prototypical SCO complex [FeL$ _2$ ][BF$ _4$ ]$ _2$ [L = 2,6-di(pyrazol-1-yl)pyridine] using solid-state PBE+U computations. Our results unveil the mechanisms by which pressure influences its SCO transition, including the onset of a phase transition, as well as the key role of low-frequency phonons in the BCE. Furthermore, we establish a computational protocol for accurately modeling the BCE in SCO crystals, providing a powerful tool for the rapid and efficient discovery of new materials with enhanced barocaloric performance.
Materials Science (cond-mat.mtrl-sci), Strongly Correlated Electrons (cond-mat.str-el)
Main text: 8 pages, 7 figures (main text); Supporting information: 4 pages, 4 figures
Type-I Multiferroic VHfO$_4$ with Strain-Switchable Magnetic Orders and Magnetoelectric Coupling
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-08-15 20:00 EDT
Qisheng Yu, Boyu Liu, Hongjun Xiang, Shi Liu
Motivated by the complementary properties of vanadium-based ferromagnets and HfO$ _2$ -based ferroelectrics, we propose a novel multiferroic oxide, VHfO$ _4$ , through 50% Hf$ ^{4+}$ substitution with V$ ^{4+}$ in the ferroelectric $ Pca2_1$ phase of HfO$ _2$ . First-principles DFT calculations reveal that the $ Pca2_1$ -like VHfO$ _4$ phase exhibits dynamic stability and concurrent ferroic orders: robust ferroelectric polarization comparable to HfO$ _2$ and V-driven magnetism. Parallel tempering Monte Carlo simulations identify an antiferromagnetic ground state, while strain engineering enables tunable magnetoelectric coupling. Biaxial in-plane strain induces four magnetic states: intralayer FM/interlayer AFM, intralayer AFM/interlayer FM, spiral-like non-collinear order, and discrete alternating spin alignment. Critically, $ c$ -axis strain modulates magnetic energy landscapes, demonstrating electromechanical control of magnetism. This work establishes VHfO$ _4$ as a Type-I multiferroic with coexisting atomic-scale ferroic origins and strain-tunable cross-coupling, offering a platform for voltage-controlled spintronics devices.
Materials Science (cond-mat.mtrl-sci), Computational Physics (physics.comp-ph)
EDIS: A Simulation Software for Dynamic Ion Intercalation/Deintercalation Processes in Electrode Materials
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-08-15 20:00 EDT
Liqi Wang, Ruijuan Xiao, Hong Li
As the core determinant of lithium-ion battery performance, electrode materials play a crucial role in defining the battery’s capacity, cycling stability, and durability. During charging and discharging, electrode materials undergo complex ion intercalation and deintercalation processes, accompanied by defect formation and structural evolution. However, the microscopic mechanisms underlying processes such as cation disordering, lattice oxygen loss, and stage structure formation phenomena are still not fully understood. To address these challenges, we have developed the Electrode Dynamic Ion Intercalation/Deintercalation Simulator (EDIS), a software platform designed to simulate the dynamic processes of ion intercalation and deintercalation in electrode materials. Leveraging high-precision machine learning potentials, EDIS can efficiently model structural evolution and lithium-ion diffusion behavior under various states of charge and discharge, achieving accuracy approaching that of quantum mechanical methods in relevant chemical spaces. The software supports quantitative analysis of how variations in lithium-ion concentration and distribution affect lithium-ion transport properties, enables evaluation of the impact of structural defects, and allows for tracking of both structural evolution and transport characteristics during continuous cycling. EDIS is versatile and can be extended to sodium-ion batteries and related systems. By enabling in-depth analysis of these microscopic processes, EDIS provides a robust theoretical tool for mechanistic studies and the rational design of high-performance electrode materials for next-generation lithium-ion batteries.
Materials Science (cond-mat.mtrl-sci)
Universal intrinsic orbital dynamics from Berry curvature in electronic two-band systems
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-08-15 20:00 EDT
The geometric structure of quantum states plays a fundamental role in determining the intrinsic dynamics of electrons in solids. In this work, we study the geometric origin of orbital angular momentum and its transport in a general two-band electronic system. Without assuming any symmetry or dimensional constraints, we show that the orbital Berry curvature, which governs the orbital Hall effect, can be universally expressed as the product of the band energy and the square of the Berry curvature. This highlights the central role of Berry curvature in engineering orbital Hall responses. We also discuss the applicability of our framework by analyzing a realistic model. Our findings underscore the geometric universality of itinerant intrinsic orbital dynamics.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
8 pages, 2 figures, Accepted version to Physical Review B
Memory effects of a static magnetic field on Brownian motion and the question of the absence of classical magnetism
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-08-15 20:00 EDT
Vladimir Lisy, Jan Busa, Jana Tothova
The Bohr-van Leeuwen (BvL) theorem, stating the absence of classical magnetization in equilibrium, a fundamental result in the field of magnetic phenomena, was originally proved for an electron gas. In the present work, we deal with the problem of whether this theorem applies to particles undergoing a non-Markovian Brownian motion in a static magnetic field. We consider a charged Brownian particle (BP) immersed in a bath of neutral particles. Generalizing the Zwanzig-Caldeira-Legget theory to the presence of a static external magnetic field, we come to the equation of motion for the BP in the form of a generalized Langevin equation that accounts for memory effects in the dynamics of the system. By using its solutions for the displacement and velocity of the BP, we calculate the angular momentum for the Ornstein-Uhlenbeck thermal noise. At long times, when the system should reach equilibrium, this momentum and, consequently, the classical magnetic moment of the BP are nonzero, in contrast to the BvL theorem. With the help of analytical and precise numerical calculations for different sets of system parameters, a simple formula for the angular momentum has been deduced.
Soft Condensed Matter (cond-mat.soft)
The work presented at the 18th Czech and Slovak Conference on Magnetism, High Tatras, Slovakia, July 7-11, 2025
Colored Sandpile
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-08-15 20:00 EDT
After the introduction of sandpile model a number of different variants have been studied. In most of
these models sand particles are indistinguishable. Here we have painted the sand particles using a
few distinct colors, and restrict them to move in linear trajectories only along their assigned lattice axes,
one axis reserved for one color. Different colored particles interact among themselves through the
toppling of unstable sand columns. Consequently, the avalanches or in general the self-organization
processes in the sandpile has no overall preferred direction, though the individual particles
execute directed motion. For such non-abelian colored sandpiles the steady states are found to be
different and also the avalanche size distributions. This sandpile so defined has a non-trivial spatial
structure and belongs to a different universality class of sandpile models. Dynamics of a granular heap
with grains of different colors and properties may be described using this sandpile.
Statistical Mechanics (cond-mat.stat-mech)
6 page, 6 figures
Variational boundary based tensor network renormalization group
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-08-15 20:00 EDT
Feng-Feng Song, Naoki Kawashima
We propose a real-space renormalization group algorithm for accurately coarse-graining two-dimensional tensor networks. The central innovation of our method lies in utilizing variational boundary tensors as a globally optimized environment for the entire system. Based on this optimized environment, we construct renormalization projectors that significantly enhance accuracy. By leveraging the canonical form of tensors, our algorithm maintains the same computational complexity as the original tensor renormalization group (TRG) method, yet achieves higher accuracy than existing approaches that do not incorporate entanglement filtering. Our work offers a practical pathway for extending TRG methods to higher dimensions while keeping computational costs manageable.
Statistical Mechanics (cond-mat.stat-mech), Strongly Correlated Electrons (cond-mat.str-el), Computational Physics (physics.comp-ph)
7 pages, 5 figures
Electronic localization on the structural inhomogeneities formed due to Bi and Te deficiency in the MBE grown films of AFM topological insulator MnBi2Te4: Evidence from spectroscopic ellipsometry and infrared studies
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-08-15 20:00 EDT
N. N. Kovaleva, D. Chvostova, T. N. Fursova, A. V. Muratov, S. I. Bozhko, Yu. A. Aleshchenko, A. Dejneka, D. V. Ishchenko, O. E. Tereshchenko, K. I. Kugel
The intrinsic substitutional and antisite defects cause unintentional doping and shift of the E_F position above the conduction band minimum in the AFM topological insulator (TI) MnBi2Te4. This prevents measurements of the quantum anomalous Hall effect (QAH) and investigation of the topological Dirac states. In the present study, the Mn-Bi-Te films grown by the MBE technique onto Si(111) substrates with decreasing Bi and Te contents and increasing Mn content were investigated by 0.5-6.5 eV spectroscopic ellipsometry. In addition, the 0.004-0.9 eV infrared (IR) transmittance spectra were examined. An effective medium model was used to reproduce the measured ellipsometric angles, Psi(omega) and Delta(omega), of the Mn-Bi-Te films in terms of the constructed model, including film thickness, surface roughness, and volume fractions of two (MnTe and Bi2Te3) or three constituents, the latter being associated with the structural inhomogeneities contribution. The results obtained for the inhomogeneous Mn-Bi-Te films using the three-phase EMA model indicate that the defect-associated optical response systematically shifts to higher photon energies from ~1.95 to ~2.43 eV with decreasing Te and Bi contents and increasing Mn content, pointing out that the electrons become more deeply localized in the formed structural inhomogeneities. The obtained results indicate that the structure of the non-stoichiometric Mn-Bi-Te films is not continuous but represented by regions of nearly stoichiometric MnBi2Te4 phase, which includes hollows or quantum anti-dots (QADs). The measured FIR transmittance spectra for the non-stoichiometric Mn-Bi-Te films show substantially reduced (or absent) contribution(s) from free charge carriers, which supports the relevance of localization effects.
Strongly Correlated Electrons (cond-mat.str-el), Materials Science (cond-mat.mtrl-sci)
10 pages, 7 figures
Edgetronics in 2D Altermagnet via Real-Space-Spin Coupling
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-08-15 20:00 EDT
Shibo Fang, Zongmeng Yang, Jianhua Wang, Xingyue Yang, Ching Hua Lee, Jing Lu, Xiaotian Wang, Yee Sin Ang
The coupling between real-space coordinates and spin (r-s) provides an alternative route to achieve efficient spin manipulation in spintronics beyond the conventional momentum-spin (k-s) coupling paradigm. Here we demonstrate an unexpected manifestation of one-dimensional (1D) r-s coupling in two-dimensional (2D) altermagnetic second-order topological insulators, where the spin-split floating edge states - energetically isolated within the bulk band gap - emerge and exhibit both Neel-vector-dependent and electrically tunable behaviors. The 1D edge-spin r-s coupling ensures carrier transport to be exclusively carried by the edge states with quantized spin conductance, giving rise to an unconventional edge tunnel magnetoresistance (edge-TMR) effect that can be switched On or Off. As a proof of concept, we computationally design an edge-TMR device based on Cr2Se2O monolayer to demonstrate its edge transportation and controllability via the Neel order or electric field. Our findings propose a general prototype altermagnetic device for next-generation low-dimensional spintronics.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Materials Science (cond-mat.mtrl-sci)
7 pages, 5 figures
Jamming of active particles in narrow pores: Implications for ratchet effect and diffusion coefficient
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-08-15 20:00 EDT
Šimon Pajger, František Slanina
We study the behavior of colloidal active particles interacting via steric repulsion in various quasi-1D geometries. We mainly focus on active particles with high Péclet number. We discuss 3 phenomena closely tied to those systems: motility-induced phase separation (or dynamical freezing), ratchet effect (which takes place if the geometry has broken spatial symmetry), and the enhanced diffusion coefficient. We study those particles using numerical simulations employing an ASEP-like model. Besides direct numerical simulations we study the model by mean-field approximation and by solving the coarse-grained hydrodynamic equations.
Statistical Mechanics (cond-mat.stat-mech)
J. Stat. Mech.: Theory Exp.,2025,2025,8,083201
Fractal depth-first search paths in statistical physics models
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-08-15 20:00 EDT
Qiyuan Shi, Youjin Deng, Ming Li
We study the fractal properties of depth-first search (DFS) paths in critical configurations of statistical physics models, including the two-dimensional $ O(n)$ loop model for various $ n$ , and bond percolation in dimensions $ d = 2$ to $ 6$ . In the $ O(n)$ loop model, the fractal dimension of the DFS path consistently matches that of the external perimeter, suggesting DFS as a convenient alternative for probing interface geometry. For bond percolation, the DFS path exhibits nontrivial fractal scaling across all studied dimensions, even in $ d > 2$ where the external perimeter is not well defined. Interestingly, when DFS is applied to the full lattice without any dilution or criticality, the path is still fractal in two dimensions, with a dimension close to $ 7/4$ , but becomes space-filling in higher dimensions. Our results demonstrate that DFS offers a robust and broadly applicable geometric probe for exploring critical phenomena beyond traditional observables.
Statistical Mechanics (cond-mat.stat-mech)
Superconductivity in imbalanced bilayer Hubbard model
New Submission | Superconductivity (cond-mat.supr-con) | 2025-08-15 20:00 EDT
We investigate the bilayer model with two layers of imbalanced densities coupled by the interlayer hybridization. Using the large-scale dynamical cluster quantum Monte Carlo simulation, we discovered that increased hybridization induces a transition in the superconducting pairing from $ d$ -wave to $ s^{\pm}$ -wave and the superconducting $ T_c$ of $ d$ -wave pairing exhibits a non-monotonic dependence on the density imbalance. Remarkably, the optimal SC occurs at a moderate imbalance, whose SC is solely hosted by the layer with higher density (lower hole doping). Our results support the possibility of $ T_c$ enhancement in composite picture where the underdoped layer provides the pairing strength while the overdoped layer promotes the phase coherence. The uncovered SC hosted by a single layer is reminiscent of our recent exploration on the trilayer Hubbard model. Our present study thus provides new insight that the SC can be enhanced via the layer differentiation.
Superconductivity (cond-mat.supr-con), Quantum Gases (cond-mat.quant-gas), Strongly Correlated Electrons (cond-mat.str-el)
12 pages, 13 figures
FastTrack: a fast method to evaluate mass transport in solid leveraging universal machine learning interatomic potential
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-08-15 20:00 EDT
Hanwen Kang, Tenglong Lu, Zhanbin Qi, Jiandong Guo, Sheng Meng, Miao Liu
We introduce a rapid, accurate framework for computing atomic migration barriers in crystals by combining universal machine learning force fields (MLFFs) with 3D potential energy surface sampling and interpolation. Our method suppresses periodic self interactions via supercell expansion, builds a continuous PES from MLFF energies on a spatial grid, and extracts minimum energy pathways without predefined NEB images. Across twelve benchmark electrode and electrolyte materials including LiCoO2, LiFePO4, and LGPS our MLFF-derived barriers lie within tens of meV of DFT and experiment, while achieving ~10^2 x speedups over DFT-NEB. We benchmark GPTFF, CHGNet, and MACE, show that fine-tuning on PBE/PBE+U data further enhances accuracy, and provide an open-source package for high-throughput materials screening and interactive PES visualization.
Materials Science (cond-mat.mtrl-sci), Computational Physics (physics.comp-ph)
Measurement of the Unusual Dielectric Response to Low-Frequency s-Polarized Evanescent Waves in Metals with {\break} Implications for the Casimir Effect
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-08-15 20:00 EDT
M. Dhital, G. L. Klimchitskaya, V. M. Mostepanenko, U. Mohideen
We report precision measurements of the lateral component of the oscillating magnetic field reflected from a copper plate, which is fully determined by s-polarized evanescent waves. The measurement data are compared with theoretical predictions of classical electrodynamics using the dielectric permittivity of copper as given by the Drude model. It is shown that these predictions are excluded by the measurement data which means that the currently used Drude model does not provide a complete description of the electromagnetic response of metals for s-polarized evanescent waves. The critical importance of this result for several fields of condensed matter physics and optics dealing with evanescent waves, including the Casimir effect, is discussed.
Materials Science (cond-mat.mtrl-sci), Quantum Physics (quant-ph)
7 pages, 3 figures
Europhys. Lett. V.151, 26002 (2025). Europhys. Lett. v.151, 26002 (2025)
Unraveling energy flow mechanisms in semiconductors by ultrafast spectroscopy: Germanium as a case study
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-08-15 20:00 EDT
Grazia Raciti, Begoña Abad, Riccardo Dettori, Raja Sen, Aswathi K. Sivan, Jose M. Sojo-Gordillo, Nathalie Vast, Riccardo Rurali, Claudio Melis, Jelena Sjakste, Ilaria Zardo
Semiconductor materials are the foundation of modern electronics, and their functionality is dictated by the interactions between fundamental excitations occurring on (sub-)picosecond timescales. Using time-resolved Raman spectroscopy and transient reflectivity measurements, we shed light on the ultrafast dynamics in germanium. We observe an increase in the optical phonon temperature in the first few picoseconds, driven by the energy transfer from photoexcited holes, and the subsequent decay into acoustic phonons through anharmonic coupling. Moreover, the temperature, Raman frequency, and linewidth of this phonon mode show strikingly different decay dynamics. This difference was ascribed to the local thermal strain generated by the ultrafast excitation. We also observe Brillouin oscillations, given by a strain pulse traveling through germanium, whose damping is correlated to the optical phonon mode. These findings, supported by density functional theory and molecular dynamics simulations, provide a better understanding of the energy dissipation mechanisms in semiconductors.
Materials Science (cond-mat.mtrl-sci), Other Condensed Matter (cond-mat.other)
Phonon anomalies, Anharmonicity, and thermal expansion coefficient in few layered PtX2 (X= S, Se): A temperature dependent Raman study
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-08-15 20:00 EDT
Atul G. Chakkar, Chaitanya B. Auti, Gaurav Bassi, Mukesh Kumar, Pradeep Kumar
Two-dimensional group-10 noble transition metal dichalcogenides have garnered growing attention due to their rich physical properties and promising applications across nanoelectronics, optoelectronics, and spintronics. Among them, PtX2 (X = S, Se) exhibits pronounced interlayer coupling driven by hybridization of the out-of-plane Pz orbitals of the chalcogen atoms. In this work, we present a detailed temperature and polarization-resolved Raman spectroscopic study of few-layer PtS2 and PtSe2 over the temperature range of ~ 5 to 300 K. Our study encompasses phonon-phonon interactions, symmetry analysis of phonon modes, low-frequency interlayer vibrations, and extraction of thermal expansion coefficients. Notable phonon anomalies in peak position, linewidth, and intensity emerge around ~ 80 K and 150 K for PtS2, and ~ 70 K and 240 K for PtSe2, indicating intricate coupling between thermal and vibrational dynamics. These results offer valuable insights for the development of devices based on PtS2, PtSe2, and related 2D materials, where interlayer interactions, anharmonic effects, and thermal expansion behaviour play crucial roles.
Materials Science (cond-mat.mtrl-sci), Other Condensed Matter (cond-mat.other)
Periodic transitions of topological charge in skyrmions confined within FeGe and Co/Pt nanodisks
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-08-15 20:00 EDT
The dynamic control of skyrmion properties such as polarity, vorticity, and topological charge is crucial for their implementation in spintronic applications. In this work, we investigate the periodic inversion of the topological charge in two distinct systems: FeGe, a bulk chiral magnet, and Co/Pt, an interfacial system with strong Dzyaloshinskii-Moriya interaction. By applying an oscillating magnetic field perpendicular to the film plane, we induce cyclic transitions in the spin texture. In FeGe, the skyrmion evolves through a $ Q=1 \rightarrow 0 \rightarrow -1$ sequence via an intermediate skyrmionium state. In Co/Pt, the process involves skyrmion annihilation and re-nucleation, resulting in alternating topological charges. These results reveal distinct dynamic mechanisms for topological charge modulation, offering potential pathways for the energy-efficient control of skyrmion-based devices.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Other Condensed Matter (cond-mat.other)
7 pages, 7 figures
J. Phys. D: Appl. Phys. 58, 335001 (2025)
Phase transitions and dynamics of one-dimensional solitons in spin-orbit-coupled Bose-Bose mixtures
New Submission | Quantum Gases (cond-mat.quant-gas) | 2025-08-15 20:00 EDT
Gui-hua Chen, Hongcheng Wang, Boris A. Malomed, Haiming Deng, Yongyao Li
We investigate the formation, stability, and dynamics of solitons in a one-dimensional binary Bose-Einstein condensate under the action of the spin-orbit-coupling (SOC) and Lee-Huang-Yang (LHY) correction to the underlying system of the Gross-Pitaevskii equations. We identify the semi-dipole (SD) family of solitons and thoroughly analyze its properties. The numerical analysis reveals intricate bifurcations, including transitions from real to complex-valued stationary wavefunctions of the SD solitons and norm-dependent dynamical instabilities. Stability maps in the plane of the solitons’ norm and interaction strength exhibit areas of monostability, oscillatory behavior, and soliton splitting. Solitons with complex stationary wavefunctions emerge as ground states in broad parameter areas, due to the effects of the LHY terms. The other soliton species, in the form of mixed modes (MMs), does not feature the compexification bifurcation. In the LHY-dominated regime, the SD and MM solitons exhibit identical values of the energy for the same norm. The results deepen the understanding of nonlinear matter-wave states and reveal multi-stable ones in quantum gases.
Quantum Gases (cond-mat.quant-gas), Pattern Formation and Solitons (nlin.PS)
11 pages, 10 figures. To be published in Physical Review A
Field-induced condensation of $π$ to 2$π$ soliton lattices in chiral magnets
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-08-15 20:00 EDT
M. Winter, A. Pignedoli, M. C. Rahn, A. S. Sukhanov, B. Achinuq, J. R. Bollard, M. Azhar, K. Everschor-Sitte, D. Pohl, S. Schneider, A. Tahn, V. Ukleev, M. Valvidares, A. Thomas, D. Wolf, P. Vir, T. Helm, G. van der Laan, T. Hesjedal, J. Geck, C. Felser, B. Rellinghaus
Chiral soliton lattices (CSLs) are nontrivial spin textures that emerge from the competition between Dzyaloshinskii-Moriya interaction, anisotropy, and magnetic fields. While well established in monoaxial helimagnets, their role in materials with anisotropic, direction-dependent chirality remains poorly understood. Here, we report the direct observation of a tunable transition from $ \pi$ to 2$ \pi$ soliton lattices in the non-centrosymmetric Heusler compound Mn1.4PtSn. Using Lorentz transmission electron microscopy, resonant elastic X-ray scattering, and micromagnetic simulations, we identify a $ \pi$ -CSL as the magnetic ground state, in contrast to the expected helical phase, which evolves into a classical 2$ \pi$ -CSL under increasing out-of-plane magnetic fields. This transition is governed by a delicate interplay between uniaxial magnetocrystalline anisotropy and magnetostatic interactions, as captured by a double sine-Gordon model. Our analysis not only reveals the microscopic mechanisms stabilizing these soliton lattices but also demonstrates their general relevance to materials with D2d, S4, Cnv, or Cn symmetries. The results establish a broadly applicable framework for understanding magnetic phase diagrams in chiral systems, with implications for soliton-based spintronic devices and topological transport phenomena.
Materials Science (cond-mat.mtrl-sci)
11 pages, including 9 figures
Moment closure through spectral expansion in open stochastic systems
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-08-15 20:00 EDT
Gianni Valerio Vinci, Roberto Benzi, Maurizio Mattia
The derivation of dynamical laws for general observables (or moments) from the master equation for the probability distribution remains a challenging problem in statistical physics. Here, we present an alternative formulation of the general spectral expansion, which clarifies the connection between the relaxation dynamics of arbitrary moments and the intrinsic time scales of the system. Within this framework, we address the moment-closure problem in a way that streamline the conventional treatment of open systems. The effectiveness of the theory is illustrated by deriving analytical expressions for two representative cases: spectral amplification in stochastic resonance and the moment dynamics of a non-Gaussian system, namely the Bessel process with constant drift. We also identify a direct relationship between our theory and the Koopman operator approach. Finally, we apply our approach to the nonlinear and out-of-equilibrium mean-field description of interacting excitatory and inhibitory populations.
Statistical Mechanics (cond-mat.stat-mech)
Crystalline electric field excitations in Weyl semimetal \textit{R}AlSi (\textit{R} = Ce, Pr and Nd)
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-08-15 20:00 EDT
Lin Yang, Yili Sun, Xiutong Deng, Weizheng Cao, Xiaoyan Ma, Yinguo Xiao, Zhentao Wang, Ze Hu, Xiaowen Hao, Yuan Yuan, Zecong Qin, Wei Luo, Qingyong Ren, Xin Tong, Mohamed Aouane, Manh Duc Le, Youguo Shi, Yanpeng Qi, Devashibhai Adroja, Huiqian Luo
The rare earth intermetallic system \textit{R}Al\textit{X} (\textit{R} = rare earth elements, \textit{X} = Si and Ge) is known to be a promising candidate of magnetic Weyl semimetal. Due to the complex interactions between the rare earth elements and surrounding atoms, as well as hybridization with itinerant electrons, this family likely possesses highly intriguing and novel magnetic structures and thus exhibits dynamic behaviors. We systematically probe polycrystalline samples of \textit{R}AlSi (\textit{R} = La, Ce, Pr and Nd) combining inelastic neutron scattering (INS), heat capacity and magnetic susceptibility measurements. The INS measurements identify well-resolved crystalline electric field (CEF) excitations at 19.2 and 24.9 meV in CeAlSi, at 5.4 meV in PrAlSi, and at 2.5 and 4.2 meV in NdAlSi. We analyzed the INS data using the corresponding CEF models and determined the CEF parameters and ground state wave functions of \textit{R}AlSi (\textit{R} = Ce, Pr and Nd). Our results suggest strong single-ion anisotropy in their ground states: $ |\pm3/2\rangle$ (94.5%) in CeAlSi, $ |\pm3\rangle$ (99.2%) in PrAlSi, and $ |\pm9/2\rangle$ (76.2%) in NdAlSi. Notably, the weaker anisotropy and strong exchange interactions in NdAlSi promote competing magnetic orders and CEF splitting at low temperature, contrasting with the robust CEF levels in magnetic states of CeAlSi and PrAlSi.
Strongly Correlated Electrons (cond-mat.str-el), Materials Science (cond-mat.mtrl-sci), Other Condensed Matter (cond-mat.other)
10 pages, 7 figures, Accepeted by Physical Review B
The 6H-Perovskite Dimer Lattice with Antiferromagnetic Interactions: Ba$_3$ARu$_2$O$_9$
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-08-15 20:00 EDT
Daniel M. Pajerowski, David A. Dahlbom, Daniel Phelan, Yu Li, Alexander I. Kolesnikov
We investigate the magnetic behavior of the 6H-perovskite dimer lattice Ba$ _3$ Zn$ _{1-x}$ Ca$ _x$ Ru$ _2$ O$ _9$ using analytical theory, density functional theory, inelastic neutron scattering, and modeling of historical magnetization and neutron-scattering data. A dimer mean-field theory built upon classical Luttinger-Tisza analysis generates a phase diagram revealing a transition from a nonmagnetic singlet to a finite-moment ground state as interdimer couplings increase. A (generalized) linear spin-wave theory captures multiplet mixing, excitation gap closing, and fluctuation-induced moment suppression. Density functional theory on select compounds and neutron spectroscopy on dilute Ba$ _3$ Zn(Ru$ _{1-x}$ Sb$ _x$ )$ _2$ O$ _9$ confirm the exchange hierarchy, enabling quantification of previously published experiments within this framework. Our results identify three mechanisms for magnetic moment suppression: quantum fluctuations, ligand hybridization, and nonmagnetic-singlet/magnetic-multiplet mixing.
Strongly Correlated Electrons (cond-mat.str-el), Materials Science (cond-mat.mtrl-sci)
Effective permeability conditions for diffusive transport through impermeable membranes with gaps
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-08-15 20:00 EDT
Molly Brennan, Edwina F. Yeo, Philip Pearce, Mohit P. Dalwadi
Membranes regulate transport in a wide variety of industrial and biological applications. The microscale geometry of the membrane can significantly affect overall transport through the membrane, but the precise nature of this multiscale coupling is not well characterised in general. Motivated by the application of transport across a bacterial membrane, in this paper we use formal multiscale analysis to derive explicit effective coupling conditions for macroscale transport across a two-dimensional impermeable membrane with periodically spaced gaps, and validate these with numerical simulations. We derive analytic expressions for effective macroscale quantities associated with the membrane, such as the permeability, in terms of the microscale geometry. Our results generalise the classic constitutive membrane coupling conditions to a wider range of membrane geometries and time-varying scenarios. Specifically, we demonstrate that if the exterior concentration varies in time, for membranes with long channels, the transport gains a memory property where the coupling conditions depend on the system history. By applying our effective conditions in the context of small molecule transport through gaps in bacterial membranes called porins, we predict that bacterial membrane permeability is primarily dominated by the thickness of the membrane. Furthermore, we predict how alterations to membrane microstructure, for example via changes to porin expression, might affect overall transport, including when external concentrations vary in time. These results will apply to a broad range of physical applications with similar membrane structures, from medical and industrial filtration to carbon capture.
Soft Condensed Matter (cond-mat.soft), Analysis of PDEs (math.AP), Dynamical Systems (math.DS), Biological Physics (physics.bio-ph)
Symmetry-Constrained Multi-Scale Physics-Informed Neural Networks for Graphene Electronic Band Structure Prediction
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-08-15 20:00 EDT
Wei Shan Lee, I Hang Kwok, Kam Ian Leong, Chi Kiu Althina Chau, Kei Chon Sio
Accurate prediction of electronic band structures in two-dimensional materials remains a fundamental challenge, with existing methods struggling to balance computational efficiency and physical accuracy. We present the Symmetry-Constrained Multi-Scale Physics-Informed Neural Network (SCMS-PINN) v35, which directly learns graphene band structures while rigorously enforcing crystallographic symmetries through a multi-head architecture. Our approach introduces three specialized ResNet-6 pathways – K-head for Dirac physics, M-head for saddle points, and General head for smooth interpolation – operating on 31 physics-informed features extracted from k-points. Progressive Dirac constraint scheduling systematically increases the weight parameter from 5.0 to 25.0, enabling hierarchical learning from global topology to local critical physics. Training on 10,000 k-points over 300 epochs achieves 99.99% reduction in training loss (34.597 to 0.003) with validation loss of 0.0085. The model predicts Dirac point gaps within 30.3 $ \mu$ eV of theoretical zero and achieves average errors of 53.9 meV (valence) and 40.5 meV (conduction) across the Brillouin zone. All twelve C$ _{6v}$ operations are enforced through systematic averaging, guaranteeing exact symmetry preservation. This framework establishes a foundation for extending physics-informed learning to broader two-dimensional materials for accelerated discovery.
Materials Science (cond-mat.mtrl-sci), Machine Learning (cs.LG), Computational Physics (physics.comp-ph)
36 pages and 14 figures
Edge Reconstruction in a Quantum Spin Hall Insulator
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-08-15 20:00 EDT
Rahul Soni, Matthias Thamm, Gonzalo Alvarez, Bernd Rosenow, Adrian Del Maestro
We study interaction-driven edge reconstruction in a quantum spin Hall insulator described by the Bernevig-Hughes-Zhang model with Kanamori-Hubbard interactions using the real-space density matrix renormalization group method in both the grand-canonical and canonical ensembles. For a two-dimensional cylinder with a smooth edge, we identify discrete particle-number transitions that lead to a spin-polarized edge state stabilized by an emergent ferromagnetic exchange interaction. The reconstruction is orbital-selective, occurring predominantly in the $ s$ -orbital channel. Our results reveal a fully microscopic mechanism for emergent spin polarization at the edge that could compromise the topological protection of helical edge states by time reversal symmetry.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
6 pages with End Matter, 3 pages supplement, For associated data and code repository see: this https URL
Machine-Learning-enabled ab initio study of quantum phase transitions in SrTiO$_3$
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-08-15 20:00 EDT
(1)Jonathan Schmidt, (1)Nicola A. Spaldin ((1) Department of Materials, ETH Zürich, Zürich, Switzerland)
We use the self-consistent harmonic approximation (SSCHA) with machine learning interatomic potentials to calculate the effect of $ ^{18}$ O substitution on the properties of quantum paraelectric SrTiO$ _3$ (STO). We find that calculations including both quantum and anharmonic effects are able to reproduce the experimentally observed isotope effect, in which replacement of $ ^{16}$ O by $ ^{18}$ O induces the ferroelectric state, and demonstrate that the ferroelectric phase transition in ST$ ^{18}$ O can be reproduced in a purely displacive manner. We calculate the ferroelectric soft mode frequency as a function of volume, lattice parameters and temperature for ST$ ^{16}$ O and ST$ ^{18}$ O, and find that the phase space in which ST$ ^{16}$ O shows quantum paraelectric behaviour, while ST$ ^{18}$ O becomes ferroelectric is narrow. Our study shows that machine learning interatomic potentials enable temperature-dependent simulations that include quantum and anharmonic phonon effects, however quantitative prediction of phase diagrams remains challenging due to a lack of universally accurate electronic structure methods.
Materials Science (cond-mat.mtrl-sci)
Reconfiguration of a Magnetic Tunnel Junction as a Way to Turn It into a Field-Free Vortex Oscillator
New Submission | Other Condensed Matter (cond-mat.other) | 2025-08-15 20:00 EDT
Maksim Stebliy, Alex Jenkins, Luana Benetti, Ricardo Ferreira
Magnetic tunnel junctions (MTJs) are key elements in practical spintronics, enabling not only conventional tasks such as data storage, transmission, and processing but also the implementation of compute-in-memory processing elements, facilitating the development of efficient hardware for neuromorphic computing. The functionality of an MTJ is determined by the properties of its free layer (FL) and reference layer (RL) with fixed magnetization, separated by an MgO tunnel barrier. This paper presents a mechanism for reconfiguring the RL, which is the upper layer of a pinned synthetic antiferromagnet, enabling a reversible transition from a single-domain state to a vortex magnetic state with different core positions. When the RL is in the vortex state, it generates a spin current with a vortex-like polarization distribution, enabling stable vortex oscillations in the FL even in the absence of external magnetic fields. This effect has been confirmed in MTJs with diameters ranging from 400 to 1000 nm. It is demonstrated, using experimental data with comparative micromagnetic simulation, that the pinning antiferromagnet retains a long term memory of previous reannealing states resulting in a deformation of the vortex polarised spin current, which in turn introduces a strong dynamical vortex core polarity symmetry breaking. The analogue reprogrammable nature of both the static and dynamic properties of the MTJ demonstrate different possible routes for the introduction of non-volatility into radiofrequency spintronic neuromorphic paradigms.
Other Condensed Matter (cond-mat.other), Applied Physics (physics.app-ph)
Formation and protection of an Eu-Ir surface compound below hexagonal boron nitride
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-08-15 20:00 EDT
Alaa Mohammed Idris Bakhit, Khadiza Ali, Frederik Schiller
Europium (Eu) intercalation below hexagonal boron nitride (hBN) on an Ir(111) substrate at various Eu coverages is investigated. The structural and electronic properties were examined using low energy electron diffraction (LEED), scanning tunnelling microscopy (STM), x-ray photoelectron spectroscopy (XPS) and angle-resolved photoemission spectroscopy (ARPES). Depending on the deposition temperature, different superstructures, (5 $ \times$ $ M$ ), (5 $ \times$ 2), and ($ \sqrt{3}$ $ \times$ $ \sqrt{3})R30^{\circ}$ with respect to the Ir substrate were identified by LEED. The (5 $ \times$ $ M$ ) superstructure ($ M$ $ >$ 2), at 0.1 monolayer (ML), preserved the hBN/Ir Moir{é} pattern and exhibited a unidirectional ordering of Eu atoms. At higher coverage of 0.26 ML, a (5 $ \times$ 2) superstructure emerged, where excess Eu atoms diffused into the bulk and were analyzed as Eu in a tri-valent state. At the highest preparation temperature with a one-third ML Eu, the formation of a ($ \sqrt{3}$ $ \times$ $ \sqrt{3})R30^{\circ}$ superstructure indicates the presence of a EuIr$ _{2}$ surface alloy beneath the hBN layer, with di-valent Eu atoms suggesting potential ferromagnetic properties. Air exposure was used to evaluate the protection of the hBN layer, and the results indicate that the EuIr$ _{2}$ surface alloy was partially protected. However, the hBN layer remained intact by intercalation and air exposure, as confirmed by ARPES analysis.
Materials Science (cond-mat.mtrl-sci)
10 pages, 6 figures
Collision of surfactant-laden droplets: insights from molecular dynamics simulation
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-08-15 20:00 EDT
Soheil Arbabi, Piotr Deuar, Rachid Bennacer, Zhizhao Che, Panagiotis E. Theodorakis
We study the collision dynamics of surfactant-laden droplets and compare it with that of pure water droplets, with a focus on the bridge growth rate, energy balance, and disk dynamics, distinguishing the cases of head-on and off-centre collisions. By using molecular dynamics simulation of a coarse-grained model, it is found that initial linear scaling describes the first stage of the collision process, which is followed by power-law dynamics, in contrast to an initial thermal regime and a subsequent power-law behaviour observed for droplet coalescence. The transition between the two regimes occurs faster for surfactant-laden droplets. At higher collision velocities, the linear regime dominates the process with a gradual reduction of the power-law behaviour, reaching a situation in which the bridge growth is fully characterised by linear dynamics. The different behaviour of the droplets is presented in the form of a diagram of different scenarios, namely coalescence, separation, and splattering. In particular, it is found that higher velocities and larger offsets increase the likelihood of separation and splattering, with water droplets producing a greater number of satellite droplets due to reduced viscous damping. Also, a disk-like structure is observed as a result of collision, but it is less pronounced in the case of surfactant-laden droplets, due to higher dissipation of energy.
Soft Condensed Matter (cond-mat.soft)
12 pages, 7 figures
Soft Matter 21, 6366 (2025)
Reinforcement-Learning-Designed Field-Free Sub-Nanosecond Spin-Orbit-Torque Switching
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-08-15 20:00 EDT
We demonstrate deterministic, field-free magnetization reversal of a single-domain nanomagnet within 300 ps under a current density of $ 3 \times 10^{10}~\mathrm{A/m^2}$ by coupling reinforcement learning (RL) to the Landau-Lifshitz-Gilbert equation with the spin-orbit torques (SOTs). The RL agent autonomously discovers a current waveform that minimizes the magnetization trajectory path and exploits a precessional shortcut enabled by the field-like SOT and hard-axis anisotropy. From the learned pulse, we extract a clear physical picture of the dynamics and develop a model-based analytical framework that establishes a lower bound on the switching time. The control strategy remains robust across a wide range of damping constants and is stabilized against thermal fluctuations at higher current densities. We also discuss feasible experimental implementations for the precessional switching.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
5 pages, 5 figures
Snap-through time of arches is controlled by slenderness and imperfections
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-08-15 20:00 EDT
William Simpkins, Matthew G. Hennessy, Matteo Taffetani
Snap-through occurs in elastic structures when a stable equilibrium configuration becomes unstable, resulting in rapid motion towards a new and distinct stable state. While static analyses of snap-through are well documented, the dynamics of snap-through remain under-explored, particularly in structures with natural curvature. Using a combination of finite element simulations and multiple-scales analysis, we show that the snap-through dynamics of an arch under a central point load are controlled by its slenderness and imperfections embedded in the system. As the slenderness increases, the snap-through dynamics slow down, and the mode of snap-through changes from limit-point buckling to bifurcation buckling. When bifurcation buckling occurs, snap-through is preceded by an extended period of oscillatory behaviour. The duration of these pre-snap-through oscillations, and hence the snap-through time, is entirely controlled by imperfections in the system. Increasing the strength of imperfections dramatically reduces the snap-through time. Analytical expressions for the snap-through times are presented for limit point and bifurcation buckling. Our work suggests that natural curvature and deliberately introduced imperfections can be used to tune the snap-through dynamics of new functional materials.
Soft Condensed Matter (cond-mat.soft)
Ion-Specific Effects at the Surface of Water
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-08-15 20:00 EDT
Sanghamitra Sengupta, Jan Versluis, Huib J. Bakker
We studied the interaction between salts and surfactants on the water surface using heterodyne-detected vibrational sum frequency generation (HD-VSFG) spectroscopy. We used sodium dodecyl sulfate (SDS) as a prototype surfactant system at 75 micromolar bulk concentration in water. The vibrational response of the OH band of near-surface oriented water molecules and the CH bands of the hydrophobic tails of the surfactant are measured. We observed a dramatic enhancement of the surface density of the negatively charged SDS (DS-) within a narrow range of added salt concentrations. We demonstrated this increase is strongly ion-specific, and induced by the screening of the lateral Coulomb repulsion of the sulfate headgroups by the added cations, followed by strong hydrophobic interactions (hydrophobic collapse) when the DS- surface density reaches a critical value. For a solution of 75 micromolar SDS, the required concentrations of CsCl, KCl, and NaCl for this transition are 2, 5, and 10 mM, respectively.
Soft Condensed Matter (cond-mat.soft), Chemical Physics (physics.chem-ph)
14 pages, 4 figures
Unified Theory of Dark Count Rate and System Detection Efficiency for NbN, WSi Based Superconducting Single Photon Detectors
New Submission | Superconductivity (cond-mat.supr-con) | 2025-08-15 20:00 EDT
Daien He, Leif Bauer, Sathwik Bharadwaj, Zubin Jacob
Predicting the behavior of superconducting nanowire single photon detectors (SNSPDs) is important as their use becomes more widespread in fields ranging from quantum computing to quantum remote sensing. Here, we present a vortex crossing theory of photon detection which provides a unified definition of system detection efficiency and dark count rates. Our approach quantitatively captures the plateau region of system detection efficiency for NbN and WSi based SNSPDs. We concurrently predict the temperature dependence of dark count rates and the intrinsic timing jitter of SNSPDs. We extensively benchmark our model against various experiments to aid in the design of the next generation of SNSPDs.
Superconductivity (cond-mat.supr-con), Quantum Physics (quant-ph)
15 pages, 4 figures
Concentration-Free Quantum Kernel Learning in the Rydberg Blockade
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-08-15 20:00 EDT
Ayana Sarkar, Martin Schnee, Roya Radgohar, Mojde Fadaie, Victor Drouin-Touchette, Stefanos Kourtis
Quantum kernel methods (QKMs) offer an appealing framework for machine learning on near-term quantum computers. However, QKMs generically suffer from exponential concentration, requiring an exponential number of measurements to resolve the kernel values, with the exception of trivial (i.e., classically simulable) kernels. Here we propose a QKM that is free of exponential concentration, yet remains hard to simulate classically. Our QKM utilizes the weak ergodicity-breaking many-body dynamics in the Rydberg blockade of coherently driven neutral atom arrays. We demonstrate the fundamental properties of our QKM by analytically solving an approximate toy model of its underpinning quantum dynamics, as well as by extensive numerical simulations on randomly generated datasets. We further show that the proposed kernel exhibits effective learning on real data. The proposed QKM can be implemented in current neutral atom quantum computers.
Strongly Correlated Electrons (cond-mat.str-el), Quantum Physics (quant-ph)
Gauging the variational optimization of projected entangled-pair states
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-08-15 20:00 EDT
Wei Tang, Laurens Vanderstraeten, Jutho Haegeman
Projected entangled-pair states (PEPS) constitute a powerful variational ansatz for capturing ground state physics of two-dimensional quantum systems. However, accurately computing and minimizing the energy expectation value remains challenging, in part because the impact of the gauge degrees of freedom that are present in the tensor network representation is poorly understood. We analyze the role of gauge transformations for the case of a U(1)-symmetric PEPS with point group symmetry, thereby reducing the gauge degrees of freedom to a single class. We show how gradient-based optimization strategies exploit the gauge freedom, causing the tensor network contraction to become increasingly inaccurate and to produce artificially low variational energies. Furthermore, we develop a gauge-fixed optimization strategy that largely suppresses this effect, resulting in a more robust optimization. Our study underscores the need for gauge-aware optimization strategies to guarantee reliability of variational PEPS in general settings.
Strongly Correlated Electrons (cond-mat.str-el), Quantum Physics (quant-ph)
7 + 10 pages, 5 figures
Field-free superconducting diode effect in two-dimensional Shiba lattices
New Submission | Superconductivity (cond-mat.supr-con) | 2025-08-15 20:00 EDT
Sayak Bhowmik, Dibyendu Samanta, Ashis K. Nandy, Arijit Saha, Sudeep Kumar Ghosh
The superconducting diode effect (SDE) refers to non-reciprocal transport, where current flows without resistance in one direction but becomes resistive in the opposite direction, but its typical reliance on magnetic field hinders scalability and device integration. In this article, we present a theoretical framework for realizing a field-free SDE based on a two-dimensional (2D) Shiba lattice featuring a conical spin texture. Using the real-space Bogoliubov-de Gennes (BdG) calculations, we illustrate that the conical spin configuration alone is sufficient to break the necessary inversion and time reversal symmetries, enabling nonreciprocal supercurrent flow without any external magnetic field, yielding diode efficiency exceeding 40%. Furthermore, we find that the efficiency of such a diode effect becomes strongly dependent on the direction of current flow, revealing a pronounced angular dependence that can be tuned by varying the pitches of the spin texture along the two spatial lattice directions. Our findings offer a pathway toward scalable, field-free superconducting components for non-dissipative electronics and quantum technologies.
Superconductivity (cond-mat.supr-con), Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Materials Science (cond-mat.mtrl-sci)
9 pages, 5 figures, Supplementary material is included, Comments are welcome
Dynamically tunable hydrodynamic transport in boron nitride-encapsulated graphene
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-08-15 20:00 EDT
Akash Gugnani, Aniket Majumdar, Kenji Watanabe, Takashi Taniguchi, Arindam Ghosh
Over the past decade, graphene has emerged as a promising candidate for exploring the viscous nature of electronic flow facilitated by the availability of extremely high-quality devices employing a graphene channel encapsulated within dielectric layers of hexagonal boron nitride (hBN). However, the level of disorder in such systems is mainly determined by the device fabrication protocols, making it impossible to obtain a tunability between the impurity-dominated and the viscous transport within the same device. In this work, using a combination of ultraviolet (UV) radiation and gate electric field, we have demonstrated a dynamic modulation of charge hydrodynamics, quantified in the thermal and electrical transport by the extent of departure from the Wiedemann-Franz (WF) Law in monolayer graphene devices at room temperature. We achieved this by tuning the disorder level continuously and reversibly using UV light to create transient trap states in the encapsulating hBN dielectric. With progressive UV radiation, we observed a dramatic increase in the momentum-relaxing scattering relative to that between the electrons and also the Lorentz number, by nearly a factor of ten, with increasing disorder, thereby approaching the restoration of the WF law in highly disordered graphene. Our experiments outline a potent strategy to tune the fundamental mechanism of charge flow in state-of-the-art graphene devices.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Materials Science (cond-mat.mtrl-sci), Strongly Correlated Electrons (cond-mat.str-el)
9 pages, 4 figures
Interaction enhanced inter-site hoppings for holons and interlayer exciton insulators in moiré correlated insulators
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-08-15 20:00 EDT
In moiré-patterned van der Waals structures of transition metal dichalcogenides, correlated insulators can form under integer and fractional fillings, whose transport properties are governed by various quasiparticle excitations including holons, doublons and interlayer exciton insulators. Here we theoretically investigate the nearest-neighbor inter-site hoppings of holons and interlayer exciton insulators. Our analysis indicates that these hopping strengths are significantly enhanced compared to that of a single carrier. The underlying mechanism can be attributed to the strong Coulomb interaction between carriers at different sites. For the interlayer exciton insulator consisting of a holon and a carrier in different layers, we have also obtained its effective Bohr radius and energy splitting between the ground and first-excited states.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Strongly Correlated Electrons (cond-mat.str-el)
Deterministic roughening in the dc-driven precessional regime of domain walls
New Submission | Disordered Systems and Neural Networks (cond-mat.dis-nn) | 2025-08-15 20:00 EDT
E. F. Pusiol, V. Lecomte, S. Bustingorry, A. B. Kolton
We numerically study the dynamics of extended domain walls in homogeneous ferromagnets driven by a uniform magnetic field at zero temperature. Using both micromagnetic Landau-Lifshitz-Gilbert simulations and a collective-coordinate model, we show that flat domain walls become linearly unstable above the Walker breakdown field and below a higher threshold, provided their length exceeds a characteristic value. This instability is captured by a quasi-universal spectral diagram, parameterized solely by the Gilbert damping, that predicts the onset of deviations from rigid-wall behavior. Beyond the linear regime, large domain walls with bands of unstable modes exhibit spatiotemporal chaos, intricate Bloch line motion, and deterministic roughening. The system undergoes a dynamical phase transition from a flat to a rough moving phase at a critical field.
Disordered Systems and Neural Networks (cond-mat.dis-nn)
5 pages, 6 figures
Exchange-driven self-diffusion of nanoscale crystalline parahydrogen clusters on graphite
New Submission | Other Condensed Matter (cond-mat.other) | 2025-08-15 20:00 EDT
Computer simulations yield evidence of superfluid behavior of nanoscale size clusters of parahydrogen adsorbed on a graphite substrate at low temperature ($ T\lesssim 0.25 \text{ K}$ ). Clusters with a number of molecules between 7 and 12 display concurrent superfluidity and crystalline order, reflecting the corrugation of the substrate. Remarkably, it is found that specific clusters with a number of molecules ranging between 7 and 12 self-diffuse on the surface like free particles, despite the strong pinning effect of the substrate. This effect is underlain by coordinated quantum-mechanical exchanges of groups of identical molecules, i.e., it has no classical counterpart.
Other Condensed Matter (cond-mat.other)
6 pages, 3 figures
New Materials, New Functionalities: Molecular Beam Epitaxy of Ultra-High Conductivity Oxides
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-08-15 20:00 EDT
Gaurab Rimal, Tanzila Tasnim, Brian Opatosky, Ryan B. Comes, Debarghya Mallick, Simon Kim, Rob G. Moore, Seongshik Oh, Matthew Brahlek
Understanding fundamental properties of materials is necessary for all modern electronic technologies. Toward this end, the fabrication of new ultrapure thin film materials is critical to discover and understand novel properties that can allow further development of technology. Oxide materials are a vast material class abound with diverse properties, and, therefore, harnessing such phases is critical for realizing emerging technologies. Pushing forward, however, requires understanding basic properties of insulating, semiconducting and metallic oxides, as well as the more complex phases that arise out of strong electronic correlations unique to this class of materials. In this review, we will focus on one of the unique aspects of oxides: the ultra-high conductivity metallic state, which can be a critical component for future all-oxide microelectronics such as low-loss interconnects and gate-metals, spintronics, as well as future quantum technologies that employ emergent magnetic or superconducting ground states. Like most oxides, a critical challenge to understanding and ultimately integrating high-conductivity metals into new technologies is the ability to synthesize high-quality materials. Therefore, we will frame the discussions in the context of epitaxial film growth via molecular beam epitaxy (MBE), which has provided insights into the electronic behavior of specific materials while providing samples with unprecedented quality. We will highlight and underscore how MBE has enabled developments and deeper understanding of their properties and how it plays a critical role in the future of this unique class of materials.
Materials Science (cond-mat.mtrl-sci), Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Strongly Correlated Electrons (cond-mat.str-el), Superconductivity (cond-mat.supr-con)
Discovery of Niobium Hydride Precipitates in Superconducting Qubits
New Submission | Superconductivity (cond-mat.supr-con) | 2025-08-15 20:00 EDT
Zuhawn Sung, Daniel Bafia, Arely Cano, Akshay Murthy, Jaeyel Lee, Matthew J Reagor, Juan Rubio-Zuazo, Anna Grassellino, Alexander Romanenko
We report the evidence of the formation of niobium hydride phase within niobium films on silicon substrates in superconducting qubits fabricated at Rigetti Computing. For this study, we combined complementary techniques, including room-temperature and cryogenic atomic force microscopy (AFM), synchrotron Xray diffraction, and time of flight secondary ion mass spectroscopy (ToF-SIMS), to directly reveal the existence of niobium hydride precipitates in the Rigetti chip area. Upon cryogenic cooling, we observed variation in the size and morphology of the hydrides, ranging from small (5 nm) irregular shapes to large (~10-100 nm) domain within the Nb grains, fully converted to niobium hydrides. Since niobium hydrides are non-superconducting and can easily change in size and location upon different cooldowns to cryogenic temperature, our finding highlights a new and previously unknown source of decoherence in superconducting qubits. This contributes to both quasiparticle and two level system (TLS) losses, offering a potential explanation for changes in qubit performance upon cooldowns. Finally, by leveraging the RF performance of a 3D bulk Nb resonator, we can quantify RF dissipation on a superconducting qubit, caused by hydrogen concentration variation, and are able to propose a practical engineering pathway to mitigate the formation of the Nb hydrides for superconducting qubit applications.
Superconductivity (cond-mat.supr-con)
Random Permutation Circuits are Quantum Chaotic
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-08-15 20:00 EDT
Bruno Bertini, Katja Klobas, Pavel Kos, Daniel Malz
Random permutation circuits were recently introduced as minimal models for local many-body dynamics that can be interpreted both as classical and quantum. Standard indicators of chaos such as damage spreading, show that these systems exhibit sensitivity to initial conditions in the classical setting. Here, we address their quantum chaoticity by studying the time evolution of local operator entanglement (LOE). We show that the behaviour of LOE in random permutation circuits depends on the dimension of the local configuration space q. When q = 2, i.e. the circuits act on qubits, random permutations are Clifford and the LOE of any local operator is bounded by a constant, indicating that they are not truly chaotic. On the other hand, when the dimension of the local configuration space exceeds two, the LOE grows linearly in time. We prove this in the limit of large dimensions and present numerical evidence that a three-dimensional local configuration space is sufficient for a linear growth of LOE. Our findings highlight that quantum chaos can be produced by essentially classical dynamics. Moreover, we show that LOE can be defined also in the classical realm and put it forward as a universal indicator chaos, both quantum and classical.
Statistical Mechanics (cond-mat.stat-mech), Mathematical Physics (math-ph), Chaotic Dynamics (nlin.CD), Cellular Automata and Lattice Gases (nlin.CG), Quantum Physics (quant-ph)
6+11 pages, 2 figures
Exceptional flat bands in bipartite non-Hermitian quantum crystals
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-08-15 20:00 EDT
Juan Pablo Esparza, Vladimir Juricic
Flat bands, in which kinetic energy is quenched and quantum states become macroscopically degenerate, host a rich variety of correlated and topological phases, from unconventional superconductors to fractional Chern insulators. In Hermitian lattices, their formation mechanisms are now well understood, but whether such states persist, and acquire new features in non-Hermitian (NH) quantum crystals, relevant to open and driven systems, has remained an open question. Here we show that the Hermitian principle for flat-band formation in bipartite lattices, based on a sublattice degeneracy mismatch, extends directly to the NH regime: whenever one sublattice hosts a momentum-independent eigenvalue with degeneracy exceeding that of its partner on the other sublattice, flat bands arise regardless of gain, loss, or complex couplings. Strikingly, at exceptional points, dispersive bands coalesce to form \emph{exceptional flat bands} that persist beyond these singularities, exhibiting biorthogonal eigenmodes spanning both sublattices, with energies and lifetimes tunable via sublattice asymmetry and non-reciprocal couplings. This general framework unifies Hermitian and NH flat-band constructions, and reveals dispersionless states with no closed-system analogue. The proposed construction is applicable to synthetic platforms, from classical metamaterials, where flat bands can be directly emulated, to quantum-engineered systems such as photonic crystals and ultracold atom arrays, which should host correlated and topological phases emerging from such exceptional flat bands.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Main text + supplementary material