Statistical Mechanics · Cross-listed from nlin.AO
Time delay in the 1d swarmalator model
K. P. O'Keeffe and Jason Hindes
We study the 1d swarmalator model augmented with time delayed coupling. Along with the familiar sync, async, and phase wave states, we find a family of unsteady states where the order parameters are time periodic, sometimes with clean oscillations, sometimes with irregular vacillations. The unsteady states are born in two ways: via a
Hopf bifurcation from the phase wave, and a zero
eigenvalue bifurcation from the async state. We find both of these boundary curves analytically. A surprising result is that stabilities of the async and sync states are independent of the delay {\tau}; they depend only on the coupling strength.
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Mesoscale and Nanoscale Physics
Symmetry, Disorder and Transport Through Altermagnetic Quantum Dots and Their Antiferromagnetic Twins
George Kirczenow
Altermagnetic
crystals resemble antiferromagnets in that they have no macroscopic magnetization, but unlike antiferromagnets they exhibit
spin-split band structures. Here the transport properties of altermagnetic
quantum dots and their
antiferromagnetic twins are explored theoretically with the help of Landauer-Buttiker theory,
symmetry considerations and tight-binding models. The influence of the
symmetries of the
quantum dots, their parent
crystal lattices, their shapes and edges, lead arrangements and disorder on the anomalous
Hall effect, the
spin-
Hall effect and
spin filtering by the
quantum dots are investigated.
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Materials Science
Region-Resolved Interface Descriptors in III-nitride-nanocluster photocatalysts
Shuaishuai Yuan, Gunther G. Andersson, Gregory F. Metha et al. (+2 more)
Understanding how nanocluster cocatalysts modify the electronic structure of III-nitride surfaces is central to the rational design of efficient photocatalytic interfaces. Here, we introduce a region-resolved first-principles framework for analyzing GaN-, InGaN-, and ScGaN-based slabs decorated with six-atom elemental nanoclusters. Using a region-resolved projected local density of states (PLDOS) analysis, we separate electronic response of nanocluster-covered regions from that of uncovered
semiconductor surface regions, revealing that
semiconductor–nanocluster interfaces behave as laterally heterogeneous systems. In this picture, nanocluster-covered regions are associated with local band bending, charge injection, and nanocluster-induced gap states, whereas uncovered nitride regions retain surface-localized states and in-plane dipoles that may influence adsorbate interactions and water-activation pathways. These distinct regional responses motivate the definition of region-resolved interface descriptors, which are further integrated into an Interface Score: a physics-informed comparative metric that combines injection, activation, and interfacial-coupling contributions to rank heterogeneous model interfaces on a common descriptor basis. Machine-learning models trained on global and region-resolved descriptors are used primarily as interpretability tools to assess their correlation with single-H adsorption energetics. The results show that spatially averaged descriptors capture broad adsorption-energy trends, while region-resolved descriptors expose complementary local information related to interfacial electrostatics and charge separation. Together, this work establishes a descriptor framework for moving beyond spatially averaged electronic-structure analysis and for bridging first-principles calculations with experimental interpretation of heterogeneous photocatalytic interfaces.
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All authors Shuaishuai Yuan, Gunther G. Andersson, Gregory F. Metha, Zetian Mi, Hong Guo
Soft Condensed Matter
From Connectivity to Rupture: A Coarse-Grained Stochastic Network Dynamics Approach to Polymer Network Mechanics
Shaswat Mohanty and Wei Cai
We introduce a coarse-grained
stochastic network dynamics (CGSND) framework for modeling deformation and rupture in
polymer networks. The method replaces explicit molecular dynamics (MD) or coarse-grained molecular dynamics (CGMD) with network-level
evolution rules while retaining chain entropic elasticity and force-controlled bond failure. Under uniaxial loading, CGSND reproduces the characteristic nonlinear stress–stretch response of elastomeric networks, including a well-defined ultimate tensile strength and post-peak softening due to progressive bond rupture. Comparison with coarse-grained molecular dynamics (CGMD) simulations shows that CGSND captures the qualitative form of the stress response and the onset of catastrophic damage despite its rate-independent formulation. Analysis of rupture kinetics reveals a pronounced peak in the bond-breaking hazard rate near the ultimate tensile strength in both approaches. In addition, the distribution of broken segment lengths remains statistically indistinguishable from the initial network, indicating that rupture is not biased toward short or long chains. Finally, the
evolution of the Gini coefficient of bond force magnitudes reveals strong force localization preceding failure. These results demonstrate that CGSND provides a computationally efficient and physically interpretable framework for connecting force localization and rupture kinetics to macroscopic failure in
polymer networks.
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Materials Science · Cross-listed from physics.app-ph
Spatially and Temporally Resolved Mapping of Contact Electrification on Stand-Alone Ultrathin Glass Materials via Kelvin Probe Force Microscopy
Aayush Nayyar, Ruizhe Yang, Vashin Gautham et al. (+7 more)
Contact electrification (CE) remains a critical challenge in advanced material technologies where uncontrolled surface charging can compromise manufacturability, reliability, and performance in practical applications. Ultrathin glass with micrometer-scale thickness is a state-of-the-art specialty
oxide material for flexible touchscreens in next-generation electronic devices. Here, we visualize and quantify CE-induced surface charges on ultrathin glass using sideband-mode Kelvin probe force microscopy (KPFM). Nanoscale atomic force microscopy (AFM) probes are used to scan and induce triboelectric charges on stand-alone glass surfaces under ultra-pure N$_2$ conditions. Time-dependent measurements reveal that surface charges on a 30~$\mu$m-thick glass sample decay from 4.47~V to 0.37~V over 240~minutes. Furthermore, electrostatic charges are found to exhibit capacitor-like discharging behavior primarily through the bulk material, yielding a long relaxation time constant of approximately 41~minutes. This behavior differs from the lateral surface discharging observed in thermally grown SiO$2$ thin films reported previously. A self-capacitance analytical model is developed to estimate the corresponding surface charge density ($\sigma$), yielding comparable values of 136.26~$\pm$~16.25~$\mu$C/m$^2$ at 30~$\mu$m and 131.44~$\pm$~28.41~$\mu$C/m$^2$ at 100~$\mu$m. Additionally, external bias applied to AFM tips can be used to enhance, suppress, or invert the intrinsic CE response of glass materials.
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All authors Aayush Nayyar, Ruizhe Yang, Vashin Gautham, Sagnik Das, Haiqing Lin, Andrew C. Antony, Dean Thelen, Mayukh Nath, Gabriel Agnello, Jun Liu
Soft Condensed Matter
Continuum-statistical dynamics of colloidal suspensions under kinematic reversibility
Jerome Burelbach
We present a linear response theory that establishes the continuum-mechanical origin of Onsager reciprocity in colloidal motion. By decoupling hydrostatic and hydrodynamic stress, we show that Onsager reciprocal relations emerge when the Lorentz reciprocal
theorem is applied under kinematic reversibility to the auxiliary flow problem of colloidal sedimentation. Our framework applies to suspensions containing multiple species of microparticles and derives all non-
equilibrium contributions to colloidal
diffusion from a single application of the Lorentz reciprocal
theorem, irrespective of whether a slip or no-slip hydrodynamic boundary condition is imposed at the colloidal surface. Furthermore, a boundary-layer treatment is only assumed for ciliary motion, while the hydrostatic forces giving rise to non-
equilibrium thermodynamic motion are fully resolved beyond the boundary-layer approximation. In particular, our framework is consistent with classical osmosis through a semi-permeable membrane, where fluid flow occurs without interfacial potential interactions. For diffusiophoresis due to volume exclusion of a solute, our results therefore predict colloidal motion towards higher solute concentration for thin excluded-volume layers, whereas the opposite trend is recovered for longer-ranged, moderately repulsive potentials.
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Superconductivity
Investigation of CeRh$_2$As$_2$ order parameters via ultrasound propagation anomalies
S. Galeski, C. Lee, F. Bartl et al. (+11 more)
Unconventional
superconductors with nearly degenerate pairing states are rare. CeRh$_2$As$_2$ has recently emerged as one of the few existing multi-phase
superconductors. It exhibits a first-order phase transition between two distinct superconducting states when a
magnetic field is applied along the crystallographic $c$-axis. While this behavior has been linked to locally broken inversion
symmetry, a phase diagram based on a multi-component superconducting order parameter remains a possibility. Furthermore, superconductivity appears to coexist with an ordered state (phase I). Despite being the subject of many studies, little is known about the nature of the order parameters in both superconducting phases and phase I. Here, we use ultrasound-propagation measurements at low temperatures, in high
magnetic fields and under hydrostatic pressure to address this issue. Our results strongly suggest that the superconducting order parameter in both phases is single-component, corroborating the role of local non-centrosymmetry in the development of multi-phase superconductivity in CeRh$_2$As$_2$. In addition, analysis of the elastic anomalies within the Landau framework of phase transitions strongly suggests the presence of an incommensurate
magnetic order parameter in phase I.
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All authors S. Galeski, C. Lee, F. Bartl, J. Sourd, S. Zherlitsyn, A.T.M. Breugelmans, R. Amdouni, P. Khanenko, E. Hassinger, S. Khim, J. Wosnitza, P. Thalmeier, P. M. R. Brydon, M. Brando
Statistical Mechanics
Linear Response and Optimal Fingerprinting for Nonautonomous Systems
Valerio Lucarini
We provide a link between response theory, pullback measures, and optimal fingerprinting method that paves the way for a) predicting the impact of acting forcings on time-dependent systems and b) attributing observed anomalies to acting forcings when the reference state is not time-independent. We derive formulas for linear response theory for time-dependent Markov chains and
diffusion processes. We discuss existence, uniqueness, and differentiability of the equivariant measure under general (not necessarily slow or periodic) perturbations of the transition kernels. Our results allow for extending the theory of optimal fingerprinting for detection and attribution of
climate change (or change in any complex system) when the background state is time-dependent amd when the optimal solution is sought for multiple time slices at the same time. We provide numerical support for the findings by applying our theory to a modified version of the Ghil-Sellers energy balance model. We verify the precision of response theory - even in a coarse-grained setting - in predicting the impact of increasing CO$_2$ concentration on the temperature field. Additionally, we show that the optimal fingerprinting method developed here is capable to attribute the
climate change signal to multiple acting forcings across a vast time horizon.
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Materials Science · Cross-listed from physics.optics
Topological photonics in one-dimensional settings
Shiqi Xia, Ziteng Wang, Domenico Bongiovanni et al. (+7 more)
Over the past decade, topological photonics has emerged as a vibrant field, attracting significant
attention and witnessing remarkable advancements. This growth can be attributed to its fundamental appeal and the unique opportunities it offers for unconventional control of light, promising innovations in next-generation photonic devices. At the heart of topological photonics lies the one-dimensional (1D) SSH model. Originally conceived to elucidate the physics of a molecular chain of polyacetylene, this model has found widespread applications in exploring a wide range of topological phenomena in photonics and beyond. In this chapter, we aim to provide an overview of topological photonics in one-dimensional (1D) settings. After briefly introducing paradigmatic 1D models, including the SSH, Rice-Mele, and AAH models, we review recent advances in experimental studies and applications of topological photonics based on 1D platforms. Our discussion highlights demonstrated examples, such as the nonlinear tuning of topological states in both Hermitian and non-Hermitian photonic SSH
lattices, as well as nonlinear harmonic generation and topological lasing in SSH-type photonic microstructures. We further discuss characteristic topological phenomena in other representative 1D settings, including Floquet systems, topological pumping, quasicrystals, and synthetic non-Hermitian systems. Finally, we examine selected examples of two-dimensional (2D) photonic topological crystalline
insulators that are closely linked to the SSH model. Towards the end, we summarize the chapter and provide a list of key contributions, together with an outlook on possible future directions in 1D topological photonics. While this review focuses specifically on 1D topological photonics, it is not intended to be comprehensive or exhaustive.
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All authors Shiqi Xia, Ziteng Wang, Domenico Bongiovanni, Dario Jukić, Daohong Song, Liqin Tang, Jingjun Xu, Roberto Morandotti, Hrvoje Buljan, Zhigang Chen
Superconductivity
Anisotropic Electronic Correlations in the Spin Density Wave State of La$_3$Ni$_2$O$_7$
Ge He, Jun Shen, Shiyu Xie et al. (+21 more)
The
bilayer nickelate
superconductor La$_3$Ni$_2$O$_7$ undergoes a density wave transition near 150 K that has attracted intensive scrutiny, yet its microscopic origin remains elusive. Here we report polarization-resolved electronic Raman scattering measurements on high-quality single
crystals of La$_3$Ni$_2$O$_7$. Below 150\,K, we observe a pronounced,
symmetry-dependent redistribution of spectral weight in B$_{1g}$ and B$_{2g}$ channels, consistent with the formation of
spin-density-wave (SDW) gaps. Quantitative analysis reveals momentum-selective SDW gap amplitudes, with intermediate-to-strong coupling near X/Y points of the Brillouin zone and weaker coupling along the diagonal direction, indicating an unconventional SDW driven by anisotropic electronic correlations. Our results establish the electronic character of the SDW in La$_3$Ni$_2$O$_7$, and provide a microscopic foundation for understanding the emergence of high-temperature superconductivity under pressure in nickelates.
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All authors Ge He, Jun Shen, Shiyu Xie, Haotian Zhang, Mengwu Huo, Jun Shu, Deyuan Hu, Xiaoxiang Zhou, Yanmin Zhang, Lei Qin, Liangxin Qiao, Hengjie Liu, Chuansheng Hu, Xijie Dong, Dengjing Wang, Jun Liu, Wei Hu, Jie Yuan, Yajun Yan, Zeming Qi, Kui Jin, Zengyi Du, Meng Wang, Donglai Feng
Superconductivity
Coexistence of Antiferromagnetic Spin Fluctuations and Superconductivity in La2SmNi2O7 Thin Films
Minhui Xu, Yibo Wang, Jia Liu et al. (+9 more)
The interplay between
magnetic fluctuations and superconductivity is fundamental for understanding unconventional high-temperature
superconductors. In the recently discovered Ruddlesden-Popper phase nickelates-which achieve superconducting transition temperatures up to ~100 K-this connection has been theoretically predicted but experimentally unverified. Using compressively strained La2SmNi2O7 thin films, we report direct evidence for this interplay. We observe a characteristic 'Mexican hat'-shaped magnetoresistance, a signature of superconductivity coexisting with emergent
antiferromagnetic (AFM) fluctuations. This distinctive feature arises from a competition between the
magnetic field's suppression of AFM fluctuation-driven scattering and its suppression of superconducting fluctuations. We quantify these AFM fluctuations by a crossover field, B*, whose magnitude decreases with increasing temperature and vanishes near the superconducting onset-behavior contrasting sharply with that in high-Tc cuprates. Our results establish not merely coexistence, but also a direct and novel correlation between AFM instability and superconductivity in nickelates, offering crucial insight into their pairing mechanism.
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All authors Minhui Xu, Yibo Wang, Jia Liu, Long Cheng, Shuyin Li, Shuaishuai Yin, Xu Zheng, Lixin Yu, Aidi Zhao, Xiaolong Li, Jiandi Zhang, Xiaofang Zhai
Statistical Mechanics
Hierarchical Lorentz Mirror Model: Normal Transport and a Universal $2/3$ Mean–Variance Law
Raphael Lefevere and Hal Tasaki
The Lorentz mirror model provides a clean setting to study macroscopic transport generated solely by quenched environmental randomness. We introduce a hierarchical version whose distribution of left–right crossings satisfies an exact recursion. In dimensions $d\ge3$, we prove two-sided bounds that support normal transport: the mean conductance scales as (cross-section)/(length). A Gaussian closure, supported by numerics, predicts that the variance-to-mean ratio of the dimensionless conductance converges to the universal value $2/3$ for all $d\ge2$ (the “$2/3$ law”). We provide numerical evidence for the $2/3$ law in the original (non-hierarchical) Lorentz mirror model in $d=3$, and
conjecture that it is a universal signature of normal transport induced by random current matching. In the marginal case $d=2$, our hierarchical recursion reproduces the known scaling of the mean and variance of conductance. A YouTube
video discussing the background and the main results of the paper is available: https://youtu.be/G1nqKd6MiXo
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Materials Science
Unveiling the impact of anti-site defects in magnetic transitions of few-layer MnBi2Te4 by operando heating
Xinyu Chen, Jingjing Gao, Shuang Wu et al. (+11 more)
As the first experimentally discovered intrinsic
magnetic topological
insulator, MnBi2Te4 has attracted widespread attentions, providing a unique platform for the exploration of topological
quantum phases, such as
quantum anomalous
Hall effect and
axion insulator state. Despite the increasing number of potential factors affecting samples being identified, obtaining the high-quality device performance with desired topological
quantum phases remains a challenge. In this work, by comparing the reflective
magnetic circular dichroism (RMCD) of
crystals with different defect densities that are characterized by atomically resolved scanning tunneling microscopy, we demonstrate that anti-site defects play an essential role in achieving ideal
magnetic states. By measuring RMCD hysteresis loops with operando heating, we find that MnBi2Te4 few-layer samples are highly susceptible to thermal impact, even at temperature as low as 45{\deg}C. The
magnetic behavior of heating-treated samples is akin to that of samples fabricated into devices, revealing the thermal impact on devices as well. Starting from few-layers with ideal layer-dependent
magnetic order, thermal heating leads to the convergence of magnetization and transition fields between odd- and even-layers. The observed heating-induced
magnetic evolution can serve as a valuable reference for assessing the sample quality or the density of anti-site defects. Our findings not only point out the long-standing hidden factor that arose controversies in MnBi2Te4, but also pave the way for controllably engineering the topological
quantum phenomena.
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All authors Xinyu Chen, Jingjing Gao, Shuang Wu, Zhiwei Huang, Zhongxun Guo, Canyu Hong, Ruohan Chen, Mingyan Luo, Zhaochen Liu, Zeyuan Sun, Wei Ruan, Jing Wang, Yuanbo Zhang, Shiwei Wu
Statistical Mechanics · Cross-listed from quant-ph
Higher-Order Corrections to Scrambling Dynamics in Brownian Spin SYK Models
Tingfei Li, Miao Wang and Jianghui Yu
We investigate operator growth in a Brownian
spin Sachdev–Ye–Kitaev (SYK) model with random all-to-all interactions, focusing on the full operator-size distribution. For
Hamiltonians containing interactions of order two up to $L$, we derive a closed master equation for the Pauli-string expansion coefficients and recast their dynamics into a generating-function formulation suitable for the large-$N$ limit. This approach allows us to diagonalize the leading-order
evolution operator explicitly and obtain exact solutions for arbitrary initial operator distributions, including the effects of decoherence. Going beyond leading order, we develop a systematic $1/N$ expansion that captures higher-order corrections to the operator-size dynamics and the late-time behavior. Our results demonstrate that higher-order effects play a crucial role in operator scrambling and that the full operator-size distribution provides a more refined probe of
quantum chaos in Brownian and open
quantum systems.
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Soft Condensed Matter · Cross-listed from physics.comp-ph
dewi-kadita: A Python Library for Idealized Fish Schooling Simulation with Entropy-Based Diagnostics
Sandy H. S. Herho, Iwan P. Anwar, Faruq Khadami et al. (+5 more)
Collective motion in fish schools exemplifies emergent self-organization in active matter systems, yet computational tools for simulating and analyzing these dynamics remain fragmented across research groups. We present dewi-kadita, an open-source Python library implementing the three-dimensional Couzin zone-based model with comprehensive
entropy diagnostics tailored for marine collective behavior research. The library introduces seven information-theoretic metrics – school cohesion
entropy, polarization
entropy, depth stratification
entropy, angular momentum
entropy, nearest-neighbor
entropy, velocity correlation
entropy, and school shape
entropy – that characterize distinct organizational features inaccessible to classical order parameters. These metrics combine into an Oceanic Schooling Index (OSI) providing a single scalar measure of collective disorder. Validation across four canonical configurations (swarm,
torus, dynamic parallel, highly parallel) confirms correct reproduction of known phase behaviors: the swarm maintains disorder with polarization $P < 0.1$ and OSI $\approx 0.71$, while the highly parallel state achieves $P = 0.998$ with OSI $= 0.24$ and velocity correlation
entropy vanishing to zero. The
entropy framework successfully discriminates the
torus and dynamic parallel configurations that exhibit comparable order parameter magnitudes through different organizational mechanisms. Numba just-in-time (JIT) compilation accelerates pairwise interaction calculations by $10$–$100\times$, enabling simulations of $150$–$250$
agents over $1000$–$2000$ time steps within five minutes on standard workstation hardware. NetCDF4 output ensures interoperability with oceanographic analysis tools. The library addresses the need for standardized, reproducible infrastructure in collective behavior modeling analogous to established molecular dynamics codes.
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All authors Sandy H. S. Herho, Iwan P. Anwar, Faruq Khadami, Alfita P. Handayani, Karina A. Sujatmiko, Kamaluddin Kasim, Rusmawan Suwarman, Dasapta E. Irawan
Strongly Correlated Electrons · Cross-listed from nucl-th
New solution to the hyperon puzzle of neutron stars: Quantum many-body effects
Hao-Fu Zhu, Guo-Zhu Liu, Xufen Wu et al. (+1 more)
The hyperon puzzle refers to the challenge of reconciling the existence of hyperons in
neutron star cores and the observed high masses of
neutron stars. The recent discovery of PSR J0952-0607 ($2.35\pm0.17 M_{\odot}$) has intensified this challenge. Existing solutions fail to achieve such a high mass, and often predict unrealistically fast cooling that is at odds with observations. Here, we propose a novel solution to the hyperon puzzle. Using the Dyson-Schwinger equation approach, we incorporate the
quantum many-body effects caused by strong
baryon-
meson interactions into the equation of state for cold baryonic matter and find it stiff enough to support a maximum hyperon-
star mass of $M_{\mathrm{max}} \approx 2.59 M_{\odot}$, which can explain all the observed high
neutron-
star masses. The resulting
proton and hyperon fractions are remarkably low, thus the nucleonic and hyperonic direct Urca processes are significantly suppressed. As a result, fast cooling typically does not occur in ordinary
neutron stars.
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All authors Hao-Fu Zhu, Guo-Zhu Liu, Xufen Wu, Ye-Fei Yuan
Superconductivity · Cross-listed from physics.ins-det
Mutual Inductance Sensing SQUID: Cryogenic microcalorimeter based on mutual inductance readout of superconducting temperature sensors
Jodok Zeuner, Constantin Schuster and Sebastian Kempf
Superconducting microcalorimeters, such as superconducting transition-edge sensors and
magnetic microcalorimeters, have emerged as state-of-the-art detectors for X-ray emission spectroscopy by combining near-unity
quantum efficiency with excellent energy resolution. Despite these achievements, their resolving power has not yet reached the level required to rival modern wavelength-dispersive grating or
crystal spectrometers. Here, we introduce a next-generation SQUID-based microcalorimeter concept that exploits the strong temperature dependence of the
magnetic penetration depth of a
superconductor operated close to its critical temperature. The resulting mutual-inductance-based readout enables in situ tunable signal amplification, while inherently avoiding hysteretic effects that commonly limit superconducting sensors. Experiments with prototype devices demonstrate robust and reproducible operation over a wide temperature range. Based on our measurements and modeling, we project that, using an optimized absorber-sensor combination, an energy resolution below 100meV (FWHM) should be achievable for soft X-ray
photons with energies below 800eV. This approach therefore represents a promising pathway towards next-generation cryogenic detectors for high-precision X-ray emission spectroscopy.
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Materials Science
CDW Gap Collapse and Weyl State Restoration in Ta$_2$Se$_8$I via Coherent Phonons: A First-Principles Study
Tao Jiang, Jigang Wang and Yong-Xin Yao
Coherent
phonon excitation offers a nonthermal route to control
quantum phases of condensed matter. In this work, we employ first-principles calculations to investigate the
phonon landscape of (TaSe$_4$)$_2$I in its charge-density-wave (CDW) phase. We identify nine
symmetry-preserving Raman-active modes that can suppress the $\Gamma$-Z direct gap to the meV scale and render the system globally gapless by generating Weyl nodes at generic k points. Among them, the 2.52 THz CDW amplitude mode A(18) directly weakens the Ta-chain tetramerization, approaching a transient restoration of the uniform-chain geometry, while its low frequency and relatively small, Ta-dominated displacement make it the most efficient mode. Other Raman modes, dominated by Se vibrations, require significantly larger displacements to reach the Weyl-semimetallic regime and are generally less effective than A(18) at reducing the Ta-chain tetramerization. Furthermore, among the IR-active modes considered, the low-frequency B$_3$(7) mode (1.15 THz) provides the most favorable channel for nonlinear modulation of the A(18) potential. Although the coupling favors displacement toward the CDW-suppressing direction, the estimated indirect response remains far below that required for strong gap suppression. Direct excitation of A(18) therefore remains the most effective pathway to the Weyl-semimetallic regime.
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Statistical Mechanics
Roumen Tsekov
Entropy is critically examined as a fundamental concept in contemporary science and informatics. Although the typical Shannon
entropy provides a proper framework for describing the canonical ensemble, it fails to represent adequately the microcanonical ensemble. This discrepancy manifests additionally in its inability to support a theoretical derivation of the Second Law of thermodynamics.
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Materials Science
Epitaxial lift-off of La$_{2/3}$Sr$_{1/3}$MnO$_3$ membranes enabled by BaO sacrificial layers and restoration of the Curie temperature
Takahito Takeda, Daigo Matsubara, Yuki K. Wakabayashi et al. (+7 more)
Ultrathin complex-
oxide membranes provide a powerful platform for strain engineering, interfacial control, and heterogeneous integration; however, their formation remains constrained by the availability and performance of suitable water-soluble sacrificial layers. This letter demonstrates that barium
oxide (BaO) serves as a highly efficient and rapidly dissolving water-soluble sacrificial layer, enabling the epitaxial lift-off and transfer of ultrathin La$_{2/3}$Sr$_{1/3}$MnO$_3$ (LSMO) membranes onto SiO$_x$/Si substrates. LSMO membranes with a thickness of approximately 8 nm are released using a BaO sacrificial layer grown by molecular beam epitaxy, while high crystallinity is preserved and Ba interdiffusion is limited to a narrow interfacial region of approximately 0.5 nm. Post-transfer oxygen annealing at 600 ${}^\circ$C increases the Curie temperature ($T_C$) from 342 K to 346 K by eliminating Mn$^{2+}$ states associated with oxygen vacancies generated through oxygen extraction into the BaO layer. These results show that BaO provides a fast, scalable, and compositionally simple route for complex-
oxide membrane release, while brief oxygen annealing is essential to restore the optimal Mn valence state and achieve the intrinsic high $T_C$.
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All authors Takahito Takeda, Daigo Matsubara, Yuki K. Wakabayashi, Kohei Yamagami, Munetoshi Seki, Hitoshi Tabata, Le Duc Anh, Masaki Kobayashi, Masaaki Tanaka, Shinobu Ohya
Materials Science
Influence of Elastic Oscillations on Nucleation in Metals
A.S. Nuradinov, O.V. Chistyakov, K.A. Sirenko et al. (+2 more)
This work is devoted to establishing the mechanisms of elastic oscillation influence on nucleation processes in metal melts. The method of physical modeling with low-temperature metallic
alloys (Wood and Rose) and transparent organic media (salol, camphene, diphenylamine) was used. It was established that vibration and ultrasound significantly reduce the supercooling required to initiate crystallization. The effectiveness of the influence significantly increases for samples with solid substrates. The hypotheses about the influence through changes in melt viscosity and the exclusive role of cavitation were experimentally refuted. The transition from pre-cavitation to cavitation ultrasound regime is not accompanied by qualitative changes in the influence on nucleation. The mechanism of elastic oscillation influence is substantiated, which consists in mechanical impact on adsorbed
crystal nuclei on the surfaces of solid substrates. Elastic oscillations increase the nucleation rate by creating growth steps (dislocations) on the surfaces of adsorbed
nuclei as a result of mechanical friction of solid substrates and cavitation erosion. The results have fundamental significance for understanding the physical nature of metal crystallization and practical application for developing technologies for controlling structure formation.
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All authors A.S. Nuradinov, O.V. Chistyakov, K.A. Sirenko, I.A. Nuradinov, D.O. Derecha
Statistical Mechanics
The 4-$\epsilon$ Expansion for Long-range Interacting Systems
Zhiyi Li, Kun Chen and Youjin Deng
The establishment of the Wilson-Fisher fixed point (WFP) for $O(n)$
spin models in $d=4-\epsilon$ dimensions stands as a cornerstone of the renormalization group (RG) theory for critical phenomena. However, when long-range (LR) interactions, algebraically decaying as $\propto 1/r^{d+\sigma}$, are introduced, the fate of the short-range WFP (SR-WFP) has remained a subject of intense debate since the 1970s. We employ two complementary techniques – the standard field-theoretic RG and a perturbative bootstrap scheme, and perform the $\epsilon$-expansion calculations up to the two-loop level. We show that, as long as $\sigma<2$, the SR-WFP becomes unstable and a stable LR-WFP emerges, and, in the non-classical regime with $d/2 < \sigma < 2$, the critical exponents, including the anomalous dimension, are functions of $\epsilon$, $\delta=2-\sigma$ and $n$, which reduce to the exact results in the limiting cases $\epsilon \to 0$, $\delta \to 0$ or $n \to \infty$. Our $(4-\epsilon)$-expansion calculations support the scenario that the threshold between the LR- and SR-WFP occurs strictly at $\sigma_*=2$, well consistent with the recent high-precision numerical study while different from the widely accepted Sak's criterion.
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Quantum Gases
Engineering a Bound State in the Continuum via Quantum Interference
Alexander Guthmann, Louisa Marie Kienesberger, Felix Lang et al. (+2 more)
Quantum mechanical interaction potentials typically support either localized bound states below the dissociation threshold or delocalized scattering states above it. While bound states are energetically isolated, scattering states embed a
quantum system in a continuum of environmental modes, making dissipation and loss intrisic features of open
quantum systems. A striking exception are bound states in the continuum (BICs), which remain localized despite lying within the scattering continuum due to destructive interference. It was predicted that such states can arise from the interference of two Feshbach resonances coupled to a common continuum, yet this mechanism has remained experimentally inaccessible in genuine
quantum systems. Here we demonstrate the formation of such an interference-stabilized state in ultracold collisions of ${}^6$Li atoms by coherently coupling two tunable Feshbach resonances using Floquet engineering. At a critical parameter point, both elastic and inelastic coupling to the continuum vanish, yielding a molecular state above the dissociation threshold. Loss spectroscopy, quench dynamics, and rf-photoassociation directly reveal the resulting decoupling from scattering states. Our observations are quantitatively captured by full coupled-channel calculations and a minimal non-Hermitian model, identifying a Friedrich-Wintgen BIC. Our results establish
quantum interference as a powerful mechanism for controlling openness in
quantum matter and for engineering non-Hermitian
Hamiltonians.
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All authors Alexander Guthmann, Louisa Marie Kienesberger, Felix Lang, Eleonora Lippi, Artur Widera
Materials Science
Proton Quantum Effects on Electronic Excitation in Hydrogen-bonded Organic Solid: A First-Principles Green's Function Theory Study
Sampreeti Bhattacharya, Jianhang Xu, Ruiyi Zhou et al. (+1 more)
Nuclear quantum effects of
protons on electronic excitations in hydrogen-bonded organic materials remains underexplored. In theoretical studies, modeling
excitons in these extended systems is particularly difficult because they tend to have a large
exciton binding energy and sometimes exhibit charge transfer character. We demonstrate how first-principles Green's function theory combined with the
nuclear-electronic orbital method enables us to examine the nature of
excitons in a prototypical organic solid of eumelanin, for which the extensive hydrogen bonds have been proposed to facilitate the formation of delocalized
excitons. We investigate how the quantization of
protons impacts electronic excitations. We discuss the extent to which the resulting
proton quantum effects can be described as being derived from structure and how they induce molecular-level anisotropy for the
excitons in the organic solid.
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All authors Sampreeti Bhattacharya, Jianhang Xu, Ruiyi Zhou, Yosuke Kanai
Mesoscale and Nanoscale Physics
Spin Splitter and Inverse Effects in Altermagnetic Hybrid Structures
Nicolás Sigales, Tim Kokkeler, Gonzalo de Polsi et al. (+1 more)
We provide a theoretical description of diffusive charge and
spin transport in hybrid devices containing altermagnets. Based on recently derived drift–
diffusion equations for coupled charge and
spin dynamics and general boundary conditions, our approach provides a unified description of the
spin-splitter effect, i.e., the conversion of charge currents into
spin currents, and its inverse in terms of experimentally accessible parameters. We analyze, analytically and numerically, the
spin-splitter effect, demonstrating that an injected
spin accumulation generates a measurable voltage difference across the transverse direction in the altermagnet. Motivated by a recent experiment, we also analyze a nonlocal
spin-valve geometry in which an altermagnetic strip injects
spin into a diffusive normal metal. We derive the resulting nonlocal voltage detected by a
ferromagnetic electrode as a function of the relative orientation of the N'eel vector and the
ferromagnetic polarization, accounting for the main experimental findings. For this setup, we further address
spin precession during diffusive transport by analyzing the
spin Hanle effect. Our results provide theoretical explanations and predictions for several altermagnet hybrid structures.
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All authors Nicolás Sigales, Tim Kokkeler, Gonzalo de Polsi, Sebastian Bergeret
Strongly Correlated Electrons
La$_{2-x}$Ba$_x$CuO$_4$ ($x=\frac{1}{8}$) $\mu$SR data are inconsistent with spin stripe but consistent with spin spiral
Oleg P. Sushkov
I analyze available $\mu$SR data and show that it is inconsistent with the
spin stripe but consistent with the coplanar
spin spiral. The plane of the spiral coincides with the CuO$_2$-plane. The static expectation value of the
spin is $S=0.37\times\frac{1}{2}$.