Statistical Mechanics · Cross-listed from hep-th
Modular Krylov Complexity as a Boundary Probe of Area Operators and Entanglement Islands
Niloofar Vardian
We show that the area operator of a
quantum extremal surface can be reconstructed directly from boundary dynamics without reference to bulk geometry. Our approach combines the operator-
algebra quantum error-correction (OAQEC) structure of AdS/CFT with modular Krylov complexity. Using Lanczos coefficients of boundary modular dynamics, we extract the spectrum of the modular
Hamiltonian restricted to the
algebra of the
entanglement wedge and isolate its central contribution, which is identified with the area operator. The construction is purely boundary-based and applies to superpositions of semiclassical geometries as well. As a prospective application, we discuss island formation and the Page transition in evaporating black holes using boundary modular
evolution, bypassing any bulk extremization. More broadly, our results establish modular Krylov complexity as a probe of emergent spacetime geometry, providing a new route to accessing black hole interiors from boundary
quantum dynamics.
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Quantum Gases · Cross-listed from quant-ph
Floquet-engineered fidelity revivals in the PXP model
Francesco Perciavalle, Francesco Plastina and Nicola Lo Gullo
We explore the dynamics of the PXP model when subjected to a periodic drive, and unveil the mechanism through which the interplay between spectral properties and initial states governs the emergence of dynamical revivals and their
evolution across the space of driving parameters. For Néel-ordered initial states, revivals follow well-defined trajectories in the parameter space of the driving, primarily determined by a dominant quasi-energy spacing in the Floquet spectrum. Initial states interpolating between Néel and fully polarized configurations exhibit hybrid dynamics, which can be controlled by tuning their overlap with Floquet eigenstates via the driving parameters. This control also allows steering different routes for avoiding Floquet thermalization, showing how both initial state choice and driving protocol shape long-lived dynamics in this driven
quantum many-body systems.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Gradually opening Schrödinger's box reveals a cascade of sharp dynamical transitions
Barkay Guttel, Danielle Gov, Noam Netzer et al. (+9 more)
Quantum mechanics predicts that unobserved systems may exist in a superposition of states, yet measurement produces definite outcomes, a tension at the heart of the
quantum-to-classical boundary. How the transformation between these opposing regimes unfolds as observation strength increases has remained experimentally unexplored. Here, by continuously tuning the measurement strength on a superconducting
qubit, we reveal that measurement-dominated dynamics emerge not gradually but through three distinct transitions: coherent oscillations abruptly halt; the system then freezes near a stable
quantum state; and finally enters the
quantum Zeno regime, where stronger observation paradoxically slows relaxation. Decoherence, rather than washing out this structure, reorganizes it, inverting the order in which transitions appear and decoupling signatures that coincide in idealized models. These results establish that the route from
quantum dynamics to measurement-dominated behavior unfolds in sharp transitions governed by the interplay between observation and environment.
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All authors Barkay Guttel, Danielle Gov, Noam Netzer, Uri Goldblatt, Sergey Hazanov, Lalit M. Joshi, Alessandro Romito, Yuval Gefen, Parveen Kumar, Kyrylo Snizhko, Fabien Lafont, Serge Rosenblum
Strongly Correlated Electrons
Approaching the Thermodynamic Limit with Neural-Network Quantum States
Luciano Loris Viteritti, Riccardo Rende, Subir Sachdev et al. (+1 more)
Accessing the thermodynamic-limit properties of strongly correlated
quantum matter requires simulations on very large
lattices, a regime that remains challenging for numerical methods, especially in frustrated two-dimensional systems. We introduce the Spatial
Attention mechanism, a minimal and physically interpretable inductive bias for Neural-Network
Quantum States, implemented as a single learned length scale within the
Transformer architecture. This bias stabilizes large-scale optimization and enables access to thermodynamic-limit physics through highly accurate simulations on unprecedented system sizes within the Variational Monte Carlo framework. Applied to the
spin-$\tfrac12$ triangular-
lattice Heisenberg antiferromagnet, our approach achieves state-of-the-art results on clusters of up to $42\times42$ sites. The ability to simulate such large systems allows controlled finite-size scaling of energies and order parameters, enabling the extraction of experimentally relevant quantities such as
spin-wave velocities and uniform susceptibilities. In turn, we find extrapolated thermodynamic limit energies systematically better than those obtained with tensor-network approaches such as iPEPS. The resulting magnetization is strongly renormalized, $M_0=0.148(1)$ (about $30\%$ of the classical value), revealing that less accurate variational states systematically overestimate
magnetic order. Analysis of the optimized wave function further suggests an intrinsically non-local sign structure, indicating that the sign problem cannot be removed by local basis transformations. We finally demonstrate the generality of the method by obtaining state-of-the-art energies for a $J_1$-$J_2$ Heisenberg model on a $20\times20$ square
lattice, outperforming Residual Convolutional Neural Networks.
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All authors Luciano Loris Viteritti, Riccardo Rende, Subir Sachdev, Giuseppe Carleo
Statistical Mechanics · Cross-listed from quant-ph
Tailoring Quantum Chaos With Continuous Quantum Measurements
Preethi Gopalakrishnan, András Grabarits and Adolfo del Campo
We investigate the role of
quantum monitoring in the dynamical manifestations of
Hamiltonian quantum chaos. Specifically, we analyze the generalized spectral form factor, defined as the survival probability of a coherent Gibbs state under continuous energy measurements. We show that
quantum monitoring can tailor the signatures of
quantum chaos in the dynamics, such as the extension of the ramp in the spectral form factor, by varying the measurement strength and detection efficiency. In particular, a typical
quantum trajectory obtained by monitoring with unit efficiency exhibits enhanced
quantum chaos relative to the average dynamics and to
unitary evolution without measurements. Our results hold for systems across
symmetry classes and for other diagnostics of
quantum chaos, such as out-of-time-order correlators and Liouvillian spectral statistics.
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Strongly Correlated Electrons
Non-Hermitian free-fermion critical systems and logarithmic conformal field theory
Iao-Fai Io, Fu-Hsiang Huang and Chang-Tse Hsieh
Conformal invariance often accompanies criticality in Hermitian systems. However, its fate in non-Hermitian settings is less clear, especially near exceptional points where the
Hamiltonian becomes non-diagonalizable. Here we investigate whether a 1+1-dimensional gapless non-Hermitian system can admit a conformal description, focusing on a PT-symmetric free-
fermion field theory. Working in the biorthogonal formalism, we identify the conformal structure of this theory by constructing a traceless energy-momentum tensor whose
Fourier modes generate a Virasoro
algebra with central charge $c=-2$. This yields a non-Hermitian, biorthogonal realization of a logarithmic conformal field theory, in which correlation functions exhibit logarithmic scaling and the spectrum forms Virasoro staggered modules that are characterized by universal indecomposability parameters. We further present a microscopic construction and show how the same conformal data (with finite-size corrections) can be extracted from the
lattice model at exceptional-point criticality, thereby supporting the field-theory prediction.
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Disordered Systems and Neural Networks
Quantum criticality at strong randomness: a lesson from anomaly
Yasamin Panahi, Subhayan Sahu, Naren Manjunath et al. (+1 more)
Quantum criticality in the presence of strong quenched randomness remains a challenging topic in modern condensed matter theory. We show that the
topology and anomaly associated with average
symmetry can be used to predict certain nontrivial universal properties. Our focus is on systems subject to average Lieb–Schultz–Mattis constraints, where
lattice translation
symmetry is preserved only on average, while on-site
symmetries remain exact. We argue that in the absence of spontaneous
symmetry breaking and intrinsic topological order, the system must exhibit critical correlations of local operators in two distinct ways: (i) for some operator $O_e$ charged under exact
symmetries, the first absolute moment correlation $\overline{|\langle O_e(x)O^{\dagger}_e(y)\rangle|}$ decays slowly; and (ii) for some operator $O_a$ charged under average
symmetries, the first-moment correlation $\overline{\langle O_a(x)O^{\dagger}_a(y)\rangle}$ decays slowly. We verify these predictions in a few examples: the random-singlet Heisenberg
spin chain in one dimension, and the disordered free-
fermion critical states in
symmetry class BDI in one and two dimensions. Surprisingly, even for these well-studied systems, our anomaly-based argument reveals critical correlations overlooked in previous literature. We also discuss the experimental feasibility of measuring these critical correlations.
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All authors Yasamin Panahi, Subhayan Sahu, Naren Manjunath, Chong Wang
Mesoscale and Nanoscale Physics
Nonreciprocal perfect Coulomb drag in electron-hole bilayers: coherent exciton superflow as a diode
Jun-Xiao Hui and Qing-Dong Jiang
Distinguishing an
exciton condensate from an excitonic gas or
insulator remains a fundamental challenge, as both phases feature bound electron-hole pairs but differ only by the emergence of macroscopic phase coherence. Here, we theoretically propose that a
spin-orbit-coupled
bilayer system can host a finite-momentum
exciton condensate exhibiting a nonreciprocal perfect Coulomb drag – the coherent-
exciton diode effect. This effect arises from the simultaneous breaking of inversion and time-reversal
symmetries in the
exciton condensate, resulting in direction-dependent critical counterflow currents. The resulting nonreciprocal perfect Coulomb drag provides a clear and unambiguous transport signature of phase-coherent
exciton condensation, offering a powerful and experimentally accessible approach to identify, probe, and control
exciton superfluidity in solid-state platforms.
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Mesoscale and Nanoscale Physics
Topologically Protected Spatially Localized Modes: An Easy Experimental Realization of the Su–Schrieffer–Heeger Model
L. Q. English, A. Halchenko and F. Palmero
In this paper, we review the basic concepts of topologically protected edge modes using the Su Schrieffer Heeger (SSH) model, originally introduced to describe electrical conductivity in doped polyacetylene
polymer chains. We then propose an electrical
circuit that emulates this model, provide its mathematical description, and present its experimental realization. The experimental setup is described in detail, with explanations designed to be broadly accessible without much prior familiarity with
lattice theory, thus offering an introduction to this active area of research. Both theoretical predictions and experimental results confirm the presence of these modes, showing very good overall agreement. Using this concrete experimental system as a motivating example, we highlight the key aspects of topological protection.
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Superconductivity
Visualizing the Odd-parity Superconducting Order Parameter and its Quasiparticle Surface Band in UTe2
Shuqiu Wang and J.C. Séamus Davis
A distinctive identifier of nodal intrinsic topological superconductivity (ITS) would the appearance of an Andreev bound state on
crystal surfaces parallel to the nodal axis, in the form of a topological quasiparticle surface band (QSB) appearing only for $T < T_C$. Moreover, theory shows that specific QSB characteristics observable in tunneling to an s-wave
superconductor can distinguish between
chiral and non-
chiral ITS order parameter $\Delta_k$. To search for such phenomena in $\text{UTe}_2$, s-wave superconductive scan-tip scanning tunneling microscopy (STM) imaging was employed. It reveals an intense zero-energy Andreev conductance maximum at the $\text{UTe}_2$ (0-11)
crystal termination. Development of the zero-energy Andreev conductance peak into two finite-energy particle-hole symmetric conductance maxima as the tunnel barrier is reduced, then signifies that $\text{UTe}_2$ superconductivity is non-
chiral. Quasiparticle interference imaging (QPI) for an ITS material should be dominated by the QSB for energies within the superconductive energy gap $|E| \le \Delta$, so that bulk $\Delta(k)$ characteristics of the ITS can only be detected excursively. Again using a superconducting scan-tip, the in-gap quasiparticle interference patterns of the QSB of $\text{UTe}_2$ were visualized. Specifically, a band of Bogoliubov quasiparticles appears as a characteristic sextet $q_i$ :$i = 1-6$ of interference wavevectors showing that QSB dispersions $k(E)$ occur only for energies $|E| \le \Delta_{max}$ and only within the range of
Fermi momenta projected onto the (0-11)
crystal surface. In combination, these phenomena are consistent with a bulk $\Delta(k)$ exhibiting
spin triplet, time-reversal conserving, odd-parity, a-axis nodal, $B_{3u}$
symmetry in $\text{UTe}_2$.
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Strongly Correlated Electrons
Orbital Magnetization of Interacting Electrons
Xi Chen and Zhi-Da Song
We derive an exact expression for the orbital magnetization of electrons with short-range interactions (such as density-density interactions) in terms of exact zero-frequency response functions of the zero-field system. The result applies to weakly and strongly correlated electrons at zero and finite temperature, provided that the local grand potential density only depends on local thermodynamic parameters. We
benchmark the formula for non-interacting and weakly-coupled electrons. To zeroth and first orders in the interaction strength, it agrees with the modern theory of orbital magnetization and its recent generalization to self-consistent Hartree-Fock bands. Our work provides an exact framework of interacting orbital magnetization beyond mean-field treatments, and paves the way for quantitative studies of strongly correlated electrons in external
magnetic fields.
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Mesoscale and Nanoscale Physics
Frequency Stability of Graphene Nonlinear Parametric Oscillator
Enise Kartal, Oriel Shoshani, Elena Botnaru et al. (+3 more)
High-frequency stability is crucial for the performance of
graphene resonators in sensing and timekeeping applications. However, the extreme miniaturization and high mechanical compliance that make
graphene attractive also render it highly susceptible to nonlinearities, degrading frequency stability. Here, we demonstrate that
graphene parametric oscillators provide an alternative nonlinear operating regime, where short-term frequency stability can be enhanced despite strong nonlinearity. By operating
graphene resonators in a phase-locked loop (PLL), we experimentally demonstrate that parametric oscillations in the post-bifurcation regime achieve lower Allan deviation at fast integration times than Duffing oscillations at identical amplitudes. This improvement originates from strong nonlinear damping inherent to parametric oscillators, which suppresses amplitude-to-frequency noise conversion at large amplitudes. A minimal theoretical model captures observed phase
diffusion and identifies nonlinear damping as the dominant mechanism governing phase noise reduction. These results highlight the role of nonlinear dissipation in enabling precision sensing beyond conventional limits of
graphene oscillators.
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All authors Enise Kartal, Oriel Shoshani, Elena Botnaru, Alberto Martín-Pérez, Tomás Manzaneque, Farbod Alijani
Materials Science · Cross-listed from physics.optics
Numerically optimized FROG results for the study of red-shifted spectra in multi-frequency Raman generation
Sakthi Priya Amirtharaj, Zujun Xu, Donna Strickland et al. (+7 more)
When multifrequency Raman scattering is driven in the transient regime by two chirped pump pulses, the resulting anti-Stokes orders exhibit asymmetric spectral broadening toward lower frequencies, leading to a characteristic double-peaked structure in each order. In this Letter, frequency-resolved optical gating (FROG) is used to investigate the spectral
evolution of the first anti-Stokes Raman component. To interpret the observed features, we introduce a double-pulse interference model and employ an adaptive learning-based reconstruction
algorithm using the Adam optimizer to retrieve the temporal field
evolution. The simulation results show good agreement with the experimental measurements. Our analysis indicates that the observed red-shifted spectral component originates from linear Raman processes within the two-
photon dressed-state framework.
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All authors Sakthi Priya Amirtharaj, Zujun Xu, Donna Strickland, Borun Chowdhury, Sagnik Acharya, Priyam Samantray, Anil Prabhakar, Kisor Kumar Sahu, Franz Bamer, S. Swayamjyoti
Statistical Mechanics
Resolution of the Two-Dimensional Ferromagnetic Spin-3/2 Ising Model via Cluster Growth
J. Roberto Viana, Octavio D. Rodriguez Salmon, Minos A. Neto et al. (+2 more)
We propose a computational methodology based on a hierarchical cluster growth process to solve
spin-3/2 Ising models efficiently. The method circumvents the exponential complexity (\(4^{N}\)) of the canonical ensemble partition function by iteratively constructing finite
magnetic clusters of size \(N_g\), where the effective
spin state of a site in generation \(g+1\) is determined by the local magnetization of a cluster from generation \(g\). This approach, which shares conceptual ground with effective field theories, allows the study of systems of effectively very large size \(N = N_0 (N_g)^{g}\). We apply the formalism to the
ferromagnetic spin-3/2 Ising model on a honeycomb
lattice, modeling the monolayer CrI$_3$, a prototypical two-dimensional Ising magnet. The model, calibrated using the experimental transition temperature (\(T_{c} \simeq 45\) K), successfully reproduces key experimental features: the temperature dependence of the magnetization \(m(T)\), including its inflection point, and the broadened peak in the specific heat \(c_v(T)\). We also compute the
entropy \(s(T)\), finding a finite residual value at low temperatures consistent with the system's double degeneracy. Our results demonstrate that this hierarchical cluster method provides a quantitatively accurate and computationally efficient framework for studying complex
magnetic systems.
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All authors J. Roberto Viana, Octavio D. Rodriguez Salmon, Minos A. Neto, Griffith Mendonça, F. Dinóla Neto
Statistical Mechanics
Renewal theory for a run-and-tumble particle with stochastic resetting and a sticky boundary
Paul C Bressloff and Samantha Linn
We consider a run-and-tumble particle (RTP) with
stochastic resetting confined to the half line $[0,\infty)$ with a sticky boundary at $x=0$. In the bulk the RTP tumbles at a constant rate $\alpha>0$ between velocity states $\pm v$ with $v>0$ and randomly resets to its initial position and orientation $(x_0,k_0)\in(\mathbb{R}^+,\pm)$. When the RTP reaches the target at $x=0$ it attaches to the boundary for a random waiting time before either detaching and continuing to navigate the bulk domain or (permanently) entering the target. These events are the analogs of adsorption, desorption, and absorption of a particle by a partially reactive surface in physical chemistry. We use renewal theory to characterize the particle trajectory in terms of successive binding events under two distinct desorption protocols: via resetting to $(x_0,k_0)$ and via continuous movement from $x=0$ with velocity $+v$. First we derive the nonequilibrum stationary state (NESS) in the case of no absorption and characterize the accumulation at the boundary. Second, we compute the mean first passage time (MFPT) statistics. In addition to observing the usual unimodal dependence of the MFPT on bulk resetting, both the NESS and MFPT strongly depend on the initial orientation $k_0$ and the desorption protocol. For instance, if the initial orientation is toward the boundary, we find that the desorption-induced resetting protocol can reduce the MFPT more effectively than the non-resetting desorption protocol. We also show how matching the desorption kinetics with the bulk resetting or tumbling rate introduces a trade-off between minimizing the adsorption and absorption times. In this setting we find that the desorption protocol which minimizes the absorption MFPT for a given set of parameters is almost always the opposite of that favored when desorption and bulk kinetics are not the same.
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Mesoscale and Nanoscale Physics
Dynamic nuclear spin polarization in the fractional quantum Hall effect spin transitions
Haotian Zhou and Yuli Lyanda-Geller
Experiments suggest that
nuclear spins play a significant role in the
quantum Hall effect (QHE) near integer and fractional QHE
spin transitions, but many of these phenomena still remain to be understood. Here we study theoretically the dynamic
nuclear polarization (DNP) in the two-dimensional electron
liquid near a
quantum point contact (QPC) or a domain wall between
spin polarized and unpolarized phases induced by electrostatic gating in the fractional QHE at a filling factor 2/3 and analyze the dependence of the
spin transition on temperature and the magnitude of the flowing current. We demonstrate that nearly all
nuclear spins in the QPC or in the domain wall can be polarized by the electric current. The Overhauser effective
magnetic field from the DNP can be strong enough to induce (or modify) a phase transition between polarized and unpolarized phases. This changes the gate voltages and
magnetic fields required for the
spin transitions, and leads to the reconstruction of the boundary between two phases and a domain wall and a current path displacement. The spread of
nuclear spin polarization and the domain wall displacement are strongly asymmetric with respect to the direction of the current flow. Equilibration due to hyperfine interactions and its role on the
nuclear spin polarization, domain wall displacements and
spin transitions is studied. Back and forth oscillatory transitions between polarized and unpolarized phases near a source contact are discussed. Hyperfine interactions of
nuclear spins provide a route for observation and control of the parafermion zero modes that can be induced when the domain wall between the polarized and unpolarized regions is placed in the proximity of a
superconductor
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Strongly Correlated Electrons
Nonlinear light cone spreading of correlations in a triangular quantum magnet: a hard quantum simulation target
A. Scheie, J. Willsher, E. A. Ghioldi et al. (+6 more)
Dynamical correlations of
quantum many-body systems are typically analyzed in the momentum space and frequency basis. However,
quantum simulators operate more naturally in real space, real time settings. Here we analyze the real-space time-dependent van Hove
spin correlations $G(r,t)$ of the 2D triangular antiferromagnet KYbSe$_2$ as obtained from high-resolution
Fourier-transformed
neutron spectroscopy. We compare this to $G(r,t)$ from five theoretical simulations of the well-established
spin Hamiltonian. Our analysis reveals non-linear sub-ballistic low-temperature transport in KYbSe$_2$ which none of the current state-of-the-art numerical or field-theoretical methods reproduce. Our observation signals an emergent collective hydrodynamics, perhaps associated with the
quantum critical phase of a
quantum spin liquid, and provides an ideal
benchmark for future
quantum simulations.
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All authors A. Scheie, J. Willsher, E. A. Ghioldi, Kevin Wang, P. Laurell, J. E. Moore, C. D. Batista, J. Knolle, D. Alan Tennant
Strongly Correlated Electrons
Electromagnetic Response of a Half-Filled Chern Band near Topological Criticality
Xinlei Yue, Fabian Pichler, Michael Knap et al. (+1 more)
We evaluate electromagnetic-response observables in a half-filled Chern band, across a topological phase transition between a composite
Fermi liquid (CFL) and a
Fermi liquid (FL) phase. While a sharp gapped
plasma mode exists deep in the CFL phase, we demonstrate that it is damped near the proposed continuous phase transition between CFL and FL. This plasmon-damping phenomenon originates from emergent gauge fields and a Dirac-
fermion-like spectrum. Similar features also occur in other continuous deconfined topological phase transitions, such as the Laughlin to superfluid transition in a bosonic system. In particular, this damping behavior extends over a finite range across the phase boundary, and, hence, we expect it to persist even when the transition is weakly first-order. Furthermore, we analyze the characteristic conductivity behavior, such as the Drude weight, the wavevector-dependent conductivity, the
chiral mirror effect, and thermodynamic behavior, including compressibility and
magnetic susceptibility across these topological phase transitions.
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All authors Xinlei Yue, Fabian Pichler, Michael Knap, Ady Stern
Materials Science
Unbounded Systematic Error in Thin Film Conductivity Measurements
Yongyi Gao, Hio-Ieng Un, Yuxuan Huang et al. (+2 more)
Electrical conductivity is the most fundamental charge transport parameter, and measurements of conductivity are a basic part of materials characterization for nearly all conducting materials. In thin films, conductivity is often measured in four bar architectures in which the current source and voltage measurement are spatially separated to eliminate systematic error due to contact resistance. Despite the apparent simplicity of these measurements, we demonstrate here that the four bar architecture is subject to significant systematic error arising from the finite conductivity of the metal electrodes. Remarkably, these systematic errors can in some cases become unbounded, producing arbitrarily high measured conductivity at modest true film conductivities, within the range relevant to emerging thin film thermoelectric materials such as conducting
polymers. These unbounded errors, which can occur even in properly conducted four-point measurements of patterned films, likely explain literature reports of extremely high conductivities in conducting
polymers, and can lead to anomalous scaling in temperature dependent studies, potentially leading to incorrect interpretation of the relevant charge transport mechanism. We characterize the device
geometric factors that control these errors, which stand partially at odds with those required for accurate Seebeck coefficient measurements. Our analyses allow us to identify device architectures that provide small systematic errors for conductivity and Seebeck coefficient while still providing a low measurement resistance, critical to reducing noise in thermal voltage measurements. These findings provide important guidelines for accurate measurements in the growing field of thin-film thermoelectric materials.
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All authors Yongyi Gao, Hio-Ieng Un, Yuxuan Huang, Henning Sirringhaus, Ian E. Jacobs
Materials Science
Mechanics of incompatible asymmetric grain boundary migration
Brandon Runnels
Grain boundary (GB) migration governs microstructure
evolution and can mediate plastic deformation through sliding or shear coupling. Numerous experimental and numerical studies have reported a wide range of behaviors associated with boundary migration, such as defect emission or mode switching. Notably, recent studies have reported directionally asymmetric migration rates under symmetric loading, attributing this behavior to intrinsically asymmetric mobility; however, a mechanistic mesoscale explanation for this behavior remains lacking. In this work, we introduce a constitutive flow rule for grain-boundary eigendeformation within a multiphase-field framework, in which interfacial shear evolves in response to its mechanically conjugate driving force through the phase field Allen-Cahn equations. The formulation systematically employs regularized grain boundary shear kinematics informed by crystallography, and enables elastic compatibility to modulate boundary motion. Migration thresholds, residual back-stress, and apparent directional asymmetry appear naturally as emergent mechanical behavior. Simulations of symmetric and asymmetric tilt grain boundaries under mechanical, synthetic, and
curvature-driven loading reveal persistent defect-like residuals following incompatible migration, transitions from planar motion to lamination at large inclinations, and even "ratcheting" behavior. These results provide a mechanically transparent explanation for behaviors such as effective mobility asymmetry and establish elastic compatibility as a constitutive mechanism in mesoscale models of boundary-mediated plasticity.
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Strongly Correlated Electrons
Reexamining the strange metal charge response with transmission inelastic electron scattering
Niels de Vries, Eric Hoglund, Dipanjan Chaudhuri et al. (+8 more)
The strange metal remains one of the great unsolved problems for 21st century science. Since the early development of the marginal
Fermi liquid phenomenology, it has been clear that progress requires detailed knowledge of the momentum- and frequency-dependent charge susceptibility, $\chi(\mathbf{q},\omega)$, particularly at large momenta. Electron energy-loss spectroscopy (EELS), performed in either reflection or transmission geometry, provides the most direct probe of $\chi(\mathbf{q},\omega)$. However, measurements over the past four decades have yielded conflicting results, with some studies reporting a dispersing RPA-like plasmon and others observing a strongly overdamped, incoherent response. Here we report a transmission EELS study of Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ (Bi-2212) that simultaneously achieves high energy resolution ($\Delta E \approx 30$ meV) and high momentum resolution ($\Delta q \approx 0.01$ Å$^{-1}$). To address issues of reproducibility, measurements were repeated ten times on five different Bi-2212 flakes, benchmarked against aluminum, a well-characterized
Fermi liquid, and quantitatively compared with prior studies spanning four decades. At momenta $q < 0.15$ Å$^{-1}$, we observe a highly damped plasmon whose linewidth is comparable to its energy. At larger momenta, $q > 0.15$ Å$^{-1}$, this excitation does not disperse but instead evolves into an incoherent continuum, with no evidence for the RPA-like dispersion reported in some earlier works. Comparison with recent RIXS measurements on Bi-based cuprates supports the view that Bi-2212 is an incoherent metal with strongly damped charge excitations.
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All authors Niels de Vries, Eric Hoglund, Dipanjan Chaudhuri, Sang hyun Bae, Jin Chen, Xuefei Guo, David Balut, Genda Gu, Pinshane Huang, Jordan Hachtel, Peter Abbamonte
Strongly Correlated Electrons
Critical behavior and evidence of dimensional crossover in quasi-two-dimensional Li$_2$FeSiO$_4$
Waldemar Hergett, Kevin Ackermann, Erik Walendy et al. (+5 more)
We report thermal expansion and heat capacity studies on Li$_2$FeSiO$_4$ single
crystals which enable us to investigate the critical behavior in the magnetically quasi-two-dimensional (2D) material. Pronounced $\lambda$-shaped anomalies at the
magnetic ordering temperature $T_{\rm N}$ imply significant magneto-elastic coupling. Our analysis of both the thermal expansion and the specific heat data implies the crossover from 2D Ising-like behavior for $|(T-T_{\rm N})/T_{\rm N}|>0.3$ to 3D Ising behavior \rev{below $\simeq 1.3\times T_{\rm N}$. The 2D-like behavior is further supported by density functional calculations which show minimal dispersion perpendicular to the crystallographic $ac$ planes of the layered structure, thereby indicating the 2D nature of magnetism at higher temperatures.} Our results extend the available model materials of quasi-2D magnetism to a high-
spin $S=2$ system with tetrahedrally coordinated Fe$^{2+}$-ions, thereby illustrating how
magnetic order evolves in a 2D Ising-like system with orbital degrees of freedom.
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All authors Waldemar Hergett, Kevin Ackermann, Erik Walendy, Sven Spachmann, Martin Jonak, Mahmoud Abdel-Hafiez, Maurits W. Haverkort, R. Klingeler
Strongly Correlated Electrons
Non-Perturbative SDiff Covariance of Fractional Quantum Hall Excitations
Hisham Sati and Urs Schreiber
Collective excitations of Fractional
Quantum Hall (FQH)
liquids at long wavelengths are thought to be of a generally covariant
geometric nature, governed by area-preserving diffeomorphisms ($\mathrm{SDiff}$). But current analyses rely solely on the corresponding perturbative $w_\infty$ Lie
algebra. We argue this is insufficient: We identify a non-perturbative construction of the effective Maxwell-Chern-Simons
quantum field theory which carries
unitary $\mathrm{SDiff}$ equivariance. But this turns out to be non-differentiable, suggesting underappreciated subtleties when the usual
Hilbert space truncation is removed.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Electrically reconfigurable dipolar polaritons with highly tunable nonlinearity in a homobilayer microcavity
Baixu Xiang, Yubin Wang, Guihan Wen et al. (+9 more)
Active control over optical nonlinearity in solid-state systems is central to unlocking exotic many-body phenomena and photonic devices. While
exciton-polaritons in transition metal dichalcogenides (TMDs) offer a promising platform, their practical utility is impeded by fixed interactions and a trade-off between nonlinearity and oscillator strength. Here, we report electrically tunable dipolar polaritons in a dual-gated
bilayer MoS2 microcavity, demonstrating in situ reshaping of the dispersion and modulation of the light-matter coupling strength via the
quantum-confined Stark effect. Crucially, this electrical control yields a seven-fold enhancement of the polariton-polariton interaction strength. This enhancement arises from the combined tuning of the effective
exciton-
exciton interaction and the excitonic Hopfield coefficient. In addition, electrostatic doping provides an independent knob to continuously drive a strong-to-weak coupling crossover. Our findings establish dual-gated TMD homobilayer as a versatile platform for on-chip, dynamically reconfigurable nonlinear light-matter physics.
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All authors Baixu Xiang, Yubin Wang, Guihan Wen, Yitong Li, Hao Wen, Zengde She, Haiyun Liu, Kenji Watanabe, Takashi Taniguchi, Timothy C. H. Liew, Zhiyuan Sun, Qihua Xiong
Materials Science
Energy-Transfer-Enhanced Emission and Quantum Sensing of VB- Defects in hBN-PbI2 Heterostructures
Eveline Mayner, Yaroslav Zhumagulov, Cristian de Giorgio et al. (+6 more)
Spin defects in two-dimensional materials hold significant potential for
quantum information technologies and sensing applications. The negatively charged boron vacancy (VB-) in hexagonal boron nitride (hBN) has attracted considerable
attention as a
quantum sensor due to its demonstrated sensitivity to temperature,
magnetic fields, and pressure.1 However, its applications have thus far been limited by inherently dim photoluminescence (PL). By fabricating a van der Waals
heterostructure with a sensitizing donor layer, lead iodide (PbI2), we effectively enhance the PL intensity from the VB- by 5-45x, while maintaining compatibility with other
heterostructures and vdW optoelectronic platforms. The type-I band
alignment at the heterojunction enables efficient
exciton migration while suppressing back-electron transfer, and the strong spectral overlap between the PbI2 emission and defect absorption supports efficient fluorescence resonance energy transfer. Ab initio density functional theory (DFT) predicts a
photon-ratcheting mechanism that boosts absorption and emission while maintaining
magnetic resonance (ODMR) contrast through minimal hybridization. Experimentally, the
heterostructure exhibits enhanced continuous-wave ODMR sensitivity and functions as a precise probe of external
magnetic fields. This work establishes a proof-of-concept for amplifying weak defect signals in nanomaterials, highlighting a new strategy for engineering their optical and
magnetic responses.
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All authors Eveline Mayner, Yaroslav Zhumagulov, Cristian de Giorgio, Feihong Chu, Prabhu Swain, Georg Fantner, Andras Kis, Oleg Yazyev, Aleksandra Radenovic
Superconductivity
Long-range phase coherence and phase patterns in hybrid Josephson junction arrays
Xi Wang, Asbjørn C. C. Drachmann, Candice Thomas et al. (+5 more)
The coherence of superconductivity and its suppression near a
quantum phase transition is governed by the interplay between local pairing and macroscopic phase coherence. Using scanning SQUID, we image the local susceptibility in a hybrid Josephson junction array. On a square
lattice of narrow islands, we simultaneously access both the amplitude and spatial phase structure of sensitive superconducting states. We observe periodic phase patterns at commensurate
magnetic fillings. At zero field the long-range phase coherence is strongest. At a finite field, smaller than one percent of flux
quantum per unit
cell, the system fragments into large regions of constant superconducting phase, as a function of the applied field. Our results provide the first direct measurement of long-range phase coherence in a Josephson junction array.
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All authors Xi Wang, Asbjørn C. C. Drachmann, Candice Thomas, Michael J. Manfra, Nandini Trivedi, Charles M. Marcus, Saulius Vaitiekėnas, Beena Kalisky
Quantum Gases
Observing weakly broken conservation laws in a dipolar Rydberg quantum spin chain
Cheng Chen, Luca Capizzi, Alice Marché et al. (+6 more)
Integrable
quantum many-body systems host families of extensive conservation laws, some of which are fragile: even infinitesimal perturbations can qualitatively alter their dynamical constraints. Here we show that this fragility leaves a clear experimental fingerprint in a one-dimensional
quantum spin chain of as few as 14 Rydberg atoms. Weak integrability breaking from interatomic dipolar couplings is directly detectable within experimentally accessible times in the dynamics of non-local observables. In particular, magnetization fluctuations are highly sensitive to the breaking of fragile conservation laws and exhibit anomalous growth, which we observe experimentally; similar signatures appear in a semilocal string observable. Numerical simulations on substantially longer chains and a simplified classical
stochastic model reproduce those features. We establish non-local observables as a sensitive probe of fragile conservation laws in
quantum spin chains and Rydberg-atom arrays as a platform to test perturbative descriptions of
quantum many-body dynamics with weak integrability breaking.
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All authors Cheng Chen, Luca Capizzi, Alice Marché, Guillaume Bornet, Gabriel Emperauger, Thierry Lahaye, Antoine Browaeys, Maurizio Fagotti, Leonardo Mazza
Materials Science
Symmetry-restricted energy landscapes as a benchmark for machine learned interatomic potentials
Abhijith S Parackal, Rickard Armiento and Florian Trybel
Machine learned interatomic potentials (MLIPs) are becoming a standard method for DFT-level accurate molecular dynamics simulation and large-scale studies of
crystal energetics. Increasingly popular are universal pre-trained potentials, also called foundation models, based one, e.g. the MACE, CHGNet, M3GNet, ORB, and SevenNet architectures. While there are many
benchmarks of these models using validation errors and materials discovery tasks, their fidelity in reproducing the detailed features of potential energy surfaces (PES) is not understood to the same degree. We evaluate the accuracy of these potentials by systematically probing their predicted energy landscapes. Two-dimensional slices of the potential energy surface are constructed where the atomic positions are varied along selected Wyckoff degrees of freedom within a fixed
crystal symmetry. This approach enables a direct, visual comparison of the interatomic potentials and DFT-calculated surfaces which reveals potential artifacts e.g., arising from unique local environments. Our analysis highlights the strengths and limitations of different potentials in capturing local minima, saddle points, and overall PES
topology, offering insights into the physical accuracy of current pre-trained IAPs and providing
benchmarks for future model development.
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Materials Science
Triplet Envelope Functions for increasing machine learning interatomic potential efficiency and stability
Emil Annevelink and Varun Shankar
Central to interatomic potential efficiency is the radial envelope function that enables linear scaling with computational cost by defining a local neighborhood of atoms. This has enabled MLIPs to revolutionize materials science over the past decade by providing DFT accuracy with linear scaling computational cost in molecular dynamics workflows. However, MLIPs still have a relatively high computational cost compared to empirical interatomic potentials, preventing them from transforming molecular dynamics workflows. A central issue is that MLIPs use relatively large cutoff radii, converging to 6A over the last few years. The large cutoffs prioritize accuracy of any material over efficiency in any particular region of phase space, capturing dispersion effects and low density materials at the expense of increased computational cost in higher density materials. Past work has aimed to address this with KNN graph sparsification, which, while significantly reducing cost, has the drawback of breaking energy conservation. In this work, we propose higher-order envelope functions that prune local atomic neighborhoods through physically inspired
geometric functions to provide the
memory and efficiency benefits of KNN graph sparsification while eliminating non-conservative energy dynamics. Through numerical experiments on solids and
liquids with 5-8A cutoffs, we show that triplet envelope functions complement radial envelope functions by doubling training and inference speed, tripling
memory efficiency, and increasing simulation stability while not impacting accuracy or data efficiency for the most common 6A cutoff. Moreover, experiments with 8A radial cutoffs show triplet envelope functions create a pathway to larger cutoff radii for efficiently and accurately modeling open structures with large interatomic distances, showing a promising new direction for engineering MLIP efficiency.
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Disordered Systems and Neural Networks
Interaction-induced moiré lattices: from mosaic mobility edges to many-body localization
Yan-Hao Yang, Zhihao Xu, Lei Ying et al. (+1 more)
We study localization driven solely by interparticle interactions in moiré
lattice systems without intrinsic disorder or externally imposed quasiperiodic potentials. We consider a one-dimensional
bilayer with incommensurate
lattice constants, described by a
spin-dependent
Fermi-Hubbard-type model with short-range interlayer interactions, where quasiperiodicity emerges only through interactions. Exact diagonalization shows that quenching hopping in one layer generates an interaction-induced mosaic potential with multiple mobility edges. When both layers are dynamical, increasing interlayer interactions drives transitions among ergodic, critical, and many-body localized regimes, with energy-dependent coexistence in certain parameter ranges. An exact mapping to a noninteracting single-particle model on a higher-dimensional structured graph provides a unified interpretation of these results and suggests an experimentally accessible route to interaction-induced moiré physics and localization.
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All authors Yan-Hao Yang, Zhihao Xu, Lei Ying, Qizhong Zhu