Statistical Mechanics
Slow mixing and emergent one-form symmetries in three-dimensional $\mathbb{Z}_2$ gauge theory
Charles Stahl, Benedikt Placke, Vedika Khemani et al. (+1 more)
Symmetry-breaking order at low temperatures is often accompanied by slow relaxation dynamics, due to diverging free-energy barriers arising from interfaces between different ordered states. Here, we extend this correspondence to classical topological order, where the ordered states are locally indistinguishable, so there is no notion of interfaces between them. We study the relaxation dynamics of the three-dimensional (3D) classical $\mathbb{Z}_2$
lattice gauge theory (LGT) as a canonical example. We prove a lower bound on the mixing time in the deconfined phase, $t_{\text{mix}} = \exp [\Omega(L)]$, where L is the linear system size. This bound applies even in the presence of perturbations that explicitly break the one-form
symmetry between different long-lived states. This perturbation destroys the energy barriers between ordered states, but we show that entropic effects nevertheless lead to diverging free-energy barriers at nonzero temperature. Our proof establishes the LGT as a robust finite-temperature classical
memory. We further prove that entropic effects lead to an emergent one-form
symmetry, via a notion that we make precise. We argue that the exponential mixing time follows from universal properties of the deconfined phase, and numerically corroborate this expectation by exploring mixing time scales at the
Higgs and confinement transitions out of the deconfined phase. These transitions are found to exhibit markedly different dynamic scaling, even though both have the static critical exponents of the 3D Ising model. We expect this novel entropic mechanism for
memory and emergent
symmetry to also bring insight into self-correcting
quantum memories.
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All authors Charles Stahl, Benedikt Placke, Vedika Khemani, Yaodong Li
Statistical Mechanics
Exact Volterra series for mean field dynamics
Ion Santra and Matthias Krüger
We derive an exact Volterra series expansion for a mean field of an interacting particle system subject to a potential perturbation, expressing the Volterra expansion kernels in terms of the field's response functions, to any order. Applying this formalism to the mean particle density of a simple fluid, we identify a form reminiscent of dynamical density functional theory, with, however, fundamental differences: A nonlocal mobility kernel appears, and forces derive from a functional of the history of mean density. The
equilibrium density functional is shown to be recovered in the limit of slowly varying perturbation. We identify a freedom in deriving this expansion, which allows different forms of mobility kernels. These developments allow for a systematic improvement of established mean field formalisms.
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Mesoscale and Nanoscale Physics
Mode-selective cloaking and phase-matching cavity resonances in bilayer graphene transport
Dan-Na Liu, Jun Zheng and Pierre A. Pantaleon
We study ballistic electron transport through electrostatic barriers in AB-stacked
bilayer graphene within a full four-band framework. A mode-resolved analysis reveals how propagating and evanescent channels couple across electrostatic interfaces and how channel selectivity governs transport at normal incidence. We show that perfect transmission can occur at discrete energies due to phase matching of a single internal mode within an individual barrier, without activating the decoupled channels. This effect is interpreted as a phase-matching cavity, namely, an effective cavity formed by internal phase coherence inside the barrier, which yields perfect transmission at discrete energies without true bound states and without opening additional transport channels. For single- and double-barrier geometries, we derive compact analytical expressions for the transmission and identify the corresponding resonance conditions. Extending the analysis to multibarrier structures using a transfer-
matrix approach, we demonstrate how perfect resonances driven by internal phase matching coexist with Fabry-Perot-type resonances arising from interbarrier interference. Our results provide a unified, channel-resolved description of tunneling suppression and resonance-assisted transport in
bilayer graphene barrier systems.
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Mesoscale and Nanoscale Physics
Karel Cuypers, Robin Smeyers, Bert Jorissen et al. (+1 more)
While in pristine
bilayer graphene the Berry
curvature dipole (BCD), a necessary ingredient for the nonlinear anomalous
Hall effect, is zero, uniaxial strain can give rise to finite BCD. We investigate this by using a tight-binding (TB) approach build on the Slater-Koster parameterization to capture
lattice deformation effects often missed by continuum models. We demonstrate that the BCD's
evolution with strain and doping is highly sensitive to the choice in parameterization, particularly when including the longer range interlayer skew hoppings. Additionally, out-of-plane compression enhances the response by broadening the Dirac cones. These findings
benchmark low-energy continuum models and highlight the necessity of realistic tight-binding models for accurately predicting strain-engineered
Hall effects in
bilayer graphene.
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All authors Karel Cuypers, Robin Smeyers, Bert Jorissen, Lucian Covaci
Materials Science
Thermally Configurable Multi-Order Polar Skyrmions in Multiferroic Oxide Superlattices
Kefan Liu, Yuhui Huang, Xiangwei Guo et al. (+3 more)
Polar topological textures in low-dimensional ferroelectrics have emerged as a versatile platform for high-density information storage and neuromorphic computing. While low-order topological states, such as
vortices and skyrmions, have been extensively studied, high-order polar topological families remain largely unexplored due to their higher energy requirements and limited stabilization methods. Here, using a BiFeO3 (BFO)-based multiferroic superlattice as a model system, we demonstrate a thermal-modulation strategy that stabilizes multi-order polar skyrmions and enables reversible tuning of their topological order through phase-field simulations. It was found that temperature modulation drives the system from polar
solitons through 1{\pi}-, 2{\pi}-, 3{\pi}-, and 4{\pi}-skyrmion states, with closed heating-cooling path analyses revealing the widest thermal stability window for 2{\pi}-skyrmions (up to 600 K). Leveraging this robustness, 2% Sm doping in BFO lowers the transition temperatures, enabling room-temperature stabilization of 2{\pi}-skyrmions. These findings enrich the fundamental understanding of multi-order polar
topologies and establish a tunable strategy for realizing variable-order topological configurations in practical
memory devices.
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All authors Kefan Liu, Yuhui Huang, Xiangwei Guo, Yongjun Wu, Juan Li, Zijian Hong
Materials Science
A Critical Examination of Active Learning Workflows in Materials Science
Akhil S. Nair and Lucas Foppa
Active learning (AL) plays a critical role in materials science, enabling applications such as the construction of machine-learning interatomic potentials for atomistic simulations and the operation of self-driving laboratories. Despite its widespread use, the reliability and effectiveness of AL workflows depend on implicit design assumptions that are rarely examined systematically. Here, we critically assess AL workflows deployed in materials science and investigate how key design choices, such as surrogate models, sampling strategies, uncertainty quantification and evaluation metrics, relate to their performance. By identifying common pitfalls and discussing practical mitigation strategies, we provide guidance to practitioners for the efficient design, assessment, and interpretation of AL workflows in materials science.
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Materials Science · Cross-listed from physics.atom-ph
Electron Energy Loss Spectroscopy of oriented targets and magnetic transitions
Ioannis Iatrakis and Valerii Brudanin
Electron beam energies in Transmission Electron Microscopes (TEMs) reach the relativistic realm constituting
Quantum Electrodynamics (QED) the appropriate framework for the study of electron matter interaction in TEMs. We focus on the inelastic scattering of relativistic electrons from a generic oriented target. The inelastic differential cross section factorizes to the fast electron part which is calculated analytically, and the dynamic form factor of the target, which encodes the response of the medium to the interaction with the beam. The properties of the dynamic form factor of oriented targets are analyzed. We then derive the scattering cross section of electrons by
magnetic targets where
spin-flip transitions are induced. We comment on the kinematic regimes where the coefficient of the transverse
magnetic interaction is amplified compared to the coulomb
matrix element.
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Soft Condensed Matter
Reverse segregation and self-organization in inclined chute flows of bidisperse granular mixtures
Joseph M. Monti, Joel T. Clemmer, Ishan Srivastava et al. (+3 more)
In the usual segregation scenario for stable inclined chute flows of bidisperse mixtures of fine and coarse spherical particles, coarse particles rise toward the free surface, forming a coarse-rich region atop the flowing pile. Beyond a threshold coarse-to-fine diameter ratio of approximately 4, conversely, the weight of the coarse particles exceeds the segregation driving forces, causing individual coarse particles to sink within the pile and producing a reversed segregation state. However, an understanding of the collective
evolution of the pile structure is still lacking when the particle diameter ratio exceeds 4 {and} the coarse particle mass fraction is appreciable. To explore this broadly bidisperse limit, we perform discrete element method simulations considering mean particle diameter ratios of up to 8 and coarse particle mass fractions spanning 0.1 to 0.9. The steady-state flow profiles reveal several intriguing behaviors that depend on the diameter ratio and mass fraction. These include a previously identified transition from usual to reverse segregation and a newfound tendency to self-organize into alternating coarse- and fine-rich particle layers stacked along the shear gradient direction, with layer thickness dictated by the coarse particle diameter. A fuller understanding of segregation at this scale could pave the way for enhanced mixing or demixing techniques at the commercial scale.
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All authors Joseph M. Monti, Joel T. Clemmer, Ishan Srivastava, Leonardo E. Silbert, Gary S. Grest, Jeremy B. Lechman
Statistical Mechanics
Phase-space networks and connectivity of the kagome antiferromagnet
Brandon B. Le, Seung-Hun Lee and Gia-Wei Chern
We study the coplanar ground-state
manifold of the kagome Heisenberg antiferromagnet using a phase-space network representation, in which nodes correspond to coplanar ground states and edges represent transitions generated by weathervane loop rotations. In the coplanar
manifold, each configuration can be mapped to a three-coloring problem on the dual honeycomb
lattice, where a weathervane mode corresponds to a closed loop of two alternating colors. By comparing networks that include all weathervane loops with networks restricted to elementary six-
spin loops, we examine how energetic constraints shape phase-space structure. We find that connectivity distributions are sharply peaked in large systems, while restrictions to short loops reduce typical connectivity. Spectral properties further distinguish the two cases, with short-loop networks exhibiting Gaussian spectra and full networks displaying non-Gaussian features associated with correlated loop updates. Finally, a box-counting analysis reveals distinct fractal properties of the two networks, demonstrating how energetic constraints control the global geometry of configuration space. These results show that the hierarchy of weathervane loop rotations provides a direct link between microscopic constraints and emergent phase-space geometry in a frustrated magnet.
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Disordered Systems and Neural Networks · Cross-listed from quant-ph
Dynamical entanglement percolation with spatially correlated disorder
Lorenzo Cirigliano, Valentina Brosco, Claudio Castellano et al. (+3 more)
The distribution of
entanglement between the nodes of a
quantum network plays a fundamental role in
quantum information applications. In this work, we investigate the dynamics of a network of
qubits where each edge corresponds to an independent two-
qubit interaction. By applying tools from percolation theory, we study how
entanglement dynamically spreads across the network. We show that the interplay between
unitary evolution and spatially correlated disorder leads to a non-standard percolation phenomenology, significantly richer than uniform bond percolation and featuring hysteresis. A two-colour correlated bond percolation model, whose phase diagram is determined via numerical simulations and a mean-field theory, fully elucidates the physics behind this phenomenon.
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All authors Lorenzo Cirigliano, Valentina Brosco, Claudio Castellano, Simone Felicetti, Laura Pilozzi, Bernard van Heck
Materials Science
First-principles study of hydrogen diffusion in polycrystalline Nickel
Bhanuj Jain, Alaa Olleak, Junyan He et al. (+2 more)
Hydrogen embrittlement in metals is strongly governed by hydrogen
diffusion and trapping, yet predicting these effects in polycrystalline systems remains challenging. This work introduces a multiscale modeling framework that links atomistic energetics to continuum-scale transport. Migration barriers for bulk and grain-boundary environments, obtained from first-principles calculations, are used in kinetic Monte Carlo simulations to compute anisotropic effective diffusivities. These diffusivities are then incorporated into finite element models of polycrystalline microstructures, explicitly accounting for grain-boundary character and connectivity. The approach captures both fast-path and trapping effects without relying on empirical parameters and reproduces experimental trends for nickel, including the dependence of effective diffusivity on grain size and boundary type. This methodology provides a physically grounded route for predicting hydrogen transport in engineering
alloys and can be extended to other materials and defect types.
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All authors Bhanuj Jain, Alaa Olleak, Junyan He, Adarsh Chaurasia, Davide Di Stefano
Quantum Gases · Cross-listed from quant-ph
Generation of squeezed optical states via stored classical pulses in a Bose gas
Sevilay Sevinçli, Dennis Rätzel, Markus Krutzik et al. (+2 more)
We propose and analyze a scheme to generate squeezed light by storing a classical probe pulse in a Bose–Einstein condensate (BEC) and exploiting the nonlinear
evolution caused by atom–atom collisions during the storage time. A $\Lambda$-type optical
memory interface maps a chosen temporal probe mode onto a single phase-matched collective
spin wave; for a coherent input this prepares a tunable coherent
spin state of a two-component BEC, with its initial
spin orientation set by the stored mean excitation number and the phase relation between the probe and control fields. Collisional interactions during storage then implement one-axis-twisting dynamics and generate
spin squeezing in the atomic ensemble. We account for realistic loss and finite
memory and
retrieval efficiencies, and model readout as a single-mode beam-splitter mapping that transfers the atomic quadrature squeezing onto a propagating optical mode. We identify optimal storage times and predict that, under realistic conditions, several dB of squeezing can be transferred to the retrieved light.
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All authors Sevilay Sevinçli, Dennis Rätzel, Markus Krutzik, Mehmet Özgür Oktel, Mustafa Gündoğan
Soft Condensed Matter · Cross-listed from physics.bio-ph
Flow-wave coupling synchronizes oscillations in growing active matter
Lara Koehler, Elissavet Sandaltzopoulou, Frank Jülicher et al. (+1 more)
Oscillatory biochemical signals and mechanical forces must coordinate robustly during development, yet the principles governing their mutual coupling remain poorly understood. In syncytial embryos and
cell-free extracts, mitotic waves propagate across millimeter scales while simultaneously generating cytoplasmic flows, suggesting a two-way interaction between chemical oscillators and mechanics. Here, we combine experiments in Xenopus Laevis cytoplasmic extracts with a minimal particle-based model to reveal a mechanochemical feedback that stabilizes phase wave propagation. In contrast to previous models of oscillatory active matter, an asymmetric size cycle, slow growth and rapid shrinkage, combined with size-dependent mechanical interactions generates a net particle displacement and flows aligned with the wave direction, which in turn drive a synchronization transition. Our results show that mechanical forces actively maintain the coherence of biochemical waves, providing a general mechanism for long-range order in oscillating active matter.
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All authors Lara Koehler, Elissavet Sandaltzopoulou, Frank Jülicher, Jan Brugués
Mesoscale and Nanoscale Physics
High-Energy Interlayer Exciton Ensembles in MoSe$_2$/WSe$_2$ Heterostructures by Laguerre-Gaussian Excitation
Mirco Troue, Johannes Figueiredo, Gabriel Mittermair et al. (+7 more)
We reveal the higher energetic luminescence part of interlayer
exciton ensembles in MoSe$_2$/WSe$_2$
heterostructures upon excitation by an optical Laguerre-Gaussian mode. The excitation is achieved with the help of a spatial light modulator giving rise to a ring-shaped distribution of interlayer
excitons. A hyperspectral analysis of the
exciton photoluminescence suggests that the excitation scheme allows the accumulation of high-energetic
excitons in the rings' center. We discuss the mechanisms leading to such a distribution, including
exciton-
exciton interaction, phase-space filling, and an incomplete thermalization.
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All authors Mirco Troue, Johannes Figueiredo, Gabriel Mittermair, Jonas Kiemle, Sebastian Loy, Hendrik Lambers, Takashi Taniguchi, Kenji Watanabe, Ursula Wurstbauer, Alexander W. Holleitner
Soft Condensed Matter
Learning microstructure in active matter
Writu Dasgupta, Suvendu Mandal, Aritra K. Mukhopadhyay et al. (+1 more)
Understanding microstructure in terms of closed-form expressions is an open challenge in nonequilibrium statistical physics. We propose a simple and generic method that combines particle-resolved simulations, deep neural networks and symbolic regression to predict the pair-correlation function of passive and active particles. Our analytical closed-form results closely agree with Brownian dynamics simulations, even at relatively large packing fractions and for strong activity. The proposed method is broadly applicable, computationally efficient, and can be used to enhance the predictive power of nonequilibrium continuum theories and for designing pattern formation.
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All authors Writu Dasgupta, Suvendu Mandal, Aritra K. Mukhopadhyay, Benno Liebchen
Soft Condensed Matter
Topological origin of peak splitting in the structure factor of liquid water
Zoé Faure Beaulieu, Volker L. Deringer and Fausto Martelli
The splitting of the principal peak in the structure factor of
liquid water is commonly interpreted as evidence of a competition between two distinct local environments. Here, we show that this peak splitting arises from medium-range topological features of the hydrogen-bond network. Using atomistic simulations, we systematically decompose the structure factor into contributions from hydrogen-bonded rings of different sizes. We find that 5-8-membered rings, which dominate the network
topology of
liquid water at low temperatures, can directly explain the experimentally observed bimodal scattering signal. Among these, 5-membered rings are particularly persistent, maintaining distinct structural signatures even above room temperature. Our findings establish a direct link between the network
topology of
liquid water and experimentally accessible diffraction features, clarifying the microscopic basis of water's behaviour and suggesting a broader conceptual framework for interpreting the anomalies in tetrahedral network
liquids and glasses.
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Quantum Gases
Vorticity-Crystalline Order Coupling in Supersolids: Excitations and Re-entrant Phases
Malte Schubert, Koushik Mukherjee, Philipp Stürmer et al. (+1 more)
Rotation is a natural tool in ultracold gases to break time-reversal
symmetry, yet its impact on the collective excitations of supersolids remains largely unexplored. We show theoretically that tuning the rotation frequency, rather than the interparticle interactions, can trigger the superfluid-to-supersolid transition in Bose-Einstein condensates (dBECs). Computing excitation spectra in the presence of
vortices and persistent currents, we uncover a
vortex-driven de-softening mechanism whereby quantized vorticity elevates the gapless Goldstone mode to a finite-energy roton, restoring superfluidity. This effect results in re-entrant supersolid phases as a function of rotation frequency, revealing a fundamental coupling between topological defects and crystalline order.
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All authors Malte Schubert, Koushik Mukherjee, Philipp Stürmer, Stephanie Reimann
Materials Science
On the Feasibility of Extreme Heating Rates in SEM using MEMS Heater Platforms
C. Koenig, P. Mayr, J.R. Jinschek et al. (+1 more)
Understanding microstructural
evolution under extreme thermal conditions is essential for advancing metal additive manufacturing (AM). This work demonstrates the feasibility of employing micro-electro-mechanical system (MEMS) heating platforms for in-situ scanning electron microscopy (SEM) characterization of bulk-like samples during rapid thermal cycling. Using electron backscatter diffraction (EBSD), we tracked the ferrite-to-austenite phase transformation in a pure iron specimen and confirmed that the sample surface temperature closely follows the MEMS temperature setpoint within device accuracy. Under
vacuum conditions, stable heating and cooling rates of up to 1000 C/s were achieved with minimal power input and without compromising EBSD pattern quality. These findings establish MEMS-based heating as a robust approach for in-situ microstructural characterization of AM-relevant thermal processes in the SEM, enabling quantitative studies of thermally activated phenomena such as
diffusion, phase transformations, and microstructural
evolution under far-from-
equilibrium conditions.
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All authors C. Koenig, P. Mayr, J.R. Jinschek, A. Bastos Fanta
Strongly Correlated Electrons
Cooperative concurrence of 4f and 3d flat bands in kagome heavy-fermion metal YbCr6Ge6
Wenxin Lv, Pengcheng Ma, Tianqi Wang et al. (+6 more)
Flat-band (FB) systems originating from special
lattice geometry like in kagome metals as well as localized orbitals in the materials such as heavy-
fermion (HF) compounds have induced intensive interest due to their band
topology and strong electron correlation effects, leading to emergent
quantum states of matter. However, the question of how these two distinct FBs coexist and interact remains unsettled. Here, we report that YbCr6Ge6 hosting both Cr-kagome
lattice and Yb-4f electrons exhibits HF behaviors and a robust
antiferromagnetic ground state with transition temperature TN = 3 K, significantly higher than other similar kagome metals with Yb ions. Angle-resolved photoemission spectroscopy measurements reveal the coexistence of FBs originating from both Cr-kagome
lattice and localized Yb-4f electrons near
Fermi energy level EF. More importantly, the clear spectroscopic signatures of a hybridization of Yb-4f FB with kagome-
lattice-derived conduction bands and the high density of states of Cr-kagome FB near EF provide the underlying microscopic mechanisms of HF behaviors and enhanced antiferromagnetism in YbCr6Ge6. Our findings demonstrate that the novel kagome HF metals can not only host the cooperative coexistence of two different types of FBs, but also provide a paradigm material platform to explore the exotic correlated topological
quantum phenomena.
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All authors Wenxin Lv, Pengcheng Ma, Tianqi Wang, Shangjie Tian, Ying Ma, Shouguo Wang, Xiao Zhang, Zhonghao Liu, Hechang Lei
Strongly Correlated Electrons
Angular-Dependent Thermal Hall Effect in a Honeycomb Magnet: Disentangling Kitaev and Dzyaloshinskii-Moriya Interactions
Shuvankar Gupta, Olajumoke Oluwatobiloba Emmanuel, Pengpeng Zhang et al. (+1 more)
Layered honeycomb magnets have garnered significant
attention recently for their exotic
quantum phenomena due to the potential anisotropic, bond-dependent Kitaev interactions. However, distinguishing the roles of Kitaev interactions and the
symmetry-allowed Dzyaloshinskii-Moriya interaction (DMI) remains challenging, since both mechanisms may lead to similar
magnetic excitations and thermal transport properties. To tackle this challenge, using a
ferromagnetic honeycomb
insulator VI3 as a model system, we systematically study the angular-dependent thermal
Hall conductivity Kxy({\theta}, {\Phi}) with both out-of-plane ({\theta}) and in-plane ({\Phi})
magnetic field rotations. Our results reveal a persistent thermal
Hall response for both out-of-plane and in-plane rotating
magnetic fields, devoid of the sign-reversal patterns characteristic of Kitaev physics. Instead, quantitative analysis shows that the angular dependent Kxy({\theta}, {\Phi}) is governed by the projection between the
magnetic moment and a tilted DM vector containing both out-of-plane and in-plane components. These results not only establish the DMI-driven topological
magnetic excitations as the origin of the thermal
Hall response in VI3 but also highlight the angular-dependent thermal
Hall effect measurements as an effective approach for distinguishing competing interactions in
quantum magnets.
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All authors Shuvankar Gupta, Olajumoke Oluwatobiloba Emmanuel, Pengpeng Zhang, Xianglin Ke
Soft Condensed Matter
Early bloodmaterial interfacial events and capillary transport on nanoparticle modified nanofibers
Romain Scarabelli, Mehdi Abbasi, Magali Gary-Bobo et al. (+3 more)
Electrospun poly(\epsilon-caprolactone) (PCL)nanofibrous mats are widely considered for blood-contacting wound dressings and small-diameter vascular applications; however, their intrinsic hydrophobicity limits rapid wetting and controlled interaction with blood. In this work, we modulate the interfacial response of PCL nanofibers by incorporating
oxide-shelled silicon nanoparticles (SiNPs) synthesized by pulsed
laser ablation in
liquid, a ligand-free approach that avoids organic stabilizers and preserves surface reactivity. Two composite architectures were designed: SiNPs embedded within the fiber bulk (PAC1,4,16) and SiNPs preferentially exposed at the fiber surface (SPAC1,4,16), with systematically increasing nanoparticle loadings. Structural characterization confirmed the retention of a homogeneous fibrous morphology and the targeted nanoparticle distribution. The dynamic interaction with whole blood was quantified using time-resolved contact-angle measurements, complemented by top-view optical microscopy and three-dimensional profilometry of dried droplets. Pristine PCL remained strongly hydrophobic whereas a hydrophilic PCL functionalized with APTES showed rapid spreading. Incorporation of SiNPs within the fiber volume led to only a moderate enhancement of wettability, and dried droplets retained compact morphologies with limited spreading. In contrast, surface-decorated mats displayed a sharp, concentration-dependent transition toward highly wettable behavior: for SPAC16, the contact angle fell below 20, droplet profiles became markedly flattened, and microscopy revealed extended
plasma-rich regions surrounding a red-
cell-rich core, indicative of pronounced phase separation within the nanofibrous network.
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All authors Romain Scarabelli, Mehdi Abbasi, Magali Gary-Bobo, Christophe Drouet, Marc Leonetti, Ahmed Al-Kattan
Mesoscale and Nanoscale Physics
Zhendong Chi, Eoin Dolan, Haozhe Yang et al. (+4 more)
Spintronics has emerged as a promising field for next-generation devices, offering functionalities beyond complementary metal-
oxide-
semiconductor (CMOS). A critical challenge in spintronics is to develop systems that can efficiently generate
spin currents and enable their long-distance transport. Here, we demonstrate a
graphene (Gr)/heavy metal (HM)
heterostructure system that combines strong charge-
spin interconversion efficiency, induced by the
spin Hall effect, with a long
spin diffusion length. By employing an industry-friendly magnetron sputtering technique, we deposit HM layers onto few-layer Gr while minimizing structural damage. The proximity effect from the HM enhances the
spin Hall angle of Gr while limiting the reduction in its
spin diffusion length. Additionally, the
spin Hall angle can be tuned via an applied gate voltage, offering high controllability of the system. Importantly, these properties are observed across
heterostructures composed of different HMs, indicating the generality of this approach. Our findings establish Gr/HM
heterostructures as a scalable and versatile platform for
spin current generation, paving the way for advanced spintronic devices with high efficiency, long
spin propagation, and straightforward fabrication processes.
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All authors Zhendong Chi, Eoin Dolan, Haozhe Yang, Beatriz Martín-García, Marco Gobbi, Luis E. Hueso, Fèlix Casanova
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Hidden time-nonlocal Floquet symmetries
Sigmund Kohler and Jesús Casado-Pascual
We investigate the Floquet spectrum of a detuned, driven two-level system and show that it exhibits exact quasienergy crossings when the detuning is an integer multiple of the energy
quantum of the driving field. This behavior can be explained by a hidden time-nonlocal parity, which allows the Floquet modes to be classified as even or odd. Then a generic feature is the emergence of exact crossings between quasienergies of different parity. A constructive proof of the existence of the
symmetry is based on a scalar recurrence relation. Moreover, we present a general scheme for its numerical computation, which can be applied to models beyond the two-level system. Analytical results are illustrated with numerical data.
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Quantum Gases
Phase Frustration Induced Intrinsic Bose Glass in the Kitaev-Bose-Hubbard Model
Yi-fan Zhu and Shi-jie Yang
We report an intrinsic "Bubble Phase" in the two-dimensional Kitaev-Bose-Hubbard model, driven purely by phase frustration between complex hopping and anisotropic pairing. By combining Inhomogeneous Gutzwiller Mean-Field Theory with a Bogoliubov-de Gennes stability analysis augmented by a novel Energy Penalty Method, we demonstrate that this phase spontaneously fragments into coherent islands, exhibiting the hallmark Bose glass signature of finite compressibility without global superfluidity. Notably, we propose a unified framework linking disorder-driven localization to deterministic phase frustration, identifying the Bubble Phase as a pristine, disorder-free archetype of the Bose glass. Our results provide a theoretical blueprint for realizing glassy dynamics in clean
quantum simulators.
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Mesoscale and Nanoscale Physics
Nonlinear mode interactions under parametric excitation in a YIG microdisk
Gabriel Soares, Rafael Lopes Seeger, Amel Kolli et al. (+13 more)
A pair of quantized
spin-wave modes is driven by two-tone parallel pumping in a YIG microdisk. The nonlinear dynamics is experimentally investigated by probing the resulting steady state, which is found to critically depend on the chosen pair of modes, the detuning between the pump frequencies and the modes parametric resonance, as well as the temporal sequence of the two rf tones. A general theory of parametric excitation in confined structures based on magnetization normal modes is developed and quantitatively accounts for the observed dependence and non-commutative behaviors, which emerge from the interplay between the self and mutual nonlinear frequency shifts of the
spin-wave modes. Owing to its high degree of external controllability and scalability to larger sets of modes, this dynamical system provides a model platform for exploring nonlinear phenomena and a promising route toward rf driven state mapping relevant to neuromorphic and unconventional computing.
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All authors Gabriel Soares, Rafael Lopes Seeger, Amel Kolli, Maryam Massouras, Titiksha Srivastava, Joo-Von Kim, Nathan Beaulieu, Jamal Ben Youssef, Manuel Muñoz, Ping Che, Abdelmadjid Anane, Salvatore Perna, Claudio Serpico, Massimiliano d'Aquino, Hugo Merbouche, Grégoire de Loubens
Soft Condensed Matter
Reservoir computing from collective dynamics of active colloidal oscillators
Veit-Lorenz Heuthe, Lukas Seemann, Samuel Tovey et al. (+1 more)
Physical reservoir computing is a computational framework that offers an energy- and computation-efficient alternative to conventional training of neural networks. In reservoir computing, input signals are mapped into the high-dimensional dynamics of a nonlinear system, and only a simple readout layer is trained. In most physical implementations, the interactions that give rise to the dynamics cannot be tuned directly and high dimensionality is typically achieved through time-multiplexing, which can limit flexibility and efficiency. Here we introduce a reservoir composed of hundreds of hydrodynamically coupled active colloidal oscillators forming a fully parallel physical reservoir and whose coupling strength and fading-
memory time can be tuned in situ. The collective dynamics of the active oscillators allow accurate predictions of chaotic time series from single reservoir readouts without time-multiplexing. We further demonstrate real-time detection of subtle hidden anomalies that preserve all instantaneous statistical properties of the signal yet disrupt its underlying temporal correlations. These results establish interacting active colloids as a reconfigurable platform for physical computation and edge-integrated intelligent sensing for model-free detection of irregularities in complex time signals.
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All authors Veit-Lorenz Heuthe, Lukas Seemann, Samuel Tovey, Clemens Bechinger
Strongly Correlated Electrons
Anomalous pressure dependence of the bulk modulus and Yb valence in cubic YbPd
B. Tegomo Chiogo, V. Balédent, J.-P. Rueff et al. (+9 more)
We investigate the Yb valence instabilities in the strongly correlated YbPd compound using resonant X-ray emission spectroscopy as a function of pressure across the charge-order (CO) transition. At a low temperature (T = 30 K) in the CO phase, the Yb $4f$ valence remains nearly constant up to a pressure P$_L$ = 1.5 $\pm {0.2}$ GPa, and then increases gradually at higher pressures. In contrast, at room temperature in the normal phase, an anomalous decrease of the Yb $4f$ valence is observed, without any accompanying structural phase transition. This behavior is corroborated by a systematic pressure-dependent decrease of the unit-
cell volume. Based on a Birch-Murnaghan analysis, the compressibility indicates hardening of the
lattice with applied pressure up to a distinct kink seen at P$_K$ = 1.6 $\pm {0.2}$ GPa. In contrast, for P $>$ P$_K$, the Yb $4f$ valence saturates and the compressibility reveals a counterintuitive pressure-induced softening. The results show a minimum in the compressibility of YbPd (with $f^{0}$-$f^{1}$ hole-type mixed-valence), reminiscent of the maximum in compressibility seen in the $\gamma$-$\alpha$ first-order isostructural phase transition in cerium (with $f^{0}$-$f^{1}$ electron-type mixed-valence).
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All authors B. Tegomo Chiogo, V. Balédent, J.-P. Rueff, E. Saïman, V. Poree, T. Schweitzer, D. Wong, C. Schulz, T. Mazet, A. Chainani, D. Malterre, K. Habicht
Materials Science
Noncollinear spin structure in Dy-doped classical ferrimagnet
Anupam K. Singh, Katayoon Mohseni, Verena Ney et al. (+13 more)
Noncollinear
spin structures have attracted tremendous
attention because they offer a versatile platform for
spin control and manipulation, essential in spintronics. Realizing noncollinearity in ferrimagnetic
insulators is of particular interest as they can be potentially utilized in low-damping spintronics with tunable
magnetic order. Within the spinel-ferrite family, Zn and Al-substituted nickel ferrite (NiZAF) has emerged as an excellent choice for low-damping spintronics. However, realizing noncollinearity in such systems remains challenging. Here, we present evidence of noncollinear
spin structure in the NiZAF thin films induced by the rare earth Dy-doping, utilizing the soft x-ray spectroscopy methods such as
magnetic circular dichroism and x-ray resonant
magnetic reflectivity (XRMR). In particular, XRMR reveals a spiral-type
spin structure, which is attributed to the Dzyaloshinskii-Moriya interaction, arising due to broken inversion
symmetry by the Dy-induced local strain field as confirmed by our theoretical calculations. The realization of noncollinearity in the spinel-ferrite opens pathway to explore the possibility of
chiral magnetic domains and topological
spin textures exhibiting promise for
oxide-based spintronics
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All authors Anupam K. Singh, Katayoon Mohseni, Verena Ney, Andreas Ney, Yicheng Guan, Ilya Kostanovski, Malleshwararao Tangi, Mostafa I. S. Marzouk, Manuel Valvidares, Pierluigi Gargiani, Jean-Marc Tonnerre, P. F. Perndorfer, P. A. Buczek, Arthur Ernst, Holger L. Meyerheim, Stuart S. P. Parkin
Materials Science
Heterogeneous ice nucleation on model substrates
Miguel Camarillo, Javier Oller-Iscar, María M. Conde et al. (+2 more)
Ice nucleation is greatly important in areas as diverse as
climate change, cryobiology, geology or food industry. Predicting the ability of a substrate to induce the nucleation of ice from supercooled water is a difficult problem. Here, we use molecular simulations to analyse how the ice nucleating ability is affected by the substrate
lattice structure and orientation. We focus on different model
lattices: simple cubic, body centred cubic and face centred cubic, and assess their ability to induce ice nucleation by calculating nucleation rates. Several orientations are studied for the case of the face centred cubic
lattice. Curiously, a hexagonal
symmetry does not guarantee a better ice nucleating ability. By comparing the body centred cubic and the cubic
lattices we determined that there is a significant role of the underlying
crystal plane(s) on ice nucleation. The structure of the
liquid layer adjacent to the substrate reveals that more efficient nucleants induce a more structured
liquid. The most efficient substrates present a strong sensitivity of their ice nucleating ability to the
lattice parameters. Introducing a novel methodological approach, we use Classical Nucleation Theory to estimate the contact angle of the ice
nucleus on the studied substrates from the calculated nucleation rates. The method also provides the nucleation free energy barrier height, the kinetic pre-factor and the critical cluster size. The latter is in agreement with the
nucleus size obtained through a microscopic analysis of the nucleation trajectories, which supports the validity of Classical Nucleation Theory down to small critical clusters.
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All authors Miguel Camarillo, Javier Oller-Iscar, María M. Conde, Jorge Ramírez, Eduardo Sanz
Mesoscale and Nanoscale Physics
Phonon-induced Markovian and non-Markovian effects on absorption spectra of moiré excitons in twisted transition metal dichalcogenide bilayers
Daniel Groll, Anton Plonka, Kevin Jürgens et al. (+2 more)
The properties of moiré
excitons in twisted
bilayers of transition metal dichalcogenides (TMDCs) vary significantly with the twist angle, ranging from quasi localized
excitons with flat dispersions for small twist angles to delocalized
excitons for larger ones. This twist angle dependence directly impacts the
exciton-
phonon coupling, which plays a significant role for the optical properties of these materials. In this work we theoretically investigate the twist angle dependent influence of
phonons on absorption spectra of intralayer moiré
excitons in a twisted TMDC hetero-
bilayer. For the lowest-lying intralayer moiré
exciton we find that the
exciton-
phonon coupling interpolates between two physically distinct regimes when tuning the twist angle. At small twist angles non-Markovian polarization dynamics and
phonon sidebands dominate the properties of absorption spectra for localized
excitons. For larger twist angles Markovian processes become more important leading to additional line broadening. Furthermore, the absorption spectra here show a characteristic asymmetric peak similar to monolayer TMDCs. When taking into account multiple bright moiré
exciton bands we find that intraband scattering due to optical
phonons has a significant impact on absorption spectra, effectively suppressing absorption peaks of higher lying bands when their bandwidth surpasses the optical
phonon energy.
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All authors Daniel Groll, Anton Plonka, Kevin Jürgens, Daniel Wigger, Tilmann Kuhn