Statistical Mechanics · Cross-listed from cs.IT
Breakdown of Edgeworth Expansion in Finite-Blocklength Regime and Exact Absorption via $q$-Deformation
Hiroki Suyari
This paper addresses the structural breakdown of the Edgeworth expansion in the finite-blocklength (FBL) regime, where conventional asymptotic approximations yield unphysical negative probabilities in the deep-tail region. We propose a $q$-deformed framework that resolves this inconsistency by replacing additive
polynomial perturbations with a
geometric deformation of the information density space. Motivated by the linearization of nonlinear dynamics, we prove that dynamically scaling the $q$-logarithmic parameter exactly absorbs the third-order skewness while preserving global nonnegativity. We establish a universal asymptotic matching, demonstrating that the framework encapsulates higher-order asymptotic scales. Numerical results confirm that the proposed method matches the state-of-the-art precision of the Cornish-Fisher bound without the risk of negative probabilities. The framework offers a robust and computationally stable foundation for evaluating operational limits in ultra-reliable communications such as 6G and URLLC.
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Mesoscale and Nanoscale Physics
Quantum Geometry Driven Optical Responses in 1T-MX$_2$ Monolayers: A Symmetry-Constrained Slater-Koster Tight-Binding Approach
Bikram Baruah, Snehasish Nandy and Subhasis Panda
Centrosymmetric 1T-MX$_2$ monolayers(MLs) have attracted considerable
attention owing to their intriguing transport properties and potential technological applications arising from the interplay among
quantum geometry, electronic band structure, and band-gap characteristics. Despite this rich physics, a comprehensive microscopic tight-binding(TB) description that simultaneously captures these properties remains insufficiently established, while first-principles approaches can be computationally demanding for systematic investigations across different materials and perturbations. Here, we develop a transferable eleven-band Slater-Koster TB description of ML 1T-MX$_2$ TMDs and use it to establish a connection among their microscopic electronic structure,
quantum geometry, and optical response. The model is constructed in an orthogonal orbital basis from the
crystal geometry and
symmetry-constrained SK parameters, with material-specific parametrizations obtained from DFT calculations for ML ZrS$_2$ and HfS$_2$. The resulting geometry-based
Hamiltonian accurately describes the low-energy electronic structures and provides a natural framework for extending the analysis to the broader isostructural 1T-MX$_2$ family. We find that the pristine MLs possess a finite
quantum metric, with the dominant contribution concentrated in the two highest occupied bands owing to the small near-gap energy separation and strong metal-chalcogen $p$-$d$ hybridization. Furthermore, we verify the interband $f$-sum rule, which directly relates the integrated optical spectral weight to the Brillouin-zone-averaged
quantum metric. Our results establish optical spectral weight as an experimentally accessible probe of the
quantum geometry of occupied Bloch states and provide a unified microscopic framework for connecting electronic structure,
quantum geometry, and measurable optical responses across the 1T-MX$_2$ family.
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Mesoscale and Nanoscale Physics
Enhanced intrinsic spin-orbit driving of a Loss-DiVincenzo qubit near the spin-valley hotspot in Si/SiGe
Alexander Willmes, Max Oberländer, Max Beer et al. (+7 more)
In most Si/SiGe-based
spin qubit implementations, high-fidelity single-
qubit gates are achieved using micromagnets, which enable the use of electric
spin dipole resonance via synthetic
spin-orbit coupling (s-SOC). In contrast, intrinsic
spin-orbit coupling (i-SOC) in silicon is generally considered to be weak. However, in Si/SiGe
heterostructures, theory predicts a substantial enhancement when the Zeeman splitting approaches the valley splitting if
symmetry is reduced by an imperfect interface. Here, we demonstrate a Si/SiGe Loss-DiVincenzo
qubit driven by i-SOC close to this so-called
spin-valley hotspot. In particular, we characterize the Rabi frequency as a function of the energy detuning from the hotspot by sweeping both the
magnetic field and
quantum dot position. We observe the predicted enhancement of the Rabi frequency near the hotspot, but also find an asymmetry that deviates from existing theoretical models as well as distortions of the Chevron patterns near the hotspot. While we achieve an average single-
qubit Clifford fidelity of 98.6 %, the strong variability of the valley splitting may impede the use of i-SOC-based control as a scalable operational strategy; understanding its effect is nevertheless important for reproducible high-fidelity control. Our results provide an empirical basis for refining current theoretical models of
spin-valley physics in Si/SiGe
heterostructures.
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All authors Alexander Willmes, Max Oberländer, Max Beer, Denny Dütz, Jhih-Sian Tu, Stefan Trellenkamp, Marco Lisker, Felix Reichmann, Lars R. Schreiber, Hendrik Bluhm
Materials Science
FDTBX - Computational Tools for Simulation of X-ray Fiber Diffraction Patterns from Atomic Coordinates
Pawel Sikorski
Fiber diffraction is one of the few experimental techniques capable of resolving molecular structure in partially ordered, non-crystalline systems such as fibrous
proteins, biopolymers and synthetic
polymers. Because fiber diffraction patterns are complex, exhibiting paracrystalline order, packing defects and broad, overlapping reflections, their interpretation relies on model-based refinement, in which theoretical patterns simulated from candidate atomic models are iteratively compared with experiment. We present fdtbx, a modern, open and extensible Python toolbox for simulating X-ray fiber diffraction patterns directly from atomic coordinates. Built on the crystallographic library cctbx and designed for readability and multicore execution, fdtbx computes structure factors from a PDB model and constructs realistic reciprocal-space reflection profiles that incorporate the principal physical broadening mechanisms of fiber diffraction: finite crystallite size, orientational disorder (with Gaussian, Lorentzian and Voigt angular peak shapes) and paracrystalline (second-kind)
lattice disorder in Hosemann's formulation. A per-reflection shell-quadrature scheme evaluates the required convolutions at arbitrary query points rather than on a fixed grid, giving direct control over the trade-off between accuracy and speed, and an analytic Ewald-projection routine maps each sampled reflection, with an appropriate Lorentz correction, onto a flat detector to produce a simulated pattern for direct comparison with measured images. We illustrate the toolbox on $\alpha$-chitin, cellulose~I$\alpha$ and I$\beta$, cellulose triacetate and A-form DNA, and outline a practical simulation workflow. By providing a transparent, well-documented and parallelizable implementation of the specialized
algorithms of fiber diffraction, fdtbx lowers the barrier to reproducible model-based analysis.
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Statistical Mechanics · Cross-listed from quant-ph
Quantum Monte Carlo in the Age of Many-Body Quantum Information
Yi-Ming Ding, Bin-Bin Mao and Zheng Yan
Quantum Monte Carlo (QMC) methods are among the central numerical tools for studying strongly correlated
quantum many-body systems, particularly in higher dimensions. As
quantum information has introduced new information-theoretic perspectives and diagnostics into many-body physics, QMC methods have accordingly been extended beyond the measurement of conventional linear observables. This review summarizes recent progress in adapting QMC to many-body
quantum-information, focusing on
qubit or
spin-$1/2$ systems as a concrete setting while keeping the discussion broadly applicable to qudit and bosonic systems. We present a unified perspective on the extraction of nonlinear diagnostics, including
entanglement entropies and
entanglement spectra, Rényi negativities for mixed-state
entanglement, stabilizer
entropies for
quantum magic, and decoherence-driven phenomena such as the interplay between imaginary-time
evolution and decoherence and strong-to-weak spontaneous
symmetry breaking.
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Mesoscale and Nanoscale Physics
Electrostatic control of Li+ density and transport rate in double-gated van der Waals devices
E. Hoenig, X. Zhang, C. Li et al. (+7 more)
Ion transport in crystalline hosts is controlled by an applied potential that simultaneously sets ionic distribution and transport rate, restricting operation to a one-dimensional control space. Here we show that the transport rate of Li+ ions in double-gated van der Waals devices can be modulated while the system occupies fixed ionic-density states. We measure the ionic current along the van der Waals interfaces between hexagonal boron nitride and
graphene or MoS2 while simultaneously monitoring the in-plane electronic response. The ionic current exhibits pronounced hysteresis, with plateaus marking discrete ionic-density states balanced by electronic charge, while an independently tuneable electrochemical-potential drop controls the ionic transport rate. The devices sustain over 1,000 switching cycles and function as hybrid ionic-electronic transistors capable of logic operations and
memory retention, with ON/OFF ratios exceeding two orders of magnitude. This work demonstrates a two-dimensional control space for ions intercalated in layered materials.
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All authors E. Hoenig, X. Zhang, C. Li, J. Tong, G. Chen, L. Chen, D. Domaretskiy, D. R. da Costa, F. M. Peeters, M. Lozada-Hidalgo
Materials Science
Predicted High $n$-Type $zT$ and Ultralow Lattice Thermal Conductivity in A$_2$AgIrCl$_6$ (A = Cs, Rb)
Neeraj Kulhari, Krishna Swaroop Sharma, Sung Gu Kang et al. (+1 more)
A useful thermoelectric device must impede heat flow without impeding charge transport. Here, we examine how closely cubic Cs$_2$AgIrCl$_6$ and Rb$_2$AgIrCl$_6$ approach this balance using first-principles calculations of structural stability, chemical bonding, elastic response,
lattice dynamics, and scattering-resolved carrier transport. Both materials satisfy the cubic elastic-stability criteria, and neither harmonic
phonon spectrum contains an imaginary mode. Replacing Cs with Rb mainly exerts chemical pressure: the
lattice contracts by 1.34% and the Ag–Cl and Ir–Cl bonds strengthen, whereas the band-edge
topology changes little. HSE06 calculations including
spin–orbit coupling yield direct X-point gaps of 1.597 and $1.637\,\mathrm{eV}$ for Cs$_2$AgIrCl$_6$ and Rb$_2$AgIrCl$_6$, respectively. The three
symmetry-equivalent X valleys have light electron masses of $0.43$–$0.57\,m_0$, whereas the hole masses span $2.10$–$4.68\,m_0$. For Cs$_2$AgIrCl$_6$ and Rb$_2$AgIrCl$_6$, respectively, the modified Debye–Callaway model gives
lattice thermal conductivities of 0.346 and $0.428\,\mathrm{W\,m^{-1}\,K^{-1}}$ at 300 K, decreasing to 0.118 and $0.150\,\mathrm{W\,m^{-1}\,K^{-1}}$ at 800 K. Treating acoustic-deformation-potential, ionized-
impurity, and polar-optical-
phonon scattering with AMSET gives peak $n$-type $zT$ values of 2.81 and 2.36 at 800 K near $6\times10^{19}\,\mathrm{cm^{-3}}$. This response arises from the convergence of light, valley-degenerate electrons, intermediate doping, and weak
lattice heat transport rather than from a single exceptional coefficient. The predicted values are experimentally testable targets, contingent on retaining the cubic phases and controlled electron doping at elevated temperatures.
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All authors Neeraj Kulhari, Krishna Swaroop Sharma, Sung Gu Kang, K. C. Bhamu
Materials Science
The Achilles tendon enthesis rebuilds its mineralization front on reloading but retains a nanoscale imprint of unloading
M.L. Stammer, C. Camy, M. Frewein et al. (+16 more)
The enthesis is a graded fibrocartilaginous interface that transfers load between tendon and bone, yet the nanoscale mechanisms stabilizing its mineralization front remain unclear. Here, we combine
multimodal 2D/3D X-ray imaging with nonlinear optical microscopy to map structural, crystalline and extracellular
matrix organization across the murine Achilles tendon enthesis under unloading and reloading. Unloading reduces the tidemark-associated two-
photon fluorescence (2PF) peak and is accompanied by diffuse mineralization into previously unmineralized fibrocartilage. This unloading-associated mineral exhibits increased apparent crystallite size, an enlarged c-axis
lattice parameter, reduced crystalline texture and a diminished collagen order gradient, consistent with an altered mineralization environment. Upon reloading, the 2PF peak recovers, but a new tidemark forms ~20 um from the original boundary, creating a zone with a persistent nanoscale imprint in the mineral tessellation. These findings establish the enthesis as a mechanically governed graded interface in which
matrix-mediated boundary control constrains mineral formation and in which a record of mechanical history is imprinted into the nanostructure.
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All authors M.L. Stammer, C. Camy, M. Frewein, I. Silva Barreto, C. Genovesio, M. Eckermann, A. Karimbana, K. Iliopoulos, R. Ranjan, N. Wittig, T. Fovet, T. Brioche, A. Chopard, M. Burghammer, S. Brasselet, H. Birkedal, M. Pithioux, S. Roffino, T.A. Grünewald
Statistical Mechanics
Universality of superdiffusion in simple random graphs
Mrinal Sarkar, Nicolò Defenu and Tilman Enss
Random walks with long-range jumps can drive superdiffusive transport, replacing ordinary
diffusion with an effective long-range kinetic operator. Such superdiffusive kinetics is also central to critical phenomena, notably the self-avoiding walk with long-range jump statistics, or Lévy-SAW. This work investigates how the critical behavior is affected when the long-range connectivity itself becomes random. We study self-avoiding walks (SAWs) on a one-dimensional long-range random ring graph, where bonds are independently generated with Bernoulli probability $\sim|i-j|^{-(1+\sigma)}$. We term this walk Sparse-SAW. The same random bonds are responsible for both long-range superdiffusive transport and quenched disorder, with both simultaneously controlled by the single parameter $\sigma$, placing the problem beyond the conventional Harris and Weinrib-Halperin frameworks. Through large-scale Monte Carlo simulations and a Gaussian-truncated field theory, we show that Sparse-SAW belongs to the same universality class as the clean superdiffusive Lévy-SAW. The random bonds generate short-range uncorrelated and long-range correlated mass disorder while simultaneously producing the long-range kinetic operator. Under coarse-graining, the latter dominates, restoring the clean critical behavior. Our study suggests that the full non-Gaussian Bernoulli statistics may lead to disorder physics beyond the conventional theory of quenched disorder, while establishing random graphs as an efficient platform for extracting the critical exponents of the clean superdiffusive Lévy-SAW universality class.
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Disordered Systems and Neural Networks · Cross-listed from math-ph
Correlation inequalities for transversal field models with application to quantum glasses
Chokri Manai and Simone Warzel
We study the class of transversal field models with pair interactions, including the
quantum Curie-Weiss and the transversal field Ising model, as well as
quantum spin glasses based on the Sherrington-Kirkpatrick (SK) and Edwards-Anderson models. Our main result is a general correlation inequality based on a Gaussian convolution estimate, which is derived from an extension of the Ding-Song-Sun inequality and an application of Brascamp-Lieb convexity techniques. The results apply for sufficiently strong transversal fields and, for
quantum spin glasses, yield a high-field regime without replica order. Combined with the previously established low-field replica-
symmetry-breaking regime, this gives distinct low- and high-field overlap phases. As a corollary of the logarithmic Sobolev inequalities for the underlying functional integrals derived here, we show the concentration of the self- and replica-overlap, and determine the high-field asymptotics of the pressure in the
quantum SK model.
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Strongly Correlated Electrons
Quantics tensor cross interpolation for high-order strong-coupling expansions
Kanghyeon Kim, Lei Geng, Philipp Werner et al. (+1 more)
Real-time
impurity solvers enable the study of transport phenomena and the description of nonequilibrium
lattice systems within the framework of dynamical mean-field theory (DMFT). They also provide direct access to the spectral functions of both
equilibrium and nonequilibrium systems. A widely used approach is the self-consistent strong-coupling expansion, whose lowest-order implementation corresponds to the non-crossing approximation. Higher-order implementations, however, are computationally demanding because the number of diagram
topologies grows factorially with expansion order, while the evaluation of self-energies and Green's functions requires increasingly high-dimensional integrations. Here, we demonstrate that the latter challenge can be mitigated by employing quantics tensor cross interpolation in a variable-separated framework. Compared with the previously used scale-separated approach, the new scheme yields substantially lower bond dimensions and capacitates self-consistent steady-state DMFT calculations up to fourth order. We illustrate its performance with representative results for both
equilibrium and photo-doped systems. In addition, we analyze the convergence of the strong-coupling expansion in the challenging noninteracting limit by computing diagrams up to sixth order. At this order, the onset of the asymptotic regime of the strong-coupling expansion becomes apparent, which allows the application of extrapolation techniques.
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All authors Kanghyeon Kim, Lei Geng, Philipp Werner, Aaram J. Kim
Materials Science
First-Principles Spin-Lattice Coupling from Downfolded Electron-Phonon Interaction
Xu He, Álvaro Adrián Carrasco Álvarez, Gian-Marco Rignanese et al. (+3 more)
We present a method to calculate
spin-
phonon coupling parameters from first-principles perturbation theory by downfolding the electron-
phonon coupling (EPC). We exploit the localized nature of
magnetic moments and atomic displacements by working in the Wannier representation of the electronic
Hamiltonian and the EPC
matrix. The
spin system is mapped to a classical Heisenberg
Hamiltonian, whose parameters are obtained by treating local
spin rotations as a perturbation within a Green's-function formalism. The
spin and
phonon perturbations are connected through the EPC parameters, which enter as
lattice-induced perturbations to the tight-binding
Hamiltonian. By combining these
lattice perturbations with local
spin rotations, we obtain real-space derivatives of
magnetic exchange parameters without performing displaced
magnetic supercell calculations. We illustrate the method on SrMnO$_3$ and show that it can be integrated directly into standard workflows.
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All authors Xu He, Álvaro Adrián Carrasco Álvarez, Gian-Marco Rignanese, Eric Bousquet, Samuel Poncé, Matthieu J. Verstraete
Materials Science
Impact of Carbon Contamination on the Low-Temperature Electric Conduction of the Spark-Plasma Sintered Barium Titanate Ceramics
Oleksandr S. Pylypchuk, Taisiia O. Kuzmenko, Denis O. Stetsenko et al. (+6 more)
The dielectric and electric conduction properties of BaTiO3 samples fabricated by the spark
plasma sintering with additional contamination by different content of carbon have been investigated in the temperature range from 77 through 408 K in small non-heating electric fields and in the range of 77 - 200K under strong electric fields up to 20 kV/cm. The effective dielectric permittivity of the samples with additional carbon achieves colossal values at low frequency, up to several units per 106 at 393 K. In the low temperature range, it remains very high magnitude, 10^4 -10^5 at low frequency and is strongly dependent on the carbon content. The electric conduction in the range of 77 - 200 K bears the hopping conduction and obeys the Mott law. We also studied electric conduction and effective dielectric permittivity vs electric field strength in the range of 77 - 200 K. The results are explained within the frames of hopping conduction theory and suggestion on different constituents in polarization processes and electric conduction.
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All authors Oleksandr S. Pylypchuk, Taisiia O. Kuzmenko, Denis O. Stetsenko, Oleksyi V. Bereznykov, Serhii E. Ivanchenko, Ihor M. Danylenko, Anna N. Morozovska, Vladimir N. Poroshin, Victor V. Vainberg
Materials Science
Multiscale Quasiparticle Electronic Structure and Excitonic Properties of CdSe Nanoclusters
Surender Kumar, Martin Thümmler, Alexander Croy et al. (+2 more)
Quantum confinement in stoichiometric $\mathrm{Cd}_n\mathrm{Se}_n$ nanoclusters dramatically attenuates electronic screening, driving a delicate, size-dependent competition between quasiparticle self-energy corrections ($\Delta_{\mathrm{QP}}$) and
exciton binding energies ($E_b$). Here, we present a $GW$/BSE study across a representative size series ($n = 3, 6, 13, 33$) and leverage it to validate a scalable atomistic tight-binding (TB) framework derived from first principles. Our results demonstrate that 1-2 eV spectral blueshifts previously reported in the literature arise from single-particle $GW$ convergence artifacts rather than deficiencies in the electron–hole kernels. We show that the near-perfect cancellation between $\Delta_{\mathrm{QP}}$ and $E_b$ breaks down as cluster volume increases, driven by the rapid onset of dielectric screening attenuating $E_b$ faster than $\Delta_{\mathrm{QP}}$ and leading to a pronounced divergence from mean-field predictions. Spatial inverse participation ratio analysis of the electronic structure reveals that optical suppression of fundamental pre-peaks stems from a severe spatial mismatch between localized valence orbitals and delocalized conduction states. Finally, we demonstrate that the confinement-induced scaling of the quasiparticle gap and the optical onset is accurately reproduced by a scissor-corrected, DFT-parameterized TB model. As such, this work provides a quantitative multiscale roadmap for
embedding effective many-body effects kernels into computationally efficient models, enabling reliable optical predictions for realistic semiconducting nanostructures containing up to thousands of atoms.
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All authors Surender Kumar, Martin Thümmler, Alexander Croy, Stefanie Gräfe, Caterina Cocchi
Materials Science
Probing the transport properties of Cantor-Wu alloys by means of femtosecond and nanosecond laser ablation
David Redka, Maximilian Spellauge, Rosemary Babu et al. (+5 more)
Single-pulse
laser ablation thresholds of selected equiatomic Cantor-Wu
alloys - FeNi, CoNi, CrFeNi, CrCoNi, and CrMnFeCoNi - are measured for femtosecond and nanosecond pulse durations and interpreted through first-principles calculations of the electronic structure, the electron-
phonon coupling, and the electronic thermal conductivity.
Alloy synthesis, ablation experiments, and theory are performed consistently on the same set of samples. The absorbed femtosecond thresholds decrease systematically by up to 36 % from FeNi to the Cr-containing
alloys, a trend that reflectance variations cannot explain. Two-temperature-model scaling of the thresholds with the electronic thermal conductivity and the electron-
phonon coupling, with all parameters taken from the
spin-disordered phase, reproduces the measured hierarchy. The nanosecond thresholds instead probe the thermal
equilibrium conductivity averaged along the heating path. The apparent outlier of CoNi, whose room-temperature transport over-predicts its thresholds by up to a factor of two for both pulse durations, is resolved quantitatively by the collapse of its conductivity upon loss of
ferromagnetic order. Single-pulse ablation thresholds thereby emerge as sensitive, contact-free probes of electronic transport and of its
magnetic-phase dependence in compositionally complex
alloys.
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All authors David Redka, Maximilian Spellauge, Rosemary Babu, Christopher D. Woodgate, Hubert Ebert, Ján Minár, Daniel J. Förster, Heinz P. Huber
Materials Science
Z1 oscillations and charge state in electronic stopping power from first principles
Noor Ul Ain and Emilio Artacho
The energy transfer rate from a projectile
nucleus to the electrons of the matter it traverses depends on the charge of that projectile, Q= e Z1. At low projectile velocities the friction coefficient is known to oscillate with atomic number Z1, since core electrons travel with the projectile screening its charge. The effective charge increases with velocity and oscillations disappear. That effect is studied here calculating electronic stopping power from first principles for O and Mg projectiles shooting through bulk Al, using real-time time-dependent density-functional theory. Both projectiles represent maximum and minimum of the first Z1 oscillation, respectively. The oscillation is found to be very sensitive to the direction of propagation, in spite of Al being quite an ideal metal for many purposes. The critical velocity for the oscillation disappearance ranges between below 0.1 a.u. and beyond 1 a.u. for the explored trajectories. The charge state is independently quantified with Hirshfeld and Voronoi analyses, offering remarkably consistent results in spite of their very different partition methods, as well as with an effective definition based on the stopping power itself. They display a gradual undressing of the projectile's core electrons with increasing velocity in qualitative accordance with expectations. However, electron density plots in real space present a richer picture in which the undressing is partly due to the electrons trailing behind the projectile, suggesting possible phenomenological descriptions correcting for the deformation of the density in terms of multipoles beyond the net charge. The plots also offer insights into dissipation by core electrons.
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Superconductivity
Three-dimensional Ising superconductors designed via inversion-symmetry breaking in intercalated NbSe$_2$ and NbTe$_2$
Wenqian Tu, Run Lv, Xiaoying Li et al. (+4 more)
Ising
superconductors exhibit in-plane upper critical fields far exceeding the Pauli paramagnetic limit, a hallmark first established in two-dimensional (2D) monolayer transition-metal dichalcogenides (TMDs). This field resilience requires the coexistence of strong
spin-orbit coupling (SOC) and broken inversion
symmetry, yet three-dimensional (3D) bulk realizations remain scarce because
equilibrium stacking typically restores inversion
symmetry. Here we demonstrate that intercalation provides a practical route to break this
symmetry, systematically designing 16 NbSe$_2$- and NbTe$_2$-based compounds from four intercalants (In, Sn, Pb, Bi) across two polytypes: non-centrosymmetric $P\bar{6}m2$ and centrosymmetric $P6_3/mmc$. Four compounds in the $P\bar{6}m2$ phase, InNbSe$_2$, SnNbSe$_2$, PbNbSe$_2$, and PbNbTe$_2$, emerge as promising 3D Ising
superconductors. They exhibit SOC splittings of 80-100 meV near the
Fermi level, dominant out-of-plane
spin polarization, and anisotropic superconductivity with $T_c=2.6$-$5.4$ K. Notably,
spin-texture analysis reveals that the efficiency of Ising protection is governed not by the magnitude of SOC splitting alone but by the out-of-plane
spin purity on the
Fermi surface. Bogoliubov-de Gennes (BdG) calculations predict in-plane upper critical fields reaching 4-7 times the Pauli limit. These findings establish intercalation as a promising
symmetry-engineering strategy for realizing 3D Ising
superconductors in TMDs.
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All authors Wenqian Tu, Run Lv, Xiaoying Li, Li'e Liu, Dingfu Shao, Yuping Sun, Wenjian Lu
Strongly Correlated Electrons
Interplay of Magnetic Order, Structural Stability, and Orbital Ordering in BaFe2X3 (X = S and Se)
Kunihiko Yamauchi, Takuya Aoyama and Kenya Ohgushi
BaFe2X3 (X= S and Se) are quasi-one-dimensional Mott
insulators with a ladder structure that exhibit Stripe- and Block-type
antiferromagnetic order, respectively. The ladder arrangement of Fe atoms and strong electron correlations give rise to rich
magnetic and orbital phenomena, including pressure-induced superconductivity and orbital-selective electronic states. Both compounds also show resistivity anomalies above the Neel temperature, suggesting that orbital degrees of freedom play an important role in their electronic properties. To clarify the interplay among
magnetic order, structural stability, orbital ordering, and transport properties, we performed resistivity measurements and first-principles calculations for BaFe2S3 and BaFe2Se3, systematically comparing candidate
magnetic and
crystal structures. We find that the
magnetic configuration strongly influences the stable
crystal structure, orbital ordering, and transport anisotropy, providing a microscopic understanding of the contrasting electronic properties of the two compounds.
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Materials Science
X-ray driven displacive excitation of coherent phonons
Oleg Dogadov, Remi Claude, Christoph Emeis et al. (+29 more)
Modulating electron-
phonon coupling offers a route to control structural displacements and tune material functionality. Valence-to-conduction band transitions, however, provide limited leverage over the driving force. Here, we demonstrate coherent
lattice dynamics in trigonal tellurium using free-electron
laser pulses tuned to the Te N4,5-edge. Over a broad fluence range, the oscillation amplitude obeys the displacive excitation of coherent
phonons framework, extended to core resonance with twice the driving efficiency of a visible pump. Ab initio calculations decompose the force into competing multiband contributions, inaccessible to optical excitation, whose balance shifts as carriers relax. Tunable extreme-ultraviolet and X-ray pulses thus open a regime in which the displacive response is set by band-dependent coupling to the
lattice, not by the number and temperature of the photocarriers alone.
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All authors Oleg Dogadov, Remi Claude, Christoph Emeis, Giovanni Batignani, Giuseppe Fumero, Roberto Costantini, Agata Azzolin, Sabine Rockenstein, Paolo Cattaneo, Rebeca Gomez Castillo, Matteo Manzi, Angelo Giglia, Dario De Angelis, Ettore Paltanin, Zeinab Ebrahimpour, Marija Krstulovic, Gabor Kurdi, Miltcho Danailov, Luca Giannessi, Riccardo Mincigrucci, Emiliano Principi, Alberto Crepaldi, Giulio Cerullo, Giovanni De Ninno, Claudio Masciovecchio, Laura Foglia, Tullio Scopigno, Fabrizio Carbone, Francesca Calegari, Fabio Caruso, Michele Puppin, Oliviero Cannelli
Soft Condensed Matter · Cross-listed from physics.bio-ph
From Maxwell Fluid to Kelvin Voigt Solid: A Transient Network Model of Condensate Aging and Morphology Transition in Phase Separation
Bhanjan Debnath
Biomolecular condensates can undergo striking changes, such as transitioning from a
liquid-like to a gel- or a solid-like aggregate due to changes in molecular interactions in response to changes in the biochemical environment. The question of how modified molecular interactions lead to such a transition in the material properties and spatial organization of condensates has not yet been elucidated. To address this question, we represent the biochemical environment as a triphasic mixture comprising a
liquid-like
protein-rich phase, a network-like
protein-rich phase, and solvent. Owing to a change in the biochemical environment,
protein molecules can reversibly switch between two conformational states. In a switched conformational state, the cross-linking domains of molecules are exposed which promote transient network formation in phase separated states. We develop a transient-network model and a continuum framework that couples phase separation, molecular switching, and dynamic cross-linking to predict condensate morphology and mechanics. The transient-network model predicts that a non-aging network behaves like a Maxwell fluid. When a network slowly ages via stabilization of cross-links, it shows Maxwell-like behavior and waiting time-dependent relaxation. However, a strongly aged network shows elastic
recoil like characteristic of a Kelvin-Voigt solid. Our coupled continuum model demonstrates that the interplay of molecular switching and dynamic cross-linking in network formation shapes the spatial organization of condensate phases. In summary, this work demonstrates a mechanistic route explaining how conformational switching and molecular cross-linking regulate material properties and morphology of condensates.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
What do position and time mean in the quantum wavefunction?
Mustafa Bakr, Zichi Zhang and Margot Stakenborg
The notation $\psi(x,t)$ is among the first pieces of
quantum mechanics that students learn. It is also among the easiest to over-interpret. Because $x$ and $t$ occur as arguments of the same function, students may ask whether they have the same mathematical status. They may also ask whether $\psi(t)$ should require a generalized bra $\bra{t}$ in the same way that $\psi(x)=\braket{x}{\psi}$ is often written. A related question is whether the absence of a universal time operator follows simply from Pauli's argument. These questions mix several structures that are usually introduced in different parts of the curriculum. We present a unified pedagogical treatment built around two maps hidden in $\psi(x,t)$. Time
evolution selects a state along a trajectory in
Hilbert space. A spectral representation then maps that state to amplitudes labelled by outcomes of a chosen observable. We formulate the position representation without generalized eigenkets. We recover Dirac's $\ket{x}$ notation as a controlled continuum shorthand and use a finite-grid limit to show where delta normalization enters. We distinguish background coordinates, translation parameters, observables, spectral labels, and physical records. We also clarify the Stone-
theorem analogy, compare prescribed-time position measurements with arrival-time measurements, state what the strong form of Pauli's argument excludes, and exhibit an exactly solvable boundary case in which a canonical self-adjoint time observable exists.
Spin,
circuit-QED, and optical-clock examples provide experimentally grounded checks. The aim is not a new interpretation of time. It is a reusable teaching framework for separating mathematical role from notation.
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Materials Science
Displacement-field-driven reconstruction of low energy transport in few-layer PtSe2
Xiao Liu, Yaroslav Zhumagulov, Yuang Jie et al. (+9 more)
In layered
semiconductors, a perpendicular displacement field generates an interlayer potential difference that competes with interlayer hybridization, modifying both the band gap and the finite-density electronic states that carry current. Resolving this interplay requires a material lying close to the
semiconductor-to-semimetal transition, where moderate electric fields can strongly reshape the low-energy electronic structure. Here, we investigate displacement-field-driven transport in dual-gated semiconducting PtSe2, whose pronounced thickness-dependent electronic structure provides access to this low-band-gap regime. Unlike thinner layers, the displacement-field response is strong in six-layer PtSe2, which lies at the verge of the
semiconductor-to-semimetal crossover with only a small residual transport gap. Even weak displacement fields rapidly suppress this residual gap near charge neutrality, driving the system toward a band-overlap regime. At the same time, the conductivity decreases in the heavily hole-doped regime, demonstrating that the displacement field modifies not only the gap but also the conducting valence-band states. Fixed-relaxation-time Wannier transport calculations reproduce both responses, showing that they originate from field-induced band overlap together with reconstruction of the valence-band dispersion. These results establish finite-density transport as a sensitive probe of displacement-field-driven electronic structure reconstruction and extend electrical control beyond conventional band-gap engineering.
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All authors Xiao Liu, Yaroslav Zhumagulov, Yuang Jie, Ahmet Enes Bozcali, Johan Felisaz, Qi Zhang, Oldvrich Cicvarek, Kenji Watanabe, Takashi Taniguchi, Zdeněk Sofer, Oleg V. Yazyev, Ahmet Avsar
Disordered Systems and Neural Networks · Cross-listed from cs.LG
A Physical Response-and-Memory Model for Muon Optimization
Yinze Hu, Hongjun Xiang, Xingao Gong et al. (+1 more)
Training large
language models is costly. How low a loss the same compute can ultimately reach depends on how each step's gradient is converted into a weight update; the rule that performs this conversion is the optimizer. From SGD and AdamW to the recent
Muon, effective update rules have mostly been shaped by engineering intuition and then selected on
benchmarks.
Muon semi-orthogonalizes the momentum
matrix before applying the update and has kept breaking records on public training
benchmarks; yet why the semi-orthogonalized direction works, and over how long a history the momentum should average, are two questions at present answered mainly by experience. Here we treat the weight
matrix during training as a responsive medium with
memory and build a physical model for it, in which both questions find answers: the semi-orthogonalized direction is the maximally dissipative response under an output-side safety budget, which explains why it works; momentum is the internal stress accumulated by the medium; how long it should average is set by the relaxation of this stress, and a real medium relaxes on more than one timescale, the simplest form being one fast and one slow. On this basis we propose the Bi-Maxwell optimizer. The framework further yields a testable consequence: gradient directions change fast early in training and more slowly later, so the optimal
memory length should grow with training stage; step-by-step measurements of a proxy for it by a read-only probe across 8 independent training trajectories are consistent with this consequence. Replacing the
memory kernel alone, from a single timescale to two, brings training to the target loss in noticeably fewer steps on a public large-
language-model optimizer
benchmark.
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All authors Yinze Hu, Hongjun Xiang, Xingao Gong, Hongyu Yu
Materials Science
Discovery of New Zintl Films and Nanowires Grown by Topotaxy Conversion of III-V Semiconductors
Man Suk Song, Lothar Houben, Jean Souza et al. (+8 more)
Zintl phases draw broad interest for their diverse structural,
magnetic, thermoelectric, topological and optical properties. Recently, Zintl Eu$_3$In$_2$As$_4$ and Eu$_5$In$_2$As$_6$ nanowires with
axion magneto-
topology have been synthesized by molecular beam epitaxy via topotactic conversion of InAs wurtzite and zincblende nanowires. Here we extend this methodology, demonstrating that topotaxial mutual-exchange growth applies not only to a broader set of III-V
semiconductors beyond InAs but also to three-dimensional substrates whose surfaces are converted into Zintl thin films, as well as to nanowires. We report the growth of two new compounds: Eu$_5$Ga$_2$As$_6$ thin films converted from GaAs substrates, and Eu$_5$Al$_2$As$_6$ thin films from AlAs films. We also convert GaAs nanowires of both wurtzite and zincblende structures into Eu$_5$Ga$_2$As$_6$ nanowires. Though the stoichiometry is the same as in the previously reported Eu$_5$In$_2$As$_6$ case, microscopy and diffraction reveal a single-phase Pnma
symmetry group rather than Pbam, highlighting
symmetry-guided topotactic pathways to new Zintl frameworks. The compounds host an intricate
magnetic phase diagram with three
magnetic transitions, including two distinct
antiferromagnetic orders and a canted
antiferromagnetic phase that evolves into another
antiferromagnetic phase under applied field through a
spin-flop transition. Ab initio calculations predict that both Zintls are
semiconductors with gaps of 0.79 eV in Eu$_5$Ga$_2$As$_6$ and 0.90 eV in Eu$_5$Al$_2$As$_6$. The lower
symmetry and increased structural complexity suggest suppressed
lattice thermal conductivity, pointing to thermoelectric potential alongside prospects in spintronics and detector technologies. These results give an epitaxy-compatible route for discovering and integrating
magnetic Zintl thin films and nanowires directly from relevant III-V
semiconductors.
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All authors Man Suk Song, Lothar Houben, Jean Souza, Edanel Fishbein, Moshe Haim, Ambikesh Gupta, Yufei Zhao, Anna-Eden Kossoy, Binghai Yan, Haim Beidenkopf, Hadas Shtrikman
Statistical Mechanics · Cross-listed from quant-ph
`It from Bit': is there a second law of quantum complexity?
S. Davatolhagh, A. Sheykhi and M.H. Zarei
At a deeper level the principle of least action is interpreted as the law of least
entropy increase consistent with Prigogine's principle of minimum
entropy production, and the implications of quasistatic information quantization rule (Proc. R. Soc. A 480: 20240024), are explored for the conjectured second law of
quantum complexity. It is thus shown that the conjectured second law of complexity is derivable from the information quantization rule such that long after heat-death the
quantum state complexity evolves as $C(t)=C_{\rm max}\exp(-1/t)$, increasing with time to a saturation value $C_{\rm max}$ that is exponential in the
equilibrium entropy $S_{\rm max}$. For the out-of-
equilibrium circumstances, however, the
quantum complexity can decrease with the time, asymptotically tending to a minimum determined by the distance from
equilibrium.
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Materials Science · Cross-listed from physics.optics
Self-consistent modelling of all-optical switching and magneto-optic readout in an integrated Si$_3$N$_4$/GdFeCo waveguide
Muhammad Arief Mulyana, Budi Adiperdana and Ayi Bahtiar
What a guided beam carries after passing through an all-optically switched
magnetic film has not been computed, although such switching has been demonstrated on a silicon nitride waveguide with electrical readout. We close the chain for an integrated Si$_3$N$_4$/GdFeCo element, an 8 nm film on a 60 $\mu$m waveguide, coupling a three-dimensional dispersive finite-difference time-domain solver to absorbed optical work, a four-temperature model, and
stochastic two-sublattice Landau-Lifshitz-Bloch dynamics with a fluctuation-dissipation-consistent Langevin field, the magnetization feeding back into the gyrotropic permittivity that a second guided shot reads. Transmission, reflection and absorption are magnetization-blind, closing to 0.974-0.975 and shifting by at most 0.02 between saturated, demagnetized and multidomain films, because magnetization enters the dielectric tensor only through an antisymmetric element on which absorbed power depends at second order; the odd-in-magnetization polarimetry separates them by an order of magnitude in Faraday rotation and two in Kerr. The guided geometry levies a cost free-space measurement does not: a $-11.77^\circ$
geometric pedestal on the reflected channel, exceeding the $8.24^\circ$ rotation it hides. Referencing against a demagnetized film returns it to $0.063^\circ$. The transmitted mode carries a second signature in its lobe balance, needing no polarimetry. Calibrated pulses toggle 0.859 of the film from either saturated state across a $2.4\times$ fluence window, and the shortfall from unity is photonic rather than
magnetic: the switched fraction is the complementary cumulative distribution of the guided-mode absorption map at the single-
cell threshold, holding to $8\times10^{-4}$ at five full-wave anchors. From exactly zero magnetization, branch selection passes to the Langevin field alone, at occupancy $0.502 \pm 0.004$ over 16 seeds.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.flu-dyn
$\mathscr{PT}$-symmetric hydrodynamics of odd viscous liquids and their oscillator counterparts
E. Kirkinis and A. Levchenko
Odd viscosity, the nondissipative part of the viscous response of a time-reversal-broken fluid, is notoriously difficult to measure precisely because it does no work. Here we show that parity-time ($\mathscr{PT}$)
symmetry, familiar from non-Hermitian optics, converts this elusiveness into a measurement principle. The odd Navier-Stokes equations, that include the nonlinear inertial terms, are $\mathscr{PT}$-symmetric, follow from a Lagrangian, and linearize to a Schrödinger equation in which the odd viscosity plays the role of Planck's constant; potential vorticity obeys a generalized Ertel conservation law. A probe trapped in an odd
liquid realizes a pair of oscillators coupled by odd friction, and supplying balanced loss and gain drives a twofold $\mathscr{PT}$ transition whose exceptional point and Rabi sidebands locate the odd viscosity with square-root-enhanced sensitivity. Upon quantization the spectrum is of Fock-Darwin form, and the dissipative pair exhibits a Liouvillian exceptional point separating linear from exponential heating. These results furnish mechanical,
stochastic, and spectroscopic protocols for measuring odd transport coefficients in classical and
quantum fluids.
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Statistical Mechanics · Cross-listed from quant-ph
Universal equilibrium magic in quantum many-body systems
Soumyadeep Sarma, Tobias Haug, John Preskill et al. (+1 more)
Thermalization conventionally describes local properties of isolated many-body systems at
equilibrium. Magic, or nonstabilizerness $\unicode{x2013}$ the resource enabling universal
quantum computation $\unicode{x2013}$ is by contrast encoded in the global structure of the many-body wavefunction. We show that, despite its global nature, the magic of
equilibrium pure states of chaotic many-body systems, including late-time evolved states and energy eigenstates, is universal: it is captured by the thermal Scrooge ensemble, the minimally informative ensemble of pure states consistent with the Gibbs state at the same effective temperature. Therefore, for systems with no conserved quantities other than the total energy,
equilibrium magic is a function of temperature alone, independent of the initial state and other microscopic features of the
equilibrium state. This yields concrete universal predictions for the stabilizer Rényi
entropies (SREs). At infinite temperature, the SRE is set by Haar-like fluctuations of the Pauli spectrum, while at finite temperature energy conservation induces a volume-law thermodynamic correction controlled by the thermal Pauli spectrum. We support these predictions with analytical arguments and extensive numerical simulations. We further show that chaotic many-body systems at high temperatures possess long-range magic and
entanglement that cannot be removed by finite-depth local
quantum circuits. Our results establish magic as a thermodynamic property of chaotic many-body systems and suggest that Scrooge ensembles may provide a unified framework for
quantum many-body resources.
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All authors Soumyadeep Sarma, Tobias Haug, John Preskill, Wai-Keong Mok
Statistical Mechanics
Kinetic heterogeneity tightens thermodynamic bounds on spectra of Markov cycles
Rongxing Xu and Cuiling Meng
Thermodynamic bounds on the spectrum of a Markov cycle are determined by quantities such as the cycle affinity and maximal escape rate, but do not distinguish cycles with different local rate profiles. In this work, we show that kinetic heterogeneity, through the
geometric means of forward ($G_+$) and backward ($G_-$) rates, tightens the bound on oscillatory relaxation. Specifically, we prove that, for each winding sector of the eigenmodes, the oscillation frequency cannot exceed that of the uniform comparison cycle with rates $G_+$ and $G_-$. Combining with existing affinity-winding bounds, we also demonstrate a contracted region for the
eigenvalues and shows that the boundary of Uhl-Seifert ellipse can be saturated if and only if cycles are uniform. Our proof provides a complex-analytic framework that unifies the kinetic and thermodynamic constraint.
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Disordered Systems and Neural Networks · Cross-listed from physics.chem-ph
Generalizing Abell-Tersoff bond-order potential with explicit high-order many-body correlations for robust extrapolation of potential energy surfaces
Ikuma Kohata
Machine-learning interatomic potentials enable accurate and efficient atomistic simulations, yet their reliability for out-of-distribution configurations far beyond the training domain remains a significant challenge. Here, we introduce a semiparametric interatomic potential based on a generalization of the Abell–Tersoff bond-order potential, incorporating a chemically informed functional form and explicit high-order many-body correlations to address this challenge. The model is trained and evaluated on various
datasets of silicon, carbon, water, and small molecules, achieving interpolation accuracy comparable to existing MLIP models while exhibiting improved extrapolation to unseen configurations, including those at high pressures and temperatures. These results provide insights into the design of specific inductive biases for reliable extrapolation in interatomic potentials. inductive biases that can be used to control extrapolation in machine-learning interatomic potentials.
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