Statistical Mechanics
Ground state energy fluctuations of pinned elastic manifolds
Yan V. Fyodorov, Bertrand Lacroix-A-Chez-Toine and Pierre Le Doussal
We describe the atypical fluctuations of the ground state energy of the random elastic
manifold, a disordered model defined on a
lattice of linear size $L$ with internal dimension $0\leq d<4$ embedded in a medium of dimension $N\gg 1$. The ground-state energy results from a competition between confinement, elasticity and disorder. We obtain an exact description of the large deviation rate function with speed $NL^d$ and its different phases, corresponding to different patterns of replica
symmetry breaking (RSB). Our results show that the ground-state energy satisfies a central limit
theorem and we obtain an explicit expression for the rescaled variance. In the (massless) limit of zero confinement, this variance vanishes for short-range disorder and the ground-state energy displays super-concentration. From our results on the large deviation function, we characterise explicitly the left tail of the distribution of the typical fluctuations of the ground state energy. It displays an exponential tail for a one step RSB pattern while for a full RSB pattern it decays super-exponentially with a non trivial exponent $\xi$ that we compute explicitly.
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Materials Science
Magnetoelectric topology: the rope weaving in parameter space
Ying Zhou, Ziwen Wang, Fan Wang et al. (+2 more)
Topology, as a mathematical concept, has been introduced into condensed matter physics since the discovery of
quantum Hall effect, which characterizes new physical scenario beyond the Landau theory. The topologically protected physical quantities, such as the dissipationless
quantum transport of edge/surface states as well as
magnetic/dipole quasi-particles like skyrmions/bimerons, have attracted great research enthusiasms in the past decades. In recent years, another kind of
topology in condensed matter was revealed in the magnetoelectric parameter space of multiferroics, which deepens our understanding of magnetoelectric physics. This topical review summarizes recent advances in this area, involving three type-II multiferroics. With magnetism-induced ferroelectricity, topological behaviors can be manifested during the magnetoelectric switching processes driven by
magnetic/electric fields, such as Roman-surface/Riemann-surface magnetoelectricity and
magnetic crankshaft. These exotic topological magnetoelectric behaviors may be helpful to pursuit energy-efficient and precise-control devices for spintronics and
quantum computing.
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All authors Ying Zhou, Ziwen Wang, Fan Wang, Haoshen Ye, Shuai Dong
Mesoscale and Nanoscale Physics
Rapid Determination of Nanodiamond Size Distribution and Impurity Concentration from Raman Spectra Using an Open Machine-Learning Toolbox
Sergei V. Koniakhin, Oleg I. Utesov, Vitaly I. Korepanov et al. (+1 more)
Ready-to-use numerical toolbox for nanodiamond Raman spectra calculation and fit is presented. The developed theoretical approach allows accounting for arbitrary nanoparticle size-distribution and the microscopic line broadening mechanisms for the optical
phonons. The two tools for solving the inverse problem of the nanodiamond properties reconstruction using a known Raman spectrum are provided. The first one utilizes a dense neural network trained on a vast array of synthetic Raman spectra. The second approach is based on the
stochastic Metropolis
algorithm, which updates the ensemble parameters by small quantities, tending to the state with minimal error. Both methods are available thanks to the computationally instant elasticity theory-like model for optical
phonon modes in diamond nanocrystals that accurately reproduces the results of the atomistic approaches. Using experimental Raman spectra for nanodiamonds prepared by various techniques, we tested our tools and observed a faithful agreement with the data as well as between the two methods. The open and documented software is accessible online (nanoraman.pythonanywhere.com) and as a Python module (github.com/KoniakhinSV/Nanoparticle_Raman).
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All authors Sergei V. Koniakhin, Oleg I. Utesov, Vitaly I. Korepanov, Andrey G. Yashenkin
Mesoscale and Nanoscale Physics
Nonequilibrium dynamics of magnetic hopfions driven by spin-orbit torque
Shoya Kasai, Shun Okumura and Yukitoshi Motome
Hopfions–three-dimensional topological
solitons with knotted
spin texture–have recently garnered
attention in topological magnetism due to their unique
topology characterized by the
Hopf number $H$, a topological invariant derived from
knot theory. In contrast to two-dimensional skyrmions, which are typically limited to small topological invariants, i.e., skyrmion numbers, hopfions can, in principle, be stabilized with arbitrary
Hopf numbers. However, the nonequilibrium dynamics, especially interconversion between different
Hopf numbers, remain poorly understood. Here, we theoretically investigate the nonequilibrium dynamics of hopfions with various
Hopf numbers by numerically solving the Landau-Lifshitz-Gilbert equation with
spin-orbit torque (SOT). For $H=1$, we show that SOT induces both translational and precessional motion, with dynamics sensitive to the initial orientation. For $H=2$, we find that intermediate SOT strengths can forcibly split the hopfion into two $H = 1$ hopfions. This behavior is explained by an effective tension picture, derived from the dynamics observed in the $H=1$ case. By comparing the splitting dynamics across different $H$, we identify a hierarchical structure governing SOT-driven behavior and use it to predict the dynamics of hopfions with general $H$. Furthermore, we show that by appropriately scheduling the time dependence of the SOT, it is possible to repeatedly induce both splitting and recombination of hopfions. These results demonstrate the controllability of hopfion
topology via SOT and suggest a pathway toward multilevel spintronic devices based on
topology switching.
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Materials Science
Ferroelectric Control of Spin Textures in Layered Hybrid Perovskites
Divyanshi Tyagi and Saswata Bhattacharya
Hybrid organic–inorganic perovskites with broken inversion
symmetry provide a fertile ground for uncovering coupled
spin-orbit and ferroelectric phenomena. Here, we investigate the layered family (PA)$_2$CsY$_2$X$_7$ (Y = Pb, Sn; X = I, Br) using density functional theory, Berry-phase polarization analysis, and effective $\boldsymbol{k \cdot p}$ modeling. Across all four members, we find indirect bandgaps with extrema near $\Gamma$, sizable
spin splittings at both band edges, and robust in-plane ferroelectric polarization that stabilizes out-of-plane persistent
spin textures (PSTs). Crucially, polarization reversal switches the
spin orientation, enabling electrical control of PSTs and thereby non-volatile manipulation of
spin states. These results establish (PA)$_2$CsY$_2$X$_7$ as a versatile materials platform where compositional design and ferroelectric switching jointly enable spintronic functionality.
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Mesoscale and Nanoscale Physics
Shoya Kasai, Shun Okumura and Yukitoshi Motome
Knots, characterized by topological invariants called the
Hopf number $H$, arise from the intertwining of strings and exhibit diverse configurations. The
knot structures have recently been observed in condensed matters, as examplified by a
magnetic hopfion, sparking interest in controlling their
topology. Here, we show that
spin-orbit torque (SOT) enables dynamic manipulation of the
Hopf number of
magnetic hopfions. We investigate the SOT-driven
evolution of hopfions, revealing the splitting of a high-$H$ hopfion into multiple lower-$H$ ones, a process that can be quantified by an effective tension picture. Comparative analysis across different $H$ uncovers a hierarchy of instabilities that dictates these dynamical topological transitions. These findings establish SOT as a powerful tool for controlling hopfion
topology, paving the way for potential applications in topological
memory devices.
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Mesoscale and Nanoscale Physics
Radial etching of strongly confined crystal-phase defined quantum dots
Markus Aspegren, Chris Mkolongo, Sebastian Lehmann et al. (+3 more)
We realize strongly confined
quantum dots (QDs) in InAs nanowires (NWs) by combining epitaxial
crystal-phase control with chemical wet etching. A strong axial confinement is first introduced by growing closely spaced wurtzite (WZ) tunnel barriers in NWs to enclose a zinc blende (ZB) QD. The NW cross-section is then reduced by isotropic etching to obtain very small QDs, with a maximum observed charging energy > 30 meV. Using low-temperature electrical characterization and finite-element method simulations, we study how charging energies and the onset of electron filling scale with QD diameter. For extremely small diameters, we identify a regime where stray capacitances become non-negligible, limiting further increase in charging energy by diameter reduction alone. This approach to increasing confinement is particularly relevant for understanding the strong
spin-orbit interaction observed in
crystal-phase QDs, possibly linked to polarization charges at the WZ/ZB interfaces. Small diameter QDs allow considerably weaker interfering electric fields when studied, but the QDs cannot be realized with epitaxial growth alone due to a loss of
crystal phase control.
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All authors Markus Aspegren, Chris Mkolongo, Sebastian Lehmann, Kimberly Dick, Adam Burke, Claes Thelander
Materials Science · Cross-listed from physics.chem-ph
Toward Unified Interphase Engineering: The Solid-Electrolyte Interphase in Batteries and Supercapacitors
Mehedi Hasan, Ishtiaq Murshed, Khayrul Islam et al. (+1 more)
The development of next-generation electrochemical energy storage requires devices that combine the high energy density of batteries with the power capability and long cycle life of supercapacitors. However, the interfacial phenomena governing performance in these systems remain poorly unified. The solid-electrolyte interphase (SEI), a nanoscale film formed by electrolyte decomposition, is well studied in batteries but its counterpart in supercapacitors has received limited systematic investigation despite growing experimental evidence. This review argues that SEI formation is a universal electrochemical process that occurs whenever electrode potentials drive electron transfer into electrolyte orbitals beyond their stability limits, independent of whether charge storage is Faradaic or non-Faradaic. Differences between battery SEIs and supercapacitor interphases arise mainly from operating conditions, not fundamental chemistry. Engineered interphases created through electrolyte additives, protective coatings, or surface functionalization suppress leakage currents, improve capacitance retention, and enable stable high-voltage operation. By identifying shared mechanisms and establishing transferable design rules, this unified framework provides a foundation for predictive interphase engineering that supports long-lived, high-performance energy-storage technologies.
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All authors Mehedi Hasan, Ishtiaq Murshed, Khayrul Islam, A.K.M. Masud
Materials Science
CsCl seed layer homogenizes co-evaporated perovskite growth for high-efficiency fully textured perovskite-silicon tandem solar cells
Viktor Škorjanc, Stefanie Severin, Alexander Veber et al. (+24 more)
Monolithic perovskite-silicon tandem
solar cells experienced a significant increase in efficiency, making them viable for industrial applications. Among the various scalable and industry-compatible metal halide perovskite deposition techniques, co-evaporation stands out as particularly well-suited for perovskite-silicon tandem
solar cells due to its ability to conformally cover textured silicon bottom
cells. Solution-processed [2-(3,6-Dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz) is commonly used as a hole-transporting material for co-evaporated metal halide perovskites. However, we show that it covers the textured surface of silicon bottom
cells unevenly, impacting the film growth and leading to the formation of residual PbI2 at the buried interface. The present study reveals via X-ray photoemission electron microscopy (XPEEM) and infrared scattering-type scanning near-field optical microscope (IR s-SNOM) that a CsCl seed layer fosters organic precursor incorporation across the MeO-2PACz/perovskite interface, even in the areas with a thin MeO-2PACz layer, thereby preventing the formation of interfacial PbI2 and leading to larger apparent grains. The improvement of the metal halide perovskite film quality on the MeO-2PACz/perovskite interface and the bulk perovskite film led to 30.3% (29.7% certified) efficient perovskite-silicon tandem
solar cell. The present work highlights the importance of a seed layer for a robust growth of co-evaporated metal halide perovskite and represents an important milestone for the transfer of perovskite-silicon tandem
solar cells from laboratory to industry.
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All authors Viktor Škorjanc, Stefanie Severin, Alexander Veber, Mauricio J. Prieto, Liviu C. Tănase, Aleksandra Miaskiewicz, Sebastian Weitz, Jing-Wen Hsueh, Mohamad-Assaad Mawass, Lucas de Souza Caldas, Suresh Manyarasu, Philippe Holzhey, Erik Wutke, Stepan Demchyshyn, Matthew R. Leyden, Angelika Harter, Roberto Felix Duarte, Jona Kurpiers, Philipp Wagner, Bernd Stannovski, Ljiljana Puskar, Roland Mainz, Daniel Abou-Ras, Thomas Schmidt, Lars Korte, Marcel Roß, Steve Albrecht
Materials Science
Observing the spatial and temporal evolution of exciton wave functions
Marcel Theilen, Siegfried Kaidisch, Monja Stettner et al. (+12 more)
Excitons, the correlated electron-hole pairs governing optical and transport properties in organic
semiconductors, have long resisted direct experimental access to their full
quantum-mechanical wave functions. Here, we use femtosecond time-resolved photoemission orbital
tomography (trPOT), combining high-harmonic probe pulses with time- and momentum-resolved photoelectron spectroscopy, to directly image the momentum-space distribution and ultrafast dynamics of
excitons in $\alpha$-sexithiophene thin films. We introduce a quantitative model that enables reconstruction of the
exciton wave function in real space, including both its spatial extent and its internal phase structure. The reconstructed wave function reveals coherent delocalization across approximately three molecular units and exhibits a characteristic phase modulation, consistent with ab initio calculations within the framework of many-body perturbation theory. Time-resolved measurements further show a $\sim 20$% contraction of the
exciton radius within 400 fs, providing direct evidence of self-trapping driven by
exciton-
phonon coupling. These results establish trPOT as a general and experimentally accessible approach for resolving
exciton wave functions – with spatial, phase, and temporal sensitivity – in a broad class of molecular and low-dimensional materials.
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All authors Marcel Theilen, Siegfried Kaidisch, Monja Stettner, Sarah Zajusch, Eric Fackelman, Alexa Adamkiewicz, Robert Wallauer, Andreas Windischbacher, Christian S. Kern, Michael G. Ramsey, François C. Bocquet, Serguei Soubatch, F. Stefan Tautz, Ulrich Höfer, Peter Puschnig
Superconductivity
Coexistence of near-EF van Hove singularity and in-gap topological Dirac surface states in superconducting electrides
Yin Yang, Peihan Sun, Ye Shen et al. (+9 more)
Superconducting electrides have attracted growing
attention for their potential to achieve high superconducting transition temperatures (TC) under pressure. However, many known electrides are chemically reactive and unstable, making high-quality single-
crystal growth, characterization, and measurements difficult, and most do not exhibit superconductivity at ambient pressure. In contrast, La3In stands out for its ambient-pressure superconductivity (TC ~ 9.4 K) and the availability of high-quality single
crystals. Here, we investigate its low-energy electronic structure using angle-resolved photoemission spectroscopy and first-principles calculations. The bands near the
Fermi energy are mainly derived from La 5d and In 5p orbitals. A saddle point is directly observed at the Brillouin zone (BZ) boundary, while a three-dimensional van Hove singularity crosses EF at the BZ corner. First-principles calculations further reveal topological Dirac surface states within the bulk energy gap above EF. The coexistence of a high density of states and in-gap topological surface states near EF suggests that La3In offers a promising platform for tuning superconductivity and exploring possible topological superconducting phases through doping or external pressure.
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All authors Yin Yang, Peihan Sun, Ye Shen, Zhijun Tu, Pengcheng Ma, Hongrun Zhen, Tianqi Wang, Longli Tian, Tian Cui, Hechang Lei, Kai Liu, Zhonghao Liu
Mesoscale and Nanoscale Physics
Interaction-Driven Chern Insulator at Zero Electric Field in ABCB-Stacked Tetralayer Graphene
Yulu Ren, Yang Shen, Chengyang Xu et al. (+2 more)
ABCB-stacked tetralayer
graphene, with intrinsic spontaneous polarization, offers a unique platform to explore electron correlation effects, whose interplay with
spin-orbit coupling may engender topological phases. Here, employing a $\mathbf{k}\cdot\mathbf{p}$ model with self-consistent Hartree-Fock calculations, we investigate its electronic ground states. Remarkably, we find that the intrinsic polarization, in conjunction with strong interactions ($U=8 \text{ eV}$) and SOC, is sufficient to drive a $C=3$
quantum anomalous
Hall state, obviating the need for an external electric field typical in ABCA stacks. Conversely, at moderate interactions ($U=6 \text{ eV}$), a minimal electric field is necessary. Furthermore, calculations predict other correlation-driven metallic phases such as quarter- and three-quarter-filled states. These results establish that the synergy of intrinsic polarization, correlations, and SOC governs the rich topological phenomena, suggesting ABCB-stacked
graphene as a highly tunable platform for exploring emergent topological phenomena.
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All authors Yulu Ren, Yang Shen, Chengyang Xu, Wanfei Shan, Weidong Luo
Statistical Mechanics
Robust Universality of Non-Hermitian Anderson Transitions: From Dyson Singularity to Model-Independent Scaling
Ali Tozar
We investigate the universality of Anderson localization transitions in one-dimensional non-Hermitian systems exhibiting the skin effect. By developing a numerically stable Log-Space Non-Hermitian Scaling (LNS) method, we overcome the severe floating-point overflow issues associated with the exponential growth of transmittance (T ~ exp(2 gamma L)), enabling precision finite-size scaling analysis up to system sizes of L = 1200. We probe the critical behavior across three distinct disorder landscapes: uniform diagonal, binary diagonal, and off-diagonal (random hopping) disorder. While the uniform model exhibits a standard mobility edge, the off-diagonal model reveals a Dyson-like singularity at the band center (E = 0), where the system resists localization even at strong disorder due to sublattice
symmetry protection. However, upon
symmetry breaking (E != 0), we demonstrate that all considered models, regardless of the disorder distribution (continuous vs. discrete) or
Hamiltonian structure (site vs. bond randomness), belong to the same robust universality class. The critical exponents are determined as nu = 1.50 +/- 0.00 and beta ~ 0.65 through unambiguous data collapse, establishing a model-independent description of non-Hermitian localization transitions.
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Statistical Mechanics
Generation of concurrence in a generalized central spin model with a three-spin interacting environment
Adithya A. Vasista, Anushka Agrawal and Tanay Nag
We consider the three-
spin Ising model to study the effect of three-
spin interacting term on bi-partitie
entanglement between adjacent
spins. The three-dominated disordered region has tri-partite
entanglement causing a vanishingly small concurrence, while it acquires maximum value around the critical points. Considering the above model as an environment, we construct a generalized central
spin model where two central
spins, initially in an unentangled pure state, are coupled locally to two distinct sites of the environmental
spin chain. We study the generation of mixed state
entanglement between the central
spins when the transverse field of the environment is kept fixed, and suddenly quenched, referring to
equilibrium and non-
equilibrium dynamics of the central
spins, respectively. For the critical environment in the
equilibrium, the concurrence shows a dip-revival structure governed by quasi-particle movement. In the non-
equilibrium study, we find an initial growth of concurrence followed by a two-stage fall for the inter-phase quench which is governed by dynamic decoherence channels. The central
spins are maximally entangled for a quench in the vicinity of a multicritical point, which arises due to three-
spin interaction only. The concurrence becomes long-lived for an intra-phase quench, and this sustainability depends on the strength of the three-
spin interaction. Therefore, the three-
spin interaction indeed helps in generating bi-partite
entanglement in the central
spins.
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Mesoscale and Nanoscale Physics
Imaging propagating terahertz collective modes in two-dimensional semiconductor double layers
Andrew T. Pierce, Chirag Vaswani, Dimitri Pimenov et al. (+7 more)
Two-dimensional transition metal dichalcogenide (TMD)
semiconductors exhibit a wide range of novel phenomena at millielectronvolt (terahertz-frequency) energy scales, including superconducting and correlation-induced insulating gaps that are frequently accompanied by
symmetry breaking. However, due to the subwavelength dimensions and the often low conductivities of these systems, their intrinsic THz plasmons and meV-scale excitation gaps are difficult to access experimentally. Here we report an optical readout method that can image propagating THz-frequency collective modes in real time. The method relies on a strong coupling between the optical polarons of monolayer TMD
semiconductors and the local THz fields in a waveguide, which enables us to image THz plasmons with micron scale spatial resolution and determine their propagation group velocities. Moreover, at finite
magnetic fields, we observe coherent cyclotron oscillations resulting from Landau level repopulation induced by the THz field. Our findings provide a new near-field platform for probing collective excitations in strongly correlated two-dimensional
semiconductors and enable "all-photonic" TMD-based architectures for time-domain THz plasmonics and optoelectronics.
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All authors Andrew T. Pierce, Chirag Vaswani, Dimitri Pimenov, Sihong Xu, Kenji Watanabe, Takashi Taniguchi, Erich Mueller, Debanjan Chowdhury, Kin Fai Mak, Jie Shan
Superconductivity · Cross-listed from quant-ph
Evidence for unexpectedly low quasiparticle generation rates across Josephson junctions of driven superconducting qubits
Byoung-moo Ann, Sang-Jun Choi, Hee Chul Park et al. (+6 more)
Recent studies find that even drives far below the superconducting gap frequency may cause drive-induced quasiparticle generation (QPG) across Josephson junctions (JJs) of superconducting
qubits (SCQs), posing a serious concern for fault-tolerant superconducting
quantum computing (FTSQC). Nonetheless, quantitative experimental estimation on QPG rates has remained vague. Here, we investigate QPG using strongly driven SCQs, reaching
qubit drive amplitudes up to $2\pi\times$300 GHz by applying intense drive fields through the readout resonators. The resonator nonlinear responses enable quantification of the energy loss at SCQs, including the contribution from QPG. Surprisingly, the estimated total energy loss rates are far lower than those expected by the Floquet-Markov formalism with QPG as the sole loss mechanism. Meanwhile, calculations that incorporate high-frequency cutoffs (HFCs) in the QPG conductance at approximately 17-20 GHz effectively explain the experimental observations. These results suggest limitations in either the QPG conductance model or the Markovian treatment of the QPG processes. Both possibilities possess crucial implications for handling QPG problems toward FTSQC and for a more deeper understanding of Josephson junctions.
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All authors Byoung-moo Ann, Sang-Jun Choi, Hee Chul Park, Sercan Deve, Robin Dekker, Gary A. Steele, Jaseung Ku, Seung-Bo Shim, Junho Suh
Strongly Correlated Electrons
Two-Electron Correlations in the Metallic Electron Gas
Zhiyi Li, Pengcheng Hou, Bao-Zong Wang et al. (+2 more)
We present high-precision ab initio calculations of the four-point vertex function for the three-dimensional uniform electron gas using variational diagrammatic Monte Carlo. From these results, we extract Landau parameters that reveal a density-driven crossover from underscreening to overscreening, and obtain the full two-electron scattering amplitude on the
Fermi surface with controlled accuracy. A residual analysis of the scattering amplitude against the charge-channel Kukkonen–Overhauser (KO$^+$) interaction shows that only a minimal s-wave correction in the antiparallel-
spin channel is needed, defining the sKO$^+$ ansatz: KO$^+$ within the local-density approximation plus this short-range correction. Using both our direct VDMC amplitudes and the sKO$^+$ ansatz, we compute the electron-electron contribution to the thermal resistivity, obtaining quantitative agreement with experiments on simple metals (Al, Na, K, Rb). sKO$^+$ thus provides a controlled UEG-based effective interaction for simple-metal transport and future first-principles extensions.
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All authors Zhiyi Li, Pengcheng Hou, Bao-Zong Wang, Youjin Deng, Kun Chen
Mesoscale and Nanoscale Physics
Generation of Ultra-Broadband Frequency Comb in Strongly Bistable Nonlinear Magnonic Resonator
Yu Jiang, Vasyl Tyberkevych, Yizhong Huang et al. (+4 more)
Magnonic frequency combs (MFCs) offer a promising route to compact, energy-efficient platforms for on-chip coherent microwave signal generation and processing. Conventional on-chip comb generation typically relies on nonlinear resonators supporting a series of equidistant, low-loss resonances driven by a strong monochromatic signal, resulting in fixed comb spacing defined by the resonator's free spectral range (FSR). Here we introduce and experimentally demonstrate a fundamentally different mechanism for ultrabroadband MFC generation using a highly nonlinear miniaturized magnonic resonator. The small resonator volume, combined with a slow-wave transducer, yields high intra-resonator power density, driving the system deep into the bistable regime where parametric excitation of propagating
spin waves facilitates comb formation. Our approach yields more than 350 comb lines spanning a 450 MHz bandwidth, with spacing continuously tunable via a two-tone external drive, representing an order-of-magnitude enhancement over prior reports while operating at relatively low power. The platform is ultra-compact (4-6 orders of magnitude smaller in size than conventional YIG sphere resonators), fully scalable, and highly tunable, enabling precise control of comb properties through
magnetic bias and pump manipulation. These results establish a new paradigm for frequency comb technology, unlocking transformative opportunities in microwave signal processing, neuromorphic computing, and precision sensing.
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All authors Yu Jiang, Vasyl Tyberkevych, Yizhong Huang, Zixin Yan, Amin Pishehvar, Andrei Slavin, Xufeng Zhang
Strongly Correlated Electrons
Development of ultra-high efficiency soft X-ray angle-resolved photoemission spectroscopy equipped with deep prior-based denoising method
Kohei Yamagami, Yuichi Yokoyama, Yuta Sumiya et al. (+3 more)
Soft X-ray angle resolved photoemission spectroscopy (SX-ARPES) is one of the most powerful spectroscopic techniques to visualize the three-dimensional bulk electronic structure in reciprocal
lattice space. Compared with ARPES employing low-energy
photon sources, the time burden imposed by a lower photoelectron yield, stemming from the photoionization cross-section, has been a persistent technical challenge. To address this challenge, we have developed a noise removal system by using the deep prior-based method and integrated it into the micro focused SX-ARPES ({\mu}SX-ARPES) system at BL25SU in SPring-8. Our implemented system effectively eliminates the grid and spike noise typically present in ARPES data acquired using the voltage Fixed-mode, within about 30 seconds. We demonstrate, through the {\mu}SX-ARPES measurements on a single
crystal of CeRu2Si2, that data with sufficient statistical accuracy can be obtained in approximately 40 seconds. In addition, we present the potential of high signal-to-noise ratio ARPES measurement, achieving an energy resolution of 51.6 meV at an excitation energy of 708 eV in {\mu}SX-ARPES measurements on polycrystalline gold. Our developed system successfully reduces the time burden in SX-ARPES and paves the way for advancements in lower photoelectron yield measurements, such as those requiring higher energy resolution and three-dimensional nonequilibrium measurements.
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All authors Kohei Yamagami, Yuichi Yokoyama, Yuta Sumiya, Hayaru Shouno, Tetsuro Nakamura, Masaichiro Mizumaki
Materials Science
Order-Disorder in Fe-Si Alloys: Implications for Seismic and Transport Properties of Earth's Inner Core
Cong Liu, Xin Deng and R. E. Cohen
Understanding the structure and dynamics of Earth's inner core is essential for constraining its composition, thermal
evolution, and seismic behavior. Silicon is widely considered a major light element in the core. Here, we use first-principles molecular dynamics and thermodynamic modeling to investigate the structural, elastic, and transport properties of iron-silicon (Fe-Si)
alloys under inner-core conditions. By computing the Gibbs free energies of multiple solid phases, including ordered B2, hexagonal close-packed (hcp), face-centered cubic (fcc), and body-centered cubic (bcc) Fe-Si, we construct a phase diagram relevant to inner-core pressures and temperatures. We identify a pronounced miscibility gap between hcp and cubic Fe–Si phases, with phase coexistence over approximately 6–11 wt% Si at 6000 K. The cubic phase exhibits a strong order-dependent elastic response, with disordered bcc showing a large intrinsic shear anisotropy (22.9% at 6000 K), in contrast to the nearly isotropic hcp phase (0.6%). Meanwhile, disordered bcc Fe–Si produces shear wave velocities ($V_S=3.73$ km$\cdot$s$^{-1}$) and Poisson's ratios comparable with seismological constraints. In addition, disordered bcc Fe–Si exhibits a lower thermal conductivity than hcp Fe–Si, providing a quantitative constraint on phase-dependent electronic heat transport. These results demonstrate that chemical ordering strongly controls the stability and physical properties of cubic Fe–Si
alloys, and suggest that metastable or localized cubic Fe–Si phases may contribute to the structural and transport complexity of Earth's inner core.
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Materials Science
Evaluating Mechanical Property Prediction across Material Classes using Molecular Dynamics Simulations with Universal Machine-Learned Interatomic Potentials
Konstantin Stracke, Connor W. Edwards and Jack D. Evans
We assess the accuracy of six universal machine-learned interatomic potentials (MLIPs) for predicting the temperature and pressure response of materials by molecular dynamics simulations. Accuracy is evaluated across 13 diverse materials (nine metal-organic frameworks and four inorganic compounds), computing bulk modulus, thermal expansion, and thermal decomposition. These MLIPs employ three different architectures (graph neural networks, graph network simulators, and graph
transformers) with varying training
datasets. We observe qualitative accuracy across these predictions but systematic underestimation of bulk modulus and overestimation of thermal expansion across all models, consistent with potential energy surface softening. From all tested models, three top performers arise; `MACE-MP-0a', `fairchem_OMAT', and `Orb-v3', with average error across metrics and materials of 41%, 44%, and 47%, respectively. Despite strong overall performance, questions arise about the limits of model transferability:
dataset homogeneity and structural representation dominate model accuracy. Our results show that certain architectures can compensate for biases, a step closer to truly universal MLIPs.
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Materials Science
Ready-to-Use Polymerization Simulations Combining Universal Machine Learning Interatomic Potential with Time-Dependent Bond Boosting for Polymer and Interface Design
Hodaka Mori, Shunsuke Tonogai, Yu Miyazaki et al. (+2 more)
Although polymerization and curing reactions govern the performance of advanced materials, their simulation remains challenging owing to the need for accurate, transferable potentials and rarity of chemical events. Conventional reactive force fields such as ReaxFF require system-specific parametrization, while universal machine learning interatomic potentials (uMLIPs) exhibit limited sampling efficiency. This paper introduces a novel simulation framework integrating a uMLIP with a time-dependent bond-boost scheme. The bias potential increases monotonically with time, and the use of a unified parameter set across reaction classes enables consistent acceleration without system-specific tuning. For radical polymerization of vinyl monomers, the proposed framework reproduces characteristic trends, such as linear molecular-weight growth with conversion, initiator-concentration scaling, and relative monomer reactivity trends. For step-growth polycondensation of nylon-6,6, it captures the characteristic sharp increase in molecular weight at high conversion rates, consistent with experimental behavior. For epoxy curing at a copper substrate, it reveals interfacial ring-opening and cross-linking events, consistent with spectroscopic evidence of Cu-O-C bond formation. Overall, coupling uMLIPs with time-dependent bond boost enables practical and transferable simulations of polymerization and curing processes. The proposed framework reliably resolves mechanistic pathways and relative reactivity, offering molecular-level insights into
polymer growth and interfacial adhesion.
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All authors Hodaka Mori, Shunsuke Tonogai, Yu Miyazaki, Akihide Hayashi, Masayoshi Takayanagi
Disordered Systems and Neural Networks · Cross-listed from q-bio.NC
Short-term plasticity recalls forgotten memories through a trampoline mechanism
Martina Del Gaudio, Federico Ghimenti and Surya Ganguli
We analyze continuous Hopfield associative
memories augmented by additional, rapid short-term associative synaptic plasticity. Through the cavity method, we determine the boundary between the
retrieval and forgetting, or
spin-glass phase, of the network as a function of the fraction of stored
memories and the neuronal gain. We find that short-term synaptic plasticity yields marginal improvements in critical
memory capacity. However, through dynamical mean field theory, backed by extensive numerical simulations, we find that short-term synaptic plasticity has a dramatic impact on
memory retrieval above the critical capacity. When short-term synaptic plasticity is turned on, the combined neuronal and synaptic dynamics descends a high-dimensional energy landscape over both
neurons and synapses. The energy landscape over
neurons alone is thus dynamic, and is lowered in the vicinity of recent neuronal patterns visited by the network, just like the surface of a trampoline is lowered in the vicinity of regions recently visited by a heavy ball. This trampoline-like reactivity of the neuronal energy landscape to short-term plasticity in synapses can lead to the recall of stored
memories that would otherwise have been forgotten. This occurs because the dynamics without short-term plasticity transiently moves towards a stored
memory before departing away from it. Thus short-term plasticity, operating during the transient, lowers the energy in the vicinity of the stored
memory, eventually trapping the combined neuronal and synaptic dynamics at a fixed point close to the stored
memory. In this manner, short-term plasticity enables the recall of
memories that would otherwise be forgotten, by trapping transients that would otherwise escape. We furthermore find an optimal time constant for short-term synaptic plasticity, matched to the transient dynamics, to empower recall of forgotten
memories.
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Mesoscale and Nanoscale Physics
Confinement-Induced Metastability and Structural Diversity of Hopfions in Chiral Magnetic Films
Andrey O. Leonov and Takayuki Shigenaga
Topological particle-like excitations such as skyrmions and hopfions offer rich opportunities for spintronic and photonic applications. While skyrmions have been extensively studied, the stabilization mechanisms and phase behavior of three-dimensional hopfions remain largely unexplored. Here, we investigate the formation, stability, and interactions of hopfions in thin
chiral magnetic films with surface anchoring, using three-dimensional micromagnetic simulations within a material-independent framework applicable to both
magnetic and
liquid crystalline systems. We identify four distinct types of isolated hopfions, generated by rotating bimeron and finger-like
solitons around a central axis. The metastability regions of these precursor textures closely follow the boundaries of modulated finger phases, enabling their size to be continuously tuned through anisotropydriven inflation and collapse. Remarkably, we demonstrate that hopfions near their inflation threshold possess energies comparable with the homogeneous state, allowing them to enclose regions of modulated phases or other
solitons, forming higher-order, bag-like domains. In contrast, periodic hopfion
lattices remain intrinsically unstable under confinement, spontaneously relaxing into finger phases. These findings establish general principles for stabilizing, tuning, and assembling three-dimensional topological
solitons in confined
chiral systems, suggesting experimentally accessible routes for texture engineering in
liquid crystals via electric-field control.
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Materials Science
Characteristic ferroelectric domains and their dynamic behavior in ordered Pb(Sc$_{1/2}$Nb$_{1/2}$)O$_{3}$
Hiroshi Nakajima, Satoshi Hiroi, Hirofumi Tsukasaki et al. (+5 more)
Pb-based perovskites with multiple cations are fascinating materials showing various phenomena such as high piezoelectric, electromechanical, and relaxor properties. While chemical disordering accompanied by polar nanoregions and nanosized domains is commonly believed to cause the relaxor nature, little is known about ferroelectric microstructures of chemically ordered Pb-based perovskites. In this study, we discovered intriguing meandering ferroelectric domains in chemically ordered ferroelectric Pb(Sc$_{1/2}$Nb$_{1/2}$)O$_{3}$ using in-situ transmission electron microscopy with dark-field imaging. Observation results demonstrate that electric polarization can fluctuate around the [111] direction despite the formation of long-range ordered rhombohedral domains, which results in unique weak relaxor properties. In-situ imaging upon heating successfully reveals the dynamic behavior of domain-wall movements with
lattice distortion and paraelectric-ferroelectric phase coexistence in the vicinity of the Curie temperature, indicating a discontinuous phase transition. Our research provides new insights into the effect of chemical ordering on ferroelectric nanodomains.
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All authors Hiroshi Nakajima, Satoshi Hiroi, Hirofumi Tsukasaki, Yonghong Bing, Stéphane Grenier, Zuo-Guang Ye, Pierre-Eymeric Janolin, Shigeo Mori