Soft Condensed Matter
Design Principles for Fluid Molecular Ferroelectrics
Calum J Gibb, Jordan Hobbs, William C Ogle et al. (+1 more)
Fluid molecular ferroelectrics are a new class of organic materials where ferroelectricity is found in conjunction with 3D fluidity whilst still retaining spontaneous polarization values comparable to their traditional solid state counterparts. One of the major challenges for soft condensed matter physics is predicting whether a fluid molecular material will form ferroelectric phase with nematic or smectic order. Through the synthesis of forty five systematically varied molecules, and by analogy to solid molecular ferroelectrics, is it shown that subtle hydrogen fluorine substitution allows for tuneable syn-parallel pairing motifs resulting in either specific pairings leading too geometrically constrained lamellar order or diversified pairings stabilising nematic ordering. Large-scale, fully atomistic molecular dynamics simulations reveal that smectic ferroelectricity emerges from discrete lateral pairing modes, whereas nematic phases arise from a multiplicity of equivalent polar configurations. Together, these findings establish experimentally validated design principles for fluid molecular ferroelectrics and provide a predictive framework for engineering functional polar fluids.
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All authors Calum J Gibb, Jordan Hobbs, William C Ogle, Richard J Mandle
Superconductivity
Current Induced Switching of Superconducting Order and Enhancement of Superconducting Diode Efficiency
Uddalok Nag, Jonathan Schirmer, Chao-Xing Liu et al. (+1 more)
We propose that the superconducting diode (SD) efficiency can be significantly enhanced near the transition between two superconducting states by choosing parameters where, before the system goes normal with increasing supercurrent, it switches into a different superconducting order for one direction of the current but not for the other. This mechanism for producing high SD efficiency relies on the expectation that the critical current depends sensitively on the superconducting order. We demonstrate this explicitly by performing detailed calculations for a
bilayer superconductor with an in-plane
magnetic field, which admits the standard Bardeen-Cooper-Schrieffer (BCS) and the orbital Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) orders as a function of the strength of the
magnetic field. We predict a sharp peak in the SD efficiency in the FFLO state close to the transition, which arises from a complex interplay between the two superconducting orders. An implication of our study is that the measurement of the SD efficiency can provide fundamental insight into the nature of the BCS-FFLO transition both as a function of the
magnetic field and the supercurrent.
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All authors Uddalok Nag, Jonathan Schirmer, Chao-Xing Liu, J. K. Jain
Materials Science
Growth and crystallographic structure of TiTe$_2$ on Au(111): From sub-monolayer structures to single- and multi-layer films
Andreas Raabgrund, Tilman Kißlinger, Alexander Wegerich et al. (+2 more)
We investigated the initial growth of TiTe$_2$ on Au(111) from sub-monolayer to multi-layer coverage by scanning tunneling microscopy (STM), low-energy electron diffraction intensity analysis (LEED-IV), and density functional theory (DFT). In the submonolayer regime we find a stable and well-ordered $(5\times\sqrt{3})_{\mathrm{rect}}$ superstructure consisting of separated TiTe$_2$ molecules, whereby the Ti atoms substitute Au atoms of the first substrate layer as proven by LEED-IV. By adding further Ti and Te in a 1:2 ratio and proper annealing dealloying sets in and a homogeneous 1T-TiTe$_2$ monolayer film on an unreconstructed substrate is formed. The resulting moiré structure is close to a $(4 \times 4)$ superstructure w.r.t. Au(111) and has a slightly expanded in-plane
lattice parameter compared to the 1T-TiTe$_2$ bulk value. With further stoichiometric deposition, thicker 1T-TiTe$_2$ films grow. Surprisingly, a five layer thick film exhibits an even larger
lattice-parameter (1.5 % larger than the bulk value). All LEED-IV analyses are based on best-fit R-factors of $R \le 0.13$.
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All authors Andreas Raabgrund, Tilman Kißlinger, Alexander Wegerich, Lutz Hammer, M. Alexander Schneider
Statistical Mechanics · Cross-listed from cs.LG
Factorization Machine with Quadratic-Optimization Annealing for RNA Inverse Folding and Evaluation of Binary-Integer Encoding and Nucleotide Assignment
Shuta Kikuchi and Shu Tanaka
The RNA inverse folding problem aims to identify nucleotide sequences that preferentially adopt a given target secondary structure. While various heuristic and machine learning-based approaches have been proposed, many require a large number of sequence evaluations, which limits their applicability when experimental validation is costly. We propose a method to solve the problem using a factorization machine with quadratic-optimization annealing (FMQA). FMQA is a discrete black-box optimization method reported to obtain high-quality solutions with a limited number of evaluations. Applying FMQA to the problem requires converting nucleotides into binary variables. However, the influence of integer-to-nucleotide assignments and binary-integer encoding on the performance of FMQA has not been thoroughly investigated, even though such choices determine the structure of the surrogate model and the search landscape, and thus can directly affect solution quality. Therefore, this study aims both to establish a novel FMQA framework for RNA inverse folding and to analyze the effects of these assignments and encoding methods. We evaluated all 24 possible assignments of the four nucleotides to the ordered integers (0-3), in combination with four binary-integer encoding methods. Our results demonstrated that one-hot and domain-wall encodings outperform binary and unary encodings in terms of the normalized ensemble defect value. In domain-wall encoding, nucleotides assigned to the boundary integers (0 and 3) appeared with higher frequency. In the RNA inverse folding problem, assigning guanine and cytosine to these boundary integers promoted their enrichment in stem regions, which led to more thermodynamically stable secondary structures than those obtained with one-hot encoding.
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Materials Science
Universal Framework for Decomposing Ionic Transport into Interpretable Mechanisms
KyuJung Jun, Pablo A. Leon, Jurğis Ruža et al. (+2 more)
Understanding mechanisms of ion transport in bulk materials is central to designing next-generation ion conductors for energy storage devices, yet studies employing all-atom molecular dynamics (MD) have largely been limited to reporting overall transport coefficients without a quantitative, spatiotemporally resolved breakdown of how charge is carried. We present a computational framework that analyzes MD trajectories to quantitatively interpret macroscopic transport by decomposing it into additive contributions from physically motivated events. They are defined either through heuristically identified microscopic transitions, capturing events such as single-ion hops, multi-ion hops, and vehicular motion, or through transitions between chemically interpretable coordination macrostates. The construction guarantees that attributed contributions sum exactly to the Onsager transport coefficients estimated via the Green-Kubo/Einstein formalism, while scanning the sampling window exposes characteristic temporal scales at which distinct transport mechanisms emerge and dominate. Applied across three prototypical electrolytes-inorganic
crystals,
liquids, and
polymers-the framework quantitatively resolves long-standing debates (e.g., the role of concerted motion and exchange), identifies dominant mechanisms and rate-limiting steps, quantifies their frequencies and effectiveness, and extracts activation energies for distinct transport modes, thereby distilling design rules for fast conduction. This general and reproducible analysis tool turns MD trajectories into quantitative mechanism maps, enabling the ion-conductor community to adjudicate mechanistic hypotheses and accelerate discovery.
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All authors KyuJung Jun, Pablo A. Leon, Jurğis Ruža, Juno Nam, Rafael Gómez-Bombarelli
Materials Science
Understanding the influence of yttrium on the dominant twinning mode and local mechanical field evolution in extruded Mg-Y alloys
Chaitali Patil, Qianying Shi, Abhishek Kumar et al. (+2 more)
Twinning is a primary deformation mechanism in Mg
alloys. This study focuses on tension twins during uniaxial compression of Mg-Y
alloys, with three key aspects: the orientation specificity of twin grains, the relative
evolution of CRSS with increasing Y content, and the local stress and strain
evolution at twin sites. Experimental characterization and
crystal plasticity modeling were performed. In Mg-7wt.%Y, TT2-{112-1} tension twins were observed in addition to the common TT1-{101-2} twins. Increasing Y suppressed TT1 formation while promoting TT2 activity. A previously unreported group of crystallographic orientations with a higher global Schmid factor for <c+a> slip was identified, which exhibited TT1 twinning with increasing compression strain. To elucidate Y effects on twin activity and local mechanical fields, both TT1 and TT2 tension twin modes were incorporated into PRISMS-Plasticity, an open-source, finite element-based
crystal plasticity solver. Four binary Mg-Y
alloys were modeled under compression, and statistical analysis was conducted to correlate initial orientations, stress-strain distributions, and twin activities as functions of Y concentration. The plasticity analysis revealed that increasing Y decreases the CRSS ratio of prismatic and pyramidal slip relative to TT1 twinning, while the slip-to-twin CRSS ratio for TT2 increases, thereby serving as a potential indicator of differential twin activity with Y addition in Mg
alloys. Additionally, despite their small volume fraction, TT2 twin sites were predicted higher local strain accumulation locally, relative to the representative volume element and TT1 twins, suggesting their potential influence on localized phenomena such as recrystallization or twin nucleation. These findings provide insight into local mechanical behavior in Mg
alloys and support
alloy design for advanced engineering applications.
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All authors Chaitali Patil, Qianying Shi, Abhishek Kumar, Veera Sundararaghavan, John Allison
Materials Science
Stoichiometry Dependent Properties of Cerium Hydride: An Active Learning Developed Interatomic Potential Study
Brenden W. Hamilton, Travis E. Jones, Timothy C. Germann et al. (+1 more)
Cerium hydride has a variety of interesting properties, including a known
lattice contraction and densification with increasing hydrogen content. However, precise stoichiometric control is not experimentally straightforward and ab initio approaches are not computationally feasible for many properties such as melting and low temperature
diffusion. Therefore, we develop a machine-learned interatomic potential for cerium hydride that is valid for H to Ce ratios from 2.0 to 3.0. A query-by-committee active learning approach is used to develop the training set. Leveraging classical molecular dynamics simulations, we assess a range of properties and provide fundamental mechanisms for the trends with stoichiometry. A majority of the properties follow the trend of
lattice contraction, being governed by the stronger
lattice binding induced by adding octahedral atoms.
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All authors Brenden W. Hamilton, Travis E. Jones, Timothy C. Germann, Benjamin T. Nebgen
Soft Condensed Matter
Phase-Field Models for Particle-Stabilised Emulsions
Elisabeth C. Eij, Joost de Graaf, Martin F. Haase et al. (+1 more)
Particle-stabilised emulsions are a cornerstone of soft matter science due to their broad application and fundamental relevance. Computer simulations provide key insights into the formation and behaviour of these emulsions, yet current methods are limited by the spatiotemporal scales accessible for study. The principal issue is that particles are resolved individually. In this work, an alternative strategy is introduced based on phase-field theory, for which we establish the framework. By evolving continuous fields, large-scale dynamics can be simulated in a computationally efficient manner. Our approach is then applied to model the complex formation of a bicontinuous interfacially jammed emulsion gel (bijel) via solvent-transfer induced phase separation (STrIPS). By resolving the coupled dynamics of
liquid phase separation and nanoparticle adsorption, the model allows for the characterisation of the influence of nanoparticles on the morphology. Higher concentrations of nanoparticles are found to reduce the average domain size of STrIPS bijels, in line with previous experimental evidence. The presented phase-field model thus represents a promising approach for the morphological investigation of complex particle-stabilised emulsions.
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All authors Elisabeth C. Eij, Joost de Graaf, Martin F. Haase, Jesse M. Steenhoff
Materials Science
Addressing Ill-conditioning in Density Functional Theory for Reliable Machine Learning
L. Arnstein, J. Wetherell, R. Lawrence et al. (+2 more)
In principle, machine learning (ML) can be used to obtain any electronic property of a many-body system from its electron density within density functional theory. However, some physical quantities are highly sensitive to small variations in the density. This 'ill-conditioning' limits the accuracy with which these quantities can be learned as density functionals from a fixed amount of data. We identify sources of ill-conditioning present in density functionals that belong to two ubiquitous classes: 1) Physical quantities that are globally gauge-dependent, meaning they change value if a constant shift is applied to the external potential – for example, the total energy; 2) Functionals of the N-electron density that have an implicit dependence on the (N+1)-electron density, such as the fundamental gap. We demonstrate that widely used ML models exhibit orders-of-magnitude greater error when applied to these ill-conditioned density functionals compared to other functionals that fall into neither class, even when the global gauge is fixed to prevent constant shifts. Owing to an absence of ill-conditioning in potential functionals, we find that providing the external potential as input to the ML model leads to significantly improved predictions of quantities in these two classes.
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All authors L. Arnstein, J. Wetherell, R. Lawrence, P. J. Hasnip, M. J. P. Hodgson
Strongly Correlated Electrons
Entanglement negativity in decohered topological states
Kang-Le Cai and Meng Cheng
We investigate universal
entanglement signatures of mixed-state phases obtained by decohering pure-state topological order (TO), focusing on topological corrections to logarithmic
entanglement negativity and mutual information: topological
entanglement negativity (TEN) and topological mutual information (TMI). For Abelian TOs under decoherence, we develop a replica field-theory framework based on a doubled-state construction that relates TEN and TMI to the
quantum dimensions of domain-wall defects between decoherence-induced topological boundary conditions, yielding general expressions in the strong-decoherence regime. We further compute TEN and TMI exactly for decohered $G$-graded string-net states, including cases with non-Abelian anyons. We interpret the results within the strong one-form-
symmetry framework for mixed-state TOs: TMI probes the total
quantum dimension of the emergent premodular anyon theory, whereas TEN detects only its modular part.
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Strongly Correlated Electrons
Anisotropic magnetism at the surface of a non-magnetic bulk insulator
Jarryd A. Horn, Keenan E. Avers, Nicholas Crombie et al. (+2 more)
The potential for topological Kondo insulating behavior in d-electron systems has attracted interest in studying the surface states of the correlated
insulators FeSb2 and FeSi. While detailed studies and theoretical description of a
spin-orbit coupled
ferromagnetic surface state have been applied to FeSi, the
magnetic properties of the surface states of FeSb2 have not been addressed. Here, we report on the surface
magnetic properties of FeSb2, utilizing the surface area dependence of
magnetic susceptibility to separate the surface Curie-Weiss temperature dependence from the bulk
spin-gap susceptibility. We use these results to further extract the surface
magnetic anisotropy of a thin, rough-surfaced single-
crystal FeSb2 to compare with the observed magnetotransport anisotropy, and find good agreement between the anisotropy in the surface magnetization and surface magnetotransport. We conclude with evidence of an anomalous
Hall contribution to the low-temperature surface transport.
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All authors Jarryd A. Horn, Keenan E. Avers, Nicholas Crombie, Shanta R. Saha, Johnpierre Paglione
Materials Science
The rise and fall of an oxide: growth and evolution of Bismuth Oxide on Au(111)
Alberto Turoldo, Marco Bianchi, Deborah Perco et al. (+4 more)
We report a comprehensive, multi-technique study of bismuth
oxide growth on Au(111) under different conditions such as temperature and exposure to molecular oxygen. By combining synchrotron-based X-ray photoelectron spectroscopy and diffraction with low-energy electron diffraction and scanning tunneling microscopy, we elucidate the structural
evolution of the system during controlled oxidation and subsequent annealing. We find that Bi deposition induces well-defined surface reconstructions, whereas oxidation triggers the formation of a complex sequence of bismuth
oxide domains. High-resolution spectroscopic and diffraction data enable us to pinpoint the structure of the
oxide consistent with the $(201)$ surface of $\beta$-Bi$_2$O$_3$. In addition, angle resolved photoemission experiments and work function measurements reveal substantial electronic modifications triggered by a complex interplay of segregation of Bi and Au. Notably, a work function of 3.4 eV is achieved for oxidation at 423 K. These results provide
benchmark structural and electronic insights into the Bi
oxide/Au(111) system and establish a framework for integrating Bi$_2$O$_3$ as a contact material in devices using two-dimensional
semiconductors, where it can enable low contact resistance.
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All authors Alberto Turoldo, Marco Bianchi, Deborah Perco, Andrea Berti, Philip Hofmann, Alessandro Baraldi, Silvano Lizzit
Statistical Mechanics · Cross-listed from math-ph
The Quantum Symmetric Simple Exclusion Process in the Continuum and Free Processes
Denis Bernard
The
quantum symmetric simple exclusion process (QSSEP) is a recent extension of the symmetric simple exclusion process, designed to model
quantum coherent fluctuating effects in noisy diffusive systems. It models
stochastic nearest-neighbor fermionic hopping on a
lattice, possibly driven out-of-
equilibrium by boundary processes. We present a direct formulation in the continuum, and establish how this formulation captures the scaling limit of the discrete version. In the continuum, QSSEP emerges as a non-commutative process, driven by free increments, conditioned on the
algebra of functions on the ambiant space to encode spatial correlations. We actually develop a more general framework dealing with conditioned orbits with free increments which may find applications beyond the present context. We view this construction as a preliminary step toward formulating a
quantum extension of the macroscopic fluctuation theory.
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Mesoscale and Nanoscale Physics
Exciton-Selective Phonon Coupling in a Lead Halide Perovskite
Pradeepa H. L., Sagnik Chatterjee, Sayantan Patra et al. (+6 more)
Exciton-
phonon interactions govern the optical response of
semiconductors, yet disentangling multiple coupling channels in lead halide perovskites remains challenging. We investigate CsPbBr3 microcrystals using photoluminescence, Raman and reflectance spectroscopy at low temperature, revealing the simultaneous presence of high-energy and Rashba
excitons, each accompanied by distinct
phonon replica series. High-energy
exciton replicas are uniquely spaced by approximately 9 meV, whereas Rashba
exciton replicas exhibit a characteristic approximately 6 meV spacing, indicating the specificity of the
exciton-
phonon coupling. Unsupervised machine learning applied to a large low-temperature photoluminescence
dataset reveals these replica features are prevalent. With increasing temperature, replica features broaden and merge, evolving into a dominant longitudinal optical
phonon coupling regime at room temperature. This work establishes direct spectroscopic evidence for concurrent,
exciton-specific
phonon coupling within a single material, offering new pathways to engineer light-matter interactions for optoelectronic and
phonon-
photon-based
quantum device applications.
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All authors Pradeepa H. L., Sagnik Chatterjee, Sayantan Patra, Swapneswar Bisoi, Saqlain Mushtaq, Hardeep, Akshay Singh, Ashish Arora, Atikur Rahman
Materials Science
Thermal Decoherence and Population Transfer of MeV Channeling Electrons in Diamond
Tadas Paulauskas
Channeling radiation from MeV-regime electrons is governed by transitions between quantized transverse bound states, but experimental spectra are strongly modified by thermal diffuse scattering. To capture these open-system dynamics, a frozen-
phonon multislice framework is combined with bound-state projection analysis to construct depth-dependent reduced density
matrices in selected transverse
manifolds. Beyond reproducing experimental channeling-radiation transition energies, this approach separates thermal population transfer, intra-
manifold decoherence, and cross-
manifold coherence loss. Applied to 16.9 MeV axial electron channeling in $\langle100\rangle$ diamond, the results show approximately exponential population decay from the initially occupied states, accompanied by strongly channel-dependent feeding among low-lying
manifolds. Starting from a coherent superposition within the degenerate 2p
manifold,
stochastic symmetry breaking by thermal displacements drives the intra-
manifold purity toward the maximally mixed limit, indicating rapid phase scrambling. Under 1s initialization, population transferred into the 2p and 3d
manifolds remains internally close to maximally mixed, yet a weak residual 2p-3d cross-
manifold coherence persists. This framework goes beyond static mean-field thermal broadening and provides a microscopic basis for evaluating population dynamics and coherence lifetimes in strongly quantized channeling-radiation systems.
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Statistical Mechanics · Cross-listed from math.PR
Entrance laws for coalescing and annihilating Brownian motions
Roger Tribe and Oleg Zaboronski
Systems of instantaneously annihilating or coalescing Brownian motions on the line are considered. The extreme points of the set of entrance laws for this process are shown to be Pfaffian point processes at all times and their kernels are identified.
Statistical Mechanics
Quantum-classical correspondence for spins at finite temperatures: theory and applications
A. El Mendili and M. E. Zhitomirsky
We derive a rigorous
quantum-to-classical mapping for interacting
spin systems at finite temperatures. Specifically, the large-$S$ asymptotic form of the partition function is given by the partition function of a classical model for vectors of length $S_C=\sqrt{S(S+1)}$.
Quantum corrections to the asymptotic result form a series in powers of $1/[S(S+1)]$. We calculate the leading temperature-independent
quantum correction to the
magnetic anisotropy constant. The established mapping justifies the use of classical Monte Carlo simulations for realistic
magnetic Hamiltonians, including anisotropic and frustrated interactions. As an application, we compute the Curie and Néel temperatures for a range of
magnetic materials with known microscopic interaction constants. The obtained transition temperatures are in good agreement with measured values. Monte Carlo results for the
magnetic susceptibility of the collinear antiferromagnet MnF$_2$ above and below the transition are also compared with experimental data.
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Statistical Mechanics
Emergent Topological Complexity in the Barabasi-Albert Model with Higher-Order Interactions
Vadood Adami, Hosein Masoomy, Mirko Luković et al. (+1 more)
We examine the homological structure of the Barabasi-Albert model, focusing on the time
evolution of $\Delta$-dimensional simplices and topological holes as functions of time $t$ and the attachment parameter $m$ (the number of edges added by each incoming node). Numerical simulations reveal a non-trivial topological transition (TT) in the $(\Delta, m)$ plane, marking a change from a topologically trivial regime to non-trivial
topology. This transition signals the emergence of topological complexity in the model, where higher-order structures develop self-similarly across scales. Beyond this transition, the network exhibits self-similar topological growth, evidenced by a power-law decay in the increments of $\Delta$-simplices with $m$-dependent exponents. An analogous transition occurs in the Betti numbers, which display self-similar behavior near the TT and an arctangent dependence farther from it. Based on simulation data, we propose explicit scaling relations describing the behavior of both $\Delta$-simplices and Betti numbers near the TT. Overall, the analysis reveals a rich, gapful topological transition structure, where topological quantities exhibit discrete jumps at the transition point.
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All authors Vadood Adami, Hosein Masoomy, Mirko Luković, Morteza Nattagh Najafi
Materials Science
When Is Structural Lubricity Load Independent? The Role of Contact Geometry and Elastic Compliance
Hongyu Gao
Using molecular dynamics simulations of an incommensurate Au(111)/graphite interface, we investigate the conditions under which structural lubricity produces load-independent friction. We show that strict load independence occurs only in laterally infinite, area-filling contacts, where dissipation is governed by
phonon-mediated viscous coupling and the shear stress scales linearly with sliding velocity. Finite contacts with explicit boundary terminations exhibit substantially higher friction yet remain load independent up to a critical load. Load dependence arises only when elastic out-of-plane deformation near the contact line exceeds a critical amplitude, activating additional dissipation channels. These results demonstrate that contact geometry and local elastic compliance, rather than normal load itself, determine the onset and breakdown of load-independent structural lubricity.
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Strongly Correlated Electrons
Monte Carlo study of the classical antiferromagnetic $J_1$-$J_2$-$J_3$ Heisenberg model on a simple cubic lattice
A.N. Ignatenko, S.V. Streltsov and V.Yu. Irkhin
An extensive Monte Carlo study of the classical Heisenberg model on a simple cubic
lattice with
antiferromagnetic exchange interactions $J_n$ between the first, second, and third neighbors is performed in a broad region of $J_2 / J_1$, $J_3 / J_1$ ratios, and temperature. The character of the phase transitions is analyzed via the Binder cumulant method. The Neel temperature $T_{\mathrm{N}}$ and the frustration parameter (the ratio $f= |\theta|/T_{\mathrm{N}}$, $\theta$ being the Curie-Weiss temperature) are calculated. A comparison with the Tyablikov approximation is carried out. The strength of the frustration effects is explored. Possible applications to
antiferromagnetic perovskites, such as CaMnO$_3$ and HgMnO$_3$, are discussed.
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Mesoscale and Nanoscale Physics
Confinement Epitaxy of Large-Area Two-Dimensional Sn at the Graphene/SiC Interface
Zamin Mamiyev, Niclas Tilgner, Narmina O. Balayeva et al. (+3 more)
Confinement epitaxy beneath
graphene stabilizes exotic material phases by restricting vertical growth and altering lateral
diffusion, conditions unattainable on bare substrates. However, achieving long-range interfacial order while maintaining high-quality
graphene remains a significant challenge. Here, we demonstrate the synthesis of large-area quasi-free-standing monolayer
graphene (QFMLG) via the intercalation of a two-dimensional (2D) Sn. While the triangular Sn(1x1) interface exhibits a robust metallic band structure, the decoupled QFMLG maintains charge neutrality, confirmed by photoemission spectroscopy. Using high-resolution Raman spectroscopy and microscopy, we distinguish between direct intercalation and
diffusion-driven expansion, identifying the latter as the critical pathway to superior QFMLG crystalline quality. Temperature-dependent analysis reveals dynamical structural coupling between the decoupled QFMLG and the Sn interface, providing a novel degree of freedom for strain engineering. Beyond uncovering the
diffusion-driven mechanism, this work establishes metal intercalation as an effective strategy for tailoring durable
graphene-metal
heterostructures with tunable properties for next-generation
quantum materials platforms.
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All authors Zamin Mamiyev, Niclas Tilgner, Narmina O. Balayeva, Dietrich R.T. Zahn, Thomas Seyller, Christoph Tegenkamp
Statistical Mechanics · Cross-listed from q-bio.PE
Evolutionary Advantage of Diversity-Generating Retroelements in Switching Environments
Léo Régnier, Paul Rochette, Raphaël Laurenceau et al. (+3 more)
Diversity-Generating Retroelements (DGRs) create rapid, targeted variation within specific genomic regions in phages and bacteria. They operate through
stochastic retro-transcription of a template region (TR) into a variable region (VR), which typically encodes ligand-binding
proteins. Despite their prevalence, the evolutionary conditions that maintain such hypermutating systems remain unclear. Here we introduce a two-timescale framework separating fast VR diversification from slow TR
evolution, allowing the dynamics of DGR-controlled loci to be analytically understood from the TR design point of view. We quantity the fitness gain provided by the diversification mechanism of DGR in the presence of environmental switching with respect to standard mutagenesis. Our framework accounts for observed patterns of DGR activity in human-gut Bacteroides and clarifies when constitutive DGR activation is evolutionarily favored.
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All authors Léo Régnier, Paul Rochette, Raphaël Laurenceau, David Bikard, Simona Cocco, Rémi Monasson
Mesoscale and Nanoscale Physics
Transition between one- and two-dimensional topology in a Chern insulator of finite width
Frode Balling-Ansø, Adipta Pal, Ashley M. Cook et al. (+1 more)
Topology in
quantum systems is typically considered in infinite
crystals in one, two, or higher integer dimensions. Here, we show that one can continuously transform a system between a topological phase associated with one dimension and a topological phase associated with two dimensions without closing the energy gap. In this process, the dimension of the system itself changes. Concretely, we investigate a modified version of the Qi-Wu-Zhang model and develop a procedure to smoothly shrink the width of the system in one direction. By tracking gaps which remain open throughout the modulation, we establish a smooth transition from a two-dimensional to a one-dimensional topological
insulator. In between the system exhibits both one- and two-dimensional
topology, and the way the system accomplishes the transition is by making the one-dimensional
topology more robust as the width decreases, while the two-dimensional
topology becomes less robust. Finally, we show how the gaps arise from hybridization of edge states due to the finite width.
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All authors Frode Balling-Ansø, Adipta Pal, Ashley M. Cook, Anne E. B. Nielsen
Soft Condensed Matter
Three dimensional contractile droplet under confinement
Adriano Tiribocchi, Marco Lauricella, Andrea Montessori et al. (+1 more)
We numerically study the dynamics of a three-dimensional contractile fluid droplet in the bulk and under confinement. We show that varying activity leads to a variety of shapes and motile regimes whose motion is driven by an interplay between spontaneous flows and elasticity. In the bulk the droplet self-propels unidirectionally, acquiring either an almost spherical shape at intermediate activity or a peanut-like geometry for larger values. Under confinement, the droplet exhibits a previously unreported oscillating dynamics characterized by periodic hits against opposite walls of a microchannel while moving forward. These results could be of interest for the study of artificial microswimmers and their biological analogs, such as living
cells.
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All authors Adriano Tiribocchi, Marco Lauricella, Andrea Montessori, Sauro Succi
Statistical Mechanics
Nonperturbative computation of thermal conductivity based on Path Integral Monte Carlo methods
Vladislav Efremkin, Stefano Mossa, Jean-Louis Barrat et al. (+1 more)
The calculation of thermal conductivity in insulating solids at temperatures below the Debye temperature is problematic, due to the breakdown of classical and semi-classical approaches. In this work, we present a fully non-perturbative
quantum methodology to compute thermal conductivity based on Path Integral Monte Carlo (PIMC) simulations combined with the Green-Kubo linear response theory. The method is applied to rare gas solids modeled by a Lennard-Jones potential, paradigmatic systems where
quantum effects strongly affect both thermodynamic and transport properties. From PIMC simulations, we obtain the temperature-dependent
phonon frequencies, lifetimes, and specific heat. From the imaginary time correlations of the energy current, we extract the thermal transport coefficients based on a physically motivated prior. We show that the experimentally observed increase of the thermal conductivity of argon and neon at low temperatures cannot be explained within a Peierls-Boltzmann framework using
phonon line-widths at
equilibrium. In contrast, a distinct transport lifetime emerges from the analysis of heat-current correlations. Our results demonstrate that
quantum Monte Carlo methods provide a robust, nonperturbative framework to investigate heat transport in insulating solids, beyond the limits of classical molecular dynamics without relying on perturbative or semi-classical approximations.
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All authors Vladislav Efremkin, Stefano Mossa, Jean-Louis Barrat, Markus Holzmann
Materials Science
Hidden universality in dislocation-loops mediated three-dimensional crystal melting
Alessio Zaccone and Konrad Samwer
Understanding why and how crystalline solids melt remains a central problem in condensed-matter physics. Dislocation loops are fundamental topological excitations that control the thermodynamic stability of
crystals, yet their role in setting universal aspects of melting has remained unclear. Here we show, within dislocation-mediated melting theory, that the free-energy condition for loop proliferation leads to a universal ratio between the energy of a minimal dislocation loop and the thermal energy at melting. For minimal dislocation loops that begin to proliferate at the onset of melting, this ratio takes the purely
geometric value $\mathcal{E}_* = E_{\rm loop}/(k_B T_m) \approx 25.1$, independent of elastic
moduli and chemistry-dependent details. This result provides a microscopic explanation for recent empirical findings by Lunkenheimer et al., who identified a closely related universal energy scale $\approx 24.6$ from viscosity data. The same framework also rationalizes the empirical $2/3$ rule relating the glass-transition and melting temperatures.
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Mesoscale and Nanoscale Physics
Photophysical properties of Eu3+ complexes approaching electronic contact to a metal surface
Adrian Ebert, Simon Fromme, Lisa Burgert et al. (+10 more)
The application of rare-earth complexes in electrically driven light sources poses a series of challenges that require specific optimization of the molecular photophysical properties. Here, we present a report on films of three different Eu3+ complexes characterized in terms of emission spectra and fluorescence decay. We compare molecular complexes in powder form and sublimed films, in films on glass and on a metal surface, and in films of thicknesses down to less than 3 nm (< 3 ML), approaching electrical coupling. Our photoluminescence experiments supported by scanning tunneling microscopy of sub-monolayers indicate that Eu3+(trensal) complexes are less affected by sublimation and more stable on the metal surface than typical beta diketonate complexes, making them promising candidates for electroluminescence devices.
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All authors Adrian Ebert, Simon Fromme, Lisa Burgert, Umar Rashid, Lukas Gerhard, Julia Feye, Senthil Kumar Kuppusamy, Barbora Brachnakova, Timo Neumann, Mario Ruben, Peter W. Roesky, Michael Seitz, Wulf Wulfhekel
Materials Science
AI-Driven Structure Refinement of X-ray Diffraction
Bin Cao, Qian Zhang, Zhenjie Feng et al. (+4 more)
Artificial intelligence can rapidly propose candidate phases and structures from X-ray diffraction (XRD), but these hypotheses often fail in downstream refinement because peak intensities cannot be stably assigned under severe overlap and diffraction consistency is enforced only weakly. Here we introduce the whole-pattern expectation–maximization (WPEM)
algorithm, a physics-constrained whole-pattern decomposition and refinement workflow that turns Bragg's law into an explicit constraint within a batch expectation–maximization framework. WPEM models the full profile as a probabilistic mixture density and iteratively infers component-resolved intensities while keeping peak centres Bragg-consistent, producing a continuous, physically admissible intensity representation that remains stable in heavily overlapped regions and in the presence of mixed radiation or multiple phases. We
benchmark WPEM on standard reference patterns (PbSO$_4$ and Tb$_2$BaCoO$_5$), where it yields lower $R_p/R_{wp}$ than widely used packages (FullProf and TOPAS) under matched refinement conditions. We further demonstrate generality across realistic experimental scenarios, including phase-resolved decomposition in multiphase materials, quantitative recovery of mixture compositions, separation of crystalline peaks from amorphous backgrounds in semicrystalline systems, high-throughput operando
lattice tracking, automated refinement of compositionally disordered solid solutions, and quantitative phase-resolved analysis of complex archaeological samples from synchrotron powder XRD. By providing Bragg-consistent, uncertainty-aware intensity partitioning as a refinement-ready interface, WPEM closes the gap between AI-generated hypotheses and diffraction-admissible structure refinement on challenging XRD data.
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All authors Bin Cao, Qian Zhang, Zhenjie Feng, Taolue Zhang, Jiaqiang Huang, Lu-Tao Weng, Tong-Yi Zhang
Materials Science · Cross-listed from quant-ph
Why the Casimir Force for Magnetic Metals Computed by the Lifshitz Theory Using the Drude Model Disagrees with the Measurement Data
G. L. Klimchitskaya, C. C. Korikov and V. M. Mostepanenko
We consider the Casimir force in configurations with
magnetic metal plates and analyze the reasons why the predictions of the Lifshitz theory using the dielectric permittivity of the Drude model are inconsistent with the measurement data. For this purpose, the contributions of the electromagnetic waves with the transverse
magnetic and transverse electric polarizations to the Casimir force are computed using the Lifshitz theory expressed in terms of the pure imaginary Matsubara frequencies. Furthermore, the fractions of the evanescent and propagating waves in these contributions are found using an equivalent formulation of the Lifshitz theory along the real frequency axis. All computations are performed for Au-Ni and Ni-Ni plates using the Drude model and the experimentally consistent
plasma model over the separation region from 0.5 to 6~mum, where the total force value is determined by conduction electrons. It is shown that the transverse
magnetic contribution to the Casimir force does not depend on the used model of the dielectric permittivity, so that the total difference between the predictions of the Lifshitz theory using the Drude model and the measurement data is determined by the transverse electric contribution. In doing so, as opposed to the case of nonmagnetic metals, both fractions of the evanescent and propagating waves in this contribution depend on the model of the dielectric permittivity used in computations, whereas the
magnetic properties of the plate metal influence the Casimir force solely through the fraction of propagating waves in the transverse electric contribution. The issue of a more adequate theoretical description of the electromagnetic response of
magnetic metals is discussed.
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Strongly Correlated Electrons
Liouvillian interpolation of the self-energy of cluster dynamical mean-field theories
Mathias Pelz, Jan von Delft and Andreas Gleis
Two widely-used non-local extensions of dynamical mean-field theory (DMFT), namely cellular DMFT (CDMFT) and the dynamical cluster approximation (DCA), both yield self-energies marred by having some unphysical properties: CDMFT yields real-space self-energies that are not translationally invariant, and DCA yields momentum-space self-energies with discontinuities in their momentum dependence. It is often desirable to remove these flaws by post-processing cluster DMFT results, using strategies called periodization for CDMFT and interpolation for DCA—for brevity, we refer to both cases as interpolation. However, traditional interpolation approaches struggle to reliably capture intricate structures such as hole pockets in the hole-doped square-
lattice Hubbard model. Further, these approaches interpolate frequency-dependent functions, which may lead to causality violations. Here, we propose Liouvillian interpolation, a novel, intuitive, and robust scheme for interpolating cluster DMFT results. Our key idea is to interpolate frequency-independent
matrix elements of the single-particle irreducible part of the Liouvillian, obtained from a continued-fraction expansion of the cluster DMFT self-energy. We demonstrate that the ingredients of such an expansion possess a more local
Fourier expansion than the functions involved in traditional interpolation schemes, and that Liouvillian interpolation conserves causality by construction. We illustrate our method for the one-dimensional Hubbard model using CDMFT, and for the two-dimensional Hubbard model using four-site CDMFT and four-patch DCA. For the latter, $\mathcal{L}$-interpolation can (depending on doping) yield
Fermi and Luttinger arcs which together seem to form a closed surface.
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