Statistical Mechanics · Cross-listed from q-bio.CB
Mean First Passage Time for Persistent Random Walks in Annular Search Domains
Fatemeh Saghafifar and Daniel Coombs
We study the mean first-passage time of a random walker to a small absorbing target at the center of a two-dimensional annulus with a specularly reflecting outer boundary. The problem is motivated by natural killer
cell migration toward a target cancer
cell, where the goal is to quantify how long it takes immune
cells to reach the target and how search efficiency depends on directional persistence and chemotactic bias.
Cell motion is modeled as a velocity-jump process. We first consider a correlated random walk with a von Mises turning kernel, with a concentration parameter controlling directional persistence. We then extend the model to a biased correlated random walk using a phase-shifted turning kernel that represents preferential motion, for example following a concentration gradient. Our analysis combines closed-form
benchmarks for simple and biased random walks,
Fourier-mode reductions of the transport equations for the correlated and biased correlated models, and a fast-turning perturbation expansion that gives an analytical correction to the
diffusion-limit mean first-passage time for the random walker. Our analytical results are supported by numerical methods that include a semi-Lagrangian solver in radial and angular coordinates, a stationary discretisation designed to handle biased transport, and an event-driven Monte Carlo simulator for cross-validation. Together, our results provide a framework relating persistent and biased immune-
cell motion to target-search times in confined two-dimensional domains.
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Materials Science
Towards Atom-by-Atom Fabrication: Mechanosynthetic donation and abstraction
Brandon Blue, Mathieu Morin, Alex Inayeh et al. (+55 more)
Enabled by inverted-mode scanning tunneling microscopy (IM-STM) and the use of functionalized molecular tools, we demonstrate positionally-controlled mechanosynthetic addition (donation) of carbon and subtraction (abstraction) of silicon atoms on a model build site: atomically clean and crystalline Si(100). The resulting structures represent the first demonstrations of an emerging ability to manipulate radical chemistry with positional control of specific atoms and moieties in 3D. Furthermore, by comparing the behavior of molecular tools designed for atomic donation versus abstraction, we highlight general principles governing molecular tool design for selective and reliable mechanosynthetic functionality.
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All authors Brandon Blue, Mathieu Morin, Alex Inayeh, Rosemary Cranston, Cameron J. Mackie, Marc Savoie, Adam Bottomley, Christian J. Imperiale, Zehra Ahmed, Rafik Addou, Aly Asani, Eduardo Barrera-Ramirez, Jeremy Barton, Doreen Cheng, Megan Cowie, Chris Deimert, Tyler Enright, James Zhangming Fan, Robert A. Freitas Jr, Alan T.K. Godfrey, Ryan Groome, Si Yue Guo, Kareem A. Clarcia, Aru Hill, Taleana Huff, Mark Jobes, Robert J. Kirby, Sam Lilak, Hadiya Ma, Adam C. Maahs, Oliver MacLean, Steven M. Maley, Michael Marshall, Terry McCallum, Ralph Merkle, Matthew Moses, Jonathan Myall, Ryan Plumadore, Adam Powell, Henry Rodriguez, Sam Rohe, Luis Sandoval, Khalil Sayed-Akhmad, Benjamin Scheffel, Kashif Tanveer, Bheeshmon Thanabalasingam, Denis A.B. Therien, Janice L. Wong, Reid Wotton, Cristina Yu, Damian G. Allis, Michael Drew, Matthew R. Kennedy, Tait Takatani, Marco Taucer, Dušan Vobornik, Ryan Yamachika, Mathieu Durand
Materials Science
Dynamical multiferroicity in framework materials
Marek Matas and Carl P. Romao
Dynamical multiferroicity, which describes the
magnetic fields generated by circularly polarized
phonons in materials, is an established mechanism for optical control of magnetism. Here we perform ab initio calculations of dynamical multiferroicity in inorganic and organic framework materials, with the goal of identifying materials which enable the generation of large
magnetic fields by light. We find the metal–organic framework material Zn(NH$_4$)(formate)$_3$ to have modes with
magnetic moments almost twice that of SrTiO$_3$; these modes involve circular motions of NH$_4^+$ hydrogen ions with high gyromagnetic ratios. The complex structure and flexibility of framework materials can allow such angular momentum localization, and also increase the maximum light-induced magnetization permitted by the Lindemann melting criterion.
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Materials Science
DFTB coupled with NEGF study of the structural, electronic and transport properties of goldene 2D material
Taoufik Sakhraoui and František Karlický
We report the structural, electronic, and transport properties of the goldene 2D material using the density functional tight-binding (DFTB) method. Electronic transport calculations were conducted in conjunction with the non-
equilibrium Green's functions (NEGF) technique. Our study reveals that the Au 2D material is dynamically and thermally stable, and it possesses good elastic properties. On the other hand, goldene has a linear relationship between current and voltage at low potentials, indicating its metallic character. The calculated current-potential curve correlates well with transmission functions and the electronic density of states around the
Fermi level. We also investigated the electronic structure and
magnetic properties of silicon (Si)-doped Au 2D material. Our results show that the Si atom can induce a local
magnetic state in the goldene monolayer. The resulting
magnetic moment is 0.63 $\mu_B$.
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Materials Science
Closed-loop discovery of out-of-distribution processing protocols by evolutionary search and uncertainty-aware learning
Yu Liu, Stanislav Udovenko, Ching-Che Lin et al. (+4 more)
Many materials and chemical systems exhibit history-dependent responses, where functional outcomes are governed not only by final-state variables but by the time-dependent sequence of fields, temperatures, or chemical potentials applied during operation. Discovering new processing protocols is therefore a high-dimensional search problem in which the control variable is an entire waveform or sample history, and conventional strategies either remain confined to conservative interpolative families or become prohibitively measurement intensive. Here, a closed-loop workflow is introduced that couples evolutionary search over a compact waveform representation with uncertainty-aware deep kernel learning to generate, rank, and experimentally validate candidate protocols. Applied to ferroelectric thin films, with the scanning-probe tip-bias waveform as the protocol and the nonlinear electromechanical response as the reward, the workflow discovers waveform families that enhance nonlinearity by de-aging the film. Spatially resolved before/after measurements show that the best-performing waveforms selectively activate pre-existing, weakly pinned domain-wall segments, whereas the worst drive long-range irreversible switching. This framework reframes protocol tuning as out-of-distribution discovery, generalizable to synthesis and annealing trajectories, battery formation protocols, and other high-dimensional control problems.
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All authors Yu Liu, Stanislav Udovenko, Ching-Che Lin, Jaegyu Kim, Lane W. Martin, Susan Trolier-McKinstry, Sergei V. Kalinin
Disordered Systems and Neural Networks · Cross-listed from quant-ph
Local correlations in long-range dual-unitary kicked Hamiltonian chains
Vladimir Al. Osipov, Marc Cedric Spyra, Jana Carolina Schumann et al. (+2 more)
Many-body Floquet models with exact space–time
symmetry, such as the kicked Ising
spin chain (KIC), provide natural examples of systems with dual-
unitary dynamics. The requirement of exact space–time
symmetry is, however, highly restrictive, as it permits only nearest-neighbor interactions. Based on a pair of Hadamard
matrices, we construct a wide family of dual-
unitary kicked
spin chains with long-range interactions. We show that local two-point correlations in such models propagate along the light-cone edges \( |n| = r|t| \), where \(r\) is the interaction range, and can be derived analytically for operators with local support. This approach is illustrated using the example of a kicked Ising
spin chain with next-to-next-neighbor interactions.
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All authors Vladimir Al. Osipov, Marc Cedric Spyra, Jana Carolina Schumann, Thomas Guhr, Boris Gutkin
Materials Science
Machine-learned dynamics of surface polarons at reduced oxide surfaces
Luca Leoni and Cesare Franchini
Reducible
oxides exhibit a rich interplay of electronic, structural, and chemical properties that underpins applications in catalysis, photovoltaics, batteries, and energy storage. This interplay is strongly shaped by excess electrons, often introduced by oxygen vacancies, that localize as small polarons and influence charge transport and surface chemistry. At surfaces, these polarons play a central role in charge localization, mobility, and reactivity, yet their finite-temperature dynamics remain difficult to access from first principles due to the long time scales needed to adequately sample polaron's hopping. To overcome this limitation, we extend machine-learning-assisted polaron dynamics to redox-active
oxide surfaces, using oxygen-deficient rutile TiO$_2$(110) as a paradigmatic case. By accessing several nanoseconds of dynamics over a range of temperatures, we show that small-polaron mobility at the reduced rutile TiO$_2$(110) surface is suppressed by several orders of magnitude relative to the corresponding bulk material, providing a microscopic interpretation of the lower electron mobilities observed in porous rutile TiO$_2$ compared with single-
crystal samples. This suppressed mobility arises from the loss of favourable hopping pathways: surface polaron motion is largely confined to planar inter-row trajectories within the second topmost layers, with only rare interlayer hopping events. These results establish a transferable machine-learning strategy for investigating polaron dynamics in reducible
oxides.
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Materials Science
Combining Frozen Trajectory Excitation and TACAW for in silico Time-Resolved Vibrational Electron Energy Loss/Gain Spectroscopy
Wojciech Marciniak, Joanna Marciniak, José Ángel Castellanos-Reyes et al. (+1 more)
Seeing that ultrafast (picosecond timescale) vibrational electron energy loss spectroscopy (EELS) should soon be experimentally realizable, we present in silico approach capable of providing insight from the computational physics perspective. We present a framework that combines frozen trajectory excitation (FTE) with time auto-correlation of auxiliary wavefunctions (TACAW) to study the time-dependent spectral response of non-
equilibrium lattice dynamics in a way comparable directly to experiment - (scanning) transmission electron microscope EELS, (S)TEM-EELS. In this approach, a selected
phonon excitation is first introduced into an
equilibrium molecular dynamics trajectory using FTE, after which the atomic positions during subsequent relaxations are treated with short-time TACAW analysis performed at different pump-probe delays. This yields momentum- and energy-resolved electron-scattering signals bearing a
phonon imprint during the relaxation process, going beyond time-dependent diffuse-scattering intensities alone. We demonstrate the approach for fcc-Ni and 3C-SiC and discuss the observed
phonon mode coupling and spectral redistribution during
phonon relaxation.
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All authors Wojciech Marciniak, Joanna Marciniak, José Ángel Castellanos-Reyes, Ján Rusz
Mesoscale and Nanoscale Physics
A Collective-Spin Derivation of the Uniform Magnon Hamiltonian in Cavity Magnonics
Tomas Aguiar and Marcos Cesar de Oliveira
We present a direct collective-
spin derivation of the effective uniform-mode
Hamiltonian used in cavity magnonics. Starting from a nearest-neighbor Heisenberg ferromagnet coupled to long-wavelength
magnetic fields, we show that the relevant dynamics can be restricted to the fully symmetric
spin sector, where the exchange interaction contributes only a constant energy shift and the ferromagnet behaves as a macrospin of length $Ns$. Applying the Holstein–Primakoff transformation directly to this total
spin yields the usual uniform
magnon mode and its leading nonlinear corrections without first introducing site-resolved bosonic operators. This collective formulation makes explicit the interpretation of the ferromagnet as a synthetic large-
spin atom and provides a compact route to the effective
Hamiltonians used in driven and Floquet cavity magnonics. As a physical consequence, the leading nonlinear correction produces an occupation-dependent reduction of the effective
magnon–
photon coupling, providing a simple signature of finite-
spin saturation under strong uniform-mode driving.
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Superconductivity
Observation of intertwined charge density wave order and superconductivity in Janus monolayer
Subhajit Pramanick, Shubham Patel, Sudip Chakraborty et al. (+1 more)
Low-dimensional transition-metal dichalcogenides (TMDCs) provide an ideal platform for studying the emergence of charge density wave (CDW) and superconductivity. The discovery of emergent CDW order in 1T $\mathrm{ZrTe_2}$ monolayer raises an important question: does this instability persist when one $\mathrm{Te}$ chalcogen layer is substituted by $\mathrm{Se}$? In the present work, we investigate the CDW (2$\times$2$\times$1) and superconducting instability in 1T $\mathrm{ZrSeTe}$ Janus monolayer using first-principles calculations. The
phonon spectrum exhibits a pronounced anomaly at the $\mathrm{M}$ point of the irreducible Brillouin zone, arising from enhanced electron-
phonon interaction together with electronic instabilities originating from both interband and intraband scattering. The resulting
lattice distortion reconstructs the electronic structure, opening a small indirect band gap, driving the system from a semi-metallic to a semiconducting state. The energy gain associated with the distortion is significantly smaller than that of $\mathrm{ZrTe_2}$ monolayer, indicating that the replacement of one $\mathrm{Te}$ chalcogen layer with $\mathrm{Se}$ weakens the CDW instability. We have further investigated the effects of electronic correlation and biaxial strain, both acts as effective tuning parameters for the instabilities concerened. In the high temperature undistorted phase, $\mathrm{ZrSeTe}$ exhibits
phonon mediated two-gap superconductivity. It originates primarily from the robust coupling between the soft
phonon mode at $\mathrm{M}$ point and the electronic bands predominantly derived from $\mathrm{Zr}$ $\mathit{d}$ and $\mathrm{Te}$ $\mathit{p}$ orbitals crossing the
Fermi level.
Spin-orbit coupling (SOC) further modifies the electronic states and reduces the superconducting transition temperature.
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All authors Subhajit Pramanick, Shubham Patel, Sudip Chakraborty, A. Taraphder
Statistical Mechanics · Cross-listed from quant-ph
Universal Crossovers of Stabilizer Entropy Beyond Criticality
Reyhaneh Khasseh, E. A. Ramirez Trino and M. A. Rajabpour
Stabilizer Rényi
entropy has emerged as a probe of nonstabilizerness in
quantum many-body systems, but its scaling structure beyond critical points remains poorly understood compared with
entanglement entropy. Recent field-theory approaches indicate that stabilizer
entropy contains universal critical data and boundary-sensitive terms, raising the question of how these structures extend into massive and crossover regimes. We address this problem for a broad class of finite-range
spin chains at Rényi index one-half. We derive exact finite-size formulas for both full periodic chains and finite intervals of the infinite chain, making the universal crossover from critical to noncritical behavior analytically accessible. In periodic geometry, the
entropy obeys a volume law away from criticality and exhibits a universal finite-size crossover controlled by the competition between system size and correlation length. We also show that the large-scale SRE density develops a cusp across the field-tuned critical line, while the XX endpoint is governed by a distinct scaling regime associated with the saturation point. In the subsystem geometry, the interval
entropy separates bulk critical behavior from boundary contributions generated by the way the finite region cuts the infinite chain. The crossover from critical to massive behavior is then encoded in boundary constants and universal functions controlled by the correlation length. Through exact stabilizer-
entropy correspondences, the scaling theory extends to internal XY reductions, Finite-range
spin chains, and Cluster–Ising representatives. Our results provide an exact
lattice benchmark for the emerging QFT description of stabilizer
entropy beyond isolated conformal points.
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Mesoscale and Nanoscale Physics
Enhancement of spin current in Fe$_{85}$Co$_{15}$/Ni$_{80}$Fe$_{20}$ bilayers via interlayer ferromagnetic coupling
A. A. Pérez Martínez, D. Velázquez Rodríguez, D. Goijman et al. (+6 more)
We present a detailed study on how the strength of the interlayer
magnetic coupling on Fe$_{85}$Co$_{15}$/Ni$_{80}$Fe$_{20}$
bilayers modifies the
spin wave behavior of this system. A series of Fe$_{85}$Co$_{15}$/Ni$_{80}$Fe$_{20}$
bilayers deposited on MgO[100] substrates were grown by magnetron sputtering.
Magnetic characterization of the samples was performed using a vibrating sample magnetometer and magneto-optical Kerr effect. The in-plane hysteresis loops reveal a cubic
magnetic anisotropy of magnetocrystalline origin, with easy and hard axis along the [100] and [110] Fe-Co crystallographic directions, respectively.
Ferromagnetic resonance measurements were performed to analyze the in-plane angular dependence of the resonance field, and also the resonance field at several frequencies was determined along the hard axis. By using a
bilayer model in the frame of the Landau-Lifshitz-Gilbert magnetization equation of motion, the magnetization precession components were calculated, as well as the dependence of precession area on the Fe-Co layer thickness and the
ferromagnetic interlayer coupling. We observe a maximum in the area of the ellipsoid generated by the magnetization precession of the permalloy layer at a certain exchange constant, showing that this effect could be used to maximize the injected
spin currents, which could be tuned by changing the interlayer exchange constant in
bilayer systems, the saturation magnetization of the materials, or the excitation frequency.
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All authors A. A. Pérez Martínez, D. Velázquez Rodríguez, D. Goijman, T. Torres, M. H. Aguirre, J. Gómez, A. Butera, E. De Biasi, J. Milano
Strongly Correlated Electrons · Cross-listed from hep-th
RG Dynamics of Irrelevant Fermion Operators and the Drag Coupling Mechanism
Jeremias Aguilera-Damia, Diego Rodriguez-Gomez and Jorge Russo
We study the renormalization-group flow of higher-dimensional fermionic interactions $(\psi^\dagger \psi)^{2n}$ in the presence of a
Fermi surface. We show that the growth of the BCS four-
fermion coupling induces a drag mechanism whereby higher-order fermionic couplings are driven to strong coupling in the infrared. We derive the corresponding beta functions and show that the drag effect applies generically to the whole tower of fermionic operators. Remarkably, although all couplings are driven toward the same strong-coupling scale, the renormalization-group flow preserves a hierarchy in which higher-dimensional operators remain parametrically suppressed relative to the BCS interaction. We then investigate this mechanism in a $2+1$-dimensional non-
Fermi liquid coupled to a critical
boson. While higher-order fermionic interactions are similarly enhanced along the flow, we show that they do not destabilize the IR stable non-
Fermi-
liquid fixed point, present for sufficiently large $N$. We briefly discuss possible implications for multicomponent
superconductors and other strongly correlated metallic systems.
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Statistical Mechanics · Cross-listed from hep-th
Resurgence of the Thermal Transition between Bounce and Sphaleron
Shaun D. Hampton, Kyungsun Lee and Sungjay Lee
We study the thermal transition between the bounce and the sphaleron in
quantum mechanics with a metastable
vacuum from the viewpoint of Borel resurgence. For two models representing a second-order and a first-order transition, we compute the perturbative expansion of the thermal free energy to high orders and extract the leading Borel singularity data $(A,b,S)$ as functions of temperature. The Borel singularity location $A$ reproduces the on-shell action of the dominant saddle on both sides of the transition, joining smoothly in the second-order case and developing a kink in the first-order case. The characteristic exponent $b$ jumps between $0$ and $1/2$ across the transition, counting the zero modes of the corresponding saddle. The Stokes constant $S$ matches the one-loop determinant around the saddle. The perturbative expansion around the false
vacuum thus determines the transition temperature, the order of the transition, and the decay rate including the one-loop prefactor without relying on semiclassical inputs.
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Quantum Gases
Digital programming of spin correlations in a fermionic lattice quantum simulator
Yann Kiefer, Lars Fischer, Zijie Zhu et al. (+2 more)
Analog
quantum simulation provides a highly controlled platform to study diverse
quantum many-body phenomena. However, current methods for state initialisation are limited to thermal ensembles or uncorrelated product states. Here we present a hybrid approach that complements analog preparation with a digital
quantum-gate protocol. This approach enables the engineering of target states with specific, long-range
spin-correlations from the same initial resource state. By applying collisional gates to adiabatically prepared and filtered four-
fermion singlet chains, we program diverse
spin-correlation patterns, including that of a Heisenberg chain. We measure the
spin correlations using a sequence of
quantum gates followed by singlet-pair measurements. Our method paves the way to the targeted preparation of strongly correlated states of matter.
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All authors Yann Kiefer, Lars Fischer, Zijie Zhu, Konrad Viebahn, Tilman Esslinger
Materials Science
Electrostatic Charge Model for Dual-Layer Oxide Thin-Film Transistors
Måns J. Mattsson, John F. Wager and Matt W. Graham
A simple electrostatic two-equation model for dual-layer thin-film transistor (TFT) operation is developed. The model distributes electrostatic charge between the top and bottom
semiconductor layers, and the resulting transfer and mobility curves accurately simulate experimental dual-layer a-IGZO/a-IZO TFT operation. The model further provides an analytic expression that maps charge confinement in the high-mobility a-IZO bottom
semiconductor layer with the a-IGZO top-layer thickness and the conduction-band offset. By considering both a-IGZO/a-IZO layer charge partition and competing thickness-dependent oxygen vacancy trap density effects, the model suggests an optimal a-IGZO layer thickness of 9 to 12 nm. Importantly, this general electrostatic model extends to most dual-layer TFT systems and calculates how the top
semiconductor layer TFT turn-on voltage changes sharply with the conduction band offset and layer thickness.
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Materials Science · Cross-listed from quant-ph
Tantalum as a base material for superconducting integrated circuits
Evgeniy V. Zikiy, Nikita S. Smirnov, Stanislav A. Kotenkov et al. (+9 more)
The performance of superconducting integrated
circuits for
quantum applications is fundamentally limited by material-related losses. Tantalum, as an emerging material for next-generation
quantum circuits, has attracted considerable
attention in recent years after demonstrating breakthrough performance in both superconducting microwave resonators and
qubits. Concurrently, a growing body of work is devoted to the operation of tantalum-based
circuits and related fabrication techniques. This interest is further stimulated by tantalum thin films polymorphism resulting in a variety of its crystalline structure, superconducting properties, coherence, etc. Furthermore, tantalum
circuits exhibit distinctive features in cryogenic experiments, which have not been observed in aluminum- or niobium-based ones. In this review, we summarize the recent research of tantalum thin films growth and phase selection mechanisms on various substrates, key aspects of fabrication and performance of superconducting
circuit, including a material first-principles theoretical study. In conclusion, we address a number of open issues, including the role of e̱ta}-phase
impurities, the effect of hydrofluoric acid solutions on chain characteristics, and the anomalous behavior of {\alpha}-tantalum chains at cryogenic temperatures.
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All authors Evgeniy V. Zikiy, Nikita S. Smirnov, Stanislav A. Kotenkov, Ilya A. Stepanov, Julia A. Agafonova, Daria A. Moskaleva, Aleksei R. Matanin, Anton I. Ivanov, Dmitry O. Moskalev, Julia A. Kurochkina, Aleksander V. Andriyash, Ilya A. Rodionov
Soft Condensed Matter
Controlling Defects and Probing Dynamics in Active Nematics with Deep Reinforcement Learning
Russ Islam, Kyogo Kawaguchi and Yuto Ashida
Topological defects govern much of the flow behavior and orientational order in active nematics, making their control relevant for active matter physics, smart materials, and microfluidics. Applied activity patterns can induce self-propulsion of active nematic defects, but general-purpose methods for exploiting this effect to control defects remain largely unexplored. Here we use deep reinforcement learning (RL) to perform minimum-time position control of +1/2 defects in hybrid
lattice Boltzmann simulations of active nematodynamics. Spatiotemporally patterned activity, implemented as a control field in the active stress, steers defects through microchannel geometries and reveals finite-time reachable regions of defect position space. Reachability is shaped by director anisotropy, homeotropic wall anchoring, and the allowed activity patterns: local patterns steer defects in free domains but fail in junctions, whereas global patterns open otherwise inaccessible channels. In constrained geometries, the original defect may be unable to reach some goals intact, but controlled pair creation enlarges the effective reachable set by transferring control to a newly created +1/2 defect. The trained RL controllers outperform static and rule-based baselines, and controllers trained only on simple junctions can be combined without fine-tuning into a meta-controller that successfully steers defects through a larger test maze. Free energy visualizations show that guided defects write persistent, history-dependent distortions into the director field that can later be partially erased by -1/2 defects. Thus, RL-based control uncovers how confinement, anchoring, actuation geometry, and defect creation determine reachable motion in active nematics, providing a framework for other control tasks in soft and active matter.
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Materials Science
Morphology control and low-temperature magnetotransport in chiral 2D perovskite R-(MBA)$_2$PbI$_4$
Shehreen Aslam, Sam Saiter, Bradley Lloyd et al. (+4 more)
Two-dimensional
chiral hybrid perovskites, such as R/S-(MBA)\textsubscript{2}PbI\textsubscript{4}, are leading candidates for realizing and studying chirality-dependent charge and
spin transport. However, their prohibitive in-plane resistance has precluded the electrical characterization. Here, we overcome this bottleneck by engineering the thin-film morphology of the
chiral perovskite $R\text{-(MBA)}_2\text{PbI}_4$, enabling the first robust lateral device integration. In
Hall-bar geometries, we demonstrate
Hall measurements under dark conditions, unambiguously identifying p-type conduction with a
Hall mobility of $\sim 0.2 \text{cm}^2 \text{V}^{-1} \text{s}^{-1}$ and a carrier density of $\sim 3\times10^{14} \text{ cm}^{-2}$, parameters previously inaccessible in this class of materials. Furthermore, we observe enhanced magnetoresistance along transport paths crossing grain boundaries, highlighting the strong influence of morphology on in-plane transport. This work demonstrates in-plane magnetotransport, enabling future investigations of the fundamental mechanisms of chirality-induced
spin selectivity (CISS) and accelerating the integration of
chiral materials into functional spintronic devices.
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All authors Shehreen Aslam, Sam Saiter, Bradley Lloyd, Paul Kliewer, Matthew P. Hautzinger, Matthew C. Beard, Meenakshi Singh
Mesoscale and Nanoscale Physics
Engineering electrically-switchable quantum anomalous Hall states by spin-orbit coupling
Maosen Qin, Ziwei Wang, Gyeongmin Kim et al. (+5 more)
Nonvolatile gate-driven switching of
quantum anomalous
Hall (QAH) states in
graphene moiré systems provides a promising route toward topological electronics based on
chiral edge states. However, deliberate use of this switching mechanism requires control over both the
magnetic properties and metastability of QAH states. While previous demonstrations mostly relied on the intrinsic
magnetic energy landscape of moiré devices, here we show that this landscape can be engineered through proximity coupling to WSe2. We find that proximitizing twisted monolayer-
bilayer graphene by WSe2 reshapes the magnetization reversals responsible for nonvolatile electrical switching of QAH states. We attribute this effect to the proximity-induced
spin-orbit coupling (SOC), which can lock
spin and valley and modify the magnetization of the competing states involved in switching compared with non-proximitized
graphene systems. Our findings establish proximity-induced SOC as a new way to engineer
magnetic properties and switchable
magnetic states in
graphene-based systems. We further demonstrate that strong
magnetic metastability in tMBG allows the
magnetic states to be gate-tuned between QAH and metallic regimes, and between QAH states with Chern numbers |C| = 2 and 1 without resetting the
magnetic state. This functionality points toward new device architectures based on QAH
chiral edge states.
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All authors Maosen Qin, Ziwei Wang, Gyeongmin Kim, Kenji Watanabe, Takashi Taniguchi, Steven H. Simon, Siddharth A. Parameswaran, Hryhoriy Polshyn
Quantum Gases
Driven dynamics of an attractive Bose polaron
Saptarshi Majumdar and Aleksandra Petković
We study the out-of-
equilibrium dynamics of an
impurity driven by a constant external force through a system of homogeneous weakly-interacting
bosons in one spatial dimension. The
impurity-
boson interaction is assumed to be attractive. We show that the
impurity exhibits drifted Bloch oscillations in a wide range of forces in the absence of a
lattice. We characterize the dynamical response of the host
bosons and explain the mechanism underlying the Bloch oscillations. We analyse the behavior of the drift velocity, the Bloch amplitude and the time period of oscillations in a wide range of forces and other system parameters. In contrast to the case of repulsive
impurity-
boson interaction, the drift velocity exhibits a sub-linear dependence on a weak applied force, $V_d\sim {F}^{\alpha}$ with a positive exponent $\alpha$ smaller than unity. The drift velocity monotonically increases with force, though the scaling behavior varies considerably across different regimes of $F$. Moreover, the amplitude of the velocity oscillations displays rich behavior: it first undergoes a decay with force, reaches a minimum, and then presents a revival, increasing with force.
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Materials Science · Cross-listed from physics.optics
Electric-Field Mapping of Optically Perturbed CdTe Radiation Detectors
Adriano Cola, Lorenzo Dominici and Antonio Valletta
In radiation detectors, the spatial distribution of the electric field plays a fundamental role in their operation. Access to this field distribution is of strategic importance, especially when investigating the perturbing effects induced by incident radiation. For example, one dangerous effect that prevents their proper operation is the accumulation of internal space charge. Here, we probe the two-dimensional electric field in a Schottky CdTe detector using the Pockels effect and report on its local perturbation after exposure to an optical beam at the anode electrode. Our electro-optical imaging setup, together with a custom processing routine, allows the extraction of the electric-field vector maps and their dynamics during a voltage bias-optical exposure sequence. The results are in agreement with numerical simulations, allowing us to confirm a two-level model based on a dominant deep level. Such a simple model is indeed able to fully account for both the temporal and spatial dynamics of the perturbed electric field. This approach thus allows a deeper understanding of the main mechanisms affecting the non-
equilibrium electric-field distribution in CdTe Schottky detectors, such as those leading to polarization. In the future, it could also be used to predict and improve the performance of planar or electrode-segmented detectors.
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Soft Condensed Matter
Geometric formulation of state-dependent Langevin dynamics using scalar free energy
Kento Yasuda, Zhongqiang Xiong, Zhanglin Hou et al. (+3 more)
Stochastic dynamics with state-dependent
diffusion arise broadly in confined, anisotropic, and hydrodynamically coupled systems. The conventional Langevin equation contains a spurious drift associated with multiplicative noise. Since the restricted free energy is generally non-scalar, the covariance is not explicit. Here, we reformulate state-dependent Langevin dynamics using a scalar free energy and a
diffusion metric defined by the inverse
diffusion tensor. The conventional spurious drift is then expressed as a Christoffel contribution. Although our formulation is mathematically equivalent to the conventional one through the relation between the restricted and scalar free energies, it makes coordinate covariance explicit and enables the phenomenological construction of thermodynamic potentials directly from system
symmetries. We demonstrate its consistency in representative examples of state-dependent
diffusion arising from coordinate transformations,
geometric confinement, and projection from curved to flat spaces.
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All authors Kento Yasuda, Zhongqiang Xiong, Zhanglin Hou, Kenta Ishimoto, Xinpeng Xu, Shigeyuki Komura
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Temporal glide symmetry enforces a parity sideband selection rule in scalar bulk media
Miguel Camacho
Symmetry is a powerful way to control coupling between photonic mode families. In spatially periodic structures, glide
symmetry can protect band contacts and suppress stop bands. Here we show a different role for temporal glide, a spatiotemporal counterpart combining reflection with a half-period time translation. In a scalar time-modulated trilayer waveguide, temporal glide imposes an exact selection rule linking frequency conversion to transverse-mode
symmetry: the parity content of every Floquet eigenstate alternates with sideband index, up to a state-dependent sign. In scattering, this means that a mode of definite parity can emit only into the opposite transverse parity at odd sidebands and into the same parity at even sidebands. We verify the rule directly in bulk Floquet eigenstates and in finite-section time-domain simulations. An incident odd waveguide mode is converted into an even frequency sideband, while all
symmetry-forbidden output channels at the analysed sidebands are suppressed to numerically negligible values. Rather than acting as a temporal copy of spatial-glide band sticking, temporal glide provides a distinct
symmetry principle for converting electromagnetic energy between selected modes and frequencies.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Diffusive Dynamics of Nonstabilizerness
Zhenyu Xiao and Shinsei Ryu
Symmetries shape the
quantum-information dynamics of many-body systems, but their effect on nonstabilizerness, the resource complementary to
entanglement, is less understood. We compute the stabilizer Rényi
entropy, a measure of nonstabilizerness, in $\mathrm{U}(1)$-symmetric one-dimensional random
circuits. The disorder-averaged dynamics is captured by a four-replica tensor network, which we evaluate by $S_4$-adapted infinite time-evolving block decimation (iTEBD) directly in the thermodynamic limit. Together with a hydrodynamic argument, our results identify a diffusive universality class for the late-time approach of nonstabilizerness to its random-state value, with the stabilizer Rényi
entropy gap closing as $1/t$. The same scaling is verified in an energy-conserving nonintegrable Ising chain. More broadly, our framework provides a hydrodynamic perspective on nonstabilizerness generation and offers insight into the design of approximate Haar-random states in
Hamiltonian dynamics.
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Materials Science
Cepstral Analysis to accelerate Green-Kubo thermal conductivity calculations of Metal-Organic Frameworks
Florian P. Lindner, Egbert Zojer and Sandro Wieser
Metal-organic frameworks (MOFs) are promising porous materials for applications such as gas storage and separation, where heat transport can critically affect device performance. However, reliable computational prediction of their thermal conductivities remains challenging. In particular,
equilibrium molecular-dynamics-based Green-Kubo (GK) simulations, as the most widely used approach, are severely affected by statistical noise. Moreover, they rely on multiple ambiguous, user-defined parameters, which hinder transferability and automation. Here, we demonstrate for metal-organic frameworks that cepstral analysis in combination with GK simulations provides a robust route to massively mitigate these problems, while simultaneously reducing the required sampling times. This is shown for three prototypical frameworks, MOF-5, HKUST-1, and ZIF-8, employing machine-learned moment tensor potentials trained on DFT reference data. In contrast to conventional, direct GK analysis, which shows erratic convergence and strong sensitivity to ad hoc choices of parameters, the cepstral approach yields stable results across a wide range of correlation lengths and achieves convergence within about 1-2 ns of total sampling time. This establishes cepstral analysis base Green-Kubo simulations combined with machine-learned potentials as an efficient, reproducible and automation-ready framework for near ab initio accuracy prediction of thermal transport in MOFs and other complex low-thermal-conductivity materials.
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Soft Condensed Matter
Exploratory digital alchemy for colloidal crystal discovery
Shih-Kuang Lee, Sun-Ting Tsai and Sharon C. Glotzer
Digital Alchemy (DA), introduced by Van Anders et al., is a statistical mechanics-based generalized thermodynamic ensemble method that employs computer simulations to optimize colloidal particle design. This approach applies the principles of statistical mechanics to predict and tailor particle attributes that lead to desired self-assembled structures or material properties. However, as an inverse design method, its main limitation is that the target structure must be known a priori. Therefore, the optimal design from DA does not guarantee the targeted structure is the most or the only stable one. This highlights the importance of forward design with an exploratory scheme for optimizing novel colloid designs, which becomes more suitable in such cases. In this paper, we introduce Exploratory Digital Alchemy (EDA), an enhanced forward design scheme that begins by releasing the constraint of the target
crystal from DA, followed by an exploration-oriented bias that has been extensively used in enhanced sampling methods such as metadynamics (MetaD). We demonstrate the utility of EDA through examples involving particles interacting via a two-dimensional Lennard-Jones Gauss potential (LJGP) and a three-dimensional oscillating pair potential (OPP). We applied EDA to study the free energy landscapes given different potential parameters of LJGP at different temperatures. With the exploratory scheme, we've also successfully identified a wide range of OPP potential parameters that stabilize metastable Frank-Kasper phases. Our approach fuses the standard DA framework with metadynamics, which could potentially be useful for studying alchemical reactions in a generalized ensemble.
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Soft Condensed Matter
Limits of constant-parameter constitutive models for hydrogels under inertial cavitation
Tianyi Chu, Joseph Beckett, Zhiren Zhu et al. (+2 more)
Mechanical characterization of soft materials at high strain rates is challenging due to their high compliance, nonlinear viscoelastic behavior, and potentially history-dependent responses. Inertial microcavitation rheometry (IMR) addresses this challenge by coupling
laser-induced cavitation (LIC) experiments with numerical simulations of bubble dynamics models to infer constitutive models and material parameters. Both IMR and its variants infer parameters that depend on the chosen fitting window, which suggests that a constant-parameter constitutive model is insufficient to describe the full cavitation event. We use this window dependence to identify when the constant-parameter assumption fails, rather than to report a single effective parameter set. The constitutive parameters are estimated over moving, overlapping windows using a modified iterative ensemble Kalman smoother with multiple data assimilation (MIEnKS-MDA). Within the neo-Hookean Kelvin–Voigt (NHKV) constitutive model, we obtain time-resolved estimates of the constitutive response in polyacrylamide (PAAm) hydrogels with different crosslinker concentrations. The inferred shear modulus and viscosity generally decrease and then plateau during cavitation, while exhibiting relatively weak temperature sensitivity. For gelatin gels, by contrast, the inferred property
evolution shows a pronounced temperature dependence, with distinct trends at low and high temperatures. Moreover, both the apparent shear modulus and viscosity exhibit significant variations during the first two bubble collapses. These results show that time-resolved parameter estimation within the prescribed NHKV constitutive structure can diagnose where the constant-parameter model assumption falls short during cavitation, thereby guiding the development of improved physics-based models of complex bubble–material interactions.
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All authors Tianyi Chu, Joseph Beckett, Zhiren Zhu, Jonathan B. Estrada, Spencer H. Bryngelson
Materials Science
Tuning perpendicular magnetic anisotropy in ultra-low damping Li$_{0.5}$Al$_{x}$Fe$_{(2.5-x)}$O$_4$ thin films for efficient spin-orbit torque switching
Daisy O'Mahoney, Sauviz P. Alaei, Anna Janni et al. (+5 more)
Ultra-thin
magnetic insulator films that simultaneously exhibit ultra-low
magnon damping, perpendicular
magnetic anisotropy (PMA), and low
spin-orbit torque (SOT) switching current densities are highly desirable, albeit challenging, for next-generation spintronic technologies that exploit
spin waves to transport information without dissipative charge currents. Here, we demonstrate this combination of properties in ferrimagnetic spinel Li$_{0.5}$Al$_{x}$Fe$_{(2.5-x)}$O$_4$ (LAFO) thin films. Through this model system, we find that PMA can be tuned by epitaxial strain in the form of chemical composition and substrate choice and that low SOT switching current densities correlate with small but finite PMA. Ultra-low damping is stabilized primarily by having only Fe$^{3+}$ as magnetically active cations with secondary effects due to increased disorder from Al substitution distribution. SOT efficiency is governed by interface quality and independent of chemical composition. By varying the Al concentration, we systematically tune the saturation magnetization and
magnetic anisotropy while maintaining ultra-low Gilbert damping parameters as low as $2\times10^{-4}$ and composition-independent damping-like SOT efficiencies. We identify an optimal composition LAFO x=0.7 (Li$_{0.5}$Al$_{0.7}$Fe$_{1.8}$O$_4$), which combines ultra-low damping, stable PMA with small anisotropy fields, and low critical current densities for SOT switching, establishing it as a promising material platform for energy-efficient
spin-wave and spintronic devices.
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All authors Daisy O'Mahoney, Sauviz P. Alaei, Anna Janni, Muzhda Mehrzad, Christoph Klewe, Alpha T. N'Diaye, Zbigniew Galazka, Yuri Suzuki
Materials Science
Lone-Pair-Induced Lattice Softness Enables Ultralow Thermal Conductivity in Hybrid Organic-Inorganic Perovskite GuaPbI$_3$
Rudra P. Singh, Shantanu Pathak, Saswata Bhattacharya et al. (+1 more)
Thermal conductivity ($\kappa$) minimization of inorganic thermoelectrics can only be achieved to a certain extent via nanostructural engineering. Here, we introduce a lone-pair-driven materials design strategy based on chemically induced
lattice softness to develop hybrid organic-inorganic perovskites with ultra-low $\kappa$. A physics-guided symbolic-regression machine-learning framework identifies a lone-pair-dominated compositional regime statistically associated with suppressed
lattice $\kappa$ and selects $\text{GuaPbI}_3$ as a candidate material. Mechanochemical synthesis yields $\text{GuaPbI}_3$ with an ultra-low room-temperature $\kappa \approx 0.088\text{ W m}^{-1}\text{ K}^{-1}$. Electrical measurements reveal electronically active, bias-dependent bulk conduction pathways despite strong
phonon suppression, while impedance spectroscopy confirms predominantly bulk-dominated transport. Density functional theory calculations indicate weakly dispersive valence bands, pronounced valence-conduction asymmetry, and localized electrostatic microenvironments arising from
lattice charge redistribution. Calculated transport coefficients suggest strong sensitivity of carrier transport to chemical potential, while Lorenz-number analysis reveals deviations from conventional Wiedemann-Franz behavior near band edges. These observations indicate that lone-pair-rich hybrid frameworks generate intrinsically soft and electronically heterogeneous
lattice environments capable of strongly suppressing
phonon transport while preserving electronically accessible states. This work establishes chemically induced
lattice softness as a viable design principle for identifying ultralow-thermal-conductivity hybrid materials without relying on nanostructuring or extrinsic disorder engineering.
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All authors Rudra P. Singh, Shantanu Pathak, Saswata Bhattacharya, R Lakshmi Narayan