Soft Condensed Matter
Brownian dynamics with soft constraints in soft matter systems
Sophie Marbach, Adam Carter and Miranda Holmes-Cerfon
Stiff forces, which bind objects together or otherwise confine motion, are found widely in soft-matter systems – colloids with short range attractions, ligand-receptor contacts, particles in optical traps, fibres that resist stretching, etc. To assess the long-term effect of these stiff forces on dynamics and structure, it is useful to consider the limit where they are treated as constraints, so the system evolves strictly within allowed configurations. Efforts to derive equations involving both constraints, and the
stochastic motion appropriate at the scales of soft matter, began around 50 years ago, yet, we are still lacking a straightforward way to extract the projected equations and apply them in modern formulations of mesoscale dynamics. Here, we address this gap with two key contributions: (1) a practical summary of the constrained Brownian dynamics equations with “soft” constraints, i.e. constraints imposed by stiff forces, which is illustrated through several representative examples, taking care to highlight the nontrivial effects of the constraints; and (2) a novel derivation using singular perturbation theory, establishing the validity of these equations over timescales exceeding the relaxation of stiffly constrained degrees of freedom. We further extend our approach to “soft soft” constraints, where mobility varies on lengthscales comparable to the restraining forces – a scenario typical for particles in fluids experiencing hydrodynamic interactions. We hope our results will be useful for soft matter research, as a robust toolkit for studying tethered or confined systems.
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Mesoscale and Nanoscale Physics
Dynamical Stabilization of Inverted Magnetization and Antimagnons by Spin Injection in an Extended Magnetic System
Emir Karadza, Hanchen Wang, Niklas Kercher et al. (+4 more)
Dynamical perturbations can modify the energy landscape of a physical system, such that unstable
equilibrium configurations become stable when subject to an external drive. The
magnetic analog of such dynamical stabilization corresponds to saturation of the magnetization against an external field. Here we report dynamical stabilization of the magnetization in thin film bismuth-substituted yttrium iron garnet by
spin current injection from an adjacent Pt layer. Magneto-optical Kerr effect measurements demonstrate magnetization reversal against
magnetic fields up to 3000 times larger than the film's coercivity once the
spin injection surpasses a critical threshold associated with negative damping. Micromagnetic simulations reveal that this process is mediated by the excitation of a large population of incoherent
magnons with non-zero wave vector, leading to a transient shortening and subsequent stabilization of the inverted magnetization. The elementary excitations of the high-energy inverted magnetization state are shown to be antimagnons, quasi-particles carrying opposite energy and
spin relative to
magnons. Our results further reveal how the system's size and minimization of nonlinear
magnon scattering processes play a key role in dynamical stabilization, opening new avenues for
magnetic state control beyond conventional magnetization switching. Dissipation-driven phase transitions in large-area
magnetic systems provide a solid-state platform to study magnonic analogs of relativistic phenomena, such as Klein tunneling and black holes, as well as
spin-wave amplification and lasing.
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All authors Emir Karadza, Hanchen Wang, Niklas Kercher, Paul Noel, William Legrand, Richard Schlitz, Pietro Gambardella
Strongly Correlated Electrons
Lattice fermion simulation of spontaneous time-reversal symmetry breaking in a helical Luttinger liquid
V. A. Zakharov, J. Sánchez Fernán and C. W. J. Beenakker
We extend a recently developed "tangent
fermion" method to discretize the
Hamiltonian of a helical Luttinger
liquid on a one-dimensional
lattice, including two-particle backscattering processes that may open a gap in the spectrum. The
fermion-doubling obstruction of the sine dispersion is avoided by working with a tangent dispersion, preserving the time-reversal
symmetry of the
Hamiltonian. The numerical results from a tensor network calculation on a finite
lattice confirm the expectation from infinite-system analytics, that a gapped phase with spontaneously broken time-reversal
symmetry emerges when the
Fermi level is tuned to the Dirac point and the Luttinger parameter crosses a critical value.
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Materials Science
Is it possible to determine unambiguously the Berry phase solely from quantum oscillations?
Bogdan M. Fominykh, Valentin Yu. Irkhin and Vyacheslav V. Marchenkov
The Berry phase, a fundamental
geometric phase in
quantum systems, has become a crucial tool for probing the topological properties of materials.
Quantum oscillations, such as Shubnikov-de Haas (SdH) oscillations, are widely used to extract this phase, but its unambiguous determination remains challenging. This work highlights the inherent ambiguities in interpreting the oscillation phase solely from SdH data, primarily due to the influence of the
spin factor $R_S$, which depends on the Landé $g$-factor and effective mass. While the Lifshitz-Kosevich (LK) theory provides a framework for analyzing oscillations, the unknown g-factor introduces significant uncertainty. For instance, a zero oscillation phase could arise either from a nontrivial Berry phase or a negative $R_S$. We demonstrate that neglecting $R_S$ in modern studies, especially for topological materials with strong
spin-orbit coupling, can lead to doubtful conclusions. Through theoretical analysis and numerical examples, we show how the interplay between the Berry phase and Zeeman effect complicates phase determination. Additionally, we also discuss another underappreciated mechanism - the
magnetic field dependence of the
Fermi level. Our discussion underscores the need for complementary experimental techniques to resolve these ambiguities and calls for further research to refine the interpretation of
quantum oscillations in topological systems.
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Superconductivity
Nanoscale Spatial Tuning of Superconductivity in Cuprate Thin Films via Direct Laser Writing
Irene Biancardi, Valerio Levati, Jordi Alcalà et al. (+9 more)
Cuprate high-temperature
superconductors, such as Yttrium Barium Copper
Oxide (YBCO), are extremely promising for emerging technologies such as low-power computing, data storage,
quantum sensors and superconducting electronics. However, the realization of high-performance functional nanostructures presents formidable challenges due to the difficulty of applying conventional nanofabrication methods to such sensitive materials, making the search for alternative methods a key enabling factor. Since YBCO's superconducting and normal-state properties are highly dependent on oxygen stoichiometry, precise nanoscale control of the oxygen content represents a highly appealing approach for creating advanced nanoengineered devices. In this work, we demonstrate the precise fabrication of sub-micrometer, grayscale patterns over large areas in epitaxial YBCO thin films, achieving finely tuned optical and superconducting transport properties by locally controlling the stoichiometry through maskless direct
laser writing under ambient conditions. Cryogenic magneto-optical imaging and transport measurements in irradiated devices directly demonstrate the spatial tuning of the critical temperature and carrier density with the patterning conditions. Correlated Raman microscopy and reflectometry indicate a
laser-power dependent oxygen depletion in the irradiated regions. The proposed
laser-controlled stoichiometry approach provides a direct and scalable method to navigate the phase diagram of high-TC superconducting
oxides, offering new possibilities for integrating functional nanostructures into superconducting devices.
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All authors Irene Biancardi, Valerio Levati, Jordi Alcalà, Thomas Günkel, Nicolas Lejeune, Riccardo Girelli, Alejandro V. Silhanek, Valeria Russo, Narcís Mestres, Daniela Petti, Anna Palau, Edoardo Albisetti
Materials Science
Ab initio study of carrier mobility in Bi$_2$O$_2$Se
Yubo Yuan, Ziye Zhu, Jiaming Hu et al. (+1 more)
Bi$_2$O$_2$Se is an emerging high-performance layered
semiconductor with excellent stability. While experimental studies have explored carrier transport across various doping levels for both $n$-type and $p$-type conduction, a comprehensive theoretical understanding remains incomplete. In this work, we present parameter-free first-principles calculations of the electron and hole mobilities in Bi$_2$O$_2$Se, based on iterative solution of the Boltzmann transport equation that includes electron-
phonon scattering and ionized
impurity scattering on an equal footing. Intriguingly, we find that Bi$_2$O$_2$Se exhibits high electron mobilities in both the in-plane and out-of-plane directions, whereas the hole mobilities are only significant in the in-plane direction, displaying a unique three-dimensional (3D) electron transport and two-dimensional (2D) hole transport behavior. At 300~K, the calculated intrinsic electron and hole mobilities along the in-plane direction are 447~$\mathrm{cm^2\,V^{-1}\,s^{-1}}$ and 29~$\mathrm{cm^2\,V^{-1}\,s^{-1}}$, respectively, which are primarily affected by Fröhlich electron-
phonon interactions. Due to its large static dielectric permittivity, Bi$_2$O$_2$Se exhibits an exceptionally high low-temperature electron mobilities above $1.0\times10^5~\mathrm{cm^2\,V^{-1}\,s^{-1}}$, and its electron mobilities above 50~K is robust against ionized
impurity scattering over a wide range of
impurity concentrations. By incorporating the
Hall effect into our analysis, we predict an in-plane electron
Hall mobility of 517~$\mathrm{cm^2\,V^{-1}\,s^{-1}}$ at 300~K, in excellent agreement with experimental data. These results provide valuable insights into the carrier transport mechanisms in Bi$_2$O$_2$Se, and offer predictive
benchmarks for future theoretical and experimental investigations.
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All authors Yubo Yuan, Ziye Zhu, Jiaming Hu, Wenbin Li
Disordered Systems and Neural Networks
Facets of Many Body Localization
Konrad Pawlik, Maksym Prodius, Pedro R. Nicácio Falcão et al. (+1 more)
Many-body localization (MBL) appears to be a robust example of ergodicity breaking in many-body interacting systems. Here, we review different aspects of MBL, concentrating on various ways the disorder may be introduced into the system studied. In particular, we consider both the random and quasiperiodic diagonal (i.e., on-site) disorder as well as bond disorder as realized in randomly distributed atoms interacting via long-range interactions. We also review the
quantum sun model, which seems to be the ideal, albeit artificial, model exhibiting MBL.
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All authors Konrad Pawlik, Maksym Prodius, Pedro R. Nicácio Falcão, Jakub Zakrzewski
Statistical Mechanics
Structural Comparison of Error Mitigation Methods for Ising Machines: Penalty-Spin Model versus Stacked Model
Tetsuro Abe, Kanta Hino and Shu Tanaka
Error-mitigation methods for Ising machines are reexamined not merely as noise-suppression techniques but as a structural design problem of replica-coupled Ising models. Using simulated annealing as a hardware-noise-free testbed, we systematically compare the penalty-
spin (PS) model, which couples replicas through a centralized auxiliary layer, with the stacked model, which couples adjacent replicas directly. Numerical experiments on the quadratic assignment problem reveal that the ferromagnetically coupled stacked model stably maintains constraint satisfaction and improves solution quality over a broad parameter range, exhibiting favorable scalability with both the number of replicas and problem size. In contrast, the PS model suffers from cooperation collapse at large parallelism: many-replica averaging in the PS layer washes out sparse solution information, preventing effective inter-replica coordination. These findings demonstrate that the
topology of inter-replica couplings decisively influences search robustness, and provide practical guidelines for model selection and parameter tuning in constrained optimization.
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Mesoscale and Nanoscale Physics
Topological connections between the 2D Quantum Hall problem and the 1D quasicrystal
Anuradha Jagannathan
1D quasicrystals such as the Fibonacci chain have been said to “inherit" their topological properties from the 2D
Quantum Hall problem. Yet, a direct way to see the connection was lacking until a common ancestor, the Fibonacci-
Hall model, was introduced recently \cite{aj2025}. This 2D ancestor model relates the role of the external
magnetic flux in the
Hall problem and that of a
geometric flux which describes the winding of the quasicrystal in 2D, in the cut-and-project method. Doing this enables us to extend the notion of Chern numbers as defined in 2D, to the energy bands of the 1D chain by adiabatic continuity. The older notion of gap labels in the 1D system are now seen to be derivable from the Chern numbers of the 2D bands. The Fibonacci-
Hall model thus provides an important link between physics of two paradigmatic models, the Fibonacci quasicrystal and the
quantum Hall insulator. The generalization to other 1D quasiperiodic models is expected to be relatively straightforward. The extension to 2D cut-and-project tilings is left for future studies.
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Disordered Systems and Neural Networks · Cross-listed from physics.optics
Machine-learning-enabled characterization of individual ring resonators in integrated photonic lattices
Elizabeth Louis Pereira, Amin Hashemi, Faluke Aikebaier et al. (+3 more)
Accurately determining the underlying physical parameters of individual elements in integrated photonics is increasingly difficult as device architectures become more complex. Inferring these parameters directly from spectral measurements of the system as a whole provides a practical alternative to traditional calibration, allowing characterization of photonic systems without relying on detailed device-specific models. Here, we introduce a supervised machine-learning strategy to learn the onsite losses and resonant frequency shifts of each individual ring in an array of coupled ring resonators from measured spectral power distributions of the whole array. The neural network infers these parameters with high accuracy across multiple experimental configurations. Our methodology provides a scalable and non-invasive method for extracting intrinsic parameters in coupled photonic platforms, paving the way for future development of automated calibration and control methods.
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All authors Elizabeth Louis Pereira, Amin Hashemi, Faluke Aikebaier, Hongwei Li, Jose L. Lado, Andrea Blanco-Redondo
Strongly Correlated Electrons
Quasiparticle to local moment crossover in bad metals
A. Chen, F. B. Kugler, P. Doležal et al. (+4 more)
Non-
Fermi-
liquid charge transport in the vicinity of electronic instabilities has been intensely studied for decades. Deviations from $\rho_{\rm FL}=\rho_0+AT^2$ in bad and strange metals are commonly ascribed to a breakdown of Landau's quasiparticle (QP) concept. Yet, it remains unclear what mechanism drives the temperature dependence of $\rho(T)$ beyond $\rho_{\rm FL}$. Here, we examine the bad metal upon approaching the Mott metal-
insulator transition via chemical pressure in $\kappa$-[(BEDT-STF)$_x$(BEDT-TTF)$_{1-x}$]$\rm _2 Cu_2 (CN)_3$. Through
nuclear magnetic resonance (NMR) and transport experiments on the same single
crystals, we directly link the onset of deviations from Korringa law $(T_1T)^{-1} = \mathrm{const.}$ with the rise of $\rho(T)$ beyond $\rho_{\rm FL}$. From the NMR relaxation rate, we can identify the gradual crossover between the QP-dominated regime at low $T$ to predominant local moments at higher $T$. By comparing our experimental findings with dynamical mean-field theory calculations, which accurately reproduce the transport data, we reveal how this crossover is reflected in $T$-dependent changes of the QP spectrum. Near the Mott
insulator, where $d\rho/dT<0$ at high $T$, an Einstein-relation analysis shows that bad-metal behavior with $d\rho/dT>0$ is driven by the temperature dependence of the electronic compressibility rather than the
diffusion constant.
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All authors A. Chen, F. B. Kugler, P. Doležal, Y. Saito, A. Kawamoto, A. Georges, A. Pustogow
Superconductivity
Paul Leask, Calum Ross and Egor Babaev
We study composite topological excitations in
ferromagnetic superconductors consisting of bound states of
magnetic spin textures (skyrmions) and superconducting
vortices. Using a Ginzburg–Landau framework with Zeeman coupling between the magnetization and superconducting
magnetic field, we demonstrate that skyrmion-
vortex pairs (SVPs) form energetically stable bound states. By analyzing their asymptotic interactions, we identify regimes in which SVPs exhibit both short-range repulsion and long-range attraction, leading to clustering phenomena. Our results provide a field-theoretical basis for understanding suggest pathways for controlling hybrid topological matter through long-range interactions.
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Mesoscale and Nanoscale Physics
Interface effects and dielectric mismatch in ultrathin silicon on insulator films
Andrea Pulici, Gabriele Seguini, Fabiana Taglietti et al. (+6 more)
The role of interface states and dielectric mismatch is studied in ultrathin P-doped silicon-on-
insulator (SOI) films with thickness of the device layer ($H_{SOI}$) varying from 30 to 8 nm and dopant concentration ($n_{D}$) ranging from 10$^{18}$ to nearly 10$^{20}$ cm$^{-3}$. P concentration is determined by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). Sample resistivity ($\rho$), carrier concentration ($n_e$), and mobility ($\mu_e$) are extracted by combining sheet resistance and
Hall measurements in van der Pauw configuration. When $H_{SOI}$ = 30 nm, transport properties at room temperature are fully compatible with those of a similarly doped bulk Si. Progressive 2D confinement by reduction of $H_{SOI}$ below 30 nm results in a reduction of the carrier concentration and a concomitant degradation of $\mu_e$. These effects, which are steadily enhanced decreasing $n_D$, are attributed to non-passivated interface states at the SiO$_2$/Si interface and can be significantly mitigated by high temperature rapid thermal oxidation (RTO). The effectiveness of this approach was verified by electron-paramagnetic resonance (EPR) spectra and capacitance-voltage (CV) measurements, which allowed the assessment of the quality of the RTO-SiO$_2$/Si interface and the correlation with observed electrical properties. After effective interface engineering, low temperature electrical characterization revealed a significant increase in P ionization energy in samples with $H_{SOI}$ <= 15 nm, a result directly related to the dielectric mismatch.
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All authors Andrea Pulici, Gabriele Seguini, Fabiana Taglietti, Roman Gumeniuk, Riccardo Chiarcos, Michele Laus, Johannes Heitmann, Marco Fanciulli, Michele Perego
Materials Science
Batch-Fabricated PDMS Templates for the Robotic Transfer of 2D Materials
Zhili Lin, Luosha Han, Jinkun He et al. (+5 more)
Robotic stacking of van der Waals
heterostructures has been at the verge thanks to the convergence between artificial intelligence (AI) and two-dimensional (2D) materials research. Key ingredients to fulfill this pursuit often include
algorithms to identify layer compounds on chips, hard-wares to realize sophisticated operations of motion and/or rotation in a microscale, and, as importantly, highly-standardized and uniform transfer stamps that are often used in picking up layered materials under a microscope. Here, we report a hot-casted-droplet batch fabrication method for polydimethylsiloxane (PDMS) templates tailored for dry transfer of 2D materials. Controlled precursor formulation, degassing, and motorized-syringe dispensing produce dome-shaped PDMS templates with ultra-smooth surfaces (root-mean-square roughness about 0.3 nm at relatively low curing temperatures). By tuning the curing temperature, the reproducible and controllable apex
curvature allows precisely defined contact area between the organic adhesive film and substrate, via thermal expansion. Our results further reveals thermalmechanical behaviors with different casting parameters of such PDMS domes. This scalable and parameterized fabrication protocol gives rise to uniform transfer-stamps with ultra-smooth surface, which may be beneficial for future AI-driven robotic assembly of 2D material
heterostructures.
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All authors Zhili Lin, Luosha Han, Jinkun He, Xiaoxue Fan, Tongyao Zhang, Xiaoxi Li, Baojuan Dong, Kai Zhao
Soft Condensed Matter
Interplay of Micellar Architecture and Viscosity Governs Active Droplet Motility
Salini Kar, Rohit V. Menon, Sanbed Das et al. (+3 more)
The autonomous motion of
liquid crystal oil droplets in micellar media arises from spontaneous breaking of time reversal
symmetry via nonlinear coupling between Marangoni stresses and surfactant transport. While this phenomenon has been widely studied, the influence of micellar solute structure remains unexplored. By modifying micellar architecture using a structure forming salt, we uncover a pronounced non monotonic dependence of droplet velocity on salt concentration. Increasing salt simultaneously raises the medium viscosity and drives a transition of micelles from spherical to rod-like or worm like morphologies. Using complementary experiments, we quantify the viscosity and micellar interaction lengthscale as functions of the salt to surfactant ratio and develop a theoretical model that consistently reproduces the measured propulsion speeds. Flow fields around the droplets are characterized by particle image velocimetry. Our results demonstrate that salt surfactant composition governs active droplet propulsion by jointly controlling micellar solute interaction lengthscales and medium viscosity.
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All authors Salini Kar, Rohit V. Menon, Sanbed Das, Parth Pandya, Sayantan Dutta, Mithun Chowdhury
Materials Science
Molecular-based coordination polymer as reversible and precise acetonitrile electro-optical readout
Esther Resines-Urien, Enrique Burzurí, Estefania Fernandez-Bartolome et al. (+5 more)
Efficient detection of harmful organic volatile compounds is a major health and environmental need in industrialized societies. Tailor-made metal-organic frameworks and other coordination
polymers are emerging as promising sensing molecular materials thanks to their responsivity to a wide variety of external stimuli, and could be used to complement conventional sensors. Here, a non-porous crystalline 1D Fe(II) coordination
polymer acting as a porous acetonitrile host is presented. The desorption of interstitial acetonitrile is accompanied by magneto-structural transitions easily detectable in the optical and electronic properties of the material. The structural switch and therefore its (opto)electronic readout are reversible under exposition of the
crystal to acetonitrile vapor. Coordination
polymers can be versatile sensors for volatile acetonitrile and potentially other organic compounds.
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All authors Esther Resines-Urien, Enrique Burzurí, Estefania Fernandez-Bartolome, Miguel Ángel García García-Tuñón, Patricia de la Presa, Roberta Poloni, Simon J. Teat, Jose Sanchez Costa
Disordered Systems and Neural Networks
R-transforms for non-Hermitian matrices: a spherical integral approach
Pierre Bousseyroux and Marc Potters
In this paper, we establish a connection between the formalism of $\mathcal{R}$-transforms for non-Hermitian random
matrices and the framework of spherical integrals, using the replica method. This connection was previously proved in the Hermitian setting and in the case of bi-invariant random
matrices. We show that the $\mathcal{R}$-transforms used in the non-Hermitian context in fact originate from a single scalar function of two variables. This provides a new and transparent way to compute $\mathcal{R}$-transforms, which until now had been known only in restricted cases such as bi-invariant, Hermitian, or
elliptic ensembles.
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Materials Science
Field report from Collaborative Research Center 1625: Heterogeneous research data management using ontology representations
Doaa Mohamed, Samuel García Vázquez, Behnam Mardani et al. (+4 more)
The goal of the Collaborative Research Center 1625 is the establishment of a scientific basis for the atomic-scale understanding and design of multifunctional compositionally complex solid solution surfaces. Next to materials synthesis in form of thin-film materials libraries, various materials characterization and simulations techniques are used to explore the materials data space of the problem. Machine learning and artificial intelligence techniques guide its exploration and
navigation. The effective use of the combined heterogeneous data requires more than just a simple research data management plan. Consequently, our research data management system maps different data modalities in different formats and resolutions from different labs to the correct spatial locations on physical samples. Besides a graphical user interface, the system can also be accessed through an application programming interface for reproducible data-driven workflows. It is implemented by a combination of a custom research data management system designed around a relational database, an ontology which builds upon materials science-specific ontologies, and the construction of a Knowledge Graph. Along with the technical solutions of research data management system and lessons learned, first use cases are shown which were not possible (or at least much harder to achieve) without it.
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All authors Doaa Mohamed, Samuel García Vázquez, Behnam Mardani, Victor Dudarev, Alfred Ludwig, Maribel Acosta, Markus Stricker
Materials Science
The Diffusion Kinetics of Ba Cations in Perovskite BaTiO$_3$: A Combined Tracer Diffusion and Metadynamics Study
Sylvia Koerfer, Bianca Dißmann, Norman Schier et al. (+3 more)
Tracer
diffusion experiments and metadynamics (MtD) simulations were used to study the
diffusion of Ba cations in the cubic phase of the perovskite
oxide BaTiO$_3$. $^{130}$BaTiO$_3$ thin films were used as
diffusion sources to introduce barium tracer
diffusion profiles into single-
crystal samples at temperatures $1348 \leq T/\mathrm{K} \leq 1498$. The $^{130}$Ba profiles were determined by time-of-flight secondary ion mass spectrometry, and then analysed to yield Ba tracer
diffusion coefficients ($D_\mathrm{Ba}^\ast$). MtD simulations were performed in order to obtain barium-vacancy
diffusion coefficients ($D_\mathrm{v_{Ba}}$) for selected vacancy mechanisms as a function of temperature. $D_\mathrm{v_{Ba}}$ is predicted to be increased significantly by an adjacent oxygen vacancy, and even more, by an adjacent titanium vacancy. From the combined consideration of $D_\mathrm{Ba}^\ast$ and $D_\mathrm{v_{Ba}}$, we conclude that Ba
diffusion in these samples occurred most probably by the migration of defect associates, and not by the migration of isolated barium vacancies. More generally, our results draw
attention to the dangers of relying solely on activation enthalpies to interpret
diffusion data.
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All authors Sylvia Koerfer, Bianca Dißmann, Norman Schier, Han-Ill Yoo, Manfred Martin, Roger A. De Souza
Statistical Mechanics · Cross-listed from quant-ph
Eigenstate Thermalization and Spectral Imprints of the Hamiltonian in Local Observables
Shivam Mishra, C Jisha and Ravi Prakash
The Eigenstate Thermalization Hypothesis explains thermalization in isolated
quantum systems through the statistical properties of observables in the energy eigenbasis. We investigate the crossover from integrability to chaos in the
spin-$1/2$ XXZ chain, establishing a direct correspondence between the spectral correlations of the
Hamiltonian and local observables expressed in the energy eigenbasis as a signature of ergodicity breaking. By introducing a local perturbation that drives the system from integrability to chaos, we track the standard ETH indicators and the eigenstate
entanglement entropy. We introduce a submatrix-based framework for analyzing local observables in the energy eigenbasis. By extracting real-symmetric blocks along the diagonal of the local observables represented in eigenbasis, we show that these submatrices exhibit both the short-range and long-range spectral features of the
Hamiltonian. Remarkably, this correspondence persists even in a partially ergodic regime, indicating that the emergence of chaos is already encoded locally within the observables'
matrix structure and that small blocks are sufficient to capture the underlying spectral correlations.
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Strongly Correlated Electrons
Probing the Dynamical Structure Factor of Quantum Spin Chains via Low-Temperature Gibbs States with Matrix Product State Subspace Expansion
Tomoya Takahashi, Wei-Lin Tu, Ji-Yao Chen et al. (+1 more)
Studying finite-temperature properties with tensor networks is notoriously difficult, especially at low temperatures, due to the rapid growth of
entanglement and the complexity of thermal states. Existing methods like purification and minimally entangled typical thermal states offer partial solutions but struggle with scalability and accuracy in low-temperature regime. To overcome these limitations, we propose a new approach based on generating-function
matrix product states (GFMPS). By directly computing a large set of Bloch-type excited states, we construct Gibbs states that moderate the area-law constraint, enabling accurate and efficient approximation of low-temperature thermal behavior. Our
benchmark results show magnificent agreement with both exact diagonalization and experimental observations, validating the accuracy of our approach. This method offers a promising new direction for overcoming the longstanding challenges of studying low-temperature properties within the tensor network framework. We also expect that our method will facilitate the numerical simulation of
quantum materials in comparison with experimental observations.
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All authors Tomoya Takahashi, Wei-Lin Tu, Ji-Yao Chen, Yusuke Nomura
Materials Science
Chemical heterogeneity at conducting ferroelectric domain walls
Kasper A. Hunnestad, Guo-Dong Zhao, Mao-Hua Zhang et al. (+7 more)
Natural interfaces in ferroic
oxides have developed into versatile playgrounds for studying electronic correlation effects in 2D systems. The microscopic origin of the emergent local electronic properties is often debated, however, as quantitative atomic-scale characterization remains challenging. A
prime example is enhanced conductivity at ferroelectric domain walls, attributed to mechanisms ranging from local band gap reduction to point defect accumulations. Here, we resolve the microscopic mechanisms for domain wall conduction in the ferroelectric model system BiFeO3, by combining transport measurements with atom probe
tomography to quantify the local chemical composition and correlate it with the electrical properties. Significant chemical variations along the walls are observed, demonstrating an outstanding chemical flexibility at domain walls, which manifest in spatially varying physical properties. The results give a unifying explanation for the diverse electronic behavior observed and establish the fundamental notion that multiple conduction mechanisms can coexist within individual domain walls.
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All authors Kasper A. Hunnestad, Guo-Dong Zhao, Mao-Hua Zhang, Tiannan Yang, Elzbieta Gradauskaite, Antonius T. J. van Helvoort, Morgan Trassin, Long-Qing Chen, Tadej Rojac, Dennis Meier
Mesoscale and Nanoscale Physics
RKKY signatures as a probe for intrinsic magnetism and AI/QAH phase discrimination in MnBi$_2$Te$_4$ films
Ya-Xi Li, Zi-Jian Chen, Rui-Qiang Wang et al. (+2 more)
We present a systematic study of the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in MnBi$_2$Te$_4$ films under both dark and illuminated conditions. In the dark, the intrinsic magnetism of MnBi$_2$Te$_4$ is shown to yield a stronger anisotropic RKKY
spin model compared to nonmagnetic topological
insulators, providing a clear signature for differentiating these systems. Furthermore, key band properties – such as energy gap, band degeneracy/splitting, and topological deformations of the
Fermi surface – imprint distinct signatures on the RKKY interaction, enabling clear discrimination between
axion insulators (AI) and
quantum anomalous
Hall (QAH)
insulators in even- and odd-septuple-layer (SL) films. This discrimination manifests in multiple ways: through the
Fermi-energy dependence or spatial oscillations of the interaction for
impurities on the same surface, or via the presence versus absence of
spin-frustrated terms for those on different surfaces. Under off-resonant circularly polarized light, additional phase-transition-related fingerprints also emerge to distinguish these two phases, such as sign reversals of
spin-frustrated terms in even-SL films versus chirality-selective double-dip structures of collinear RKKY components in odd-SL films. Overall, this work establishes RKKY interactions as a sensitive
magnetic probe for distinguishing between AI phase (even-SL) and QAH phase (odd-SL), thereby complementing conventional electrical measurements while providing new insights into the influence of intrinsic magnetism on the surface-state band structure.
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All authors Ya-Xi Li, Zi-Jian Chen, Rui-Qiang Wang, Ming-Xun Deng, Hou-Jian Duan
Statistical Mechanics
A first passage problem for a Poisson counting process with a linear moving boundary
Ivan N. Burenev, Michael J. Kearney and Satya N. Majumdar
The time to first crossing for the Poisson counting process with respect to a linear moving barrier with offset is a classic problem, although key results remain scattered across the literature and their equivalence is often unclear. Here we present a unified and pedagogical treatment of two approaches: the direct time-domain approach based on path-decomposition techniques and the Laplace-domain approach based on the Pollaczek-Spitzer formula. Beyond streamlining existing derivations and establishing their consistency, we leverage the complementary nature of the two methods to obtain new exact analytical results. Specifically, we derive an explicit large deviation function for the first-passage time distribution in the subcritical regime and closed-form expressions for the conditional mean first-passage time for arbitrary offset. Despite its simplicity, this first crossing process exhibits non-trivial critical behavior and provides a rare example where all the main results of interest can be derived exactly.
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Strongly Correlated Electrons · Cross-listed from hep-th
Relaxation Process During Complex Time Evolution In Two-Dimensional Integrable and Chaotic CFTs
Chen Bai, Weibo Mao, Masahiro Nozaki et al. (+2 more)
We investigate the complex time
evolution of a
vacuum state with the insertion of a local primary operator in two-dimensional conformal field theories (2d CFTs). This complex time
evolution can be considered as a composite process constructed from Lorentzian time
evolution and a Euclidean
evolution induced by a post-selected measurement. Our main finding is that in the spatially-compact system, this complex time
evolution drives the state of the subsystems to those of the primary state with the same conformal dimensions of the inserted operator. Contrary to the compact system, the subsystems of the spatially non-compact system evolve to states that depend on the non-
unitary process during a certain time regime. In
holographic systems with a compact spatial direction, this process induced by a heavy local operator can correspond to the relaxation from a black hole with an inhomogeneous horizon to that with a uniform one, while in the ones with a non-compact spatial direction, it can correspond to the relaxation to that with a horizon depending on the non-
unitary process.
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All authors Chen Bai, Weibo Mao, Masahiro Nozaki, Mao Tian Tan, Xueda Wen
Materials Science · Cross-listed from cs.LG
Enhancing Spatial Reasoning in Large Language Models for Metal-Organic Frameworks Structure Prediction
Mianzhi Pan, JianFei Li, Peishuo Liu et al. (+5 more)
Metal-organic frameworks (MOFs) are porous crystalline materials with broad applications such as carbon capture and drug delivery, yet accurately predicting their 3D structures remains a significant challenge. While Large
Language Models (LLMs) have shown promise in generating
crystal structures, their application to MOFs is hindered by MOFs' high structural complexity arising from the large number of atoms in unit
cell. Inspired by the success of block-wise paradigms in deep generative models for MOFs, we pioneer the application of LLMs in this domain by introducing MOF-LLM, the first LLM framework specifically adapted for block-level MOF structure prediction. To effectively harness LLMs for this 3D modular assembly task, our training paradigm integrates spatial-aware continual pre-training (CPT), structural supervised fine-tuning (SFT), and matching-driven reinforcement learning (RL). By incorporating explicit spatial priors and optimizing structural stability via Soft Adaptive Policy Optimization (SAPO), our approach substantially enhances the spatial
reasoning in a Qwen-3 8B model for MOF structure prediction. Comprehensive experiments demonstrate that MOF-LLM achieves state-of-the-art performance with a match rate of 35.78% while exhibiting superior sampling efficiency of 0.04 seconds per structure.
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All authors Mianzhi Pan, JianFei Li, Peishuo Liu, Botian Wang, Yawen Ouyang, Yiming Rong, Hao Zhou, Jianbing Zhang
Mesoscale and Nanoscale Physics
Tunnel-Barrier-Engineered Ultrafast Demagnetization and Spin Transport in Graphene-Based Heterostructures
Suchetana Mukhopadhyay, David Muradas-Belinchon, Francesco Foggetti et al. (+3 more)
Heterostructures combining
graphene with 3d transition metal ferromagnets (FMs) enable various
spin-based phenomena at ultrafast timescales. However, challenges such as the interfacial impedance mismatch, FM deposition-induced defect generation, and interface modification by interfacial coupling or hybridization can impede their functionalization for
spin-orbitronics. In this work, we utilize insulating TiOx barrier layers (BLs) to modify the interfacial
spin conductance structurally, disentangle
spin pumping and
magnetic proximity effects (MPE), and establish external control over ultrafast magnetization dynamics in single-layer
graphene/TiOx/Co systems. All-optical time-resolved magneto-optical Kerr effect measurements of femtosecond to nanosecond
spin dynamics reveal systematic tunability of ultrafast
magnetic parameters via barrier engineering. The thickness-dependent damping modulation in Co indicates strong
spin pumping, with interfacial
spin transparency close to half its physical limit in the presence of an ultrathin BL, where MPE is eliminated. Our results show that appropriately chosen ultrathin BLs can prevent interfacial alterations from
ferromagnetic metals, facilitating efficient
spin detection in
graphene and enhancing control over
spin angular momentum dissipation in
graphene/FM interfaces.
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All authors Suchetana Mukhopadhyay, David Muradas-Belinchon, Francesco Foggetti, Peter M. Oppeneer, M. Venkata Kamalakar, Anjan Barman
Soft Condensed Matter
Representative-volume sizing in finite cylindrical computed tomography by low-wavenumber spectral convergence
Fernando Alonso-Marroquin, Abdullah Alqubalee and Christian Tantardini
Choosing a representative element volume (REV) from finite cylindrical Computed
Tomography (CT) scans becomes ambiguous when a key field variable exhibits a slow axial trend, reflecting either geological variability or CT acquisition/reconstruction artifacts. In such cases, estimated statistics may vary systematically with subvolume size and position rather than converging by simple averaging. We present a practical workflow for sizing an REV under nonstationary conditions by first suppressing axial drift/trend to obtain a residual field suitable for second-order analysis, and then selecting the smallest analysis diameter for which the low-wavenumber spectral content stabilizes within a prescribed tolerance. The method is demonstrated on Thalassinoides-bearing rocks, where branching burrow networks introduce heterogeneity at length scales comparable to laboratory core diameters, making imaging-based microstructural statistics and digital-rock estimates sensitive to subvolume choice. From segmented data, we define a scalar “burrowsity” field capturing burrow-related pore spaces and infills. Axial detrending, with optional normalization, mitigates acquisition drift and nonstationary trends, while covariance/spectral convergence is evaluated on nested cylinders consistent with the core geometry. Representativeness is posed as diameter convergence on nested inscribed cylinders: the two-point covariance and isotropic spectrum $\widehat{C}$ are estimated, and the smallest diameter at which the low-wavenumber plateau becomes stable is selected. Applied to a segmented Thalassinoides core, the method gives $D_{\mathrm{REV}}\simeq 93~\mathrm{mm}$ and $H_{\mathrm{REV}}\simeq 83~\mathrm{mm}$, enabling reproducible correlation-scale reporting and connectivity-sensitive property estimation.
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Mesoscale and Nanoscale Physics
One-Dimensional Frenkel and Wannier Excitons in Electric Fields: Stark Effect, Ionization, Polarizability and Electroabsorption
Thomas Garm Pedersen
One-dimensional
semiconductors are characterized by strongly bound
excitons. Therefore, the Frenkel regime of
excitons localized within a few unit
cells is readily reached and traditional Wannier
exciton models become inadequate. In the presence of strong electric fields,
excitons are polarized and, in extreme cases, ionized. Such strong-field effects have previously been described analytically for Wannier
excitons. In the present work, we show that analytical results can be extended to the more involved Frenkel case as well. Hence, by analytically solving the difference equation describing Frenkel
excitons in electric fields, we derive close-form expressions for resonances providing Stark shifts and ionization rates. Moreover, closed-form results for
exciton electroabsorption spectra and dynamic polarizability are obtained.
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Strongly Correlated Electrons
Multiple-$Q$ spin textures induced by spiral–staggered interference in one-dimensional itinerant magnets
Satoru Hayami and Kazuki Okigami
We theoretically investigate multiple-$Q$
magnetic states emerging from the interference between finite-$Q$ spiral and staggered
spin modulations in a one-dimensional itinerant electron system. The multiple-$Q$
spin textures are characterized by a superposition of
symmetry-unrelated ordering wave vectors in the same direction with distinct periodicities rather than rotationally
symmetry-related ones. Motivated by recent experimental observations of broken helix
magnetic structures in EuIn$_2$As$_2$, we focus on the microscopic interaction conditions in stabilizing such multiple-$Q$ states.We employ two effective
spin models: One is the momentum-space-based model, and the other is the real-space-based model, both of which include bilinear and biquadratic easy-plane anisotropic interactions. By analyzing their ground state via simulated annealing, we find that a superposition of a spiral and a staggered modulation yields a robust double-$Q$
magnetic structure. Moreover, we demonstrate that the obtained double-$Q$
spin configuration exhibits an antisymmetric
spin-split band structure even without the relativistic Dzyaloshinskii-Moriya interaction, and further reveals asymmetric band modulations when the
magnetic field is applied along the out-of-plane direction. Our results provide a theoretical framework for understanding unconventional multiple-$Q$
magnetic textures in one-dimensional systems.
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