Materials Science
Accidental accuracy and formal consistency in $GW$+BSE: Exact benchmarks and regime-dependent error cancellation
Michael O. Atambo
Standard many-body perturbation theory for optical excitations combines the $GW$ approximation for quasiparticle energies with the Bethe-Salpeter equation (BSE) for the electron-hole response. Formally, the BSE kernel must equal the functional derivative of the self-energy, $K=\delta\Sigma/\delta G$. In routine practice, however, the kernel is built from a statically screened direct interaction and a bare exchange interaction, which breaks this consistency. Using exact diagonalization of the extended Hubbard dimer, we construct a controlled
benchmark that isolates the price of this inconsistency. We show that the internally inconsistent practical $GW$+BSE construction frequently yields accurate optical gaps through accidental cancellation between an underestimated $GW$ gap and an oversized bare-exchange kernel, and we map the regions of parameter space where this accidental accuracy occurs. Upon switching on the nearest-neighbor interaction and binding the
exciton, the practical construction remains the accurate one throughout the weak-binding regime, with cancellation optima at parts in $10^{3}$, while the frozen-$W$ construction fails at every binding strength. Beyond a binding threshold both static constructions deteriorate, showing that deeply bound
excitons require physics beyond any static kernel. Accidental accuracy is therefore a property of the weak-binding regime, and the systematic failure of the frozen-$W$ derivative kernel within the explored parameter space traces to its overscreening of the exchange channel. The accuracy of the practical kernel is an accidental cancellation of two independent errors, an underestimated quasiparticle gap and an oversized exchange term, not a hidden consistency. These results provide a controlled taxonomy of approximation failure in $GW$+BSE and a precise diagnostic for when standard workflows can be trusted.
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Disordered Systems and Neural Networks · Cross-listed from cs.LG
Breakdown of Local Denoising as Semantic Speciation
Guangkuo Liu, Mert Okyay, Yifan F. Zhang et al. (+3 more)
The dynamics of generative models exhibit two apparently distinct temporal windows: a speciation window, in which a sample commits to a semantic class, and a nonlocality window, in which local context windows become insufficient for generation. Motivated by evidence of their near-concurrence in a variety of frontier models, we investigate their relationship through the spatial distribution of semantic information. Under a "common cause" hypothesis, we prove that the nonlocality window must lie in the speciation window. This hypothesis postulates that semantic labels explain a fraction of the correlations between distant
tokens, a condition that is natural for many real
datasets. We further give conditions under which both windows shrink to a single limiting time as system size grows, defining a "phase transition", and verify this behavior analytically in Gaussian mixtures. Together, these results identify conditions under which semantic information explains the concurrence of speciation and nonlocality, connecting two complementary perspectives on the emergence of semantic structure in generative modeling.
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All authors Guangkuo Liu, Mert Okyay, Yifan F. Zhang, Fangjun Hu, Rahul Nandkishore, Xun Gao
Superconductivity
Imaging phase winding in topological superconductors with a fork-tip Josephson STM
Vladislav Poliakov and Archisman Panigrahi
The complex phase winding in a topological
superconductor remains challenging to access by conventional real-space probes. We propose a scheme to probe this winding with a fork-tip Josephson STM near an impurity, where two superconducting tips form an interferometer sensitive to phase differences between two positions. The signal remains accessible even if the relative phase between the fork-tip and sample fluctuates, establishing a route towards a local phase-sensitive STM probe of topological superconductivity. We numerically compute the interference pattern to demonstrate that the magnitude and phase of the order parameter can be reconstructed as a function of angle, providing a route towards resolving the longstanding open experimental problem of directly detecting phase winding in topological
superconductors.
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Statistical Mechanics
Classification of topological phases of matter in stochastic systems
Dexin Li and Evelyn Tang
Topological phases of matter support edge states protected from random perturbations, and the identification of the discrete non-spatial
symmetries and dimensions that support such phases was systematically developed for
quantum systems and analogous platforms. While topological phases were also discovered in
stochastic systems and posited as mechanisms for key biochemical processes, a classification consistent with their Markovian constraints remains lacking, impeding generalization to new scenarios. To address this, we develop new methods including a new homotopy approach, real-space invariants and a redefinition of the point gap to classify both transient and steady states. We find robust transient states in two
symmetry classes, no
symmetry and pseudo-Hermiticity respectively, while topological steady states are expected only in systems without
symmetry. We identify the dimensions with non-trivial phases and their group structure, creating a rigorous framework for predicting robust behavior in active and living matter.
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Strongly Correlated Electrons
Neural-quantum-state based downfolding of the three-band Emery model for cuprates and nickelates
Hannah Lange, Julius F. A. Tirpitz and Annabelle Bohrdt
Understanding the physics underlying high-temperature superconductivity in cuprates and, more recently, infinite-layer nickelates has remained a central challenge in condensed-matter physics. We establish neural
quantum states (NQS), specifically Hidden
Fermion Determinant States (HFDS), as a scalable variational approach to the three-band Emery model of the copper- and nickel-oxide layers in these materials. After benchmarking HFDS against
matrix product states on width-two geometries, we study ground states of fully two-dimensional (2D) systems of up to $10\times10$ unit
cells ($300$ sites). We characterize the momentum-space distribution of dopants and find a pronounced electron-hole dichotomy similar to cuprate experiments. We further downfold the three-band model to effective single-band descriptions by constructing interacting Wannier functions. We consider a wide range of parameters – from the charge-transfer regime relevant to cuprates to the Hubbard-Mott regime of nickelates, as well as systematic scans of the charge-transfer gap that has been demonstrated to impact the critical superconducting temperatures. Across all regimes, the effective model significantly deviates from the usual Fermi-Hubbard model: The typical ratio $U/t$ is enhanced, some parameters experience a significant doping dependence, and sizable terms beyond the conventional Hubbard model are present, most notably a density-assisted hopping $t_n$. Notably, in all effective models, $t_n$ has the largest contribution to particle-hole asymmetry, rather than next-nearest-neighbor hopping contributions. The effective parameters sensitively depend on the charge-transfer energy, doping, and interaction ratios. Our results establish HFDS as an efficient tool for studying the 2D Emery model and demonstrate that single-band descriptions can require interaction terms generated by the underlying multi-band models.
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Superconductivity
Anisotropic interface-confined superconductivity in FeTe-based heterostructures
Bicky Singh Moirangthem, Kamal R. Joshi, Zi-Jie Yan et al. (+4 more)
Interface-confined superconductivity emerges from the interaction of electronic states across chemically distinct boundaries, providing a route to engineer superconducting phases where magnetism and
topology coexist. Determining the intrinsic nature of such superconductivity, however, is challenging because the superconducting layer is only a few nanometers thick and buried beneath several normal layers. Here, we measure the whole-sample Meissner response of six $\mathrm{FeTe}$-based
heterostructures in a uniform
magnetic field using a frequency-domain tunnel-diode resonator. In the ultrathin limit, the conventional normalization of the measured susceptibility, $\chi(T\to0)=-1$, fails by tens of percent. We establish the appropriate calibration and invert $\chi(T)$ to determine the London penetration depth $\lambda(T)$. Two key results emerge. First, the broad transitions observed in $\chi(T)$ arise naturally from the extreme geometry and large $\lambda$, without requiring chemical or structural inhomogeneity; the extracted $\lambda(T)$ closely tracks the resistive transition. Second, $\lambda(T)$ and the corresponding superfluid density are inconsistent with a fully gapped isotropic $s$-wave state and instead indicate a strongly anisotropic order parameter possibly with line nodes or deep gap minima. The inferred $\lambda(0)$ is of order $1\,\mu$m, consistent with an independent analysis of the 2D phase stiffness. Despite the distinct chemical,
magnetic, and topological character of the three overlayers, all six FeTe
heterostructures exhibit similar low-temperature power-law behavior, with no systematic dependence of the superconducting response on overlayer identity. These results point to the interfacial $\mathrm{FeTe}$ layer as the common origin of superconductivity.
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All authors Bicky Singh Moirangthem, Kamal R. Joshi, Zi-Jie Yan, Pu Xiao, Lok-Kan Lai, Cui-Zu Chang, Ruslan Prozorov
Disordered Systems and Neural Networks · Cross-listed from quant-ph
Local autonomous inference machines for quantum LDPC codes
Siddhant Midha and Dmitry A. Abanin
We introduce a local and distributed framework for decoding
quantum LDPC codes. Built atop belief propagation (BP), the architecture combines strictly local processing of syndrome information, local feedback, autonomous operation, and highly parallelized decoding. We establish the framework at two complementary levels. First, we show that any code exhibiting a threshold under iterative BP decoding can be promoted to an autonomous local measurement-and-feedback dynamics while preserving that threshold. We then turn to codes for which naive BP does not itself exhibit threshold behavior. Our key observation is that BP can nevertheless provide sufficiently accurate local marginal information: active syndrome defects use these local beliefs to move, pair, and annihilate through asynchronous feedback. We demonstrate numerically that this construction exhibits threshold behavior in the point-like sectors of the two- and three-dimensional toric codes, where conventional BP decoding fails. Exploiting the graph-generality of BP, we then study the inference dynamics on the membrane-like sector of the three-dimensional toric code and in a family of bivariate-bicycle
quantum LDPC codes.
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Materials Science
How Thermodynamically Accessible are Quaternary Mixed-Metal Chalcohalides?
Pascal Henkel, G. Krishnamurthy Grandhi, Jarno Laakso et al. (+6 more)
Quaternary mixed-metal chalcohalides (MMCHs) are a promising mixed-anion
semiconductor family, but their thermodynamic accessibility remains largely unexplored. We combine density functional theory with the Alexandria Materials Database to carry out a rapid and reliable evaluation of the thermodynamic accessibility of 54 M(II)$_2$M(III)Ch$_2$X$_3$ compounds. All evaluated MMCHs are predicted to be thermodynamically unstable, but a considerable fraction of MMCHs lie within computational uncertainty of the convex hull. Their predicted decomposition follows five distinct reaction pathways, most commonly into M(III)$_2$Ch$_3$, M(II)X$_2$, and M(II)Ch. Solution processing of six Sn-based MMCHs supports our analysis. Notably, this includes the first synthesis of the previously unreported Sn$_2$InS$_2$Br$_3$ in a multiphase film. Our approach identifies convex hull proximity and competing phase formation as key constraints on MMCH synthetic accessibility during solution processing, thereby guiding future MMCH exploration.
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All authors Pascal Henkel, G. Krishnamurthy Grandhi, Jarno Laakso, David Rovira Ferrer, Edgardo Saucedo, Jingrui Li, Paola Vivo, Miguel A. L. Marques, Patrick Rinke
Statistical Mechanics
The Principle of Minimum Justified Correlation
John H Van Drie
It is shown that Shannon
entropy, Fisher information, and
quantum-mechanical kinetic energy may all be viewed as measures of correlation. We begin with a fundamental correlation-destroying map: a joint probability density $\rho(x,y)$ is replaced by $\rho_x(x)\rho_y(y)$, the product of its marginal distributions. In the discrete case, Shannon's
entropy is nondecreasing under this map. For continuous distributions, this fundamental map leads to a well-behaved, coordinate-invariant correlation measure, analogous to the discrete Shannon
entropy: \[ I[\rho] = h[\rho_x] + h[\rho_y] - h[\rho]. \] In the continuous case, however, another measure appears: Fisher information. The relative Fisher information $J(\rho\|\rho_x\rho_y)$ behaves similarly under the fundamental map. For a normalized real
quantum wavefunction, this decrease is exactly proportional to the decrease in mean kinetic energy, \[ \langle T\rangle_\psi - \langle T\rangle_\Phi = \frac{\hbar^2}{8m} J(\rho\|\rho_x\rho_y), \qquad \Phi = \sqrt{\rho_x \rho_y}. \] In Jaynes's
language, the result supports a principle of minimum justified correlation: given physical constraints and a set of possible distributions or related amplitudes satisfying those constraints, select from that set those with the least correlation. This is Part I of a two-part paper. Here we develop the
entropy, Fisher-information, and kinetic-energy identities above, and state the principle they support. Part II addresses questions which Part I raises but leaves unanswered: multiple solutions, time dependence, the role of
spin, a route to the Schrödinger equation itself, and a proposed experimental test. AI has been used.
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Mesoscale and Nanoscale Physics
Spatially dispersive photogalvanic effects as a probe of quantum geometric tensor
Yicong Chen, Bumseop Kim, Senin Ahammed Akkara Paramban et al. (+8 more)
Berry
curvature and
quantum metric of Bloch states govern a wide range of phenomena, yet unified experimental access to both remains limited. Here we show that light spatial-dispersion alters the selection rules of second-order photocurrents and responses forbidden by parity become allowed in centrosymmetric
crystals without any external fields,
magnetic order, interfaces, strain, or engineered
symmetry breaking. The resulting response is intrinsic and its weight is set by the
quantum geometry of the Bloch states. Conventional photogalvanic effects are constrained by
crystal symmetry and entangle the
quantum metric with shift vector contributions. The spatially-dispersive response instead isolates the
quantum metric and Berry
curvature in distinct polarization channels. Implementing this approach in 1T'-MoTe2 across its temperature-driven transition to Td-Weyl phase, we resolve helicity-even and helicity-odd photocurrents corresponding to
quantum metric and Berry
curvature contributions, respectively, from the same device. The metric-dominated response persists across both phases and exhibits a robust spectral structure reproduced by first-principles calculations and linked to momentum-resolved
quantum metric hotspots. In contrast, the
curvature-driven channel emerges only when inversion
symmetry is broken and shows strong sensitivity to carrier doping through competing momentum-space contributions. Our results establish photogalvanic effects with spatially varying optical fields as a general route to accessing
quantum geometry in materials where
photon energy and electronic filling probe different parts of the excitation
manifold.
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All authors Yicong Chen, Bumseop Kim, Senin Ahammed Akkara Paramban, Zhurun Ji, Utkarsh Khandelwal, Shupeng Xu, Jiachen Shi, Sergiy Krylyuk, Albert V. Davydov, Andrew M. Rappe, Ritesh Agarwal
Strongly Correlated Electrons
Boundary Criticality in (2+1)-dimensional U(1) Dirac Quantum Spin Liquid
Huan Jiang, Zhiming Pan, Xue-Jia Yu et al. (+1 more)
An emergent gauge field can control boundary critical behavior without changing the bulk
quantum spin liquid. We investigate the boundary criticality in $(2+1)$-dimensional $U(1)$ Dirac
spin liquid, whose low-energy physics is described by massless
quantum electrodynamics. Using a perturbative renormalization-group analysis in a half-space, we show that Neumann and Dirichlet boundary conditions for the emergent gauge field lead to distinct boundary universality classes. We determine the boundary scaling dimensions of the fundamental fields and gauge-invariant operators that provide observable signatures. We further propose a
fermion-gauge
lattice model with tunable boundary interactions as a microscopic setting for realizing and probing these boundary universality classes.
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All authors Huan Jiang, Zhiming Pan, Xue-Jia Yu, Shao-Kai Jian
Statistical Mechanics · Cross-listed from math-ph
On the Spectrum of Some Temperley-Lieb Spin Chains
Robert Ferydouni and Bruno Nachtergaele
We review mathematical results about the spectrum of
spin-$s$ chains with a nearest neighbor interaction given by the projection onto the singlet state of two
spin-$s$ degrees of freedom. Up to normalization, these interaction terms generate a Temperley-Lieb
algebra at loop parameter $d=2s+1$. We also present several new results. First, we prove a ferromagnetic ordering of energy levels across
symmetry sectors of the model, thus generalizing a previous result of Nachtergaele, Spitzer and Starr (2004) for the
spin-$\tfrac12$ $XXZ$ chain. This enables us to determine a uniform lower bound on the finite volume spectral gap for these
spin chains. By combining a variational estimate with Knabe's finite size criterion, we show that the exact spectral gap of the GNS
Hamiltonian of the fully polarized state is $1-2/d$. Furthermore, this value serves as a lower bound for the gap of the maximally mixed ground state. Finally, we show that the ground state projectors on open chains satisfy the Jones-Wenzl recursion, thereby recovering a known result that the degeneracies are the
quantum integers $[L+1]_q$ for $q+q^{-1}=d$. We discuss how the high degeneracy of the ground states allows the model to break a continuous
symmetry while remaining gapped, and renders that gap unstable.
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Materials Science
3/8 charge-density wave instability in the kagome metal CsV$_3$Sb$_5$
Luca Buiarelli, Hyeonseo H. Park, Ethan T. Ritz et al. (+2 more)
The kagome metal CsV$_3$Sb$_5$ exhibits charge density wave (CDW) and superconducting transitions, both of which are substantially affected by pressure. Recent x-ray diffraction experiments identify a new charge-ordered phase at a pressure coinciding with the dip of the superconducting dome. This CDW phase displays a distinctive wavevector $\mathbf{Q} = (3/8, 0, 1/2)$ and monoclinic
symmetry, in contrast to the $2\times2\times 2$ and $2\times2\times 4$ orders reported at ambient pressure. In this letter, we show that density functional perturbation theory (DFPT) calculations on a fine reciprocal-space grid predict the leading
lattice instability of CsV$_3$Sb$_5$ to be at this wavevector. Finite-displacement calculations reveal that while anharmonic effects stabilize the conventional $L_2^-$ CDW at ambient pressure, the competing $3/8$ instability becomes energetically favorable above $\sim$1 GPa, consistent with experimental observations. Interestingly, the nesting function displays a peak at the same wavevector. A Landau free energy analysis explains the emergence of the monoclinic distortion observed in x-ray diffraction, in addition to several bond-ordering patterns that may be relevant to the observed trends in the superconducting $T_c$.
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All authors Luca Buiarelli, Hyeonseo H. Park, Ethan T. Ritz, Rafael M. Fernandes, Turan Birol
Mesoscale and Nanoscale Physics
Interlayer Fermi Polarons in Bilayer MoTe$_2$
Ruihao Ni, Eugen Dizer, Maximilian Wolf et al. (+15 more)
Atomic bilayers of transition metal dichalcogenides (TMDs) host
quantum phases governed by the layer degree of freedom, including bilayer Wigner
crystals, fractional Chern
insulators, and
exciton condensates. These phases are probed primarily through
exciton spectroscopy, yet it remains poorly understood how
excitons and carriers interact to form Fermi polarons in bilayers, where both the impurity and the Fermi sea carry a layer pseudospin. Progress has been limited because most TMD bilayers have momentum-indirect optical bandgaps, in which non-radiative decay and inhomogeneous broadening obscure the intrinsic spectra. Here, we show that bilayer MoTe$_2$, unlike most TMD bilayers, retains a direct optical bandgap, providing a clean platform for studying bilayer Fermi-polaron physics. In a dual-gated device, an out-of-plane electric field continuously tunes the hybridization between intralayer and interlayer
excitons, forming layer-coherent
excitons. Upon electrostatic doping, the excitonic spectrum evolves into multiple polaron branches, controlled by both carrier doping and the out-of-plane electric field. Among these, we identify a polaron with no analog in monolayers, in which a layer-coherent
exciton is dressed by carriers in the opposite layer, and is quantitatively captured by our field-theoretic model. Our results establish that pseudospin structure in both the impurity and the bath reshapes polaron formation, opening new avenues to many-body states such as Bose-Einstein condensates with interlayer coherence.
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All authors Ruihao Ni, Eugen Dizer, Maximilian Wolf, Son T. Le, Sharadh Jois, Jeffrey J. Schwartz, Liuxin Gu, Rundong Ma, Suji Park, Beini Gao, Lifu Zhang, Houk Jang, Takashi Taniguchi, Kenji Watanabe, Aubrey T. Hanbicki, Adam L. Friedman, Richard Schmidt, You Zhou
Mesoscale and Nanoscale Physics
Rundong Ma, Konstantin Davydov, Liuxin Gu et al. (+9 more)
Interlayer
excitons in transition metal dichalcogenide (TMD)
heterostructures exhibit long lifetimes and long-range transport, making them promising for excitonic devices and
quantum many-body phases, such as Bose-Einstein condensates. Achieving these goals requires a precise understanding of
spin-allowed bright and nominally
spin-forbidden dark
excitons, because the lowest-energy
exciton species governs population, transport, and condensation. Despite substantial progress, unambiguously distinguishing singlet and triplet interlayer
excitons has been challenging, as moiré
excitons in these
heterostructures can mimic their optical signatures. Here, we report the direct spectroscopic identification of bright (singlet) and dark (triplet) interlayer
excitons in high-quality, dual-gated WSe$_2$/hBN/WSe$_2$ homobilayers. Electric-field-dependent photoluminescence and reflectance reveal two momentum-direct interlayer transitions with distinct
spin configurations. The interlayer dark
excitons obey selection rules that differ from those of bright
excitons. Strikingly, interlayer dark
excitons retain strong valley polarization, even with their ultralong lifetime exceeding microseconds. Finally, we demonstrate twist-angle control, wherein twist-induced electron-hole momentum mismatch modulates interlayer
exciton emission. These results provide critical insights into the electronic and excitonic structure of TMD
heterostructures, opening new avenues for excitonic many-body physics and optoelectronic devices.
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All authors Rundong Ma, Konstantin Davydov, Liuxin Gu, Lifu Zhang, Hassan Alnatah, Beini Gao, Ruihao Ni, Suji Park, Houk Jang, Takashi Taniguchi, Kenji Watanabe, You Zhou
Disordered Systems and Neural Networks · Cross-listed from math-ph
Simon Becker and Izak Oltman
For Bernoulli bond percolation on every regular tree of degree at least three, we prove that infinite clusters appear strictly before absolutely continuous spectrum. Throughout an explicit supercritical interval, the adjacency operator of every open cluster almost surely has no absolutely continuous component. Together with Bordenave's
theorem, this gives $p_c<p_{ac}<1$.
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Strongly Correlated Electrons
Variational Monte Carlo for the Hubbard model
Luca F. Tocchio
In these lecture notes, we introduce the variational Monte Carlo method for the Hubbard model. First, we briefly introduce the single-orbital Hubbard model and its multi-orbital extension, focusing only on electronic models. Then, we introduce the general scheme under which variational Monte Carlo works and we present the variational wave functions that can properly describe superconductive and
magnetic states in single-orbital and multi-orbital Hubbard models. We also detail how to perform Monte Carlo calculations for the given wave functions. We also describe how to optimize a variational wave function with the
stochastic reconfiguration method. Finally, we present a few results for correlation functions that can be computed in variational Monte Carlo, to determine, for instance, the presence of charge or
spin order and superconductivity.
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Superconductivity
Reversible field-free superconducting diode effect controlled by an antiferromagnet
Filip Krizek, Kamil Olejník, Tobias Edwinson et al. (+19 more)
The
semiconductor diode, which allows current to flow preferentially in one direction, is a fundamental building block of numerous modern electronic
circuits. Its superconducting analogue—the superconducting diode effect—enables directional dissipationless current flow and may provide similar functionality in future superconducting
quantum circuits. Realization of such a nonreciprocal supercurrent requires broken time-reversal
symmetry. At zero applied field, this has been typically associated either with intrinsic unconventional superconductivity or extrinsic
spin-split electronic states induced by
magnetic proximity. Here we demonstrate a field-free superconducting diode effect in conventional superconducting Al proximitized by collinear antiferromagnetic CuMnAs, whose electronic structure breaks time-reversal
symmetry without generating
spin splitting. By tuning the proximity effect through an insulating AlAs interlayer and correlating the reversal of the diode polarity with the reversal of the remanent Néel state, we establish that the antiferromagnet controls the superconducting diode effect. Our results show that neither
spin-split bands nor net magnetization is required for a magnetically controlled field-free superconducting diode effect, extending superconducting nonreciprocity to a broader class of collinear compensated magnets.
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All authors Filip Krizek, Kamil Olejník, Tobias Edwinson, August Jacobi, Athira Suresh, Andrej Farkaš, Jan Kraus, Vít Novák, Christoph Müller, Vojtěch Pařízek, Niclas Heinsdorf, Peter Wadley, Oliver Amin, Kevin Edmonds, Tomas Jungwirth, Libor Šmejkal, Anna Birk Hellenes, Sumit Ghosh, Michal Mazur, Dominik Kriegner, Lucas Casparis, Saulius Vaitiekėnas
Strongly Correlated Electrons
Strong-to-Weak Spontaneous Symmetry Breaking of Dephased Fermions
Abhijat Sarma
Strong-to-weak spontaneous
symmetry breaking (SWSSB) is a novel phase transition in mixed states associated with the loss of global charge information. In this work we study
fermions with $U(1)$
symmetry under infinite density dephasing and derive the SWSSB properties of the resulting mixed states. Our central observation is that at infinite dephasing every Renyi correlator is exactly the
spin-
spin correlator of a compact XY model, whose Boltzmann weight is the squared full-counting-statistics generating function of a classical ensemble built from the parent state. For the Renyi-2 correlator it is the full counting statistics of the parent state itself. We complement the infinite dephasing mapping with a novel diagrammatic expansion for the Renyi-1 correlator, applicable to any diagonal mixed state, which computes the couplings of the Renyi-1 XY model. We also study a replica field theory for even Renyi index quantities, applicable at finite dephasing. Our analysis indicates that fully dephased metals display long-range SWSSB in $d\geq 2$, as confirmed numerically and experimentally in $d=2$, and quasi-long-range SWSSB in $d=1$. For insulating parent states both an SWSSB and a trivial phase are possible at infinite dephasing depending on UV details. Long-range SWSSB in $d\geq 3$, or quasi-long-range SWSSB in $d=2$, survives above a nonuniversal, Renyi-index-dependent threshold and is lost when the parent state is deep in the insulating phase, with the exception of
quantum Hall
insulators which generically have quasi-long-range SWSSB. For even Renyi indices we also determine the stability of the SWSSB phase away from infinite dephasing and derive the universality class of the SWSSB transition.
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Disordered Systems and Neural Networks · Cross-listed from physics.soc-ph
Multiscale Reconstruction of Weighted Networks from Coarse-Grained Data
Mattia Marzi, Frank P. Pijpers and Diego Garlaschelli
Network reconstruction from partial information is usually performed at the same resolution level at which constraints are observable. This becomes problematic when only coarse-grained information is available, while the relevant process occurs at a finer scale. Here we employ the multiscale model of weighted networks introduced in a companion paper and turn it into a probabilistic framework for reconstructing weighted networks across arbitrary aggregation levels. The model is built to preserve its functional form under coarse-graining, so that global parameters calibrated on an observable aggregate layer can be transferred to finer layers without refitting. We test the method on two empirical systems with different aggregation mechanisms. In the International Trade Network, countries are aggregated into geographic macro-regions and the observed coarse-grained layer is used to infer the underlying country-level network. In the Dutch production network, sectoral flows are reconstructed across the hierarchical industrial classification, using coarser sectoral layers to infer finer ones. In both geographical and sectoral settings, we
benchmark our genuinely multiscale reconstruction method against a state-of-the-art weighted reconstruction model calibrated directly at the target resolution, and therefore using additional information available at the same (finer) scale at which performance is evaluated. Remarkably, despite this informational disadvantage, our method recovers the fine-scale binary structure with high accuracy, improving precision, specificity, accuracy and maximum degree-error diagnostics, while remaining nearly equivalent in sensitivity.
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Soft Condensed Matter
Emergent activity powers a path to chaos for pairs of acoustically trapped spheres
Matthew K. Gronert, Ben Cao, Ella M. King et al. (+1 more)
Pairs of spheres sharing an acoustic trap sometimes
spin intermittently despite having no self-propulsion, no obvious power source, and no
symmetry-breaking mechanism, switching between rocking and spinning within a single trajectory. Nonreciprocal wave scattering powers this emergent activity, and drag shapes their dynamics by coupling rotations to translations. Mismatched pairs can pass through a supercritical Hopf bifurcation into a quasiperiodic
torus on which the pair's orbit reverses regularly and, farther from
equilibrium, into deterministic chaos. Experiments motivate this mechanism and share its qualitative signatures; simulations reveal a full noise-free route from passivity to chaos, and suggest how analogous dynamics can emerge in other active-matter systems.
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All authors Matthew K. Gronert, Ben Cao, Ella M. King, David G. Grier
Statistical Mechanics
Blind directions of linear response and the limits of finite-perturbation bounds on efficiency fluctuations
Badr Farih
Thermodynamic uncertainty relations bound the fluctuations of time-antisymmetric currents.
Stochastic efficiency is not one: a ratio of two odd quantities, it is even under path reversal, and for the conventional ratio $-W/Q_h$ no moment exists. We work with the exergetic ratio $\eta=W/(W+T_0S)$, whose moments exist, and ask how much of its variance a finite perturbation of the dynamics can certify when linear response cannot. The question is specific to nonlinear observables: for every current, and every observable linear in transition counts and residence times, the multiparameter Cramér-Rao bound over rate and site perturbations already equals the variance. For $\eta$ it does not. The Cramér-Rao bound vanishes on a hyperplane of perturbation directions, while the Barankin multi-point bound, applied to tilted path measures, stays positive there and recovers 75% of the variance of $\eta$ in a three-state motor model where every linear-response bound is zero. The Gram
matrix of tilted Markov-jump path measures is a Feynman-Kac
matrix exponential whose potential is the Hellinger integrand of the jump intensities, and the cost of a perturbation is its $\chi^2$ divergence, which no dissipation bound controls. The bound captures 1.25-1.57 times the best linear-response bound, and the gain persists on networks of up to sixteen states. For an Ornstein-Uhlenbeck process the construction is exactly solvable: the optimal tilt scales as $T^{-1/2}$ and three test points nearly reach the supremum. Two limits are established. The gain is a short-window effect that disappears as the counts become Gaussian, and the bound cannot be turned into inference: coarse measurements bound $\chi^2$ only from below. The construction is a computational instrument for a model in hand, not an uncertainty relation.
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Materials Science
Irreducible Weyl Semimetals
Ke-Xin Pang and Yan Gao
A key objective in Weyl-semimetal (WSM) research is to identify phases built from minimal configurations of Weyl points (WPs), which provide the simplest settings for investigating the intrinsic physics of chiral topological charges. Pang et al. [Phys. Rev. Res. 8, 033304 (2026)] recently established that crystallographically realizable WSMs can be decomposed into linear combinations of 16 minimal "irreducible Weyl molecules" (IWMs). A fundamental question remains unresolved: which of these non-decomposable configurations can themselves form standalone crystalline phases? Here we introduce irreducible Weyl semimetals (IWSMs), in which two bands crossing near the Fermi level form an elementary
symmetry-compatible complex whose complete Weyl-node configuration is charge neutral and crystallographically indivisible. Combining all 1651
magnetic space groups with Weyl-orbit multiplicities and band-compatibility relations, we classify IWSMs formed by crystalline-
symmetry-protected twofold WPs. Only ten of the sixteen primitive inventories admit one-copy realizations, comprising four Pair, four Split, and two Mixed charge-node architectures. Remarkably, this classification uncovers five unconventional and previously unrecognized topological phases: the charge-three Pair IWSM {3, -3}; the Split IWSMs {3, -1, -1, -1}, and {4, -1, -1, -1, -1}; and the Mixed IWSMs {3, 1, -2, -2} and {3, 3, -2, -2, -2}. For all ten classes,
symmetry-constrained
lattice models verify the complete node inventories, Chern charges, and surface chiral-flow incidence. Our results establish crystalline irreducibility as a phase-level organizing principle beyond individual Weyl nodes and provide a
symmetry-resolved framework for identifying minimal Weyl complexes in electronic, phononic, and photonic systems.
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Statistical Mechanics · Cross-listed from math.PR
Non-equilibrium fluctuations of gradient exclusion processes in dimension $d\le 3$
Claudio Landim and Sunder Sethuraman
We consider a gradient, speed-change, symmetric exclusion process on the discrete
torus $T^d_n$, $d\le 3$, whose empirical measure evolves, on the diffusive scale, according to a non-linear parabolic equation. We prove that, starting from a sequence of initial states whose relative
entropy with respect to the inhomogeneous product measure associated with the initial profile is $o(n^{d/2})$, and whose density fluctuation field converges, the density fluctuation field converges, in $L^1(0,T; H_{- r})$, to the solution of a linear
stochastic partial differential equation with time-dependent coefficients driven by a conservative space-time white noise.
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Materials Science
Disentangling octahedral distortion and symmetry breaking in the ordered double perovskite SrLaCoNbO$_6$
Ajay Kumar, Clemens Ulrich, Yaroslav Mudryk et al. (+1 more)
We report a comprehensive high temperature structural investigation of the B-site ordered double perovskite SrLaCoNbO$_6$ using combined Raman spectroscopy and x-ray diffraction (XRD) over the range 25–900~$^\circ$C. Two distinct temperature-driven anomalies are identified at $T_\mathrm{OD} = 300\pm 25~^\circ$C and $T_\mathrm{PT} = 750\pm 25~^\circ$C through pronounced renormalizations in the
phonon frequency and linewidth, accompanied by the
evolution and suppression of characteristic XRD reflections. The low-temperature anomaly at $T_\mathrm{OD}$ is associated with an isostructural octahedral distortion within the monoclinic $P2_1/n$ phase. At $T_\mathrm{OD}$, the radial and angular distortion parameters of the CoO$_6$ and NbO$_6$ octahedra decrease to near-zero values before reversing upon further heating due to an inversion of the in-plane Co–O and Nb–O bond-length hierarchy. The high-temperature anomaly at $T_\mathrm{PT}$ corresponds to a
symmetry-breaking structural phase transition from $P2_1/n$ to the monoclinic $I2/m$ phase, confirmed by group-theoretical analysis and Rietveld refinement. These results demonstrate that integrating temperature-dependent Raman spectroscopy with laboratory-based XRD, complemented by quantitative octahedral distortion analysis, provides a robust approach to disentangle isostructural octahedral distortions from
symmetry-breaking phase transitions in complex double perovskite oxides without recourse to synchrotron or
neutron diffraction facilities.
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All authors Ajay Kumar, Clemens Ulrich, Yaroslav Mudryk, Rajendra S. Dhaka
Materials Science
Electronic Coupling and Charge-Transfer Landscape of Graphene on Ge(001)/Si(001): Multiscale Analysis Assisted by Machine Learning
Pawel Dabrowski, Przemysław Przybysz, Maciej Rogala et al. (+11 more)
Understanding and controlling charge transfer at
graphene-
semiconductor interfaces is essential for the integration of two-dimensional materials into silicon-compatible technologies. Here, we combine ultraviolet photoelectron spectroscopy (UPS), Kelvin probe force microscopy (KPFM), angle-resolved photoemission spectroscopy (ARPES), scanning tunneling spectroscopy (STS) and density functional theory (DFT) to resolve work-function modulation and electronic coupling in
graphene grown on Ge(001)/Si(001). UPS and KPFM reveal a spatially non-uniform work-function landscape correlated with the nanofaceted morphology of the substrate. ARPES and DFT calculations for the pristine interface consistently indicate n-type doping and electron transfer from Ge to
graphene. In contrast, modeling of the oxidized interface predicts a reversal to p-type doping, providing a plausible explanation for the different doping polarities reported in the literature. Machine-learning-assisted classification of the STS data resolves distinct local electronic regimes, ranging from nearly free-standing
graphene on nanofacet tops to more strongly coupled inter-facet regions and nanoribbon-like regions with distinct local electronic responses. By identifying the mechanisms governing local
graphene-substrate interactions and charge transfer, our study provides guidelines for tailoring the synthesis process and minimizing defect formation during delamination. These insights support the production of high-quality
graphene layers for electronic devices and for transfer as protective coatings for air-sensitive materials.
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All authors Pawel Dabrowski, Przemysław Przybysz, Maciej Rogala, Iaroslav Lutsyk, Paweł Krukowski, Witold Kozłowski, Michał Piskorski, Piotr Milczarski, Iwona Pasternak, Jakub Sitek, Marek Kopciuszyński, Ryszard Zdyb, Jagoda Sławińska, Pawel J. Kowalczyk
Mesoscale and Nanoscale Physics
Multiscale modelling of nanoscaled FETs based on 2D ferroelectric materials
Alejandro Toral-Lopez, Michele Virgilio, Gianluca Fiori et al. (+1 more)
Ferroelectric materials are highly attractive for low-power, high-speed electronics and emerging neuromorphic computing architectures. However, the severe physical scaling limits of conventional bulk (3D) ferroelectrics at the nanoscale have shifted
attention towards two-dimensional (2D) ferroelectric monolayers. Accurate device-level performance predictions are essential to accelerate the experimental testing and screening of these novel materials. In this work, we present a multiscale simulation framework that bridges first-principles density functional theory with Non-
Equilibrium Green's Function (NEGF) transport calculations. Using a 2D Indium Phosphide monolayer as a case study, our approach leverages a continuously interpolated, polarization-dependent
Hamiltonian embedded within a self-consistent Poisson-NEGF solver. The model captures the dynamic interplay between ion movement and electronic transport, naturally reproducing macroscopic hysteresis loops and
memory windows without empirical parameters. This predictive pipeline provides a computationally efficient tool to evaluate and optimize next-generation 2D ferroelectric field-effect transistors.
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All authors Alejandro Toral-Lopez, Michele Virgilio, Gianluca Fiori, Damiano Marian
Materials Science
Hierarchical Fourier Phase Projection for Local Electronic Observables
Tao Hu, Weiqing Zhou, Zhichang Fu et al. (+2 more)
Large-scale electronic-structure calculations require efficient access to local observables without explicitly constructing all occupied orbitals. We develop hierarchical
Fourier phase projection (HPP), which organizes
Fourier probes into a reusable spatial hierarchy that progressively removes short-range aliasing while exploiting density-
matrix locality. The method provides systematic refinement from low-cost local estimates to the projection-exact limit of the chosen numerical occupation operator, without discarding previously evaluated responses. Tests using frozen Kohn–Sham
Hamiltonians for semiconducting and metallic systems demonstrate controllable convergence of electron densities and nonlocal pseudopotential forces, weak size dependence of the probing resolution required for a fixed local accuracy, and near-linear growth of the direct computational cost at fixed probing workload. Inter-level changes further provide practical information for terminating the refinement at finite accuracy. HPP connects electronic locality, observable accuracy, and computational effort within a single hierarchical framework, providing a scalable route to local quantities in large-scale electronic-structure calculations.
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All authors Tao Hu, Weiqing Zhou, Zhichang Fu, Yechen Chen, Shengjun Yuan
Strongly Correlated Electrons
Correlation-assisted topological and metamagnetic transitions in Rashba-coupled superconductors: $t$-$J$-$U$ model study
Tushar Dey, Maciej Fidrysiak and Józef Spałek
Unconventional superconductivity commonly emerges in systems characterized by strong electronic correlations, with layered copper-oxides serving as a canonical example. Observation of
spin-momentum locking within Bi-family of the cuprates, compatible with the presence of non-negligible Rashba-type
spin-orbit coupling (RSOC), calls for an investigation of the joint effects of electronic correlations and RSOC on pairing in copper-oxide and related
superconductors. Employing statistically-consistent variational approximation (SGA), we carry out such an analysis by constructing the phase diagram for the case of square-
lattice t-J-U model incorporating RSOC. We also investigate the effects of time-reversal-
symmetry breaking by Zeeman field, as well as characterize emergent topological superconducting (TSC) states. Chern number $C = \pm 4$ TSC is found in a broad regime of on-site Coulomb repulsion close to half-filling. The latter is not governed by correlations and emerges also within the weak-coupling Bogoliubov-de Gennes (BdG) scheme. Yet, we identify a distinct $C = \pm 2$ TSC state that is driven specifically by electronic correlations via a topological transition occurring with no bulk quasiparticle gap closure, and is accompanied by discontinuous metamagnetic and Lifshitz transitions. Moreover, a qualitatively distinct doping
evolution of the $d$- and $p$-wave components of the underlying mixed-parity SC order parameter above the metal-to-
insulator transition is demonstrated. Our work points toward the relevance of joint correlation and RSOC effects beyond BdG scheme to phase diagrams of RSOC-coupled
superconductors.
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Materials Science
From Chemical Complexity to Tunable Magnetic Ordering in Highly Disordered High-Entropy Spinel Oxides
Neha Sharma, Sushanta Mandal, Nikita Sharma et al. (+10 more)
High-
entropy stabilization chemistry is redefining materials design by transforming configurational disorder, arising from the deliberate incorporation of multiple principal cations, into a thermodynamic advantage that promotes phase stability and enables emergent functionalities. In this work, we investigate the
evolution of
magnetic ordering in spinel-type high
entropy oxides by systematically varying the cation composition of the B site within a fixed high-
entropy A-site
matrix, (Ni$_{0.2}$Mg$_{0.2}$Co$_{0.2}$Cu$_{0.2}$Zn$_{0.2}$)B$_2$O$_4$. Upon introducing multicomponent B-site configurations, we uncover a strikingly linear dependence of the
magnetic transition temperature (T$_C$) on the T$_C$s of the corresponding single B-site high-
entropy systems. Remarkably, this trend persists even in highly complex (Ni$_{0.2}$Mg$_{0.2}$Co$_{0.2}$Cu$_{0.2}$Zn$_{0.2}$)(Cr$_{0.2}$Mn$_{0.2}$Fe$_{0.2}$Ga$_{0.2}$X$_{0.2}$)$_2$O$_4$, X = Al and Ti. Despite the material's extremely high degree of disorder, absence of a dominant
magnetic ion or a straightforward superexchange pathway, detailed magnetization measurements, low-temperature X-ray
magnetic circular dichroism, and
neutron powder diffraction studies reveal robust long-range ferrimagnetic ordering. These results reveal an emergent predictability in ferrimagnetic high-
entropy spinel oxides, where, despite extreme configurational disorder and competing interactions, robust ferrimagnetic order can arise from, rather than be hindered by, extreme configurational disorder. This establishes a pathway for predictively tuning
magnetic transition temperatures in high-
entropy oxides beyond conventional ordered systems.
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All authors Neha Sharma, Sushanta Mandal, Nikita Sharma, Amritpal, Sangeeta Thakur, Viktor Ukleev, Chen Luo, Florin Radu, S. D. Kaushik, Tirthankar Chakraborty, Sanjoy Kr. Mahatha, Denis Pelloquin, Sourav Marik