Statistical Mechanics
Steering Dynamical Regimes of Diffusion Models by Breaking Detailed Balance
Haiqi Lu and Ying Tang
We show that deliberately breaking detailed balance in generative
diffusion processes can accelerate the reverse process without changing the stationary distribution. Considering the Ornstein–Uhlenbeck process, we decompose the dynamics into a symmetric component and a non-reversible anti-symmetric component that generates rotational probability currents. We then construct an exponentially optimal non-reversible perturbation that improves the long-time relaxation rate while preserving the stationary target. We analyze how such non-reversible control reshapes the macroscopic dynamical regimes of the phase transitions recently identified in generative
diffusion models. We derive a general criterion for the speciation time and show that suitable non-reversible perturbations can accelerate speciation. In contrast, the collapse transition is governed by a trace-controlled phase-space contraction mechanism that is fixed by the symmetric component, and the corresponding collapse time remains unchanged under anti-symmetric perturbations. Numerical experiments on Gaussian mixture models support these findings.
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Soft Condensed Matter
Surface Block Identity Controls Transport of Symmetric Diblock Copolymer Through Nanopores
Sang Yup Lee, Tae-Young Heo, Uiseok Hwang et al. (+4 more)
Understanding how
polymer architecture governs transport through nanopores is essential for nanocomposite fabrication, membrane design, and
polymer upcycling. However, the effect of the nanoscale structure of copolymers on chain transport through nanoporous media remains poorly understood. In this study, we demonstrate that simply inverting the surface orientation of lamellar poly(styrene-block-2-vinylpyridine) (PS-b-P2VP) diblock copolymers, composed of two monomers with strongly contrasting affinities for SiO2, at the entrance of nanoporous silica significantly alters the kinetics of capillary rise infiltration. Using in situ spectroscopic ellipsometry, we find that infiltration of symmetric PS-b-P2VP into silica nanoparticle (SiO2 NP) packings is significantly faster when the P2VP domain is the top layer of the film and first contacts the nanoparticles, compared to when the PS domain is the top layer. Coarse-grained molecular dynamics simulations reveal that this difference originates from block-specific adsorption pathways that reorganize the nanophase structure around nanoparticles: P2VP-first infiltration forms thin adsorbed layers that drive PS into the pore interiors, generating continuous interfacial pathways that enable rapid, interface-mediated transport. In contrast, PS-first infiltration produces thicker P2VP layers that isolate PS domains and disrupt pathway connectivity, forcing chains to rely on a slower, connectivity-limited transport mechanism through P2VP-rich interstitial regions. Above the order-disorder transition, or upon silanizing nanoparticles to neutralize surface affinity, the rate difference disappears. These findings demonstrate how the interplay between nanoscale domain configuration and
polymer-surface affinity governs infiltration dynamics, providing mechanistic insight into tuning transport in nanostructured block copolymers.
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All authors Sang Yup Lee, Tae-Young Heo, Uiseok Hwang, Theophile Ienn, Julien Bernard, Robert A Riggleman, Daeyeon Lee
Other Condensed Matter
Displacement general solutions in strain gradient elasticity: review and analysis
Y. Solyaev, E. Hamouda and S. Sherbakov
In this work, we provide an overview of general solutions for displacement fields in static problems of isotropic strain gradient elasticity (SGE). We not only review existing solutions but also derive new representations, showing that all classical elasticity solutions - including those of Boussinesq-Galerkin, Papkovich-Neuber, Naghdi, Lame, Love and Boussinesq - can be simply generalized to SGE framework. In general, it is shown that SGE enables the use of any classical general solution representation combined with a Helmholtz decomposition for the gradient part of the displacement field. Consistency is also established between the presented Papkovich-Neuber representation and the general solutions of SGE proposed previously by Mindlin (1964), Lurie et al. (2006) and Charalambopoulos et al. (2020). Furthermore, we establish the relationships between the stress functions of different general solutions and show their completeness.
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Strongly Correlated Electrons
Correlated electronic states at a ferromagnetic oxide interface
D. Jones, A. Weh, A. Östlin et al. (+5 more)
We propose a minimal tight-binding model for the electronic interface layer of the LaAlO$_3$/SrTiO$_3$
heterostructure with oxygen vacancies. In this model, the effective carriers are subject to oxygen vacancy induced
magnetic impurities. Both the effects of random on-site potentials and Zeeman-like exchange interactions between correlated carriers and
magnetic impurities are taken into account. By applying the combined coherent potential approximation (CPA) and dynamical mean-field theory (DMFT) for a
ferromagnetic state, we uncover a disordered
Fermi-
liquid regime for the majority-
spins and a low energy scale which controls the transport of the minority-
spin carriers, both induced by the
magnetic impurities.
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All authors D. Jones, A. Weh, A. Östlin, D. Braak, T. Kopp, P. Seiler, U. Eckern, L. Chioncel
Mesoscale and Nanoscale Physics
Polarization-resolved measurement of forward volume spin waves by micro-focused Brillouin light scattering
Krzysztof Szulc, Mengying Guo, Ondřej Wojewoda et al. (+7 more)
We show how the micro-focused BLS signal of forward volume
spin waves is formed and why it remains observable despite
symmetry-based "suppression" expectations. A reciprocity-
theorem based model with vectorial diffraction-limited focusing identifies the nonnegligible longitudinal focal-field component as the key element responsible for BLS sensitivity in the forward volume geometry. We further demonstrate that full polarization analysis, implemented through polarizer-analyzer maps of coherently excited
spin waves, provides information beyond the conventional crossed polarizer-analyzer readout. In a BiYIG thin film, the measured maps exhibit Stokes/anti-Stokes polarization asymmetries and nontrivial patterns that stem from quadratic magneto-optical coupling terms. Fitting the data with a model including Voigt and Cotton-Mouton contributions yields an effective Cotton-Mouton constant and shows that the quadratic response is comparable to the linear Voigt contribution.
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All authors Krzysztof Szulc, Mengying Guo, Ondřej Wojewoda, Hongyu Wang, Dominik Pavelka, Jan Klíma, Jakub Krčma, Xiufeng Han, Qi Wang, Michal Urbánek
Materials Science
Three-Dimensional Optical-Electrical Simulation of Cs2AgBiBr6 Double Perovskite Solar Cells
Md Shanian Moed, Adnan Amin Siddiquee and Md Tashfiq Bin Kashem
Despite significant advances in lead-free perovskite photovoltaics, achieving a balance among environmental safety and high optoelectronic performance remains challenging. The inorganic double perovskite Cs2AgBiBr6 has emerged as a promising candidate owing to its robust three-dimensional
crystal structure and suitable visible-range bandgap. However, best power conversion efficiencies (PCEs) for Cs2AgBiBr6
solar cells reported so far - 6.37% experimentally and 27.78% in numerical studies - remain below the theoretical performance potential, largely due to suboptimal charge transport layers, and interface-related recombination losses. Here, we address this gap using a 3D finite-element method (FEM) implemented in COMSOL Multiphysics, which couples optical simulations with
semiconductor drift-
diffusion transport. To our knowledge, this work represents the first comprehensive 3D FEM-based study of a double halide perovskite
solar cell. Screening of 25 electron transport layer (ETL)-hole transport layer (HTL) combinations identifies CeO2 and P3HT as the optimal ETL and HTL respectively. Device performance is further analyzed through systematic variation of layer thicknesses, doping concentrations and defect densities within the FTO/CeO2/Cs2AgBiBr6/P3HT/Au architecture. Under optimized parameters, the simulated device achieves a PCE of 31.76%, representing the theoretical upper bound predicted by the model. Overall, this work demonstrates 3D physics-based device engineering as a decisive pathway for overcoming efficiency bottlenecks in lead-free double perovskite photovoltaics.
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Statistical Mechanics · Cross-listed from math-ph
Temperley-Lieb modules and local operators for critical ADE models
Yacine Ikhlef and Alexi Morin-Duchesne
We investigate critical restricted solid-on-solid models associated to Dynkin diagrams of type $A$, $D$ and $E$, with fixed, periodic and twisted periodic boundary conditions. These models are endowed with an action of the diagrams of the Temperley-Lieb category. For each model, we obtain the decomposition of the state space as a direct sum of irreducible modules over the Temperley-Lieb
algebra $\mathsf{TL}_N(\beta)$ or its periodic incarnation $\mathsf{\mathcal EPTL}_N(\beta)$. This allows us to recover the known conformal partition functions for these models in the continuum scaling limit. For each irreducible factor arising in the decompositions, we define an associated local operator on the
lattice, which behaves like a connectivity operator. Using knowledge from the Temperley-Lieb representation theory at roots of unity, we show that these operators satisfy certain linear difference relations, which are
lattice counterparts of the singular-vector relations in conformal field theory.
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Soft Condensed Matter
A sequence of elastic patterns in a sheared bent sheet
D. Gimeno, B. K. Meghwar, G. Fisher et al. (+3 more)
We document a sequence of bifurcations and elastic patterns in sheared bent sheets of intermediate aspect ratio. The sheets undergo inversion of
curvature through the passage of localized features, often in S-shaped pairs. Nested force-displacement hysteresis loops provide experimental evidence for snaking. Several mechanisms for coarsening and refinement of the patterns are observed, including splitting, merging, and escape through open boundaries. While most forces, including that required for full snap-through, scale with the length of the sheet, the initial drop in force upon pattern nucleation decreases rapidly with length.
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All authors D. Gimeno, B. K. Meghwar, G. Fisher, R. S. Hutton, E. Hamm, J. A. Hanna
Materials Science
Revealing 3D Strain and Carbide Architectures in Additively Manufactured Ni Superalloys
James A. D. Ball, David M. Collins, Yuanbo T. Tang et al. (+4 more)
Fast directional solidification during
Laser Additive Manufacturing (LAM) produces a complex microstructure in nickel-based superalloys, comprising columnar grains with cellular sub-grain structures and carbides. Using non-destructive Scanning 3D X-ray Diffraction (S3DXRD), we reveal spatially complex orientation and intergranular strain relationships that couple strongly to processing-induced cellular sub-grain networks and a primary cubic metal carbide (MC) phase. We have examined 3D orientation and elastic strain tensor fields across 82 $\gamma$ grains together with the spatial distribution of over 37,000 MC carbides in an ABD-900AM
alloy sample manufactured by the Directed Energy Deposition (DED) LAM process. Carbides are spatially associated with the cellular sub-grain network with a weak but present orientation relationship with their parent $\gamma$ grains. The MC carbides, known to be Ti, Ta and Nb rich, form in regions of high solute segregation, resulting in a significant volumetric
lattice parameter patterning in the associated $\gamma$ phase regions. These chemically distinct solute-rich regions possess a higher associated elastic modulus compared to intercellular regions and determine the local residual stress patterning. These results provide the first non-destructive 3D study of the relationship between rapid solidification-induced segregation, deformation heterogeneity and carbide architectures in an additively manufactured Ni-based superalloy. The insights provide crucial detail to rationalise LAM process parameter optimisation and the coupled spatially governed structural performance.
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All authors James A. D. Ball, David M. Collins, Yuanbo T. Tang, Jonathan P. Wright, Can Yildirim, Julia Richter, Yunhui Chen
Soft Condensed Matter
Flexoelectricity-driven softening of bend elasticity leads to spontaneous chiral symmetry breaking in a polar fluid
Aitor Erkoreka, Josu Martinez-Perdiguero, Luka Cmok et al. (+6 more)
The origin of the recently observed spontaneous
chiral symmetry breaking in polar fluids composed of achiral molecules is an unsolved problem, raising fundamental questions about how heliconical structures emerge in such systems. Here, we investigate the pretransitional fluctuations leading to the formation of the spontaneously
chiral twist-bend ferroelectric nematic phase using dielectric spectroscopy, light scattering, and small-angle X-ray scattering. We observe simultaneous softening of the bend elastic constant and the emergence of a collective dielectric mode on approaching the transition. By developing a theoretical model, we show that these phenomena are signatures of a flexoelectricity-driven transition arising from the coupling between electric polarization and bend deformation.
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All authors Aitor Erkoreka, Josu Martinez-Perdiguero, Luka Cmok, Ema Hanžel, Jordan Hobbs, Calum J. Gibb, Richard J. Mandle, Nerea Sebastián, Alenka Mertelj
Mesoscale and Nanoscale Physics · Cross-listed from hep-th
Generalized GMP Algebra for Three-Dimensional Quantum Hall Fluids of Extended Objects
Giandomenico Palumbo
We develop a
geometric framework for three-dimensional
quantum Hall fluids of extended objects (quasi-strings) in the presence of a strong three-form background field associated with a bundle gerbe. In the strong-field regime, fast internal dynamics is frozen and the low-energy kinematics is governed by generalized guiding-center variables consisting of vectorial and tensorial coordinates. We show that these guiding-center variables obey a noncommutative geometry giving rise to a three-dimensional generalization of the Girvin-MacDonald-Platzman (GMP)
algebra for projected density operators. Moreover, we relate this
algebra to the canonical quantization of a topological BF+BB theory whose level is identified with the Dixmier-Douady invariant. Our results clarify the structure of incompressible
quantum Hall-type phases and their
geometric and topological features in three spatial dimensions.
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Statistical Mechanics
Entropy production reveals hidden dynamical constraints rather than stochastic disorder
Patrick Romanescu
Entropy production is often interpreted as a proxy for microscopic disorder or environmental roughness in
stochastic systems. We test this interpretation using controlled simulations of overdamped
stochastic dynamics on curved surfaces in which local noise, geometry, and forces are held fixed while global constraints are varied. Trajectories are generated for particles evolving toward a central attractor, and
entropy production is quantified using both a continuum probability-current
estimator and coarse-grained Markov transition statistics across multiple spatial and temporal resolutions. Across systematic sweeps of timestep size, domain extent, and boundary
topology,
entropy production is governed primarily by constraint-induced probability flow rather than local
stochastic variability. Periodic domains that permit sustained circulation yield substantially higher
entropy production than reflecting domains despite identical local
stochastic structure, with the magnitude of the separation depending on domain extent. In contrast, coarse-grained estimates decrease as temporal resolution increases and rise with finer spatial binning, demonstrating that discrete estimates depend strongly on observation scale and may fail to resolve
topology-induced irreversible structure. Ergo,
entropy production is not a direct measure of environmental roughness or randomness. Instead, it quantifies how strongly system dynamics are driven away from reversibility by global constraints, geometry, and the space of allowed trajectories. Interpreted in this way,
entropy production maps function as diagnostics of organized probability flow and provide a principled method for detecting hidden dynamical constraints from trajectory data alone.
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Strongly Correlated Electrons
Quantum Coulomb Liquids of Different Rank in the Breathing Pyrochlore Antiferromagnet
Lasse Gresista, Daniel Lozano-Gómez, Matthias Vojta et al. (+2 more)
Emergent gauge fields and Coulomb
liquids have long been central to the physics of frustrated pyrochlore magnets, yet their realization beyond conventional, i.e. rank-1 $U(1)$,
spin ice and into fully
quantum higher-rank regimes has remained elusive. Here we provide a controlled demonstration of this physics in the
spin-$\tfrac{1}{2}$
quantum Heisenberg antiferromagnet on the breathing pyrochlore
lattice with
symmetry-allowed Dzyaloshinskii–Moriya interactions, using the pseudofermion functional renormalization group. We show that tuning the breathing asymmetry stabilizes extended
quantum analogues of both rank-1 and rank-2 $U(1)$ Coulomb
liquids within a single microscopic model, directly distinguished by their characteristic pinch-point morphologies in momentum space. This provides the first controlled
quantum realization in three dimensions where gauge theories of different rank emerge within a single microscopic
spin Hamiltonian. In addition,
quantum fluctuations qualitatively reshape the classical nearest-neighbor atlas of phases, causing an incommensurate spiral instability and an extended
quantum-disordered regime without dipolar order, both absent from the classical model. Our results establish the breathing pyrochlore as a timely and experimentally relevant platform where higher-rank gauge constraints, conventional
magnetic order, and fluctuation-driven
quantum phases compete on equal footing, opening a direct route to diagnosing emergent gauge structure in three-dimensional
quantum magnets.
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All authors Lasse Gresista, Daniel Lozano-Gómez, Matthias Vojta, Simon Trebst, Yasir Iqbal
Statistical Mechanics
Self-phoretic oscillatory motion in a one-dimensional channel
Leah Anderson and David S. Dean
We study a simple model for a particle that is active due to self-phoresis and that has been proposed to model symmetric camphor grains. The particle generates a concentration field through the continuous emission of a chemical substance, and its motion is driven by gradients of this field as it diffuses within a confined channel whose ends perfectly reflect the chemical. The reflection of the chemical field leads to an effective confinement of the particle, which itself is reflected before encountering the channel ends. The system displays a transition from a passive state, where the particle rests at the channel midpoint, to an active state characterized by highly regular, non-chaotic oscillations. We analytically construct the phase diagram and derive the oscillation frequency and amplitude in the vicinity of the transition. A perturbative analysis perfectly describes the dynamics of the particle even for oscillations as large as half the channel size. Furthermore, we develop an analysis which explains the mechanism of particle reflection close to the channel edges in the regime of large activity.
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Materials Science
Planar Structures of Medium-Sized Gold Clusters Become Ground States upon Ionization
Mohammad Ismaeil Safa, Ehsan Rahmatizad Khajehpasha and Stefan Goedecker
This study investigates the structural stability of ionized gold clusters of sizes ranging from 22 to 100 atoms, contrasting compact, cage and planar structures. While it is well known that neutral clusters in the upper part of this size range predominantly favor compact structures, our results reveal that positively ionized gold clusters exhibit structural transitions in which planar structures become energetically preferred once the charge is sufficiently large. In addition, we study the finite-temperature stability of the structures and find that thermodynamic effects further stabilize planar configurations relative to their compact counterparts. To explore the potential energy surface, we use the Minima Hopping
algorithm combined with a machine-learned potential. Since the machine-learned potential does not apply to ionized clusters, we introduce a charge-correction term to incorporate Coulomb interactions and charge screening.
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Statistical Mechanics
Fastest first-passage time for multiple searchers with finite speed
Denis S. Grebenkov, Ralf Metzler and Gleb Oshanin
We study analytically and numerically the mean fastest first-passage time (fFPT) to an immobile target for an ensemble of $N$ independent finite-speed random searchers driven by dichotomous noise and described by the telegrapher's equation. In stark contrast to the well-studied case of Brownian particles – for which the mean fFPT vanishes logarithmically with $N$ – we uncover that the mean fFPT is bounded from below by the minimal ballistic travel time, with an exponentially fast convergence to this bound as $N \to \infty$. This behavior reveals a dramatic efficiency advantage of physically realistic, finite-speed searchers over Brownian ones and illustrates how diffusive macroscopic models may be conceptually misleading in predicting the short-time behavior of a physical system. We extend our analysis to anomalous
diffusion generated by Riemann-Liouville-type dichotomous noises and find that target detection is more efficient in the superdiffusive regime, followed by normal and then subdiffusive regimes, in agreement with physical intuition and contrary to earlier predictions.
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Soft Condensed Matter
Deformation and orientation of a capsule with viscosity contrast in linear flows: a theoretical study
Paul Regazzi and Marc Leonetti
We develop a perturbation theory to study the shape and the orientation of an initially spherical capsule of radius R with a viscosity contrast, a surface tension {\sigma} and a bending
rigidity $\kappa$ in linear flows. The elastic mechanical response of membrane to deformations is described by three elastic constitutive law which are either Hookean, Neohookean or Skalak type leading to the introduction of a surface shear elastic modulus $G_s$ and the Poisson ratio (or analog quantities). At the leading order, the deformation, i.e. the so-called Taylor parameter is proportional to the elastic capillary number Ca which evaluates the ratio between the external viscous stress and the elastic membrane response. In this linear regime, the results do not depend on the elastic constitutive law as expected. Without surface tension and bending
rigidity, we recover the results of Barthes-Biesel & Rallison (1981) and notably the fact that the Taylor parameter does not depend on the viscosity contrast $\lambda$ contrary to the case of a viscous droplet. In our more general model, the deformation does no longer depend on $\lambda$ at the upper order. Now, the Taylor parameter also depends on two other dimensionless numbers: the surface elastocapillary ratio $\sigma/G_s$ and the dimensionless bending
rigidity $B= \kappa/G_sR^2$. At the further order, the angle of inclination of the capsule with the direction of the shear flow, the analog of the Chaffey and Brenner equation for droplets is determined in each case. The results are in excellent agreement with the numerical ones performed with a code based on the boundary integral method providing an useful method to valid numerical developments.
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Strongly Correlated Electrons
Generalized local potential functional embedding theory of localized orbitals
Wafa Makhlouf, Bruno Senjean and Emmanuel Fromager
In this work we introduce a generalized
flavor, in the sense of generalized Kohn-Sham density functional theory (gKS-DFT), of the recently derived local potential functional
embedding theory (LPFET) [J. Chem. Theory Comput. 2025, 21, 20, 10293], where the in-principle exact formalism of DFT is combined with that of density
matrix embedding theory (DMET). In generalized LPFET (gLPFET), the
embedding clusters are designed from a full-size gKS system where the (in-principle non-local) Hartree-Fock exchange potential is combined with a local (in the localized orbital representation) correlation potential. The latter is optimized self-consistently such that gKS and local
embedding cluster's densities match. Unlike in DMET, which uses the same (global) chemical potential value in all clusters, each embedded orbital has its own chemical potential in gLPFET. We show analytically that, when electron correlation is strongly local, the latter potential becomes a simple functional of the correlation potential. Numerical calculations on model systems confirm the high accuracy of gLPFET in this regime, in contrast to DMET. Moreover, we show that gLPFET completely fixes the flaw of LPFET in weaker correlation regimes, through its appropriate description of the Hartree-exchange potential.
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Strongly Correlated Electrons
Ambipolar doping-induced surface in-gap state on Mott-insulating Ca$_2$RuO$_4$
M. Horio, T. Wada, V. Granata et al. (+4 more)
We report an x-ray photoemission spectroscopy study of Ca$_2$RuO$_4$ surface-dosed with Cs alkali atoms and C$_{60}$ molecules. Due to its small ionization energy (large electron affinity), deposited Cs atoms (C$_{60}$ molecules) are expected to provide a solid surface with electrons (holes). Upon dosing the dopants to Mott-insulating Ca$_2$RuO$_4$, we found a new Ru $3d$ photoemission peak emerging on the lower binding-energy side, suggesting the creation of a core-hole screening channel associated with coherent Ru $4d$ states around the
Fermi level. For both the Cs and C$_{60}$ dosing, this change occurred without an appreciable chemical potential jump. The coherent state, therefore, develops within the Mott gap through hybridization with the
impurity level of the dopants. The present work highlights the flexibility of Mott-
insulator surfaces as a playground for metal-
insulator transitions.
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All authors M. Horio, T. Wada, V. Granata, R. Fittipaldi, A. Vecchione, J. Chang, I. Matsuda
Materials Science
Neel temperature and helical spin order of altermagnetic RuO2
Markus Meinert
The
magnetic groundstate of RuO$_2$ remains controversial, with experimental evidence for a nonmagnetic groundstate of ideal bulk material and indications of a
magnetic state in strained thin films. Here, I investigate the Néel temperature of the (hypothetical) altermagnetic state of bulk RuO$_2$, stabilized via the DFT$+U$ technique, by mapping on a Heisenberg
Hamiltonian. The Néel temperature scales monotonously with the
magnetic moment up to the point where a large $+U$ term opens a band gap and turns RuO$_2$ semiconducting. The maximum Néel temperature obtained by this procedure is 408\,K at $U=3$\,eV, and much smaller values for smaller $U$. A reciprocal-space
eigenvalue analysis reveals a helimagnetic groundstate of the
spin model due to intra-sublattice
antiferromagnetic coupling. This situation resembles the isostructural $\beta$-MnO$_2$, which is a prototype helimagnet. Further comparison with calculations on CrO$_2$ and altermagnetic MnF$_2$ taking $U$ as an adjustable parameter supports the validity of the
spin model analysis.
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Quantum Gases
Stability of Bose-Fermi mixtures in two dimensions: a lowest-order constrained variational approach
Pietro Cordioli, Leonardo Pisani and Pierbiagio Pieri
We investigate the problem of mechanical stability in two-dimensional Bose-
Fermi mixtures at zero temperature, focusing on systems with a tunable Bose-
Fermi (BF) interaction and a weak but finite
boson-
boson (BB) repulsion. The analysis is carried out within the framework of the lowest-order constrained variational (LOCV) approach, which allows for a non-perturbative treatment of strong interspecies correlations while retaining analytical transparency. The BF interaction is modeled by a properly regularized attractive contact potential, enabling the exploration of both the attractive and repulsive energy branches. We determine the minimal BB repulsion required to ensure mechanical stability of the mixture by evaluating the inverse compressibility
matrix over the full range of BF coupling strengths, within the domain of validity of the LOCV approximation. The interaction contribution to the energy is benchmarked against available experimental data and
Quantum Monte Carlo results in the single-
impurity limit, showing good agreement. Our analysis reveals how the critical BB coupling depends on interaction strength, density imbalance, and mass ratio. In particular, we find that mixtures with equal
boson and
fermion masses exhibit enhanced stability, requiring the smallest BB repulsion to prevent mechanical instability. In this case, a relatively small BB interaction is sufficient to stabilize attractive mixtures for all values of the BF interaction. These results provide a theoretical framework for assessing stability conditions in experimentally realizable two-dimensional Bose-
Fermi mixtures with tunable interactions.
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Disordered Systems and Neural Networks · Cross-listed from cs.LG
A unified theory of feature learning in RNNs and DNNs
Jan P. Bauer, Kirsten Fischer, Moritz Helias et al. (+1 more)
Recurrent and deep neural networks (RNNs/DNNs) are cornerstone architectures in machine learning. Remarkably, RNNs differ from DNNs only by weight sharing, as can be shown through unrolling in time. How does this structural similarity fit with the distinct functional properties these networks exhibit? To address this question, we here develop a unified mean-field theory for RNNs and DNNs in terms of representational kernels, describing fully trained networks in the feature learning ($\mu$P) regime. This theory casts training as
Bayesian inference over sequences and patterns, directly revealing the functional implications induced by the RNNs' weight sharing. In DNN-typical tasks, we identify a phase transition when the learning signal overcomes the noise due to randomness in the weights: below this threshold, RNNs and DNNs behave identically; above it, only RNNs develop correlated representations across timesteps. For sequential tasks, the RNNs' weight sharing furthermore induces an inductive bias that aids generalization by interpolating unsupervised time steps. Overall, our theory offers a way to connect architectural structure to functional biases.
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All authors Jan P. Bauer, Kirsten Fischer, Moritz Helias, Agostina Palmigiano
Strongly Correlated Electrons
Correlation-driven origin of shallow electron pocket in Co$_{1/3}$TaS$_2$ revealed by ARPES and cluster perturbation theory
Wojciech Sas, Yuki Utsumi Boucher, Seyed Ashkan Moghadam Ziabari et al. (+11 more)
We investigate the electronic structure and
Fermi surface of Co$_{1/3}$TaS$_2$ using angle-resolved photoemission spectroscopy (ARPES) combined with theoretical modeling beyond standard density functional theory (DFT+U). A shallow electron pocket, the so-called $\beta$ feature, is observed at the
Fermi level near the corner of the superlattice Brillouin zone, representing the first experimental observation of this feature in an intercalated TaS$_2$ compound. Similar pockets have been reported in $X_{1/3}$NbS$_2$ ($X$ = Co, Cr, Ni), where their surface versus bulk origin remains actively debated. Because conventional DFT+U does not capture this feature, we employ cluster perturbation theory (CPT) to incorporate an explicit treatment of strong electron correlations ($U$) on the Co sites. CPT successfully reproduces the $\beta$ feature, demonstrating its origin from correlation-driven bulk states rather than surface effects. To further substantiate this conclusion, we studied a reduced Co-content sample, Co$_{0.22}$TaS$_2$, where the reduced charge transfer modifies the Co-derived states near the
Fermi level. Its electronic structure remains largely similar to that of pristine 2H-TaS$_2$, showing only a minor overall energy shift and lacking the $\beta$ feature, consistent with disrupted long-range Co ordering and modified orbital character near the
Fermi level. We demonstrate that the $\beta$ feature arises from strong local correlations on the Co sites and requires long-range crystallographic order among intercalated Co atoms to maintain coherence. These results highlight the importance of strong electronic correlations in magnetically intercalated transition-metal dichalcogenides and provide a microscopic understanding of features not captured by conventional DFT+U.
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All authors Wojciech Sas, Yuki Utsumi Boucher, Seyed Ashkan Moghadam Ziabari, Gaurav Pransu, Trpimir Ivšić, Ivana Vobornik, Jun Fujii, Naveen Singh Dhami, Bruno Gudac, Mario Novak, László Forró, Neven Barišić, Ivo Batistić, Petar Popčević
Quantum Gases
Engineering interactions shape in resonantly driven bosonic gas
Damian Włodzyński and Krzysztof Sacha
In systems with fast periodic driving, there are special subsets of (resonant) states, which behavior can be described with effective, time-independent
Hamiltonian in a rotating reference frame. Here, we show that experimentally feasible system of ultracold bosonic atoms on a ring with rapidly oscillating scattering length can be used to simulate time-independent two-component atomic mixture with exotic, long-range interactions.
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Mesoscale and Nanoscale Physics
Topological Scaling of Nonlinear Injection current and the Quantized Circular Photogalvanic Effect (CPGE)in tilted multi Weyl semimetals(mWSMs)
Deepannita Das and Alestin Mawrie
We develop a microscopic theory of nonlinear magneto-optical injection currents in multi-Weyl semimetals subjected to a uniform
magnetic field. Using the Landau-level spectrum of a tilted multi-Weyl
Hamiltonian with arbitrary monopole charge $\nu$ as a starting point, we formulate a Kubo-type nonlinear response theory in the Landau-level basis and derive the second-order conductivity tensor. We identify distinct contributions originating from
chiral-
chiral,
chiral-bulk, and bulk-bulk optical transitions, revealing characteristic monopole-charge scaling and sharp resonant structures governed by Landau-level selection rules and tilt-induced asymmetry. In the untilted limit, closed-form analytical expressions emerge that expose universal frequency thresholds and provide clear experimental signatures of higher-order Weyl
topology. Our results establish nonlinear magneto-optical injection currents as a direct transport probe of
chiral Landau levels and multi-Weyl topological charge.
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Soft Condensed Matter
The physics of crêpes: Elasto-gravity control of soft folding
Tom Marzin, Barath Venkateswaran, Yuchen Xi et al. (+2 more)
Like a crêpe resting on a plate, a thin elastic sheet can fold smoothly under its own weight, forming reversible shapes without creases or imposed hinges. Such soft folds arise from a balance between elastic bending and
gravity, yet their stability, packing limits, and dynamics remain poorly understood. Here we show that these behaviors are governed by a single physical length scale, the elasto-
gravity length $\ell_{eg}$. Using experiments and heavy-elastica theory, we demonstrate that $\ell_{eg}$ sets the characteristic fold geometry, determines when a fold becomes unstable and unfolds, and limits how many reversible folds can be stacked in rectangular and circular sheets. In particular, when lengths are rescaled by $\ell_{eg}$, fold shapes and stability thresholds collapse across materials and thicknesses. We further show that unfolding follows a universal speed scaling $v \sim \sqrt{g\,\ell_{eg}}$, revealing a
gravity-controlled time scale for the release of stored bending energy. Together, these results establish a unified physical framework for reversible folding, compact storage, and
gravity-assisted deployment of thin elastic sheets.
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All authors Tom Marzin, Barath Venkateswaran, Yuchen Xi, Sunghwan Jung, P.-T. Brun
Materials Science
Reactive Coarse Grained Force Field for Metal-Organic Frameworks applied to Modeling ZIF-8 Self-Assembly
Sangita Mondal, Cecilia M. S. Alvares and Rocio Semino
Decoding the self-assembly mechanism of metal-organic frameworks is a crucial step in reducing trial-and-error tests in their synthesis protocols. Atomistic simulations have proven essential in revealing molecular-level features of MOF nucleation, but they still exhibit limitations in the simulation setups due to size constraints (inability of reaching realistic concentrations or exploring non-stoichiometric metal:ligand ratios). In this contribution, we develop a methodology to derive reactive coarse grained force fields based on multiscale coarse graining methods. We apply our novel methodology to the case of the archetypal zeolitic-imidazolate framework ZIF-8. Our coarse grained force field, which we call nb-CG-ZIF-FF, does not contain any explicit connectivity information, but learns the tetrahedral Zn-connectivity from many body correlations within an atomistic
benchmark. nb-CG-ZIF-FF quantitatively reproduces the features of bulk, crystalline ZIF-8 as well as the structural
evolution of pre-nucleation species in terms of Zn n-fold coordination populations from the atomistic
benchmark. While the range of rings that are formed along the synthesis process are well captured by nb-CG-ZIF-FF, the model cannot exactly reproduce ring populations. Our reactive CG force field fitting approach can be applied to any MOF, opening new research avenues in modeling MOF formation, decomposition, defect dynamics and phase transition processes.
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Statistical Mechanics · Cross-listed from quant-ph
Observing quantum many-body dynamics in emergent curved spacetime using programmable quantum processors
Brendan Rhyno, Bastien Lapierre, Smitha Vishveshwara et al. (+2 more)
We digitally simulate
quantum many-body dynamics in emergent curved backgrounds using 80 superconducting
qubits on IBM Heron processors. By engineering spatially varying couplings in the
spin-$\frac12$ XXZ chain, consistent with the low-energy description of the model in terms of an inhomogeneous Tomonaga-Luttinger
liquid, we realize excitations that follow geodesics of an effective metric inherited from the underlying spatial deformation. Following quenches from Néel and few-
spin-flip states, we observe curved light-cone propagation, horizon-induced freezing in the local magnetization, and position-dependent oscillation frequencies set by the engineered spatial deformation. Despite strong spatial inhomogeneity, unequal-time correlators reveal ballistic quasiparticle propagation in the
spin chain. These results establish large-scale digital
quantum processors as a flexible platform for detailed and controlled exploration of many-body dynamics in tunable and synthetic curved spacetimes.
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All authors Brendan Rhyno, Bastien Lapierre, Smitha Vishveshwara, Khadijeh Najafi, Ramasubramanian Chitra
Statistical Mechanics
Anomalous transport in the Fermi-Pasta-Ulam-Tsingou model: a review and open problems
Stefano Lepri, Roberto Livi and Antonio Politi
This review provides an up-to-date account of energy transport in
Fermi-Pasta-Ulam-Tsingou (FPUT) chains, a key testbed for nonequilibrium statistical physics. We discuss the transition from the historical puzzle of thermalization to the discovery of anomalous heat transport, where the effective thermal conductivity $\kappa$ diverges with system size $L$ as $\kappa \propto L^\delta$. The article clarifies the distinction between two universality classes: the FPUT-$\alpha \beta$ model, characterized by $\delta = 1/3$ and linked to Kardar-Parisi-Zhang (KPZ) physics, and the symmetric FPUT-$\beta$ model, where numerical and theoretical evidence support $\delta = 2/5$. We investigate how finite-size effects - unavoidably induced by the thermostatting protocols - can disguise the asymptotic scaling. Additionally, we analyze the role of conservative noise in preserving hydrodynamic properties and examine how proximity to integrable limits leads to long-lived quasi-particles and, thereby, to diffusive regimes over intermediate spatial scales.
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Statistical Mechanics
Ising Model with Power Law Resetting
Anagha V K and Apoorva Nagar
We investigate the nonequilibrium dynamics of the nearest-neighbour Ising model subjected to
stochastic resetting, where the system is intermittently returned to an initial configuration with magnetisation $m_0$, with the inter-reset times drawn from the power law distribution $\alpha \tau_0^\alpha / \tau^{\alpha+1}$. The heavy-tailed resets generate magnetisation distributions that differ significantly from both
equilibrium dynamics and the previously studied Ising model with exponentially distributed reset times. In two dimensions, for $T > T_C$, we find a quasi-ferro state for all $\alpha$, marked by a double-peaked distribution that diverges at $m=0$ and $m=m_0$; no steady state exists for $\alpha < 1$, while a stationary state emerges for $\alpha > 1$. For $T < T_C$, power law resetting produces two distinct regimes separated by a crossover exponent $\alpha^* = 1-c$: a single-peak
ferromagnetic phase localised at $m_{eq}$ for $\alpha < \alpha^*$, and a dual-peak
ferromagnetic phase with divergences at $m_{eq}$ and $m_0$ for $\alpha > \alpha^*$. Analytic results in one and two dimensions, supported by simulations, yield a rich phase diagram in the $(T,\alpha)$ plane and reveal how heavy-tailed resetting generates nonequilibrium phases very different from those seen in the case of exponential resetting.
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