Superconductivity
Optical and magnetic signatures of drive-enhanced coherence in phase-disordered superconducting bilayers
Duilio De Santis, Sambuddha Chattopadhyay, Marios H. Michael et al. (+4 more)
Recent experiments demonstrating superconducting-like characteristics in materials above their
equilibrium transition temperatures following strong sub-picosecond optical excitation have stimulated theoretical interest in phase-disordered
superconductors subject to a periodically modulated superfluid stiffness. Previous analyses of the single-layer optical conductivity have shown that such a drive can enhance the low-frequency $1/\omega$ response, even when the period-averaged stiffness remains unchanged. We extend these studies to bilayer systems, such as the YBa$_2$Cu$_3$O$_{6+x}$ (YBCO) cuprate, by considering drives with different
symmetries. Specifically, we investigate a layer-symmetric drive, in which the two planes stiffen and soften simultaneously, and a layer-antisymmetric drive, in which one plane stiffens while the other softens. Both drives enhance correlations of the layer-averaged phase and generate comparable superconducting-like optical conductivities. Only the symmetric drive, however, strengthens relative-phase locking and the associated counterflow response to a
magnetic field parallel to the planes. Thus, an enhanced $1/\omega$ optical conductivity does not by itself imply enhanced
magnetic screening. In view of applications to driven YBCO, where superconducting-like in-plane optics and transient diamagnetism have both been reported, our result provides a
symmetry diagnostic: within a phase-synchronization mechanism, the experimentally active low-frequency stiffness modulation must contain a substantial layer-symmetric component.
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All authors Duilio De Santis, Sambuddha Chattopadhyay, Marios H. Michael, Andrea Cavalleri, Gil Refael, Patrick A. Lee, Eugene A. Demler
Strongly Correlated Electrons · Cross-listed from hep-th
Exact group invariant scar towers in two dimensional gauge theories
João Barata, Kiryl Pakrouski and Andrey V. Sadofyev
We construct exact many-body scar towers in two dimensional gauge theories with two flavors of massless fundamental
fermions. For oppositely charged
fermions, the scar subspace is generated by a gauge-neutral $\eta$-pairing operator, and admits a purely algebraic construction. Exact diagonalization methods reveal anomalously low
entanglement and long-range pair correlations in the scar states. Charge conjugation maps the $\eta$-tower to a vector-flavor polarization sector of the equal charge model, yielding an interpretation as a coherent flavor mode with Josephson-like phase dynamics. Finite
fermion masses mix the protected pair with an orthogonal channel and destroy the exact tower. The identified scar tower can be algebraically realized in a large family of
lattice field theories, revealing a universal character of these states. Our results provide an analytical construction of invariant scar subspaces in a gauge theory with a nontrivial continuum interpretation.
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Strongly Correlated Electrons · Cross-listed from hep-th
Single-Instance Observables in the Sachdev-Ye-Kitaev Model
Brian Swingle
We present a diagrammatic expansion for thermal expectation values of low-weight Majorana strings in a fixed realization of the $N$-
fermion Sachdev–Ye–Kitaev (SYK) model. At each order in the expansion, the observable is expressed as a finite sum of
polynomials in the couplings multiplied by temperature-dependent kernels built from the large-$N$ melonic propagator. At fixed $\beta J$, the expansion is organized in powers of $N^{-1/2}$, and each order can be efficiently evaluated with classical resources
polynomial in $N$. The expansion also extends to correlations at arbitrary imaginary times and sufficiently short real times. For the four-body SYK model, we show that the diagrammatic predictions give an excellent account of exact diagonalization results at sizes up to $N=24$. We also apply the method to the Maldacena–Qi (MQ) model formed from two identical copies of a fixed SYK realization. This enables the identification of a nearby SYK-like
Hamiltonian whose thermofield double state has higher fidelity with the Maldacena–Qi ground state than the thermofield double of the original SYK
Hamiltonian.
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Mesoscale and Nanoscale Physics
Anderson localization in topological metals
A.A. Burkov
We address the question of whether topological metals (TM) retain their nontrivial characteristics in the presence of disorder. While in the clean case, the issue is what protects the gaplessness of the spectrum, i.e. the band-touching nodes in TM, this question needs to be reformulated in the presence of disorder. The concept of gaplessness loses its sharp meaning in this case, since spectral gaps can be filled in by disorder-induced states. What is still meaningful is
entanglement: one may ask whether the long-range
entanglement of the clean gapless TM survives in the presence of disorder or, in other words, whether nontrivial
topology protects the TM from Anderson localization. We demonstrate that such a protection exists in the case of three-dimensional (3D) Weyl semimetals, but not in 2D and 3D (type-I) Dirac or 3D nodal line semimetals. We establish this by combining the idea of unquantized anomaly as the topological response of TM with the decorated domain wall construction, used previously to discuss average
symmetry-protected topological insulating phases.
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Strongly Correlated Electrons · Cross-listed from quant-ph
Large-scale quantum simulations of dissipative spin-1/2 Heisenberg chains
João C. Getelina, Andrew Cox, Muhammad Asaduzzaman et al. (+4 more)
A
quantum many-body system coupled to an environment relaxes to a nonequilibrium steady state that can sustain order with no
equilibrium counterpart. Computing such steady states is harder than closed-system dynamics as the density
matrix problem squares the
Hilbert-space dimension, and no free energy selects the steady state. The dissipative
spin-1/2 Heisenberg chain is a
benchmark example for nonequilibrium steady state physics; various methods have each calculated its phase diagram but do not agree, and a controlled determination at large system size has remained out of reach. Here we simulate the Lindblad dynamics of chains of up to 50 sites on the superconducting processor ibm_kingston – 100 simultaneously active
qubits at up to 1700 entangling-gate depths – realizing the dissipation via Stinespring dilation. The system's dissipative
evolution is a self-correcting mechanism that effectively erases errors, so hardware noise enters only as a weak competing dissipator. We measure static structure factors and resolve ferromagnetic, antiferromagnetic,
spin-density-wave, and paramagnetic steady states, mapping the phase diagram with 117
quantum hardware data points across the $J_x$–$J_y$ plane. We uncover a rich non-
equilibrium phase diagram of ordered phases with only remnants of the mean-field order, and where sharp transitions give way to the crossovers expected in one dimension. We also find the existence of an incipient (Trotter-induced)
spin density wave phase, highlighting the potential of controlled Trotterization as a tool to engineer various
magnetic phases in dissipative
spin systems. Our
quantum simulations largely settle the lingering uncertainty regarding the correct phase diagram of this
benchmark system. Moreover, they show that
quantum computers are now a feasible tool for addressing scientific questions involving dissipative
quantum systems.
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All authors João C. Getelina, Andrew Cox, Muhammad Asaduzzaman, Omar Alsheikh, Ryan S. Bennink, James K. Freericks, Alexander F. Kemper
Disordered Systems and Neural Networks · Cross-listed from quant-ph
Direct Observation of Dipolar-Driven Anisotropic Quantum Projection Noise in a Solid-State Spin Ensemble
Tasuku Ono, Weijie Wu, Haopu Yang et al. (+9 more)
The nitrogen-vacancy (NV) center in diamond is a prominent
quantum-sensing platform. Combining readout at the
quantum projection noise limit with strong dipolar interactions promises substantial gains in sensitivity. However, experimentally accessing this regime has remained a longstanding challenge. In this work, we demonstrate
quantum-projection-noise-resolved readout of a strongly-interacting, two-dimensional ensemble of NV centers. Our approach leverages repetitive readout via the NV's intrinsic $^{15}$N nuclear
memory at a moderate
magnetic field ($\sim 0.3$ T), improving the readout fidelities by nearly an order of magnitude. This enables us to directly resolve the
quantum projection noise of a coherent
spin state and to watch the ensemble's intrinsic dipolar interactions shear this noise into an anisotropic profile. Our results open the door to direct measurements of
spin squeezing and
entanglement-enhanced sensing in the solid state.
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All authors Tasuku Ono, Weijie Wu, Haopu Yang, Lillian B. Hughes Wyatt, Benjamin Brenner, Che Liu, Collin Fan, Chris R. Laumann, Jonathan N. Hallén, Emily J. Davis, Ania C. Bleszynski Jayich, Norman Y. Yao
Superconductivity
Topological superconductors and Majorana fermions based on $X$-wave magnets with $X=p,d,f,g,i $
Motohiko Ezawa
We study
superconductors coupled with $X$-wave magnets with $X=p,d,f,g,i$. They are essentially different between altermagnets with $X=d,g,i$ and odd-parity magnets $X=p,f$ due to the compatibility of the
spin-singlet formation of the $s$-wave
superconductor. The altermagnets and odd-parity magnets show rich superconducting phase diagrams depending on the strength of the
magnetic order, the chemical potential and the ratio of the on-site and nearest-neighbor interactions. Especially, we find that the altermagnetic order stabilizes the chiral ($p_{x}+ip_{y}$)-wave
superconductor, which is a class D topological
superconductor hosting Majorana chiral edge states. It is characterized by the Chern number. Especially, there emerge two chiral edge modes in the $i$-wave altermagnet, which are characterized by the Chern number 2. On the other hand, the $p$ ($f$)-wave odd-parity
magnetic order stabilizes the $p$ ($f$)-wave topological
superconductor, which is a class DIII topological
superconductor hosting Majorana flat bands. It is characterized by the winding number. Majorana flat bands are robust in the presence of the mixing with the $s$-wave superconductivity, which is inevitable for odd-parity magnets although the magnitude of the mixing is tiny.
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Mesoscale and Nanoscale Physics
Shot noise signatures of Majorana-assisted transport in an Aharonov-Bohm interferometer
Ignacio Román-Pérez, Juan Pablo Ramos-Andrade, Pedro Orellana et al. (+1 more)
In this work, we investigate the finite-bias charge current, shot noise, and Fano factor in an Aharonov-Bohm interferometer composed of two parallel
quantum dots, each side-coupled to a topological superconducting nanowire represented by an effective Kitaev chain hosting Majorana bound states at its ends. The transport properties are calculated using the nonequilibrium Green's function formalism within the equation-of-motion approach. Our results show that coupling to the Majorana bound states significantly modifies the interference pattern, producing distinctive signatures in the current, shot noise, and Fano factor. These signatures are particularly pronounced at the half-flux condition, where destructive interference suppresses the conventional transport background and enhances the visibility of Majorana-assisted transport. These findings demonstrate that finite-bias shot-noise spectroscopy provides a sensitive indirect probe of Majorana bound states in hybrid superconducting-nanowire interferometers.
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All authors Ignacio Román-Pérez, Juan Pablo Ramos-Andrade, Pedro Orellana, Luis Rosales
Strongly Correlated Electrons · Cross-listed from hep-lat
Continuous Hasenbusch transport towards gauge diffusion with fermions
Akio Tomiya
Incorporating dynamical
fermions is a central challenge for
diffusion samplers of
lattice gauge theories. We propose an analytic pseudofermion sampler based on continuous Hasenbusch transport as a component for gauge
diffusion. The construction uses shifted linear solves and a finite-path correction, requiring neither explicit
fermion determinant evaluation nor a learned pseudofermion model. We demonstrate the coupling in the two-flavour Schwinger model without neural networks, obtaining corrected physical observables compatible with independent references. We also show why accurate covariance transport can leave large weight fluctuations, tracing them to the backward transition density. This analysis leads to a correction based on the Wilson operator trace that reduces log-weight variance without changing the generated fields or increasing the number of Dirac operator applications. The predicted improvement is verified on previously unused gauge backgrounds. These results provide an analytic option for incorporating
fermions in gauge
diffusion and a guide to controlling its correction weights.
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Superconductivity
Stripe-Like Superconducting Enhancement and Coexisting Magnetic Texture in an Infinite Layer Nickelate
Ryan Laing, Dung Vu, Jacob Pfund et al. (+7 more)
Despite their promise as structural and electronic analogs to cuprates, nickelate thin films consistently exhibit broadened superconducting transitions in many experiments that remain poorly understood. Local measurements are ideal for revealing the presence of defects or competing phases, which may cause this transition broadening through a phase-separation. Here, we use scanning SQUID microscopy to investigate local superfluid density and
magnetic texture of optimally doped $\mathrm{Nd}_{1-x}\mathrm{Eu}_{x}\mathrm{NiO}_{2}$ (NENO) (x=0.25) grown via molecular beam epitaxy. We observed a weakly-
magnetic texture coexisting with superconductivity. Spatially resolved susceptibility imaging reveals a highly non-uniform superconducting state, characterized by a robust stripe-like enhancement pattern appearing near the phase transition. By resolving the mesoscopic landscape of electronic and
magnetic inhomogeneities, these findings suggest that a competing
magnetic phase is a primary contributor to the unusually broad superconducting transitions of these optimally doped NENO samples. Understanding the uncovered superconducting enhancement may provide a path to raising superconducting temperatures in these materials.
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All authors Ryan Laing, Dung Vu, Jacob Pfund, Wenzheng Wei, Frederick J. Walker, Haiyan Tan, Pavel Volkov, Menka Jain, Charles Ahn, Ilya Sochnikov
Strongly Correlated Electrons
Charge order before superconductivity in the doped kagome Dirac spin liquid
Yasir Iqbal
Doping a
quantum spin liquid is expected to produce a
superconductor. We show that for the Dirac
spin liquid on the kagome
lattice the doped charge orders first. The charge is carried by a chargon doublet whose two gauge components are degenerate on the square and triangular
lattices, and the kagome
lattice, as the line graph of the honeycomb
lattice, splits them. One component disperses and condenses in four valleys. The other has flat lowest bands and stays empty over a window in the bare mass whose width, $(\sqrt6-1)t$, follows from the band structure alone. Within that window, in the mean-field chargon theory constructed from the projective
symmetry group of the
spin liquid, the doped state forms charge and loop-current
crystals with the electromagnetic U(1) unbroken and no superconductivity. Pairing requires a gapped descendant of the
spin liquid as the parent and then takes the form of a pair-density wave, with no uniform $d+id$ channel at leading order and none at any order for the
crystals at the $M$ point. The predicted charge order is odd under the twofold rotation and has no cubic invariant, which distinguishes it from the charge order of the kagome metals.
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Strongly Correlated Electrons
Cecilie Glittum, Han Yan and Johannes Reuther
Spiral
spin liquids are
magnetic states whose classical ground-state
manifold consists of planar incommensurate
spin spirals with wave vectors lying on a continuous ring or surface in reciprocal space. The resulting subextensive degeneracy suppresses
magnetic long-range order and gives rise to
liquid-like behavior. Despite numerous material realizations and theoretical investigations, the structure of low-temperature
spin configurations of
spin-isotropic Heisenberg spiral
spin liquids has remained poorly understood. Here, we classify and characterize the classical topological defects supported by these systems. We uncover a rich family of
vortex types involving concerted windings of
spin directions, spiral-plane normals, and wave-vector orientations, yielding a $\mathbb{Z} \times \mathbb{Z}_2$ classification. Remarkably, the elementary defects are half-
vortices carrying fractional $2\pi$ windings in both
spin and momentum space and obey fusion rules resembling to those of Ising anyons. Large-scale classical simulations of a square-
lattice spiral
spin liquid reveal that these
vortices are dense in the spiral-
spin-
liquid regime, and bind tightly below an order-by-disorder phase transition, eventually fusing to
vacuum.
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Materials Science
An Open-Source Hardware and Software Toolkit to Enable Agentic RHEED-Guided Thin-Film Synthesis
Asraful Haque, Christopher M. Rouleau, Rama K. Vasudevan et al. (+1 more)
Reflection high-energy electron diffraction (RHEED) provides rich information about evolving surfaces during thin-film growth, but non-automated, operator-dependent
alignment and fragmented analysis workflows limit its potential in fully autonomous synthesis. Here, we present an open-source hardware and software toolkit that makes RHEED control and quantitative analysis accessible to operators and artificial intelligence (AI)
agents. Demonstrated on a pulsed
laser deposition system, the toolkit provides programmable electron-optics control, automated beam
alignment and rocking-curve acquisition, and a training-free method for crystallographic azimuthal
alignment. The auto RHEED application extracts structural and growth-related observables through shared graphical and programmatic interfaces, including a Model Context Protocol (MCP) server. An
agent-driven demonstration shows how natural-
language requests can guide the selection, configuration, and execution of quantitative analyses. An extensible adapter interface streamlines the incorporation of community-developed methods for AI analysis and RHEED simulation as they emerge, supported by Markdown implementation guides designed for AI coding
agents. These capabilities support complementary descriptions of surface
evolution through physical measurements and learned image representations while providing a practical route for incorporating new computational methods. Together, these tools reduce barriers to automated and agentic RHEED measurements and establish a foundation for future agentic control of thin-film synthesis guided by the evolving surface.
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All authors Asraful Haque, Christopher M. Rouleau, Rama K. Vasudevan, Sumner B. Harris
Soft Condensed Matter · Cross-listed from physics.bio-ph
Multiflagellarity facilitates bacterial upstream motility
Ran Tao, Nathaniel C. Esteves, Wanho Lee et al. (+8 more)
Upstream swimming drives bacterial spreading and surface colonization. Many pathogens encounter fluid flows as they infect the intestines, lungs, and urinary tract, so how bacteria use their flagella to counter these flows matters for disease and treatment. Yet how morphology and flagellar arrangement govern motility against flow remains unknown. Here, we investigate the biophysical determinants of rheotaxis by combining microfluidics, directed
evolution, genetics, holography, and hydrodynamics simulations. Using upstream swimming competitions, we find that peritrichous E. coli and S. enterica rapidly outcompete monotrichous P. aeruginosa and V. cholerae, accumulating upstream at densities up to five orders of magnitude higher, even though Vibrio swims three times as fast. Motility selection experiments show that rheotaxis increases with flagellar number and length, confirmed by overexpressing the master regulator flhD/C. Three-dimensional holography and single-
cell tracking reveal that multiflagellarity stabilizes surface residence and promotes the weathervane effect that reorients
cells upstream, a mechanism further supported by simulations that fully resolve flagellar arrangement and fluid-structure interactions. These results establish multiflagellarity as a key facilitator of upstream navigation, governed by near-wall residence and shear-driven reorientation rather than by swimming speed.
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All authors Ran Tao, Nathaniel C. Esteves, Wanho Lee, Lauren Altman, Liuni Chen, David Gao, Ling Li, Yongsam Kim, Jun Zhu, Sookkyung Lim, Arnold J. T. M. Mathijssen
Soft Condensed Matter
Dynamically triggered snap-through
Gregory Kozyreff, Lucie Domino, Basile Radisson et al. (+1 more)
Snap-through is a sudden and large mechanical deformation that is usually triggered by driving a control parameter beyond a bifurcation threshold. Here, we study a buckled strip that undergoes a saddle-node bifurcation as one of its clamps is rotated. We show experimentally, theoretically, and numerically that the effective snapping threshold can be markedly lowered by speeding up the rotation. For actuation times that are short but nevertheless longer than the fundamental flexural period, the strip is observed to remain close to the instantaneous quasi-static
equilibrium for most of the loading process. This allows us to derive an energetic criterion that accurately estimates a dynamic instability threshold well below the saddle-node bifurcation point. On the other hand, very near the bifurcation point, the
evolution of the quasi-static
equilibrium undergoes a
geometric boost, which entrains the general motion of the beam. As a result, a slower actuation of the clamp than predicted by the energy argument suffices to produce snap-through. A distinct scaling is derived in that limit, based on the aforementioned boost and critical slowing down of the least stable vibration mode of the beam. More broadly, our results show how finite-rate forcing can trigger snap-through before the quasi-static instability threshold is reached
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All authors Gregory Kozyreff, Lucie Domino, Basile Radisson, Hadrien Bense
Materials Science · Cross-listed from physics.chem-ph
Toward Predictive Hydride Bond Energetics with Neural-Network Wavefunctions
Aqsa Shaikh, Lubos Mitas, P. Ganesh et al. (+1 more)
Accurate prediction of transition-metal hydride (TM-H) bond dissociation energies (BDEs) remains challenging because of strong electron correlation, relativistic effects, and nuclear
quantum contributions. Here, we assess the performance of neural-network variational Monte Carlo (NN-VMC) based on the Psiformer ansatz for systems with increasing complexity (LiH, OH, TiH and NiH), and compare it against CCSDT(Q)/CBS as well as available theoretical and experimental data. Throughout this study, both NN-VMC and ab initio calculations employ a common ccECP
Hamiltonian to enable tractable and consistent comparisons. To reduce finite-training errors, we introduce complementary zero-variance and infinite-step extrapolation schemes. For LiH and OH systems, NN-VMC yields total energies that differ within sub-milli Hartree compared to CBS extrapolated ab initio results and the BDE differences remain under 2$\sigma$. In case of Ti and TiH, the variational NN-VMC energies at the end of training are already consistent with CCSD(T)/CBS, while post-training extrapolation systematically closes the gap towards the CCSDT(Q)/CBS results. In contrast, NiH provides a stringent test of wavefunction expressivity, where increasing the number of determinants in NN-wavefunction ansatz improves the recovered correlation energy. The comparison of NiH BDE reveals that, while the existing theoretical predictions cluster into distinct high and low BDE groups, the broad scatter in available experimental data prevents a definitive assessment of the most accurate theoretical approach. This work demonstrates that NN-VMC with ccECPs
Hamiltonian provides a competitive framework for quantitative prediction of main-group and early TM-H energetics, while identifying late TM-H as an important
benchmark for future developments in neural-network wavefunctions and electronic structure theory.
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All authors Aqsa Shaikh, Lubos Mitas, P. Ganesh, Jaron T. Krogel
Statistical Mechanics
Bridging Control, Inference, Transport, and Thermodynamics: From Theory to Applications in Learning
Emmy Blumenthal, Nikolas Claussen, Benjamin Eysenbach et al. (+4 more)
The last decade has seen the development of powerful methods for learning complex structure from high-dimensional data. These advances have brought to the foreground fundamental connections between subdisciplines of physics, applied mathematics, and machine learning. In this review, we bring together some of these ideas, often expressed in different
languages, to highlight a conceptual thread that links five distinct fields: control theory, optimal transport, probabilistic inference, non-
equilibrium thermodynamics, and machine learning. A common theme is the optimization of free-energy-like functionals under dynamical or statistical constraints. We offer a guided tour through this thread and present selected applications in reinforcement learning, variational inference, and generative modeling. The review does not assume prior familiarity with these topics, and begins with principles originating from physics.
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All authors Emmy Blumenthal, Nikolas Claussen, Benjamin Eysenbach, Catherine Ji, Gautam Reddy, Colin Scheibner, Benjamin Sorkin
Statistical Mechanics
Modulated structures in discrete approximations to a three-dimensional cholesteric model on a recursive lattice
William de Castilho
We study finite-state approximations to a chiral nematic
lattice model whose local directors are embedded in three-dimensional orientational space. The model analyzed here is formulated in terms of a rotated quadrupolar interaction, which provides a direct angular chirality parameter $\Delta$ and reduces to the usual planar chiral-nematic form for directors confined to the xy plane. On a rooted Cayley tree, the statistical problem is written as a nonlinear recursion for branch partition functions. In the infinite-coordination limit, with $rJ_Q$ fixed, the recursion becomes a softmax map for the state probabilities. We analyze Cartesian three-state, planar four-state, and non-planar four-state discretizations. The first supports ordered and period-two attractors, whereas the planar four-state discretization displays a sequence of commensurate and longer-period modulated attractors. Its disordered fixed point loses stability at $t=9/16$ through a complex-conjugate pair with phase $q=\pm 2\Delta$, so a modulated critical mode is selected for every nonzero chirality. The non-planar four-state set is intrinsically anisotropic and, when the stated model is reconstructed directly, supports prominent period-three as well as period-two and higher-period cycles. Because attractor stability does not by itself establish global thermodynamic stability, the diagrams reported here are interpreted as attractor/stability diagrams rather than
equilibrium phase diagrams.
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Materials Science
High-Temperature Hydrogen Sensors Based on Gallium Oxide Heterojunction Diodes
William A. Callahan, Kingsley Egbo, Anna Sacchi et al. (+5 more)
Long-term, high temperature operation of Ga2O3 devices is a crucial hurdle that must be overcome before widespread adoption of the technology can be achieved, but is largely absent from the overall body of work. Demonstrations up to this point show devices are either limited by material or dopant instability that leads to performance degradation with time. Herein, Ga2O3-based hydrogen sensors employing Pt Schottky and Cr2O3/Ga2O3 p-n diodes (Mg- and N-doped) were fabricated and evaluated for long-term stability at 600C for 800-1,800 hours, with cyclic exposure to N2 and low-concentration H2 (500-1,500 ppm). Transient current density (measured at -0.1 V) and periodic J-V characterization were used to track performance. Despite gradual declines in sensor signal and sensitivity, devices distinguished hydrogen concentrations throughout weeks of operation. Degradation was architecture-dependent: Cr2O3:Mg degraded gradually, consistent with known Mg migration; the Pt Schottky diode showed dramatic changes after 1,000 hours; and Cr2O3:N showed the lowest but most stable performance before failing at 800 hours. Thermionic emission and Lambert W-based modeling confirmed hydrogen exposure reduces interfacial barrier height via a
proton-induced dipole mechanism common to both diode types. TEM of aged Pt Schottky diodes revealed Pt grain growth and microvoid formation as key degradation mechanisms. TOF-SIMS confirmed nitrogen dopants remain confined to the Cr2O3:N layer, supporting N-doping as a stable, lower-performance alternative to Mg-doping
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All authors William A. Callahan, Kingsley Egbo, Anna Sacchi, Michelle Smeaton, Michael Walker, Anna Staerz, Ryan O'Hayre, Andriy Zakutayev
Mesoscale and Nanoscale Physics
Up/down-conversion of infrared light by few-layer graphene polytypes
Patrick Johansen Sarsfield, Takaaki V. Joya, Takuto Kawakami et al. (+2 more)
Optical nonlinearity of materials with broken inversion
symmetry enables two-
photon processes where an incoming pair of
photons can generate an up-converted
photon with the combined frequency, or a high-energy
photon can be split into a correlated pair of down-converted
photons. Here, we identify few-layer
graphene films that offer up/down-conversion capability in the infrared spectral range. For mixed stacking tetralayers (ABCB), which are non-centrosymmetric 2D
crystals, we find highly efficient nearly resonant up/down-conversion of [$\omega_1,\omega_2$]
photon pairs into/from a
photon with $0.7$eV$<\Omega=\omega_1+\omega_2<1.1$eV. We also note that a pronounced second-order nonlinearity in the spectral range of $0.7$eV$<\Omega<0.9$eV can be promoted in rhombohedral tri- and tetralayers by asymmetrical encapsulation. Potentially, for fibers coated with few-layer
graphene, this opens the door for “in fiber" production of
photon pairs with correlated polarizations.
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All authors Patrick Johansen Sarsfield, Takaaki V. Joya, Takuto Kawakami, Mikito Koshino, Vladimir Falko
Strongly Correlated Electrons
Chiral Antiferromagnetism from Momentum-Space Resonance in a 2D Semiconductor
R. Okuma, T. Ikenobe, Y. Fujisawa et al. (+28 more)
Understanding the principles governing the emergence of chiral
quantum phases is a fundamental challenge, not only for uncovering new mechanisms of
quantum-state formation but also for realizing giant electronic responses and transport phenomena arising from chirality and
topology. While Fermi-surface instabilities in metals can stabilize complex ordered states through multiple competing scattering channels, their microscopic origin is often obscured by the complexity of the underlying electronic structure, limiting the development of general microscopic design principles. Here, we introduce a complementary strategy based on the simplicity of
semiconductor band extrema. Using the layered van der Waals
semiconductor GdGaI, whose low-energy electronic structure consists of simple electron and hole valleys, we discover the spontaneous emergence of an intertwined chiral triple-$q$ antiferromagnetic state accompanied by a cooperative reconstruction of the electron-hole band edges, beyond the conventional expectation of a single-$q$ ground state. This collective reconstruction generates substantial momentum-space Berry
curvature, giving rise to a pronounced spontaneous anomalous Hall effect despite the semiconducting character and negligible net magnetization. Remarkably, this chiral state is realized within an atomically well-defined ($\approx2a$), topologically nontrivial
magnetic texture, showing that such collective
quantum states can emerge at an exceptionally small length scale from a simple two-dimensional
magnetic semiconductor. More broadly, our results introduce a remarkably simple design concept for chiral
quantum matter: using simple
semiconductor band extrema as building blocks for resonance-like interplay in momentum space, providing a route to Berry
curvature, topological transport, and emergent
quantum phases.
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All authors R. Okuma, T. Ikenobe, Y. Fujisawa, K. Yamagami, H. C. H. Wu, T. Nakamura, Y. Ihara, H. Ishikawa, H. Suwa, H. Ishizuka, Y. Akagi, T. Kaneko, C. H. Hsu, Y. Obata, N. Tomoda, M. Dronova, K. Nagasawa, H. Saito, D. Ueta, H. Sagayama, J. Yamaura, M. Arita, K. Yogendra, S. Ideta, K. Kindo, T. Nakajima, S. J. Blundell, T. Kondo, K. Shimada, Y. Okamoto, Y. Okada
Soft Condensed Matter
Collective adaptation to time-dependent targets for active Brownian particles
Gerhard Jung and Eric Bertin
We consider a minimal model of active
agents which collectively learn to reach a target macroscopic state via a decentralized adaptation process.
Agents are modeled as active Brownian particles which randomly reorient to a given direction through tumbling events. An average target state is encoded into a reward function evaluated by each
agent.
Agents can tune one of the parameters of their microscopic dynamics, called `policy' (e.g., speed or reorientation direction), to optimize their reward function thanks to information exchange with neighboring
agents. We describe the
evolution of the policy distribution across the
agent population with a kinetic theory, under the assumption that the adaptation process is slow with respect to the physical dynamics. The adaptation process is illustrated on several learning protocols with either fixed or time-dependent target velocities. A characteristic learning time $\tau$ combining teaching and mutations emerges from the dynamics. For time-oscillating targets at angular frequency $\omega$, the collective dynamics oscillates in time, with an oscillation amplitude and phase shift determined by the product $\omega \tau$. An unlocking transition to a non-adaptable state is also observed for a rotating target velocity.
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Strongly Correlated Electrons
Hidden Magnetic Complexity Within a Simple van der Waals Ferromagnet Ce$_2$Te$_5$
Rajesh Tripathi, D. T. Adroja, C. Ritter et al. (+10 more)
Ce$_2$Te$_5$ is a layered $f$-electron van der Waals magnet in which reduced dimensionality and inequivalent Ce sites give rise to competing
magnetic interactions. We investigate its
magnetic ground state using
muon spin relaxation ($\mu$SR),
neutron powder diffraction (NPD), and inelastic
neutron scattering (INS). Zero-field $\mu$SR reveals an onset of static magnetism below $T_{\mathrm{C}} = 5.0(1)$~K, followed by an additional anomaly in the internal field at $T_{\mathrm{2}} = 2.3(2)$~K, consistent with features observed in bulk thermodynamic and transport measurements. In contrast, NPD data collected between $0.05-8$~K reveal a single long-range ordered
magnetic phase below $T_{\mathrm C}$, with the
magnetic Bragg intensities vanishing at $T_{\mathrm C}$ with no evidence for additional structural or
magnetic phase transitions down to base temperature. The ordered state is characterized by a commensurate propagation vector $\mathbf{k}=(0,0,0)$ and ferromagnetic
alignment of Ce moments along the crystallographic $b$ axis. Remarkably, only one of the two crystallographically distinct Ce sites carries an ordered moment of $\sim 0.85(3)~\mu_{\mathrm B}$ per Ce at 0.05~K. INS measurements establish the
crystal electric field (CEF) energy scale of Ce$^{3+}$, revealing low-lying excitations at 7.94 and 21.46~meV and a Kramers doublet ground state with strong single-ion anisotropy. These results demonstrate that Ce$_2$Te$_5$ undergoes a single
symmetry-breaking
magnetic transition, while additional low-temperature anomalies reflect subtle modifications of the ordered state driven by competing interactions and CEF effects.
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All authors Rajesh Tripathi, D. T. Adroja, C. Ritter, Leandro Liborio, Manuel dos Santos Dias, Leon Petit, D. Khalyavin, Yu Liu, T. Shiroka, M. Aouane, S. Langridge, S. Patil, Eric D. Bauer
Statistical Mechanics · Cross-listed from physics.soc-ph
Penalized Maximum Likelihood Inference of Core-Periphery Networks
Antonio Mosca and Piero Mazzarisi
Likelihood-based network models are often fitted under links' independence and low-order constraints, while empirical networks frequently exhibit systematic higher-order structures such as triangles and wedges, characterizing the observed clustering patterns. Real-world core-periphery networks such as the interbank
market or the air transportation system represent key examples, with cores displaying complex and nonlinear features. We formalize Penalized Likelihood with Structural Discrepancies (PLSD) as an inference-level correction that trades likelihood fit for agreement with targeted motifs. PLSD augments the negative log-likelihood with a penalty on standardized wedge and triangle discrepancies, yielding a controlled distortion of the likelihood surface that can be interpreted through a linear response analysis. A calibration approach for the unique tuning hyperparameter is introduced to turn off the penalization term when the model is correctly specified, thereby recovering maximum-likelihood estimation in that case. We then introduce a mixed-constraint maximum-
entropy core-periphery Exponential Random Graph Model (ERGM), derive unconditional semi-closed motif formulas under Pareto-distributed core fitness, and interpret sparse-regime scaling through a big-jump mechanism for heavy-tailed distributions. We finally corroborate the PLSD inference methodology both with Monte Carlo simulations of a toy
stochastic block model and by applying the novel core-periphery ERGM to weekly eMID interbank networks (2009-2015) and monthly US air traffic networks (1991-2000). We show that PLSD describes cores that are not only dense but also higher-order-rich and captures the observed heterogeneous degree distributions and the overexpression of wedges and triangles, at a link-level cost proportional to the model misspecification.
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Materials Science
Microstructure-Resolved Impedance Modeling of Solid-State Batteries
Kaniza Islam, Chengyin Wu, Noriko Katsube et al. (+1 more)
Solid-state batteries (SSBs) with solid electrolytes (SEs) are attracting substantial investment from the automotive industry to enable fast-charging and safer next-generation electric vehicles. The microstructure of the SE critically affects the battery performance. Electrochemical impedance spectroscopy (EIS) is a powerful, non-destructive probe of charge-transfer and transport processes within SEs and across electrode/SE interfaces but quantitatively connecting measured impedance spectra to the underlying microstructural features remains an open modeling challenge. Here we present a modeling framework that predicts the microstructure-resolved impedance response of a Li/Li6PS5Cl/Li symmetric
cell. Taking the Li6PS5Cl SE microstructures from phase-field sintering simulations, we find that increasing porosity shifts the Nyquist semicircle to higher impedance while improved inter-particle contact reduces it, and that impedance decreases monotonically as sintering proceeds. We also isolate the effect of solid electrolyte interphase (SEI) formation: grain boundaries raise impedance only slightly, but SEI volume fraction, and the conductivity of each SEI phase (Li2S, Li3P, LiCl), both strongly affect it. A realistic multi-phase SEI increases interfacial impedance by about two orders of magnitude compared with a grain boundary only network. We further demonstrate that the same pipeline can operate directly on experimental micrographs by extracting pixel-level phase information with AI-assisted image segmentation and using it to predict an impedance spectrum, illustrating a path toward quantitative microstructure-impedance correlations grounded in real, imaged SE microstructures.
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All authors Kaniza Islam, Chengyin Wu, Noriko Katsube, Yanzhou Ji
Mesoscale and Nanoscale Physics
Induced superconductivity in selective-area grown SnTe devices
Maarten J.G. Kamphuis, Yoran F.S. Starmans, Pim J.H. Lueb et al. (+9 more)
Topological
superconductors are of high interest for applications in topological
quantum computation. The required topologically superconducting state can be engineered by proximityinducing superconductivity in a topological
insulator. Here, we explore the induced superconductivity in selective-area grown nanowires of the topological crystalline
insulator SnTe on a InP substrate, through TEM/EDX and low-temperature electronic transport studies. The observed superconducting behavior likely originates from indium in the substrate diffusing upwards into the SnTe nanowire, forming a thin layer of InxSn1-xTe at the interface between the nanowire and the substrate. InxSn1-xTe is intrinsically superconducting for indium concentrations above 2%, resulting in superconductivity within the
heterostructure. Little-Parks oscillations are observed in loop-shaped nanowire networks in an out-of-plane
magnetic field. The half-period shift indicative of a topological superconducting state is absent, which is explained by dominant trivial transport channels obscuring any topological signatures.
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All authors Maarten J.G. Kamphuis, Yoran F.S. Starmans, Pim J.H. Lueb, Femke J. Witmans, Marvin M. Jansen-Zilles, Marcel A. Verheijen, Reinoud Lavrijsen, Joost Ridderbos, Fabrizio Nichele, Floris A. Zwanenburg, Erik P.A.M. Bakkers, Alexander Brinkman
Materials Science
How Accurately Can We Describe Spin Crossover?
Angel Albavera-Mata, Daniel Mejía-Rodríguez, Niranjan Govind et al. (+3 more)
The complicated physicochemical properties of metal complexes that exhibit thermal
spin crossover make it difficult for routine electronic structure calculations to yield an accurate transition temperature prediction, $T_{1/2}$. The difficulty lies in the intricate connection between the
spin-crossover energy, which is a molecular spectroscopic property, and $T_{1/2}$, a condensed phase property. Here we show how to obtain
spin-crossover energies systematically by reverse engineering of experimental $T_{1/2}$ data. The protocol is based upon fitting the range separation parameter, $\omega$, in the hybrid LC-$\omega$PBE density functional to reproduce the experimental $T_{1/2}$ values for a series of metal complexes. We provide insights into the sources of variations of at least $\pm 15$ kJ mol$^{-1}$ found from common exchange and correlation functionals by comparing their performance against our reference data. By analysis of the sensitivity of transition temperatures to $\pm 1$ % shifts in the range separation parameter, we determined a typical uncertainty of $\pm 50$ K for them, and a $\pm 2$ kJ mol$^{-1}$ uncertainty in the extracted
spin-crossover energies due to $\pm 1$ % variations of $T_{1/2}$. Lastly, we present results from the high-level, all-electron coupled cluster method for eight of the smaller molecules in the reference data set, and discuss the influence of the truncation of the excitation series upon the
spin state energies.
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All authors Angel Albavera-Mata, Daniel Mejía-Rodríguez, Niranjan Govind, Ajay Panyala, Richard G. Hennig, S.B. Trickey
Materials Science
Proximity-induced charge density waves in a moiré heterobilayer
Christopher T. S. Cheung, Arash A. Mostofi and Johannes Lischner
Twisted heterobilayers of two-dimensional materials have emerged as a platform for studying emergent phases of matter. In this work, we investigate charge density waves (CDW) in a twisted NbSe$_2$/MoSe$_2$ bilayer using first-principles calculations. We observe CDW formation in both layers, even though MoSe$_2$ does not feature a CDW in its monolayer form. Moreover, we find that the CDW is highly non-uniform with filled-center, hollow-center and hexagonal CDWs coexisting in the moiré unit
cells of both layers. We assess different mechanisms of CDW formation in the MoSe$_2$ layer and conclude that the dominant one is the steric repulsion between Se atoms across the van der Waals gap. The strength of this effect is highly sensitive to the interlayer separation, which explains why the CDW amplitude in the MoSe$_2$ layer depends strongly on the local stacking arrangement. Our work demonstrates that novel broken-
symmetry phases can be induced in twisted heterobilayers through proximity effects.
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Mesoscale and Nanoscale Physics
Spatiotemporal programming via asymmetric dielectric engineering for nonvolatile 2D optoelectronics
Xiaoguang Luo, Xiaolong Zhang, Honglei Chen et al. (+11 more)
Ambipolar two dimensional (2D)
semiconductors integrated with floating-gate architectures offer a promising platform for nonvolatile, reconfigurable electronics. However, the switching between p-n and n-p junction polarities has conventionally required complex multi-gate designs, hindering the scalability and integration density. Here, we demonstrate a spatiotemporal programming strategy using a dual-floating-gate architecture with a
symmetry broken tunneling dielectric. An asymmetric dielectric stack creates distinct tunneling thresholds for two floating gates, enabling a single input gate to encode spatial doping profiles in the 2D channel via defined voltage pulse sequences. We achieve on demand, nonvolatile, and reversible switching between p-n and n-p configurations with excellent retention and endurance. The reconfigurable homojunction serves as a multifunctional platform for logic encoding, rectification, photodetection, and in sensor computing. This work establishes a design paradigm that replaces spatial input complexity with spatiotemporal programming, paving the way for high-density, multifunctional intelligent hardware.
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All authors Xiaoguang Luo, Xiaolong Zhang, Honglei Chen, Jiaming Wang, Fan Liu, Jiongtao Zhang, Junqiang Zhang, Yihan Yin, Jinpeng Xu, Lei Ying, Renjing Xu, Yingchun Cheng, Xuetao Gan, Wei Huang
Materials Science
Freestanding Antiferromagnetic Oxide Membranes: Synthesis and Characterization of Cr$_2$O$_3$
Ella Blake, Tiffany C. Wang, Yi Cui et al. (+9 more)
Antiferromagnetic (AFM)
insulators stand out as a promising class of materials for fast switching, energy-efficient
magnon-based technology, but our understanding of how to tune these properties with the
lattice remains limited. As an AFM
insulator with strong magnetoelectric response, Cr$_2$O$_3$ membranes stand out as a promising platform to explore multi-modal tunability via strain. However, fabricating these membranes is challenging due to the scarcity of etchable sacrificial layers with compatible
lattice constants and sufficient surface quality. We address this issue by utilizing La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO) as a sacrificial layer, enabling successful fabrication of millimeter-scale Cr$_2$O$_3$ membranes. Substrate-free characterization reveals that strain due to the
lattice mismatch during growth is released by the formation of small polycrystalline domains, preserving single-crystalline order over ~90% of the membrane area. Bulk-like structural properties are confirmed by transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and second-harmonic generation spectroscopy. Platinum Hall measurements reveal an above-room-temperature N$\'e$el transition. These results establish Cr$_2$O$_3$ membranes as a viable platform for strain-tuning antiferromagnetism and magnetoelectricity.
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All authors Ella Blake, Tiffany C. Wang, Yi Cui, Minyong Han, Yinchuan Lv, Christopher T. Parzyck, Octave Duros, Yan Che, Matthias C. Hoffmann, Wei-Sheng Lee, Yi Cui, Harold Y. Hwang