Statistical Mechanics
Efficient Monte Carlo sampling of metastable systems using non-local collective variable updates
Christoph Schönle, Davide Carbone, Marylou Gabrié et al. (+2 more)
Monte Carlo simulations are widely used to simulate complex molecular systems, but standard approaches suffer from metastability. Lately, the use of non-local proposal updates in a collective-variable (CV) space has been proposed in several works. Here, we generalize these approaches and explicitly spell out an
algorithm for non-linear CVs and underdamped Langevin dynamics. We prove reversibility of the resulting scheme and demonstrate its performance on several numerical examples, observing a substantial performance increase compared to methods based on overdamped Langevin dynamics as considered previously. Advances in generative machine-learning-based proposal samplers now enable efficient sampling in CV spaces of intermediate dimensionality (tens to hundreds of variables), and our results extend their applicability toward more realistic molecular systems.
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All authors Christoph Schönle, Davide Carbone, Marylou Gabrié, Tony Lelièvre, Gabriel Stoltz
Materials Science
Comparing Hubbard parameters from linear-response theory and a Hartree-Fock-based approach
Wooil Yang, Iurii Timrov, Francesco Aquilante et al. (+1 more)
Density-functional theory with on-site $U$ and inter-site $V$ Hubbard corrections (DFT+$U$+$V$) is widely used to predict properties of transition-metal and rare-earth compounds, but its accuracy depends critically on how these parameters are obtained. While they can be determined empirically, first-principles approaches offer better consistency, though their results can differ and a systematic comparison is lacking. Here, we compare two widely used approaches, linear-response theory (LRT) and the Hartree–Fock-based pseudohybrid functional formalism, applied to representative
oxides (MnO, NiO, CoO, FeO, BaTiO$_3$, ZnO, and ZrO$_2$). For partially occupied transition-metal $d$ states, both methods yield comparable $U$ values, but they differ significantly for nearly empty or fully filled $d$ shells. For O-$2p$ states, LRT systematically predicts large $U$ values ($\sim 10~\mathrm{eV}$), whereas the pseudohybrid approach gives system-dependent values. Even larger differences appear for the inter-site $V$: the former yields small values ($<1~\mathrm{eV}$), while the latter gives larger values ($\sim 3~\mathrm{eV}$) due to its dependence on charge redistribution. We further show that the pseudopotential choice, which defines Hubbard projectors, affects the parameters and their agreement. Overall, while parallels between these two methods exist, they rely on different assumptions, leading to variations in predictions of material properties.
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All authors Wooil Yang, Iurii Timrov, Francesco Aquilante, Young-Woo Son
Quantum Gases · Cross-listed from nucl-th
Relativistic superfluid profiles near critical surfaces
Lorenzo Gavassino and Alexander Soloviev
Landau's two-fluid model of superfluidity ceases to apply in regions where the condensate amplitude exhibits rapid spatial variation, such as
vortex cores or in the vicinity of container walls. A recently proposed relativistic Gross-Pitaevskii-type framework treats the condensate as an independent scalar degree of freedom, enabling a controlled analysis of such regimes. We use it to construct stationary superflows close to the superfluid-normal phase boundary, and examine their stability. We obtain an exact expression for Landau's critical velocity and show that the standard Newtonian profiles (such as the near-
vortex condensate depletion or the boundary-layer decay) persist unmodified in the relativistic setting. We further analyse a genuinely relativistic configuration in which an accelerated superfluid develops a phase boundary induced by Tolman temperature gradients.
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Superconductivity
Magneto-elasto-resistivity in FeSe
M. Wissmann, L. Fanfarillo, X.-C. Hong et al. (+6 more)
FeSe stands out among iron-based
superconductors due to its extended nematic phase without the onset of long-range
magnetic order. While strain-dependent electrical resistivity has been extensively explored to probe nematicity, its influence on magneto-transport properties remains less understood. In this work, we present measurements of the magneto-elasto-resistivity in FeSe as a function of temperature and applied
magnetic field. Using a minimal multiband Boltzmann model for transport we derive analytical expressions that capture the
magnetic behavior of the whole set of experimental data both in the paramagnetic and in the nematic phase. These findings indicate that a multiband framework can robustly describe the magneto-elasto-transport properties in FeSe and arguably in other iron-based
superconductors.
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All authors M. Wissmann, L. Fanfarillo, X.-C. Hong, S. Caprara, S. Aswartham, B. Büchner, C. Hess, G. Seibold, F. Caglieris
Strongly Correlated Electrons
Strain-Controlled Magnetic Phase Transitions through Anisotropic Exchange Interactions: A Combined DFT and Monte Carlo Study
Sudip Mandal, Mihir Ranjan Sahoo and Kalpataru Pradhan
Epitaxial strain provides a powerful, non-chemical route to tune the properties of functional materials by manipulating the coupling between
spin, charge, and
lattice degrees of freedom. Using density functional theory (DFT) calculations and $\rm BiFeO_3$ as a model system, we first demonstrate how epitaxial strain exactly leads to anisotropic
magnetic interactions where the exchange coupling along the $c$-axis differs from that in the $ab$-plane. We show that subtle structural modifications, specifically the distortion from a cubic to a tetragonal
lattice, drive a
magnetic phase transition from a G-type to a C-type
antiferromagnetic (AF) phase. The anisotropy in
magnetic interactions, which becomes prominent in the lower
symmetry tetragonal phase, provides a direct link between the structural distortion and the potential change in
magnetic ordering. For a more comprehensive study, we next investigate the role of strain in driving
magnetic phase transitions within a half-filled one-band Hubbard model in three dimensions. In this framework, strain is introduced through anisotropic hopping processes between nearest- and next-nearest-neighbor sites, inspired by the DFT calculations. Using a semiclassical Monte Carlo (s-MC) approach, we construct ground state phase diagrams in the nonperturbative regime, which show how uniaxial strain stabilizes distinct
magnetic ground states: Compressive strain drives a transition from a G-type to a C-type AF
insulator, whereas tensile strain suppresses the C-type AF order, favoring an A-type AF phase. Overall, our combined DFT and s-MC calculations highlight that strain is a powerful tuning parameter for controlling competing
magnetic phases by governing exchange coupling mechanisms in correlated systems, offering valuable insights for the design of strain-controlled materials.
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Soft Condensed Matter · Cross-listed from cs.LG
Pattern recognition in complex systems via vector-field representations of spatio-temporal data
Ingrid Amaranta Membrillo Solis, Maria van Rossem, Tristan Madeleine et al. (+5 more)
A complex system comprises multiple interacting entities whose interdependencies form a unified whole, exhibiting emergent behaviours not present in individual components. Examples include the human
brain, living
cells, soft matter, Earth's
climate, ecosystems, and the economy. These systems exhibit high-dimensional, non-linear dynamics, making their modelling, classification, and prediction particularly challenging. Advances in information technology have enabled data-driven approaches to studying such systems. However, the sheer volume and complexity of spatio-temporal data often hinder traditional methods like dimensionality reduction, phase-space reconstruction, and attractor characterisation. This paper introduces a
geometric framework for analysing spatio-temporal data from complex systems, grounded in the theory of vector fields over discrete measure spaces. We propose a two-parameter family of metrics suitable for data analysis and machine learning applications. The framework supports time-dependent images, image gradients, and real- or vector-valued functions defined on graphs and simplicial complexes. We validate our approach using data from numerical simulations of biological and physical systems on flat and curved domains. Our results show that the proposed metrics, combined with multidimensional scaling, effectively address key analytical challenges. They enable dimensionality reduction, mode decomposition, phase-space reconstruction, and attractor characterisation. Our findings offer a robust pathway for understanding complex dynamical systems, especially in contexts where traditional modelling is impractical but abundant experimental data are available.
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All authors Ingrid Amaranta Membrillo Solis, Maria van Rossem, Tristan Madeleine, Tetiana Orlova, Nina Podoliak, Giampaolo D'Alessandro, Jacek Brodzki, Malgosia Kaczmarek
Quantum Gases
Structure of the mean-field yrast spectrum of a two-component Bose gas in a ring: role of interaction asymmetry
Hui Tang, Guan-Hua Huang, Shizhong Zhang et al. (+2 more)
The mean-field yrast spectrum of an SU(2)-symmetric two-component Bose gas confined to a ring geometry is known to exhibit an intricate nonanalytic structure that is absent in single-component systems. In particular, due to the interplay between the species concentration and the atomic interactions, a sequence of plane-wave states can emerge as yrast states at fractional values of the angular momentum per particle. This behavior stands in sharp contrast to the single-component case, where plane-wave states occur only at integer angular momenta. In this paper, we investigate how the structure of the yrast spectrum in a two-component Bose gas is modified by interaction asymmetry. By numerically solving the coupled Gross-Pitaevskii equations for propagating
soliton states, we compute the mean-field yrast spectrum and, in particular, determine the critical curves associated with the emergence of various plane-wave yrast states. We find that both the behavior of these critical curves and the mechanisms by which plane-wave yrast states arise depend sensitively on the relative strengths of the inter- and intra-component interactions. When the intra-component interaction is weaker, the plane-wave yrast states replace
soliton states through a continuous
evolution, as in the SU(2)-symmetric case, although the conditions for their existence become more restrictive. In contrast, when the intra-component interaction is stronger, plane-wave yrast states may emerge by overtaking
soliton states via branch crossings, and their stability is significantly enhanced. Our results have important implications for the existence and stability of persistent currents in asymmetric, two-component Bose gases.
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All authors Hui Tang, Guan-Hua Huang, Shizhong Zhang, Zhigang Wu, Eugene Zaremba
Statistical Mechanics
Correlation between the first-reaction time and the acquired boundary local time
Yilin Ye and Denis S. Grebenkov
We investigate the statistical correlation between the first-reaction time of a diffusing particle and its boundary local time accumulated until the reaction event. Since the reaction event occurs after multiple encounters of the particle with a partially reactive boundary, the boundary local time as a proxy for the number of such encounters is not independent of, but intrinsically linked to, the first-reaction time. We propose a universal theoretical framework to derive their joint probability density and, in particular, the correlation coefficient. To illustrate the dependence of these correlations on the boundary reactivity and shape, we obtain explicit analytical solutions for several basic domains. The analytical results are complemented by Monte Carlo simulations, which we employ to examine the role of interior obstacles on correlations in disordered media. Applications of these statistical results in chemical physics are discussed
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Materials Science
Spin-Dependent Nonorthogonal Generalized Wannier Functions and their Integration with PAW and Hubbard Corrections in Linear-Scaling DFT
Miguel Escobar Azor, David D. O'Regan, Ali Safavi et al. (+3 more)
We present a
spin-dependent extension of the non-orthogonal generalized Wannier function (NGWF) formalism within the framework of linear-scaling density functional theory (LS-DFT) as implemented in the ONETEP code. In traditional LS-DFT representations, both
spin channels are constrained to share a common variational basis, which limits the accuracy for systems that are
spin-polarized or exhibit
magnetic order. Our approach allows NGWFs to vary independently for each
spin channel, enabling a more accurate representation of
spin-polarization in the electronic density. We demonstrate the efficacy of this method through a series of test cases, including localized
magnetic defects in two-dimensional hBN, transition metal complexes, two-dimensional van der Waals
magnetic materials, and both bulk and nanocluster
ferromagnetic Co. In each scenario, the incorporation of
spin-dependent NGWFs results in enhanced accuracy for total energy calculations, improved localization of
spin density, and accurate predictions of
magnetic ground states. This improvement is particularly notable when combined with DFT+U and DFT+U+J corrections. In this work, we take the opportunity to describe the combination of DFT+U+J and the projector-augmented wave (PAW) formalism within the LS-DFT framework, including how PAW participates in the ionic Pulay force, and in the minimum-tracking linear response approach for computing parameters in situ. Our findings demonstrate that
spin-dependent NGWFs are a crucial and computationally efficient advancement in the linear-scaling DFT simulation of
spin-polarized materials.
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All authors Miguel Escobar Azor, David D. O'Regan, Ali Safavi, Jacek Dziedzic, Chris-Kriton Skylaris, Nicholas D. M. Hine
Soft Condensed Matter
Accurate coarse-graining of small organic molecules in melts and thin films using density-dependent potentials
Sayan Dutta, Maria C. Lesniewski, Muhammad Nawaz Qaisrani et al. (+3 more)
Conjugated organic molecules play a central role in a wide range of optoelectronic devices, including organic light-emitting diodes, organic field-effect transistors, and organic
solar cells. A major bottleneck in the computational design of these materials is the discrepancy between simulation and experimental time and length scales. Coarse-graining (CG) offers a promising solution to bridge this gap by reducing redundant degrees of freedom and smoothing the potential energy landscape, thereby significantly accelerating molecular dynamics simulations. However, standard CG models are typically parameterized from homogeneous bulk simulations and assume density-independent effective interactions. As a consequence, they often fail to replicate inhomogeneous systems, such as (free-standing) thin films, due to an incorrect representation of
liquid-
vacuum interfacial properties. In this work, we develop a CG parametrization strategy that incorporates local-density-dependent potentials to capture material heterogeneities. We evaluate the methodology by simulating free-standing films and comparing interfacial orientational order parameters between all-atom and CG simulations. The resulting CG models accurately reproduce bulk densities and radial distribution functions as well as molecular orientations at the
liquid-
vacuum interface. This work paves the way for reliable, computation-driven predictions of atomically resolved interfacial ordering in organic molecular systems.
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All authors Sayan Dutta, Maria C. Lesniewski, Muhammad Nawaz Qaisrani, W. G. Noid, Denis Andrienko, Arash Nikoubashman
Materials Science
Self-supported bulk MXene electrodes for electrochemical hydrogen applications
Rebeca Miyar, Bar Favelukis, Eva B. Mayer et al. (+7 more)
MXenes are promising candidates for electrochemical applications due to their high conductivity, tunable surface chemistry, and catalytic potential. However, their use in bulk electrode form remains unexplored despite advantages such as higher current density and improved mechanical integrity. Herein, we present a methodology for the fabrication of self-supported vdW solid Ti3C2Tz MXene electrodes, produced by cold compaction followed by
vacuum heat treatment at 600 {\deg}C, which effectively removes interlayer confined water and stabilizes the bulk 3D structure. The resulting binder-free electrodes exhibit enhanced mechanical robustness along with structural and chemical stability in various electrolytes. The MXene electrodes demonstrate adequate HER activity while maintaining electrochemical stability over time, with minimal oxidation or changes in termination surface chemistry. This approach is scalable and cost-effective, overcoming limitations of nanoscale MXene architectures in electrochemical environments and offering a practical pathway toward MXene-based materials for sustainable hydrogen energy technologies.
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All authors Rebeca Miyar, Bar Favelukis, Eva B. Mayer, Manoj Prabhakar, Yug Joshi, Gerhard Dehm, Jochen M. Schneider, Maria Jazmin Duarte, Barak Ratzker, Maxim Sokol
Disordered Systems and Neural Networks
Reduction of interaction order in hard combinatorial optimization via conditionally independent degrees of freedom
Alexandru Ciobanu, David Dahmen, John Paul Strachan et al. (+1 more)
Combinatorial optimization problems have a broad range of applications and map to physical systems with complex dynamics. Among them, the 3-SAT problem is prominent due to its NP-complete nature. In physics terms, its solution corresponds to finding the ground state of a disordered Ising
spin Hamiltonian with third-order, or tensor, interactions. The large growth of the number of third-order interactions with number of variables poses technical difficulties for the physical implementation of minimizers. Therefore, researchers have proposed quadratization techniques which reduce the order of the system, however, at the cost of including additional degrees of freedom. Their inclusion induces a drastic slow down in the minimization, which makes such procedures technically infeasible for large problems. In this work, we take a physics approach by employing the renormalization group to create a pairwise interacting system from the original third-order system while preserving the free energy. Our procedure utilizes additional degrees of freedom that exhibit an independent dynamics provided the original degrees of freedom are fixed. A step-wise trace of the extra variables while running the minimization is therefore theoretically manageable, yielding a state-dependent effective interaction. We use the effective interaction to reconstruct the original third-order energy spectrum, as this yields equal scaling of computations-to-ground-state compared to the original tensor formulation. Here, the original degrees of freedom interact with a subsystem that appears to be in a superposition of an exponentially large number of states. In the zero-temperature limit, the superposition concentrates on one state. Our spectrum-engineering techniques reveal new routes toward the ground state of disordered Ising systems, through Markov chains, and allow for efficient technological implementations.
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All authors Alexandru Ciobanu, David Dahmen, John Paul Strachan, Moritz Helias
Soft Condensed Matter
Approximation of forces and torques from anisotropic pairwise interactions using multivariate polynomials
Mohammadreza Fakhraei, Michaela Bush, Chris A. Kieslich et al. (+1 more)
The dynamics of anisotropic particles are dictated by forces and torques that can be challenging to mathematically represent in computer simulations. Several data-driven approaches have been developed to approximate these interactions, but they often rely on having large amounts of training data that may be practically difficult to generate. Here, we extend a framework we recently developed for approximating anisotropic pair potentials to the approximation of pairwise forces and torques. The framework uses multivariate
polynomials and physics-motivated coordinate transformations to produce accurate approximations using limited amounts of data. We first derive expressions relating the force and torque to partial derivatives of the potential energy with respect to the transformed coordinates used to represent the particle configuration. We then explore several options for approximating the forces and torques, and we critically assess their accuracy using model two- and three-dimensional shape-anisotropic nanoparticles as test cases. We find that interpolation of the pairwise potential energy produces the best result when it is known, but force and torque matching (regression) is a viable strategy when only the force and torque is available.
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All authors Mohammadreza Fakhraei, Michaela Bush, Chris A. Kieslich, Michael P. Howard
Materials Science
High-Throughput Prediction of Exfoliable Non-van der Waals Materials from a Universal Potential
Tom Barnowsky, Carsten Timm and Rico Friedrich
Exfoliation and cleavage create two-dimensional (2D) materials and surfaces with physical and chemical properties distinct from their bulk parents. The rising class of non-van der Waals (non-vdW) 2D materials derived from non-layered
crystals provides a fascinating platform, expanding the landscape of low-dimensional materials. Current computational models, however, provide limited guidance: existing descriptors are largely tailored to vdW layered systems. Here, we introduce a general framework predicting
crystal cleavage and exfoliable 2D subunits directly from bulk structures. At its core is a universal eXfoliation and Cleavage Potential (XCP) enabling large-scale screening of diverse materials at negligible computational cost. Applying this approach, we obtain 44,030 cleavable surfaces and candidate non-vdW 2D materials from which we investigate - according to our criteria - 2,531 likely exfoliable ones using high-throughput density functional theory. A large fraction of these candidates is found to be dynamically and thermodynamically stable, while showing negligible overlap with existing 2D materials databases. Our study thus opens a systematic route to explore and design 2D materials with high chemical and structural diversity.
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Materials Science · Cross-listed from physics.optics
Intrinsic temporal and spectral mixing in time-resolved terahertz spectroscopy
Benjamin J. Dringoli and David G. Cooke
In an ultrafast optical-pump terahertz-probe measurement, the photoinduced material response can be modulated on a timescale shorter than the extent of the THz pulse. In this situation, the measured time-frequency response deviates from a simple time-dependent linear response. When full two-dimensional time-frequency maps are measured, this yields complex features that can be incorrectly assigned to a photoexcited coherent response. We investigate this experimentally via the measured response of photoexcited SnSe, whereby photoinduced phase change dynamics lead to ultrafast changes of the charge carrier and
lattice optical conductivity response. Two-dimensional time-frequency THz transmission maps subsequently show unexpected time-frequency features at early pump-probe delay times. These features are reproduced in both finite-difference time-domain simulations of the THz experiment and in an extension of non-
equilibrium response function theory, demonstrating their systematic origin. This work improves the understanding of systematic effects in high time resolution optical-pump THz-probe spectroscopy, and explores the conditions in which they are likely to appear.
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Materials Science
How accurate are foundational machine learning interatomic potentials for heterogeneous catalysis?
Luuk H. E. Kempen, Raffaele Cheula and Mie Andersen
Foundational machine learning interatomic potentials (MLIPs) are being developed at a rapid pace, promising closer and closer approximation to ab initio accuracy. This unlocks the possibility to simulate much larger length and time scales. However,
benchmarks for these MLIPs are usually limited to ordered, crystalline and bulk materials. Hence, reported performance does not necessarily accurately reflect MLIP performance in real applications such as heterogeneous catalysis. Here, we systematically analyze zero-shot performance of 80 different MLIPs, evaluating tasks typical for heterogeneous catalysis across a range of different data sets, including adsorption and reaction on surfaces of alloyed metals,
oxides, and metal-
oxide interfacial systems. We demonstrate that current-generation foundational MLIPs can already perform at high accuracy for applications such as predicting vacancy formation energies of perovskite
oxides or zero-point energies of supported nanoclusters. However, limitations also exist. We find that many MLIPs catastrophically fail when applied to
magnetic materials, and structure relaxation in the MLIP generally increases the energy prediction error compared to single-point evaluation of a previously optimized structure. Comparing low-cost task-specific models to foundational MLIPs, we highlight some core differences between these model approaches and show that – if considering only accuracy – these models can compete with the current generation of best-performing MLIPs. Furthermore, we show that no single MLIP universally performs best, requiring users to investigate MLIP suitability for their desired application.
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Materials Science
Structural transitions related to order-disorder and thermal desorption of D atoms in TbFe$_{2}$D$_{4.2}$
V. Paul-Boncour and O. Isnard
TbFe$_{2}$D$_{4.2}$ deuteride crystallizes in a monoclinic structure ($Pc$ space group) with deuterium inserted into 13 [Tb$_{2}$Fe$_{2}$] and 5 [TbFe$_{3}$] tetrahedral interstitial sites. Its structural
evolution versus temperature has been investigated by combining in-situ X-ray and
neutron diffraction (XRD and NPD) with differential scanning calorimetry (DSC) experiments.Upon heating, the deuteride undergoes a reversible order-disorder transition from an ordered monoclinic structure to a disordered cubic structure between 320 and 380 K. Then, a multipeak thermal desorption occurs between 400 and 550 K, which can be explained by the transitions between different cubic deuterides separated by two-phase ranges. After controlled partial D desorption of TbFe$_{2}$D$_{4.2}$,the XRD patterns of several TbFe$_{2}$D$_{x}$ deuterides were measured ex-situ using synchrotron radiation at room temperature, revealing the formation of different phases with cubic or monoclinic structures separated by two phase ranges.A tetragonal superstructure was observed for a phase with $x$ = 2. This work can explain previous results of the literature indicating the existence of cubic and or rhombohedral hydrides depending on the hydrogenation conditions and the H content. The monoclinic structures reported here correspond to a slight distortion of the previous rhombohedral structures described by other authors.
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Strongly Correlated Electrons · Cross-listed from quant-ph
Topological magic response in quantum spin chains
Ritu Nehra, Poetri Sonya Tarabunga, Martina Frau et al. (+3 more)
Topological matter provides natural platforms for robust, non-local information storage, central to
quantum error correction. Yet, while the relation between
entanglement and
topology is well established, little is known about the role of nonstabilizerness (or magic), a pivotal concept in fault-tolerant
quantum computation, in topological phases. We introduce the concept of topological magic response, the ability of a state to spread over stabilizer space when perturbed by finite-depth non-Clifford
circuits. Unlike a topological invariant or order parameter, this response function probes how a phase reacts to non-Clifford perturbations, revealing the presence of non-local
quantum correlations. In Ising-type
spin chains, we show that
symmetry-broken and paramagnetic phases lack such a response, whereas
symmetry-protected topological (SPT) phases always display it. To capture this, we utilize a combination of stabilizer Rényi
entropies that, in analogy with topological
entanglement entropy, isolates non-locally stored information. Using exact analytic computations and
matrix product states simulations based on an algorithmic technique we introduce, we show that SPT phases doped with $T$ gates support robust topological magic response, while trivial phases remain featureless.
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All authors Ritu Nehra, Poetri Sonya Tarabunga, Martina Frau, Mario Collura, Emanuele Tirrito, Marcello Dalmonte
Soft Condensed Matter
Deep learning directed synthesis of fluid ferroelectric materials
Charles Parton-Barr, Stuart R. Berrow, Calum J. Gibb et al. (+6 more)
Fluid ferroelectrics, a recently discovered class of
liquid crystals that exhibit switchable, long-range polar order, offer opportunities in ultrafast electro-optic technologies, responsive soft matter, and next-generation energy materials. Yet their discovery has relied almost entirely on intuition and chance, limiting progress in the field. Here we develop and experimentally validate a deep-learning data-to-molecule pipeline that enables the targeted design and synthesis of new organic fluid ferroelectrics. We curate a comprehensive
dataset of all known longitudinally polar
liquid-
crystal materials and train graph neural networks that predict ferroelectric behaviour with up to 95% accuracy and achieve root mean square errors as low as 11 K for transition temperatures. A graph variational autoencoder generates de novo molecular structures which are filtered using an ensemble of high-performing classifiers and regressors to identify candidates with predicted ferroelectric nematic behaviour and accessible transition temperatures. Integration with a computational retrosynthesis engine and a digitised chemical inventory further narrows the design space to a synthesis-ready longlist. 11 candidates were synthesised and characterized through established mixture-based extrapolation methods. From which extrapolated ferroelectric nematic transitions were compared against neural network predictions. The experimental verification of novel materials augments the original
dataset with quality feedback data thus aiding future research. These results demonstrate a practical, closed-loop approach to discovering synthesizable fluid ferroelectrics, marking a step toward autonomous design of functional soft materials.
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All authors Charles Parton-Barr, Stuart R. Berrow, Calum J. Gibb, Jordan Hobbs, Wanhe Jiang, Caitlin O'Brien, Will C. Ogle, Helen F. Gleeson, Richard J. Mandle
Materials Science
Photoinduced phase heterogeneity and charge localization in SnSe
Benjamin J. Dringoli, Stefano Mocatti, Giovanni Marini et al. (+4 more)
Time-resolved multi-terahertz (THz) spectroscopy is used to observe pump fluence-dependent dynamics in the optical conductivity of photoexcited tin selenide (SnSe) over an ultrabroadband spectral range of 0.5 - 11 THz at fluences from 0.1 - 7.5 mJ/cm$^2$. A free carrier Drude spectrum is observed at pump fluences below 3 mJ/cm$^2$, with optical
phonons well described by the
equilibrium Pnma structural phase. With increasing fluence, a suppression of the DC photoconductivity is observed, indicating an interruption of long range transport due to phase disorder. Concomitantly, the optical
phonons exhibit features that can no longer be explained by a pure Pnma phase, with a frequency shift and narrowing of the $B^2_{1u}$ mode and a new mode appearing at $\sim$3.0 THz consistent with a transition to a higher-
symmetry structure. At an intermediate fluence of 3.1 mJ/cm$^2$, a high frequency Lorentzian component consistent with phase heterogeneity appears that rapidly
redshifts after 2 ps and whose amplitude exponentially decays on a 90 ps time scale. Our experimental measurements and theoretical calculations provide evidence for a non-thermal, photo-induced nucleation of higher
symmetry, semi-metallic phase domains in SnSe appearing within 200 fs.
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All authors Benjamin J. Dringoli, Stefano Mocatti, Giovanni Marini, Zhongzhen Luo, Matteo Calandra, Mercouri G. Kanatzidis, David G. Cooke
Statistical Mechanics · Cross-listed from physics.geo-ph
Self-Affine Scaling of Earth's Islands
Matthew Oline, Jeremy Hoskins, David Seekell et al. (+2 more)
Earth's relief is approximately self-affine, meaning a zoom-in on a small region looks statistically similar to a large region upon rescaling. Fractional Brownian surfaces give an idealized self-affine model of Earth's relief with one parameter, the Hurst exponent $H$, characterizing the roughness of the surface. We compile a large
dataset of topographic profiles of islands (N=131,063 with the range of areas covering 8+ orders of magnitude) and obtain four estimates for the Hurst exponent of Earth's surface by fitting four statistical laws from the theory of self-affine surfaces concerning islands: (i) distribution of areas, (ii) volume-area relationship, (iii) perimeter-area relationship, and (iv) maximum height-area relationship. The estimated Hurst exponents indicate different fractal scaling behavior for different
geometric features, and are sorted in order of increasing expected influence of coastal processes. This sheds light on the impact of coastal erosion and sedimentation on island geomorphology.
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All authors Matthew Oline, Jeremy Hoskins, David Seekell, Mary Silber, B.B. Cael
Statistical Mechanics · Cross-listed from quant-ph
Scalable tests of quantum contextuality from stabilizer-testing nonlocal games
Wanbing Zhao, H. W. Shawn Liew, Wen Wei Ho et al. (+2 more)
Soon after the dawn of
quantum error correction, DiVincenzo and Peres observed that stabilizer codewords could give rise to simple proofs of quantumness via contextuality. This discovery can be recast in the
language of nonlocal games: every $n$-
qubit stabilizer state defines a specific "stabilizer-testing" $n$-player nonlocal game, which
quantum players can win with probability one. If
quantum players can moreover outperform all possible classical players, then the state is contextual. However, the classical values of stabilizer-testing games are largely unknown for scalable examples beyond the $n$-
qubit GHZ state. We introduce several new methods for upper-bounding the classical values of these games. We first prove a general coding-theory bound for all stabilizer-testing games: if the classical value $p_{\mathrm{cl}}^* < 1$, then $p_{\mathrm{cl}}^* \leq 7/8$, i.e., there is no classical strategy that can perform as well as the optimal
quantum strategy even in an asymptotic sense. We then show how to tighten this bound for the most common scalable examples, namely GHZ, toric-code and cyclic cluster states. In particular, we establish an asymptotically tight upper bound for cyclic cluster states using transfer-
matrix methods. This leads to the striking conclusion that measuring an exponentially small fidelity to the cyclic cluster state will suffice to witness its contextuality.
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All authors Wanbing Zhao, H. W. Shawn Liew, Wen Wei Ho, Chunxiao Liu, Vir B. Bulchandani
Strongly Correlated Electrons
Microscopic Model of Exciton Polarons in 2D Wigner Crystals
Haydn S. Adlong, Eugen Dizer, Richard Schmidt et al. (+2 more)
Monolayer transition-metal dichalcogenides (TMDs) provide a platform for realizing Wigner
crystals and enable their detection via
exciton spectroscopy. We develop a microscopic theoretical model for
excitons interacting with the localized electrons of the Wigner
crystal, including their vibrational motion. In addition to the previously observed
exciton-Umklapp feature, the theory reproduces and explains the higher-band attractive-polaron resonances recently reported experimentally. Our model further uncovers that the appearance of two equal-strength and parallel attractive polarons, as commonly observed in WSe$_2$ and WS$_2$, is a signature of strong correlations in the electronic system. Altogether, our results demonstrate that accounting for electronic interactions is essential to reproduce and interpret the
exciton-polaron spectra of TMDs.
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All authors Haydn S. Adlong, Eugen Dizer, Richard Schmidt, Atac Imamoglu, Arthur Christianen
Superconductivity
Observation of REBCO delamination in the resistive insulation nested coils
Jun Lu, Iain Dixon, Kwangmin Kim et al. (+2 more)
The REBCO coated conductor has the potential to be widely used in ultrahigh field magnets. It is well known, however, that it is not mechanically strong against delamination in the direction normal to its surface due to its intrinsic layered structure. Therefore, conductor delamination is one of the major design challenges for REBCO magnet coils. As a part of the development of the 40 T all-superconducting magnet at the National High
Magnetic Field Laboratory, USA (NHMFL), a dry-wound resistive-insulation-nested-coils (RINC) was designed to reach 25.8 T. It used surface-treated stainless-steel tape as a co-wind to control the turn-to-turn contact resistance, and was fabricated and tested in a
liquid helium bath. During the test, two of the double pancake modules exhibited resistive transitions at a current significantly lower than the designed value. The postmortem inspection of the REBCO conductor of these modules by reel-to-reel magnetization at 77 K found sections of very low critical current. Further investigations of one section by chemical etching, visual inspection, and electron microscopy revealed that conductor of this section was delaminated. We present the detailed findings of these postmortem characterizations. The implication of this type of delamination for future magnet designs will be discussed.
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All authors Jun Lu, Iain Dixon, Kwangmin Kim, Yan Xin, Hongyu Bai
Mesoscale and Nanoscale Physics
Wigner polarons reveal Wigner crystal dynamics in a monolayer semiconductor
Lifu Zhang, Liuxin Gu, Haydn S. Adlong et al. (+12 more)
Wigner
crystals,
lattices made purely of electrons, are a quintessential paradigm of studying correlation-driven
quantum phase transitions. Despite decades of research, the internal dynamics of Wigner
crystals has remained extremely challenging to access, with most experiments probing only static order or collective motion. Here, we establish monolayer WSe2 as a new materials platform to host zero-field Wigner
crystals and then demonstrate that
exciton spectroscopy provides a direct means to probe both static and dynamic properties of these electron
lattices. We uncover striking optical resonances that we identify as Wigner polarons, quasiparticles formed when the electron
lattice is locally distorted by
exciton-Wigner
crystal coupling. We further achieve all-optical control of
spins in the Wigner
crystal, directly probing valley-dependent Wigner polaron scattering well above the
magnetic ordering temperature and in the absence of any external
magnetic field. Finally, we demonstrate optical melting of the Wigner
crystal and observe intriguingly different responses of the umklapp (static) and Wigner polaron (dynamic) resonances to optical excitation. Our results open up exciting new avenues for elucidating electron dynamics and achieving ultrafast optical control of interaction-driven
quantum phase transitions in strongly correlated electron systems.
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All authors Lifu Zhang, Liuxin Gu, Haydn S. Adlong, Arthur Christianen, Eugen Dizer, Ruihao Ni, Rundong Ma, Suji Park, Houk Jang, Takashi Taniguchi, Kenji Watanabe, Ilya Esterlis, Richard Schmidt, Atac Imamoglu, You Zhou
Other Condensed Matter · Cross-listed from hep-ph
Condensation of slow $\gamma$-quanta in strong magnetic fields
Leah Folkerts, Reinhold Egger, Carsten Müller et al. (+1 more)
The implications of the root singularity of the
vacuum polarization tensor near the first pair creation threshold on blackbody radiation are investigated for
magnetic fields above the characteristic scale of
quantum electrodynamics. We show that the
vacuum birefringence in such a strong background leads to an anisotropic behavior of the Planck radiation law. The thermal spectrum is characterized by a resonance that competes with the Wien maximum, causing a crossover in the low $\gamma$-spectrum of the heat radiation. A light state resembling a many-body condensate with slow motion is linked to the high-temperature phase. This novel state of radiation may coexist with
nuclear or
quark matter in a
neutron star's core, increasing its compactness and influencing its stability.
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All authors Leah Folkerts, Reinhold Egger, Carsten Müller, Selym Villalba-Chávez
Mesoscale and Nanoscale Physics
Controlling Spin-Waves by Inhomogeneous Spin-Transfer Torques
Lorenzo Gnoatto, Jean F. O. da Silva, Artim L. Bassant et al. (+4 more)
We investigate the interplay between
spin currents and
spin waves in nanofabricated Permalloy waveguides with geometrical constrictions. Using propagating
spin-wave spectroscopy, micromagnetic simulations, and analytical modeling, we provide experimental evidence that
spin-wave phase can be modulated by inhomogeneous
spin-transfer torques generated by current-density gradients shaped by the constriction geometry. Narrower constrictions enhance these gradients and modify the internal field for Damon-Eshbach
spin waves, resulting in pronounced changes in
spin-wave group velocity and phase. To our knowledge, this constitutes the first demonstration of deterministic phase modulation via engineered nonuniform
spin-transfer torques. Beyond enabling a scalable route to magnonic interferometry - a building block for
spin-wave-based computing - our findings establish a platform to control
spin-wave dynamics in spatially varying current landscapes, relevant for analogue-
gravity experiments in condensed matter systems.
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All authors Lorenzo Gnoatto, Jean F. O. da Silva, Artim L. Bassant, Rai M. Menezes, Rembert A. Duine, Milorad V. Milossevic, Reinoud Lavrijsen
Statistical Mechanics · Cross-listed from stat.ML
Boltzmann generators for amorphous particle systems
Louis Grenioux, Leonardo Galliano, Ludovic Berthier et al. (+2 more)
Sampling configurations in thermodynamic
equilibrium is a long-standing challenge in statistical physics. Boltzmann generators address this problem by employing generative models to propose independent configurations, which are then reweighted via importance sampling using exact likelihood evaluations. Recent Boltzmann Generators based on continuous normalizing flows and flow matching have achieved significant success for particle systems and biomolecules. However, these approaches have not been extended to amorphous materials (glasses), for which
equilibrium sampling is notoriously slow. Because of their disordered structure, the invariances and geometrical constraints of amorphous materials differ from those of
crystals and biomolecules, preventing the direct use of existing generative models. Here, we develop Boltzmann Generators tailored to amorphous materials by building the required equivariances directly into Riemannian
stochastic interpolants. Our framework incorporates periodic boundary conditions and particle
symmetries using equivariant graph neural networks. Numerical experiments demonstrate that enforcing physical
symmetries significantly improves the accuracy of Boltzmann Generators, but also reveal an intrinsic limitation of the continuous-flow formulation: accumulated numerical errors during likelihood integration break time-reversibility, compromising exact thermodynamic reweighting. These results reveal a fundamental challenge for continuous-flow generative models in statistical mechanics and call for alternative approaches that preserve exact thermodynamic consistency.
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All authors Louis Grenioux, Leonardo Galliano, Ludovic Berthier, Giulio Biroli, Marylou Gabrié
Materials Science
Recent Advances in Metallic Glasses
Silvia Bonfanti, Ralf Busch, Jesper Byggmästar et al. (+12 more)
This paper reviews recent advances in the field of metallic glasses, focusing on the development of novel experimental techniques and in silico models. We discuss progress in experimental characterization, additive manufacturing, multiscale modeling approaches, and the growing role of machine learning in understanding and designing these complex materials. On the experimental side, we highlight measurements of thermophysical properties of supercooled
liquids via fast chip calorimetry and enhancements in mechanical properties through rejuvenation treatments. This work underscores the crucial role of short-range order and medium-range order in controlling metallic glass mechanical properties. Recent progress in structural probes allows in situ observations of deformation mechanisms, positioning the field well to further advance our understanding of mechanical properties. Additive manufacturing of metallic glasses is discussed as one encouraging new manufacturing route for metallic glasses. We examine
laser powder-bed fusion process physics and the central trade-off between amorphicity and densification, including heat affected zone devitrification and defects formation, together with emerging mitigation strategies and applications. On the theoretical and simulation side, we review advances in nanoscale, mesoscale, and continuum modeling of metallic glasses that have led to promising approaches by which multiscale schemes can incorporate data sourced from atomic-scale simulations. These efforts have helped to elucidate the connection between the glass structure and mechanical and rheological responses. We also cover the development of machine learning interatomic potentials for metallic glasses, along with machine learning driven prediction of glass forming ability and inverse design methods. Finally, challenges and directions for future research are presented and discussed.
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All authors Silvia Bonfanti, Ralf Busch, Jesper Byggmästar, Jeppe C. Dyre, Jürgen Eckert, Spencer Fajardo, Michael L. Falk, Isabella Gallino, Jamie J. Kruzic, Jiayin Lu, Giulio Monaco, Misaki Ozawa, Anshul D. S. Parmar, Chris H. Rycroft, Srikanth Sastry
Materials Science
High-Temperature Activation of Single-Photon Emitters in monolayer WS2
Gyeongjun Lee, Antoine Borel, Takashi Taniguchi et al. (+3 more)
Controlled activation of defect-bound excitonic states in two-dimensional
semiconductors provides a route to isolated
quantum emitters and a sensitive probe of defect physics. Here we demonstrate that in situ high-temperature annealing of hBN-encapsulated monolayer WS$_2$ on a suspended microheater leads to the emergence of spectrally isolated single-
photon emitters at cryogenic temperatures. Annealing at temperatures around 1100 K produces a sharp emission line, $X_L$, red-shifted by approximately 80 meV from the neutral
exciton and exhibiting a linewidth below 200 $\mu$eV. Photoluminescence excitation spectroscopy and power-dependent measurements show that $X_L$ originates from annealing-induced defects in the WS$_2$ monolayer, while second-order
photon correlation measurements reveal clear antibunching with $g^{(2)}(0)<0.5$. These results establish high-temperature in situ annealing as a controlled means to access defect-bound excitonic states and single-
photon emission in van der Waals materials.
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All authors Gyeongjun Lee, Antoine Borel, Takashi Taniguchi, Kenji Watanabe, Fausto Sirotti, Fabian Cadiz