Disordered Systems and Neural Networks
Hierarchical Prototype Emergence in Modern Hopfield Models
Aditya Cowsik and Adithya Sriram
Hierarchical correlations are a universal feature of any realistic model of data, and the question of how associative
memory models may learn these correlations and generalize beyond them to construct new sensible images is an important step towards understanding more complex modern architectures such as
diffusion models. We consider a hierarchical model for
memories which are sampled and stored in a dense Hopfield network with
polynomial activation. We analytically derive conditions for each level of this hierarchy to be locally stable - that is they are local energy minima. We use prototype reconstruction as a minimal model of generalization and we find that it takes only a quasi-
polynomial amount of information to generalize beyond particular
memories and even particular groups in the hierarchy. We observe a qualitatively analogous phase diagram in the number of
memories, sharpness of the activation function (
polynomial degree) for data from Fashion-MNIST.
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Materials Science
Unusual phase coexistence regime across the ferroelectric - paraelectric transition
M. Kopecký, J. Kub, E. de Prado et al. (+1 more)
A PbTiO3 epitaxial thin film grown on a DyScO3 substrate was studied by x-ray diffraction in the temperature range of 20-500 degrees Celsius. It is found that the ferroelectric to paraelectric phase transition proceeds through a peculiar transitional coexistence state extending between 402 degrees Celsius and 414 degrees Celsius. Within this temperature interval, at a temperature of 405 degrees Celsius, a domain structure transition occurs, at which the three-domain c/a1/a2 polytwin phase transforms into an ordinary c/a2 twinned phase. It is proposed that the coexistence of two independent twinned phases with the paraelectric phase is enabled by vertical strain gradients in the film.
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All authors M. Kopecký, J. Kub, E. de Prado, J. Hlinka
Disordered Systems and Neural Networks · Cross-listed from quant-ph
Dephasing-driven suppression of superradiance and metastable dynamics in the anisotropic open Rabi model
Jivyanshu Priya, Pragna Das and Auditya Sharma
Finite-component light-matter systems realize dissipative phase transitions in a single controllable atom-cavity setup, but how atomic dephasing - ubiquitous in real cavity- and
circuit-QED devices - affects this criticality remains unknown. We study the anisotropic open Rabi model under cavity decay, spontaneous emission, and atomic dephasing together. We show that when spontaneous emission stabilizes a long-lived metastable superradiant phase, atomic dephasing actively competes with it - eroding its coherence and shortening the lifetime. This direct competition reveals that a dissipation channel's microscopic character, not its strength, controls its nonequilibrium criticality - a distinction directly tunable via independent spontaneous-emission and dephasing rates in
circuit-QED and trapped-ion platforms.
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Statistical Mechanics
Breakdown of Multipole Expansion in Emergent Electromagnetism
Tom Ben-Ami, Markus Heyl and Roderich Moessner
We find a striking departure from simple electrostatics in a family of two-dimensional
lattice models whose effective description takes the form of an emergent electromagnetism: a high-order multipolar charge configuration can induce an electric field characteristic of a lower-order multipole. Studying the archetypical hardcore dimer and U(1)
spin-1/2 link models, we trace this to a breakdown of the superposition principle: for dense charge configurations, there can be a nonlinear suppression, or even enhancement, of the far field compared to the linear expectation. Our work establishes that microscopic
lattice-scale constraints in models for emergent electromagnetism can change the far-field behaviour to differ from often utilized long-wavelength descriptions in standard effective continuum models.
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Mesoscale and Nanoscale Physics
Real-space Visualization of Emergent Electron Crystals in Rhombohedral Graphene
Yiming Sun, Jinghao Deng, Jiabin Xie et al. (+5 more)
Strongly interacting electrons can spontaneously break spatial
symmetries to form electron
crystals, exemplified by the Wigner
crystal. Recent studies of topological flat bands in rhombohedral
graphene have suggested more exotic forms of crystallization, including anomalous Hall
crystals that entangle charge order with nontrivial
topology and metallic electron
crystals in which localized and itinerant carriers coexist. Direct real-space observation of these states, however, has remained elusive. Here we use scanning tunneling microscopy and spectroscopy to visualize emergent electron
crystals in rhombohedral hexalayer
graphene. At low electric fields and over a finite range of hole doping, we observe electronic
lattice patterns that evolve from honeycomb to oblique order through a first-order
quantum phase transition with increasing hole density. The Fermi surface extracted from quasiparticle-interference measurements lacks the geometry needed to account for these patterns through conventional nesting. Together with metallic transport and a
crystal-site density much lower than the doped carrier density, this supports metallic electron
crystals in which a subset of carriers crystallizes. The honeycomb
crystal occupies the same phase space as the multiferroic orbital magnetism observed previously in transport and exhibits domain stabilization by a small
magnetic field, which may suggest a possible metallic anomalous Hall
crystal. With increasing
magnetic field, the oblique phase develops a $\sqrt{2}\times\sqrt{2}$ reconstruction with a
crystal-sublattice energy splitting that increases linearly with field, corresponding to a $g$-factor of 16. This may reflect an orbital-antiferromagnetic electron
crystal with alternating orbital magnetization across the
lattice. These results establish a new paradigm of electron crystallization in which charge order is intertwined with orbital magnetism.
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All authors Yiming Sun, Jinghao Deng, Jiabin Xie, Donghan Ge, Hongyuan Li, Takashi Taniguchi, Kenji Watanabe, Xiaomeng Liu
Statistical Mechanics
Staying positive: bounds for non-Gaussian noise in Schwinger-Keldysh effective field theory
Andrea Amoretti and Daniel K. Brattan
Modern effective field theories of dissipative hydrodynamics, built on the Schwinger-Keldysh (SK) formalism, include thermal noise that is not Gaussian. The resultant higher-order noise vertices are constrained by
symmetries, but otherwise treated as free parameters. We show explicitly that
symmetry constraints alone do not guarantee these vertices yield a genuine probability distribution. Requiring a probability interpretation yields sharp bounds between cumulants that are invisible to the
symmetry analysis. The bounds are optimal: their boundaries are attained by explicit positive distributions, and constructive completions are provided for both negative- and positive-kurtosis noise data. This gives closed-form nonlinear response and an exact sampling
algorithm, whose Monte Carlo implementation reproduces the exact cumulants and nonlinear fluctuation-dissipation relations. Confronted with microscopic results, the framework places a sharp lower bound on the time step required for a positive
stochastic completion of a quartic model of the Brownian particle used in the literature, while holographically computed $SU(2)$ noise vertices pass a nontrivial continuum fourth-order positivity test.
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Quantum Gases
Optimized quantum state transfer in a quasiperiodic ultracold atomic gas
Andreas Völkering, Arnob Kumar Ghosh, Patric Holmvall et al. (+1 more)
Ultracold atomic systems offer a highly controllable platform for investigating
quantum state transfer through the precise dynamical manipulation of system parameters. While quantized Thouless pumping has been extensively explored in these systems, adiabatic edge-to-edge transfer of localized
quantum states remains largely unexplored. Here, we consider a one-dimensional ultracold atomic gas confined in a bichromatic optical
lattice realizing a quasiperiodic Aubry–André–Harper system. We use its edge-localized winding states to implement
quantum state transfer between opposite boundaries. Starting from the instantaneous spectral properties of the corresponding tight-binding model, we construct locally adiabatic protocols and extend the approach to higher protocol orders. We then simulate their dynamics under the full continuum bichromatic-
lattice Hamiltonian. Our results reveal a tradeoff between edge localization and the minimum spectral gap: strongly localized states require longer transfer times, but can benefit substantially from higher protocol orders. We are also able to capture the main fidelity trends and coherent oscillations over a broad parameter regime using an effective two-level Landau–Zener description. Our results provide practical guidelines for selecting experimentally accessible parameters and tailoring
quantum transfer protocols in quasiperiodic ultracold atomic systems.
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All authors Andreas Völkering, Arnob Kumar Ghosh, Patric Holmvall, Paolo Molignini
Statistical Mechanics · Cross-listed from hep-th
Mutual Information in spacetime
Raúl E. Arias, Marina Huerta and Pedro J. Martinez
We compute mutual information for general spacetime regions using Sorkin's Gaussian field formalism. We show that this construction is naturally based on the reduced space of smearings that generate independent fields, making manifest that in QFTs with stress tensor the local
algebras generated by regions sharing the same causal completion. We test the method for a Weyl
fermion, the chiral current, and massless and massive real scalar fields across various spacetime regions in 1+1 Minkowski space. Across all cases, distinct spacelike-separated spacetime regions sharing the same causal completion yield identical mutual information. This formalism provides a setting in which to test the timelike tube
theorem. Indeed, we observe that the mutual information of a timelike lens approaches that of its enveloping diamond as the cutoff is increased, offering a direct numerical verification of the
theorem. In all the considered cases, our results agree with known continuum and spatial-
lattice results. Finally, this work establishes a natural framework for studying
entanglement measures in generalized free field theories, a task that is impractical within other existing prescriptions.
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Strongly Correlated Electrons
Remarks on invertible phases with non-onsite symmetry
Ryohei Kobayashi, Kansei Inamura and Ken Shiozaki
We study invertible phases protected by non-onsite
symmetries carrying nontrivial
lattice anomaly indices. While
lattice anomalies are usually viewed as obstructions to symmetric short-range-entangled (SRE) states, we show that anomalous
lattice symmetries can nevertheless admit invertible phases that are not SRE, and can moreover shift the set of
symmetry-compatible invertible phases. In particular, we consider a fermionic $\mathbb Z_4^F$
symmetry in (2+1) dimensions. For an onsite $\mathbb Z_4^F$
symmetry, symmetric invertible phases have integer chiral central charge $c_-\in\mathbb Z$, whereas a non-onsite
symmetry with nontrivial
lattice anomaly index obstructs all such phases despite having trivial continuum 't Hooft anomaly. We resolve this by constructing an exact exponentially quasi-local $\mathbb Z_4^F$
symmetry of a $p+ip$
superconductor with $c_-=1/2$. We compute its
lattice anomaly, and find that the
symmetry indeed forbids $c_-\in \mathbb{Z}$ invertible states. The allowed invertible phases are consequently shifted to $c_-\in\mathbb Z+1/2$. By gauging the
fermion parity of the $p+ip$
superconductor, one obtains an Ising topological order enriched by a $\mathbb Z_4$
symmetry. We describe the corresponding
symmetry structure in terms of a fusion 2-category. We further show that the $p+ip$ state admits an enlarged non-onsite $U(1)^f$
symmetry, providing an analogue of fractional
quantum Hall response in an invertible phase. This non-onsite $U(1)^f$
symmetry again forbids Chern
insulators carrying $c_-\in\mathbb{Z}$, while being compatible with invertible states with $c_-\in\mathbb{Z}+1/2$. This result motivates a systematic study of new classes of invertible phases and
spin liquids enriched by non-onsite
symmetries.
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Mesoscale and Nanoscale Physics
Catastrophes, Optical Multistabilities, and Chiral Photocurrent Hysteresis in Driven Weyl Semimetals
Christopher Yang, Gil Refael and Frederik Nathan
The unique band
topology of Weyl semimetals provides them with a diverse array of strong photovoltaic response phenomena. Here we explore how
plasma screening affects these phenomena. We find that the screening field is highly nonlinear, can contain topological contributions, and can amplify the photoresponse, with the self-consistent response exhibiting the hallmarks of bistability, including hysteresis and catastrophes. The bistability emerges from a crossover from linear to saturated polarization as a function of the field amplitude, because carriers in a Weyl cone have bounded group speed $v_F$. When time-reversal
symmetry is broken, tilted Weyl nodes add a Berry-
curvature contribution to the in-plane current, making the nonlinear screening response helicity selective.
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Statistical Mechanics · Cross-listed from quant-ph
Hierarchy of Rényi Coherent Information in Stabilizer Codes
Akash Vijay, Luis Colmenarez and Jong Yeon Lee
Rényi coherent information, a computable proxy for the von Neumann coherent information, is widely used to study mixed-state phases of matter and decodability transitions in noisy
quantum error-correcting codes. However, being a difference of two Rényi
entropies, it need not be monotonic in the Rényi index, and lacks the operational meaning of its von Neumann counterpart. Here we address both issues for stabilizer codes. First, for Pauli noise generated by independent Bernoulli events, we prove that the Rényi-$n$ coherent information is nondecreasing in $n \in \mathbb{Z}^+$. This follows from a general
theorem: if independent random bits are mapped linearly to a fine label $T$ and a coarse label $C$, then the Rényi
entropy difference $H_n(C)-H_n(T)$ is nondecreasing in $n$. For stabilizer codes, $T$ is the joint syndrome–logical class and $C$ is the syndrome, and the difference is the Rényi-$n$ coherent information up to a constant. The same
theorem covers classical linear codes and independent detector error models. Second, for arbitrary
stochastic Pauli noise, we give the Rényi-$n$ coherent information an operational meaning via postselection on matching syndromes between one data block and $n-1$ auxiliary blocks. We determine when this defines a
quantum channel and show that saturation of the Rényi-$n$ coherent information is equivalent to asymptotically perfect recovery of the postselected channel. Moreover, the Rényi-$n$ coherent information also upper-bounds the ordinary coherent information achievable after any syndrome-conditioned recovery.
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Strongly Correlated Electrons
Effective Ionic Valence and Local Magnetic Moment in Kagome Superconductors
Ruoshi Jiang, Zi-Jian Lang, Yuzki Oey et al. (+11 more)
In order to understand the unexpected similarity and the correlated behavior in kagome
superconductor families AV$_3$Sb$_5$ (A = K, Rb, Cs) and ATi$_3$Bi$_5$ (A = Rb, Cs), we investigate the Hartree-scale local electronic structure of these systems. Our result indicates that V and Ti ions are both of 2+ valence such that the corresponding itinerant carrier densities are similar, and the difference in electron count is instead reflected in their
quantum fluctuating ionic
magnetic moments. However, due to the frustrated
lattice geometry of these materials, such local moments are difficult to experimentally observe via standard probes. For verification, we systematically introduce nonmagnetic Sn impurities to locally relieve the
geometric frustration and experimentally demonstrate the existence of well-defined local
magnetic moments via
magnetic susceptibility and
muon spin rotation or relaxation ($\mu$SR) measurements. All experiments discover a systematic increase of
magnetic susceptibility upon increasing nonmagnetic impurity level. Our discovered ionic moments suggest a paradigm shift from the existing itinerant carrier-only picture to one incorporating strong correlation from local ionic
spins. The associated interatomic and local-itinerant correlations offer a solid ground for the emergence of the observed rich correlated behavior in this new family of superconducting materials.
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All authors Ruoshi Jiang, Zi-Jian Lang, Yuzki Oey, Andrea Capa Salinas, Stephen D. Wilson, Yongwei Li, Ilya Shipulin, Yiwen Zhang, Deng Hu, Zhiwei Wang, Hans-Henning Klauss, Zurab Guguchia, Vadim Grinenko, Wei Ku
Statistical Mechanics · Cross-listed from quant-ph
Quantifying Symmetry Breaking with Metric Adjusted Quantum Geometric Tensors
Koji Yamaguchi and Hiroyasu Tajima
Quantifying properties of
quantum states through the limits of their manipulation is a central goal of
quantum resource theories. For
symmetry breaking, the
quantum geometric tensor (QGT) governs asymptotic pure-state conversion, but a complete characterization for general mixed states has remained elusive. Here we fully resolve this problem for finite-dimensional systems under compact Lie group
symmetries in the i.i.d. asymptotic regime. Specifically, we establish a single-letter formula for the optimal conversion rate between arbitrary states, with vanishing trace-distance error, in the resource theory of asymmetry. The rate is determined by a one-parameter family of metric adjusted QGTs, obtained by rescaling
quantum Fisher information (QFI)
matrices that interpolate between the symmetric logarithmic derivative and right logarithmic derivative (RLD) QFIs. For pure states, the RLD endpoint recovers the standard QGT. No state-independent finite subset of this family suffices in general, even for $U(1)$
symmetry, revealing a qualitative distinction from pure-state conversion. Our formula further yields an exact pure-state
distillation-rate formula in terms of a single asymmetry measure, characterizes asymptotically reversible interconversion, and identifies bound asymmetry for
quantum clocks. Complementarity among members of the metric adjusted QGT family also reveals an activation mechanism: a state with zero conversion rate to a mixed clock state can still enhance another input's yield under joint processing. Our proof relies on two developments of independent interest. First, we extend
quantum local asymptotic normality to
unitary models with arbitrary rank and spectral degeneracy. Second, we characterize convertibility between
quantum Gaussian shift models in terms of the same one-parameter family of QFIs.
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Strongly Correlated Electrons
Low temperature thermodynamics of $S_{\mathrm{eff}}=1/2$ triangular lattice quantum spin liquid candidate TlYbS$_2$
Bishnu P. Belbase, Arjun Unnikrishnan, Piyush Chhallare et al. (+8 more)
Geometrically frustrated triangular-
lattice antiferromagnets exhibit a delicate competition between
magnetic order and
quantum spin liquid (QSL) behavior, with the Yb-based delafossite family $A$Yb$X_2$ providing a structurally clean platform for exploring this physics. Here, we report a comprehensive study of single-
crystal TlYbS$_2$ using DC magnetization, AC susceptibility, electron
spin resonance (ESR), and specific heat measurements extending from room temperature to the millikelvin regime. Single-
crystal X-ray diffraction confirms a trigonal $R\bar{3}m$ structure comprising well-separated triangular layers of Yb$^{3+}$ ions with no detectable site disorder. At zero field, a weak thermodynamic anomaly is observed near $530$ mK, which may indicate the onset of a weakly ordered state similar to that reported in KYbSe$_2$. Below $300$ mK, the zero-field
magnetic specific heat follows $C_{\rm m}\propto T^{1.8}$, close to a quadratic temperature dependence, in contrast to the linear temperature dependence reported for the sister compound TlYbSe$_2$, which has been described in terms of the interplay between spinons and thermally excited gauge-flux excitations. Magnetization and ESR measurements establish pronounced easy-plane
magnetic anisotropy, with $g_\perp/g_\parallel \approx 6.9$. The anomaly near $530$ mK exhibits a strongly anisotropic response to
magnetic field. For $H\perp c$, it remains visible up to approximately $2$ T and continuously evolves toward a field-induced ordered phase above approximately $2.5$ T, followed by a sequence of field-induced phases that includes a $1/3$ magnetization plateau between approximately $5$ and $8$ T and full polarization near $17$ T. In contrast, for $H\parallel c$, the anomaly weakens and is suppressed near $3$ T, consistent with the recently reported confinement–deconfinement transition from an ordered state to a field-induced QSL.
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All authors Bishnu P. Belbase, Arjun Unnikrishnan, Piyush Chhallare, Mohan B. Neupane, Eun Sang Choi, Sebastian Erdmann, Muhammad U. Akbar, Mamoun Hemmida, H.-A. Krug von Nidda, Philipp Gegenwart, Arnab Banerjee
Materials Science
Sparse data limit what a mechanistic corrosion model can predict
Conrard Giresse Tetsassi Feugmo
Mechanistic corrosion models are routinely fitted with four to six parameters to a few measurements and extrapolated across service lifetimes, yet whether the data determine them is rarely tested. We identify a reduced point defect model for the duplex oxide on Nb-stabilized AISI 347 in simulated boiling-water-reactor water from published depth profiles at three exposure times, by differentiable inversion graded against a closed-form reference. Profile likelihood, a 1000-member bootstrap and a prior-relaxation test agree that one of the five parameters is undetermined and a second only weakly so, and that 95% of the fit statistic rests on three chromium points. The kinetics track an empirical power law over the calibration window but diverge from it by a factor of 3.5 to 6.3 at ten years, outside the propagated uncertainty band. That separation, not the thickness it brackets, is what these data determine; an exposure near 3000 hours would resolve it.
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Other Condensed Matter · Cross-listed from quant-ph
Computational framework for quantum state tomography of spin ensembles
Jiwoo Seo and Vesna F. Mitrović
We present
Tomography-NMR, an open-source Python package that reconstructs
quantum density
matrices from spectroscopic measurement data. The package implements a complete analysis pipeline for two-
qubit quantum state
tomography based on the product operator formalism: raw time-domain signals are
Fourier-transformed into frequency-domain spectra, spectral peak intensities are mapped to expansion coefficients of the density
matrix, and the full
quantum state is reconstructed. Three integration methods are provided for different use cases: direct peak height measurement and fixed-parameter numerical integration require no theoretical reference and are suited to unknown states, achieving fidelities of approximately 98% on a
benchmark set of known states, while a systematic parameter optimization against a known target state achieves reconstruction fidelities exceeding 99% for the same
benchmark states. While the detailed theoretical framework for
quantum state
tomography is well established, the practical procedures for extracting density
matrices from experimental spectra are often inadequately documented in the literature and obscured within proprietary software. This package addresses that gap by providing a fully transparent, reproducible implementation of every analysis step, from spectral preprocessing to density
matrix visualization. The software has been validated on experimentally prepared two-
qubit states measured via nuclear
magnetic resonance (NMR) spectroscopy of coupled $^{31}$P
nuclei. Average reconstruction fidelities range from 0.975 to 0.995 across a
benchmark set of 20 two-
qubit states, including the computational basis states, Bell states, and the outputs of three fundamental
quantum gates (CNOT, H, and T). Although developed for NMR, the modular architecture facilitates adaptation to other spectroscopic platforms and alternative measurement protocols.
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Materials Science
High-Temperature ferromagnetism from site-selective filling in (Fe,Ni)$_{6-\delta}$GeTe$_2$
Tyler L. Werner, Jonathan T. Reichanadter, Xiang Chen et al. (+23 more)
The discovery of high-temperature ferromagnetism in the metallic van der Waals (vdW) system Fe$_N$GeTe$_2$ has brought two-dimensional (2D) magnets into technologically relevant temperature scales. Specifically at N = 5, dilution of
magnetic moments by nickel substitution counterintuitively achieves a record high Curie temperature of 478~K. Unraveling the origin of this nickel-substitution-induced enhancement is complicated by the compound's structural complexity, coexistent itinerant and local
magnetic contributions, and mesoscopic compositional domains. Through coordinated structural and electronic characterization, we identify that the high-T$_C$
magnetic phase arises from a strain-stabilized Fe$_6$GeTe$_2$ nano-precipitate. Combining first-principles calculations and
spin- and angle-resolved photoemission spectroscopy (ARPES), we uncover a site-specific electronic landscape in which interior iron atoms primarily host localized moments while the outer iron atoms neighboring the tellurium layers produce
spin-polarized itinerant carriers that cross the vdW gap. The large energy cost associated with homogeneous nickel substitution is found to favor the spontaneous precipitation of the crystallographically and electronically “clean” high-T$_C$ phase. Finally, we compare metal-rich vdW magnets with binary
magnetic alloys, and discuss the unifying roles of nano-precipitates in stabilizing otherwise unattainable bulk phases. Our work provides mechanistic insights into the record-high T$_C$ ferromagnetism in (Fe,Ni)$_{5+\delta}$GeTe$_2$, establishing a rigorous foundation for the atomic engineering of vdW
magnetic metals informed by direct electronic signatures.
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All authors Tyler L. Werner, Jonathan T. Reichanadter, Xiang Chen, Pranab K. Nag, Luna Y. Liu, Yu-Tsun Shao, Hongrui Zhang, Mingyang Guo, Wenxin Li, Zhibo Kang, Han Wu, Makoto Hashimoto, Donghui Lu, Turgut Yilmaz, Elio Vescovo, Sung-Kwan Mo, Barat Achinuq, Alexei Fedorov, Jacob C. Ruff, Ming Yi, Qiong Ma, David A. Muller, Eduardo H. da Silva Neto, Robert J. Birgeneau, Jeffrey B. Neaton, Yu He
Materials Science
High-fidelity k$\cdot$p representations of first-principles electronic band structures through covariant renormalization
Kristian Berland
The k$\cdot$p method can be applied directly to first-principles energies and momentum
matrix elements, but the resulting models converge slowly with the number of bands and are inexact wherever the underlying
Hamiltonian is nonlocal. We show that both limitations can be largely removed by renormalizing the
eigenvalue spectra of the Hermitian momentum
matrices. These spectra are gauge invariant, and are identical along
symmetry-related directions; hence scaling the recurring magnitudes provides a modest set of parameters that preserves degeneracies and
crystal symmetry without needing to construct a
symmetry-adapted basis. We choose to renormalize the models against reference
eigenvalues and band velocities on rays out of a high-
symmetry point. For GaP, a 15-band model can reproduce the band structure in the near-gap reference regions within a few meV. For zincblende and wurtzite AlN, similar accuracy requires 30- or 85-band models, which in the case of zincblende is traced to the strong warping in the [110] direction. The scheme readily generalizes to rocksalt PbTe, which includes
spin-orbit coupling, and has $L$-centered valence- and conduction-band extrema. Further, we demonstrate, for GaP, how compact four-band
Hamiltonians can be obtained by downfolding within the same renormalization scheme. Moreover, by changing the fitting regime to encompass the entire Brillouin zone, the scheme can be used to generate full-zone models that reproduce the density of states. A practical use of the method is illustrated with a 59-band k$\cdot$p model for GaP, which can be evaluated on meshes far denser than the reference calculation, that in turn can be used both to resolve fine features in the density of states and to compute the hole conductivity at low temperature.
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Strongly Correlated Electrons
Sub-cycle doublon-holon dynamics in one-dimensional Mott insulators revealed by two-color high-harmonic spectroscopy
Lance Hatch, Aditya Verma, Eric Schultz et al. (+7 more)
Solid-state high-harmonic spectroscopy is becoming an emerging tool for probing nonequilibrium many-body dynamics. Yet, direct measurements of strongly driven, sub-optical-cycle dynamics in correlated materials during high-harmonic emission remain largely unexplored. Here, we measure high-harmonic emission chirp in a prototypical one-dimensional Mott
insulator, which encodes strongly driven doublon-holon dynamics at sub-optical-cycle timescales. We observe a positive chirp for above band gap harmonics, indicating that high harmonics are dominated by doublon-holon recombinations. We further show a harmonic order-dependent dephasing, which can be understood through different doublon-holon excursion distances associated with each harmonic. These results reveal coherent doublon-holon dynamics and their ultrafast dephasing in Mott
insulators, which is relevant to other nonequilibrium light-induced phenomena, such as Floquet engineering.
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All authors Lance Hatch, Aditya Verma, Eric Schultz, Hanjun Yang, Priscila Rosa, Genda Gu, Igor Zaliznyak, Giulio Vampa, Laimei Nie, Hanzhe Liu
Materials Science
Piezomagnetism in a model cubic noncollinear altermagnet
Sudarshan Sharma, Luca Buiarelli, Richard Spieker et al. (+4 more)
Altermagnets constitute a distinct class of
magnetic materials that combine compensated
magnetic order with
spin-polarized electronic bands, hence carrying characteristics of both antiferromagnets and ferromagnets. Piezomagnetism - the linear relationship between
lattice strain and a net
magnetic moment - has emerged as smoking-gun evidence of altermagnetism that distinguishes it from antiferromagnetism. Here, we uncover a large piezomagnetic response in MnTe2, a cubic altermagnet with a noncollinear
spin arrangement and weak
spin-orbit coupling. We combine dilatometry with nuclear
magnetic resonance, a bulk local probe, to observe signatures of both direct and inverse piezomagnetism consistent with
symmetry considerations and first-principles calculations. The dilatometry measurements reveal a shear deformation proportional to an applied
magnetic field, while
magnetic resonance detects a ferromagnetic moment induced by shear strain. The respective results for the piezomagnetic coupling strength are in good agreement, and they are captured by first-principles results. These findings for simple binary MnTe2 position this material as a model altermagnet, demonstrate the utility of nuclear
magnetic resonance in investigations of piezomagnetism, and open new avenues for
multimodal strain and
magnetic-field control in spintronic and
memory applications.
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All authors Sudarshan Sharma, Luca Buiarelli, Richard Spieker, Ivan Jakovac, Damjan Pelc, Turan Birol, Martin Greven
Strongly Correlated Electrons
Block entropy area based non-local fermionic mode optimization with gradient disentanglers
Miklós Antal Werner, Gero Friesecke, Andor Menczer et al. (+2 more)
We introduce a systematic block
entropy area based mode optimization
algorithm for many-body
quantum states of interacting
fermions represented by
matrix product states. From the gradient of a global cost function, the block
entropy area, a long-ranged, non-interacting effective disentangler
Hamiltonian is formed. We then simulate the time-dependent Schrödinger equation driven by the disentangler
Hamiltonian by employing the time-dependent variational principle based on projector splitting, and minimize the cost function. The combination of the density
matrix renormalization group with this gradient-based
entanglement minimization forms an efficient low-rank iterative ground-state
algorithm that also provides an optimized single-particle basis for
matrix product state representation. We demonstrate the method on two-dimensional
lattice models of interacting
fermions and the Fe${_4}$S${_4}$ cluster, and show its robustness and superiority over earlier protocols using nearest-neighbor mode rotations and reorderings.
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All authors Miklós Antal Werner, Gero Friesecke, Andor Menczer, Kornél Kapás, Örs Legeza
Mesoscale and Nanoscale Physics
Interacting Tomonaga-Lüttinger liquid with impurity for interaction constant $K = 1/2$: Thermopower investigation, entropy variation and heat capacity densities associated with thermoelectric particle transport
Abdellah Touati, Redoune Zamoum and Farhi Houssam Eddine
We investigate thermoelectric and thermodynamic properties of a Tomonaga-Luttinger
liquid with interaction parameter $K=1/2$ in the presence of a localized impurity. Using bosonization and refermionization, we derive an exact expression for the thermopower in the nonlinear regime and obtain the corresponding Seebeck coefficient in linear response. At low temperature, the Seebeck coefficient follows a Mott-like relation governed by the energy dependence of the transmission coefficient and is found to be closely related to the
entropy per particle. This connection allows us to derive using Kelvin formula the thermopower contribution to the
entropy density variation and the charge-carriers contribution to the heat capacity density. Both quantities exhibit Mott-like behavior in the low-temperature regime. We apply our results to a fractional
quantum Hall
quantum point contact and to a one-channel
quantum conductor coupled to an Ohmic environment. Our results demonstrate the close connection between thermoelectric transport and thermodynamic properties in interacting one-dimensional
quantum systems.
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Strongly Correlated Electrons
Learning Quantum Matter through Attention in Complex Space
Mingrui Jing, Erdong Huang, Jizhe Lai et al. (+3 more)
Magnetic many-electron wavefunctions require amplitude and phase to be optimized together. Whether a complex internal representation improves this variational search is a practical question for neural wavefunction design. We introduce Complex Psiformer for interacting electrons in a
magnetic moiré continuum, combining complex hidden features and Hermitian-magnitude
attention with
magnetic boundary conditions and fermionic antisymmetry. After the same number of optimization steps, Complex Psiformer reaches lower energies than Real Psiformer in two finite supercells. Both Psiformers also improve on their respective neural Hartree-Fock references. Across five training seeds in the 25-
cell system, the mean Complex advantage is 1.458 meV per electron, with a smaller observed spread. A separately trained two-electron Complex state has a smaller energy gap to a finite configuration interaction reference than its Real counterpart. In the Complex states, flux scans show nonmonotonic density correlations and weaker honeycomb mean-density modulation at higher flux, while connected fluctuations persist. Gauge invariant current maps provide a qualitative comparison of local circulation in the optimized states. These
benchmarks support the combined architecture as a variational ansatz for studying energies and charge arrangements in finite
magnetic systems.
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All authors Mingrui Jing, Erdong Huang, Jizhe Lai, Enji Xiong, Jin-Guo Liu, Xin Wang
Quantum Gases
Condensation temperature and magnetic phases of trapped coherently coupled Bose gases
Sunilkumar V, Rajat, Sandeep Gautam et al. (+1 more)
We investigate condensation and finite-temperature
magnetic phase transitions in a coherently (Rabi) coupled Bose gas confined in a three-dimensional harmonic trap. For the noninteracting system, we derive analytical expressions for the critical temperature and condensate fraction using a semiclassical description of the single-particle spectrum and density of states. At fixed particle number, coherent coupling enhances the critical temperature relative to the uncoupled system, and this enhancement decreases with increasing particle number $N$. The finite-size correction, in contrast, lowers the transition temperature, with its effect diminishing for larger $N$. We then incorporate repulsive interactions within the Hartree–Fock–Bogoliubov–Popov framework to investigate the finite-temperature phase diagram in the temperature–Rabi coupling plane. The system undergoes successive transitions from a ferromagnetic to a paramagnetic condensate and, at higher temperature, to a thermal gas. The transition boundaries obtained from the vanishing of the condensate fraction show excellent agreement with the analytical Hartree-Fock predictions. We find that the interactions substantially suppress the variation in the condensation temperature with an increase in the coherent coupling.
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All authors Sunilkumar V, Rajat, Sandeep Gautam, Arko Roy
Materials Science
Device Engineering and Performance Optimization of Cu2NiGeS4 Thin-Film Solar Cells with In2S3/MoTe2 Charge-Selective Layers: A Computational Study
Md Tashfiq Bin Kashem and Hasib Md Abid Bin Farid
The pursuit of efficient and sustainable thin-film photovoltaics increasingly demands absorber materials that combine strong optical absorption with earth-abundant and environmentally benign constituents. Cu2NiGeS4 (CNGS) has emerged as a promising quaternary chalcogenide absorber owing to its favorable optoelectronic properties and high absorption coefficient, yet its photovoltaic potential remains comparatively underexplored, particularly in conjunction with optimized charge-selective layers. Here, we introduce and comprehensively investigate an CNGS-based solar-
cell architecture using SCAPS-1D, with In2S3 and MoTe2 serving as the electron and hole-transport layers respectively. The analysis of energy-band profiles, electric fields, carrier distributions, and generation-recombination characteristics reveals the mechanisms governing carrier separation and extraction across the heterojunctions. Systematic optimization of layer thickness, doping density, bulk and interface defect densities, recombination coefficients, parasitic resistances, temperature, and illumination intensity identifies the key factors limiting device performance. The optimized device is predicted to achieve a power conversion efficiency (PCE) of 28.44% with a open-
circuit voltage (VOC) of 0.984 V, short-
circuit current density (JSC) of 34.39 mA/cm2, and fill factor (FF) of 84.04%, under AM1.5G illumination at 300 K. This simulated efficiency exceeds the previously reported 6.25-21.17% range for CNGS-based solar
cells considered in this study. The findings establish In2S3/CNGS/MoTe2 as a promising platform for next-generation thin-film photovoltaics and provide physically grounded design guidelines for absorber optimization, interface engineering, and future experimental realization.
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Strongly Correlated Electrons
Unraveling the Kagome Antiferromagnetic $3J$ Model and Its Materials: An Integrated Approach
Xin Lu, Andreas Raikos, Menghan Song et al. (+6 more)
We investigate the ground-state and finite-temperature properties of the kagome antiferromagnetic Heisenberg model with three inequivalent couplings, dubbed the $3J$ model, which is designed for the candidate Dirac
quantum spin liquid (QSL) material YCu$_3$(OH)$_6$Br$_2$[Br$_{1-x}$(OH)$_x$] (see, e.g., Zeng et al., 2024). Employing large-scale density-
matrix renormalization group (DMRG) supplemented by neural
quantum states (NQS) simulations, we identify an intermediate QSL phase between two magnetically ordered phases. We also find that this QSL is separated from the kagome
spin liquid ground state at the isotropic limit. To establish a direct comparison with experiments, we compute the specific heat of the model by means of advanced exponential (XTRG) and tangent-space (tanTRG) thermal tensor-network methods. In the magnetically ordered phase, the specific heat over temperature exhibits a shoulder at a temperature that is a fraction of the coupling strength $J_{h}$, which disappears in the QSL phase. These universal behaviors are consistent with the experimentally observed specific heat in $3J$ materials for both ordered and QSL candidate samples. Our work thus connects microscopic models with experimentally measurable signatures, exemplifying an integrated approach to understanding QSL phenomena in frustrated
quantum magnets~ (see Meng et al., 2026), with $3J$ materials serving as a representative case and providing a foundation for future studies.
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All authors Xin Lu, Andreas Raikos, Menghan Song, Zezong Li, Lankun Han, Shiliang Li, Sylvain Capponi, Zi Yang Meng, Chengkang Zhou
Disordered Systems and Neural Networks · Cross-listed from quant-ph
Learning structural balance of graphs from quantum spectral features
Stefano Scali and Oleksandr Kyriienko
We develop a
quantum approach to spectral feature extraction from the density of states (DOS) of a problem-dependent
Hamiltonian, and apply it to machine learning on signed graphs. We propose to embed a signed graph as an Ising model instance with positive and negative interactions, and use the standardized moments of the Ising DOS as features for learning. We show that these moments count signed closed walks, are switching-invariant, and are size-free by construction. As a
benchmark, we target learning the frustration index, an NP-hard measure of structural balance that can be labeled exactly at moderate size. At zero field, the models can be sampled classically, allowing the
quantum extraction procedure to be certified against exact ground truth. We propose DOS-QPE, a phase estimation on a purified maximally mixed probe, which samples the spectral density with orders of magnitude fewer shots than Hadamard test-based trace sampling and feeds the resulting features directly into classically trained models. On $1.4\times10^5$ labeled graphs the exact DOS determines the frustration index, and five moments recover it with a mean error of 0.4, well below one sign flip. Beyond zero field, the underlying trace-estimation problem is DQC1-complete, providing access to spectral features for which no efficient classical sampling method is known. Our work opens routes towards
quantum applications in social network balance analysis,
spin-glass studies, correlation clustering, and
protein-interaction networks.
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Mesoscale and Nanoscale Physics
Hilbert-space selected switch of helical edges in an artificial quantum Hall insulator
Naijie Ren, Zhiren Xiong, Kaining Yang et al. (+9 more)
Quantum Hall effects (QHE) host one-dimensional topologically-protected edge channels, which can serve as an essential ingredient in exotic
quantum electronic systems. Yet the manual reconstruction of Landau-level
topology, by electrostatic confinement or
symmetry breaking, remains experimentally challenging. Here, we show that interfacial charge transfer in between CrOCl and large-angle twisted bilayer
graphene offsets the two otherwise decoupled Dirac Landau-level ladders in each
graphene layer, creating a new sequence of composite filling configurations. At charge neutrality, the composited $(+2,-2)$ state involves only the zeroth Landau levels and becomes fully insulating, with longitudinal resistance reaching the G$\Omega$ regime. By contrast, higher composite zero-filling
quantum Hall states, including $(+6,-6)$ and $(+10,-10)$, retain counter-propagating helical edge channels and exhibit pronounced non-local transport, reaching up to $50\%$ of the local response. We attribute such switching-behavior to the Landau-spinor
Hilbert space – as the filling is reduced from $(+6,-6)$ to $(+2,-2)$, the orthogonal $N=\pm1$ orbital components are removed, eliminating the edge-compatible channel and gapping both bulk and boundary transport. The interaction nature of the observed gapped sates was further examined both experimentally and theoretically. Our results suggest that charge transfer provides a direct route to engineer artificial
quantum Hall
insulators, opening possibilities for wavefunction-selective control of helical edge modes.
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All authors Naijie Ren, Zhiren Xiong, Kaining Yang, Yanran Shi, Hanwen Wang, Kenji Watanabe, Takashi Taniguchi, Neng Wan, Xiaojun Jia, Jianpeng Liu, Zheng Vitto Han, Yaning Wang
Mesoscale and Nanoscale Physics
Interplay of Kekulé order, flat bands and electron-phonon coupling in graphene
Dominik Szczȩśniak
The Kekulé order in
graphene is known to coexist with both an extended flat band near the van Hove singularity (VHS) and enhanced electron-
phonon coupling. However, the microscopic origin of this interplay is still not fully understood. Here, this behavior is traced to the Kekulé-induced bond distortion and the resulting redistribution of electronic delocalization. In this picture, the conduction band below the VHS is observed to flatten with increasing Kekulé order, extending its intrinsically weakly dispersive region around the saddle point over a broader momentum range. In parallel, the VHS and dimensionless electron-
phonon coupling exhibit approximately quadratic upward responses. The resulting enhancement of the electron-
phonon coupling is found to be predominantly governed by the increasing density of states, with the effective deformation potential remaining weakly affected by the distortion. As such, the obtained results are consistent with previous theoretical and experimental studies, while also pointing toward the narrowing of the conduction band and a possible departure of the electron-
phonon coupling from the conventional adiabatic regime. Altogether, they highlight the potential of controlled Kekulé ordering for engineering emergent correlated
quantum phases in
graphene.
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Soft Condensed Matter
Impact waves in soft bilayer tissues
Zhenwei Liu, Yang Liu, Michel Destrade et al. (+1 more)
In this study, we investigate impact-wave propagation in a pre-stressed compressible hyperelastic bilayer resting on a frictionless rigid substrate within the framework of nonlinear elasticity. Semi-analytical solutions for the transient displacement fields induced by localized surface impulses are derived using the
Fourier-Laplace transform, and their long-time asymptotic behavior is obtained through the method of stationary phase. Finite element simulations are further performed to validate the theoretical predictions. The results establish a direct connection between characteristic features of the transient displacement fields and the group velocities of the guided-wave modes, revealing how dispersive propagation and modal contributions shape the observed waveforms. Three representative bilayer models corresponding to human articular cartilage, gingiva, and skin are then considered to examine the effects of variations in layer stiffness and thickness. The results show that structural and material variations can substantially modify the spatial distribution, arrival positions, and characteristic velocities of impact waves. In particular, higher-order modes can make significant contributions to the displacement response in certain parameter regimes, such that the dominant features of the wavefield cannot always be characterized by the fundamental mode alone. These findings demonstrate that transient-wave measurements contain mechanical information beyond that captured by a single characteristic surface-wave velocity and provide a theoretical basis for interpreting transient wavefields in multilayered soft materials and for future non-invasive mechanical characterization.
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All authors Zhenwei Liu, Yang Liu, Michel Destrade, Yue-Sheng Wang