Quantum Gases · Cross-listed from quant-ph
Hilbert space fragmentation in driven-dephasing Rydberg atom array
Tianyi Yan, Chun Hei Leung and Weibin Li
We investigate the onset and mechanism of
Hilbert space fragmentation (HSF) in a chain of strongly interacting Rydberg atoms subject to local dephasing. It is found that the emergence of multiple long-lived metastable states is fundamentally tied to HSF of the driven-dephasing Rydberg atom system. We demonstrate that the manifesting HSF is captured by a dephasing PXP model that supports multiple degenerate zero modes. These modes form disconnected, block-diagonal subspaces of maximally mixed states, which consist of many-body
spin states sharing the same
symmetry. A key result is the identification of the underlying
symmetry in the HSF, where conserved quantities in each subspace are defined by the consecutive double excitation addressing operator. Moreover, we show explicitly that the number of the fragmented
Hilbert space grows exponentially with the chain length, following a modified Fibonacci sequence. Our work provides insights into many-body dynamics under dynamical constraints and opens avenues for controlling and manipulating HSF in Rydberg atom systems.
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Soft Condensed Matter
Surface functionalization modulates collective cell behavior at integer topological defects
Prasoon Awasthi, Aniruddh Murali, Ellen Juel Pørtner et al. (+2 more)
Living
cells establish long-range orientational order through collective
alignment, giving rise to topological defects whose functional relevance is increasingly recognized in tissue organization and morphogenesis. Engineered topographical patterns have been used to induce such defects in
cell monolayers, mimicking natural biological phenomena. In this work, we investigate the effect of
cell-surface adhesion on collective
cell dynamics at a
vortex integer topological defect imposed by a topographical ring pattern. Adhesion strength is controlled via surface functionalization with poly-D-lysine, fibronectin, or covalently bonded fibronectin, and quantified using atomic force microscopy. As surface chemistry is modified,
cell morphology changes from irregular to spindle-like, and two distinct collective modes emerge: weakly adhered
cells exhibit strong inward motion, while strongly attached
cells move tangentially to the ring. Spindle-shaped
cells exhibit higher nematic order and promote the emergence of two +1/2 topological defects in the monolayer. We further characterize collective
cell dynamics by analyzing correlation lengths and demonstrate the scaling of number density fluctuations in
cell systems.
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All authors Prasoon Awasthi, Aniruddh Murali, Ellen Juel Pørtner, Adam Cohen Simonsen, Francesca Serra
Mesoscale and Nanoscale Physics
Response regimes in on-chip THz spectroscopy
Gunda Kipp, Marios H. Michael, Alexander M. Potts et al. (+6 more)
On-chip THz spectroscopy enables quantitative measurements of the optical conductivity of sub-wavelength 2D materials by tightly confining THz fields in metallic transmission line structures interfaced to the material. However, because the probed structures are smaller than the THz wavelength, finite-size and environmental effects can strongly influence the measured response. Here, we identify the conditions under which a metallic sample exhibits a genuine Drude response and when finite-size and environmental effects must be considered. We further introduce and characterize an additional regime, the Phantom-Drude response, which mimics Drude behavior but instead originates from the superposition of multiple finite-momentum plasmonic resonances. If unrecognized, this regime can lead to misinterpretation of intrinsic material properties. We systematically show how the Phantom-Drude response can emerge and demonstrate its sensitivity to sample dimensions, transmission line geometry, material shape, and gate properties, providing practical guidelines to avoid this regime in future on-chip THz measurements.
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All authors Gunda Kipp, Marios H. Michael, Alexander M. Potts, Dorothee Herrmann, Toru Matsuyama, Guido Meier, Matthew W. Day, Hope M. Bretscher, James W. McIver
Superconductivity
Coherent subgap transport in spin-split Josephson junctions
David Caldevilla-Asenjo, Gorm Ole Steffensen, Sara Catalano et al. (+6 more)
We report the first experimental observation of subgap transport in
ferromagnetic insulator/
superconductor/
insulator/
superconductor junctions realized in EuS/Al/AlOx/Al vertical stacks. Differential conductance measurements reveal multiple Andreev reflection peaks, with odd-order peaks split by the
spin-splitting induced in the
superconductor adjacent to EuS, while even-order peaks remain unaffected. Combining experiments with quasiclassical transport modeling, we extract the
spin-splitting and the distribution of transmission channels, finding that a significant fraction ($\sim 23\%$) of highly transparent channels ($\tau \approx 0.9$) dominates transport. The observation of a Josephson current further confirms strong superconducting coupling through these channels. Our results demonstrate that a single
spin-split
superconductor is sufficient to observe the even-odd MAR effect. Our work establishes EuS/Al junctions as a versatile platform to study subgap transport, Josephson coupling, and
spin-polarized superconducting phenomena.
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All authors David Caldevilla-Asenjo, Gorm Ole Steffensen, Sara Catalano, Alberto Hijano, Maxim Ilyn, Celia Rogero, Ramon Aguado, F. Sebastian Bergeret, Alfredo Levy Yeyati
Quantum Gases
Cyprien Daix, Pok Man Tam, Maxime Dixmerias et al. (+5 more)
Pauli's exclusion principle forces
fermions to occupy distinct
quantum states, creating a filled region of momentum space at low temperature, the
Fermi sea, whose
topology governs the system's response to perturbations and the nature of its correlation functions. Recent theory predicts that for non-interacting
fermions, the Euler characteristic of a $D$-dimensional
Fermi sea – the topological invariant that describes its shape – is encoded in its ($D$+1)-point density correlations. Here we experimentally demonstrate this connection in a two-dimensional degenerate gas of neutral $^{6}$Li atoms using single-atom-resolved imaging. By measuring three- and four-point connected density correlations in real space, we directly extract topological invariants of the underlying
Fermi sea, including the Euler characteristic. Our results are in remarkable agreement with ideal-gas predictions, despite the presence of sizeable interactions, and establish a new pathway for probing many-body
topology through correlation measurements.
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All authors Cyprien Daix, Pok Man Tam, Maxime Dixmerias, Joris Verstraten, Tim de Jongh, Bruno Peaudecerf, Charles L. Kane, Tarik Yefsah
Materials Science
Dislocation-induced magnetization reversal in a ferromagnetic film
Jorge F. Soriano and Eugene M. Chudnovsky
We demonstrate that moving edge dislocations can induce the reversal of magnetization in a
ferromagnetic film due to the Barnett effect. The dynamics of magnetization is studied numerically within a discretized Landau-Lifshitz equation on a hexagonal
lattice containing over $10^5$ sites. Local coordinate frames coupled to the crystallographic axes for each
spin are used together with the laboratory coordinate frame. The parameters of a hexagonal close-packed cobalt
lattice have been chosen for illustration. The magnetization reversal from a metastable initial state created by the external
magnetic field occurs on a time scale of a few picoseconds. Our results imply that fast local elastic twists generated by moving dislocations serve as an important mechanism of magnetization dynamics in solids subjected to a mechanical stress.
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Soft Condensed Matter · Cross-listed from q-bio.SC
A theory for coexistence and selection of branched actin networks in a shared and finite pool of monomers
Valentin Wössner, Falko Ziebert and Ulrich S. Schwarz
Cellular actin structures are continuously turned over while keeping similar sizes. Since they all compete for a shared pool of actin monomers, the question arises how they can coexist in these dynamic steady states. Recently, the coexistence of branched actin networks with different densities growing in a shared and finite pool of purified
proteins has been demonstrated in a biomimetic bead assay. However, theoretical work in the context of organelle size regulation has mainly been focused on linear architectures, such as single filaments and bundles, and thus is not able to explain this observation. Here we show theoretically that the local depletion of actin monomers caused by the growth of a branched network naturally gives rise to a negative feedback loop between network density and growth rate, and that this competition is captured by one central ordinary differential equation. A comprehensive bifurcation analysis shows that the theory leads to well-defined steady states even in the case of multiple networks sharing the same pool of monomers, without any need for specific molecular processes. Under increasing competition strength, coexistence is replaced by selection. We also show that our theory is in excellent agreement with spatiotemporal simulations, implemented in a finite element framework, and that local depletion even occurs in the presence of a large pool of non-polymerizable actin. In summary, our work suggests that local monomer depletion is the decisive and universal factor controlling growth of branched actin networks.
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Other Condensed Matter · Cross-listed from quant-ph
Inhibited radiative decay enhances single-photon emitters
Florian Burger, Stephan Rinner, Andreas Gritsch et al. (+2 more)
Quantum networks and modular
quantum computers require efficient
spin-
photon interfaces, often realized using optical resonators that enhance radiative decay on a desired transition. However, this requires small mode volumes and high quality factors, which limits multiplexing capacity and demands precise frequency tuning. Here, we demonstrate an alternative approach that circumvents these bottlenecks for upscaling. Using a W1 silicon photonic
crystal waveguide with a tailored photonic bandgap, we selectively inhibit unwanted decay pathways, thereby redirecting emission to the desired transition. This enables efficient
photon collection over a large frequency range, allowing the resolution and individual addressing of tens of erbium dopants. Their lifetimes are preserved, or even increased, compared to bulk material. The extended mode volume of the devices enables the use of lower dopant concentrations, thereby improving emitter coherence. Our approach can be combined with Purcell enhancement and applied to other
spin-
qubit platforms, opening intriguing perspectives for photonic
quantum technologies.
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All authors Florian Burger, Stephan Rinner, Andreas Gritsch, Kilian Sandholzer, Andreas Reiserer
Mesoscale and Nanoscale Physics
Dual topology and edge-reconstruction in $\alpha$-Sn
Jan Skolimowski, Nguyen Minh Nguyen, Alicja Kawala et al. (+3 more)
We formulate the tight-binding model for cubic $\alpha$-Sn based on the DFT calculations. In the model, we incorporate a variable bond angle, which allows us to simulate the effect of the in-plane strain. In the bulk, we demonstrate the presence of the $\mathbb{Z}_2$ topological invariant and a non-zero mirror Chern number, making $\alpha$-Sn one of the rare cases where dual
topology can be observed. We calculate the topological phase diagram of multi-layer $\alpha$-Sn as a function of strain and number of layers. We find that a non-trivial
quantum spin Hall state appears only for compressive strain above five layers of thickness. Quite surprisingly, both in the trivial and non-trivial phases, we find a plethora of edge-states with energies inside the bulk gap of the system. Some of these states are localized at the side surfaces of the slab and some of them prefer top/bottom surfaces. We find that they can be adiabatically connected to topological states in the
chiral limit, where the model supports multiple one-dimensional winding numbers that take different values in different directions in the Brillouin zone. Finally, around high-
symmetry points their presence can also be explained by the mirror Chern number and Wilson-loop invariants
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All authors Jan Skolimowski, Nguyen Minh Nguyen, Alicja Kawala, Giuseppe Cuono, Carmine Autieri, Wojciech Brzezicki
Mesoscale and Nanoscale Physics
Exchange interaction in gate-defined quantum dots beyond the Hubbard model
Alexander Willmes, Patrick Bethke, M. Mohamed El Kordy Shehata et al. (+10 more)
A quantitative description of the exchange interaction in
quantum dots is relevant for modeling gate operations of
spin qubits. By measuring the amplitude and frequency of exchange-driven
qubit state oscillations, we measure the detuning dependence of the exchange coupling in a GaAs double
quantum dot over three orders of magnitude. Both 1D and 3D full configuration interaction simulations can replicate the observed behavior. Extending a Hubbard model by including excited states increases the range of detuning where it provides a good fit, thus elucidating the underlying physics.
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All authors Alexander Willmes, Patrick Bethke, M. Mohamed El Kordy Shehata, George Simion, M.A. Wolfe, Tim Botzem, Robert P.G. McNeil, Julian Ritzmann, Arne Ludwig, Andreas D. Wieck, Dieter Schuh, Dominique Bougeard, Hendrik Bluhm
Soft Condensed Matter
From Knots to Crystals: Machine-Learned Potentials for Self-Assembling Topological Solitons in Liquid Crystals
Arunkumar Bupathy, Darian Hall, Ivan I. Smalyukh et al. (+3 more)
Knotted fields in classical and
quantum systems have long been recognized for their non-trivial
topologies and particle-like behavior, but practical applications have been limited by the difficulty of stabilizing them. Recently, stable knotted solitonic textures–heliknotons–were discovered in
chiral liquid crystals, forming adaptive
crystal assemblies via elastic distortion-mediated interactions. We use machine learning to develop single-site coarse-grained potentials that accurately capture these
chiral anisotropic effective interactions. The resulting potentials accurately reproduce experimentally observed heliknoton assemblies and enable simulations at length and time scales far beyond the range of fine-grained continuum models. This general framework is readily transferable to other topological
solitons, providing a powerful route to understand, predict, and ultimately control their collective behavior and dynamics.
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All authors Arunkumar Bupathy, Darian Hall, Ivan I. Smalyukh, Gerardo Campos-Villalobos, Rodolfo Subert, Marjolein Dijkstra
Soft Condensed Matter
Quantifying surfactant adsorption at fluid interfaces by combining X-ray reflectivity and simulations
Kay-Robert Dormann, Joshua Reed, Chen Shen et al. (+4 more)
Adsorption of surfactants to fluid interfaces occurs in numerous daily-life and technological contexts. The surfactant surface coverage $\Gamma$ governs interface characteristics like tension $\gamma$, viscoelastic properties, and the stability of thin foam films. Directly measuring $\Gamma$ as a function of the bulk concentration $c$ is highly desirable but challenging, particularly for non-ionic surfactants that lack easily detectable labels.
Neutron reflectometry is currently the only generally applicable method, but it is not available for routine experiments. Here, we propose a simulation-assisted approach to deduce the adsorption isotherm $\Gamma(c)$ from X-ray reflectivity data: As a first step, we use atomistic molecular dynamics simulations of surfactant-loaded air/water interfaces with prespecified $\Gamma$ to obtain interfacial electron density profiles. From these profiles, we compute theoretical X-ray reflectivity curves and compare them with experimental measurements to determine the matching bulk concentration. We focus on two non-ionic surfactants (C$_{12}$EO$_6$ and $\beta$-C$_{12}$G$_2$}) with previously established force fields to illustrate how this combined approach of experiments and simulations can determine the adsorption isotherm. Additional insights are gained through comparison with the measured surface tension isotherms $\gamma(c)$, based on the equation of state $\gamma(\Gamma)$ from simulations.
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All authors Kay-Robert Dormann, Joshua Reed, Chen Shen, Daniel Mitlewski, Matej Kanduč, Benno Liebchen, Emanuel Schneck
Mesoscale and Nanoscale Physics
Controlling Dissipative Topology Through Floquet Driving: From Transient Diagnostics to Boundary States Isolation
Koustav Roy, Shahroze Shahab and Saurabh Basu
Engineering dissipative dynamics in open
quantum systems is under active focus, especially in topological settings where resilient edge modes are expected to exhibit decay rates distinct from the bulk. In this letter, we propose an efficient dynamical scheme to discern such long-lived excitations. Employing a Floquet-Lindblad framework, we explore how periodic driving reshapes the key features of a paradigmatic topological model, namely a Creutz ladder. Our results bear testimony to a drive-induced unipolar-bipolar transition in the Liouvillian skin effect, which gets dynamically manifested as a
chiral-helical damping crossover. Such a transition effectively rescales the bulk localization length, giving rise to a polarization drift that we identify as a new invariant for efficient diagnosis of the nontrivial phases. As the transition becomes more gradual via tuning drive-rescaled parameters, we uncover signatures of a scale-free localization where skin and extended modes co-exist with distinct decay rates. The emergent hierarchy of the decay rates yields two disparate timescales: a
chiral wavefront that rapidly empties the bulk followed by a long-lived regime dominated by robust edge modes. Overall, our results provide convincing evidence that periodic driving serves as a powerful handle to manipulate dissipative topological phases and dynamically isolate the boundary modes.
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Mesoscale and Nanoscale Physics
Compact localized currents in flat bands with broken time-reversal symmetry
Rohit Kishan Ray, Carlo Danieli, Alexei Andreanov et al. (+1 more)
We develop a systematic framework for constructing all-bands-flat (ABF)
lattice Hamiltonians that explicitly break time-reversal
symmetry (TRS). By threading
magnetic flux through disconnected polygonal plaquettes and applying local entangling
unitary transformations, we map plaquettes onto families of ABF models in one, two, and three dimensions. This procedure preserves the flux configuration while converting semi-detangled geometries into ABF
lattices with nontrivial hopping structure. The resulting flat bands admit compact localized states (CLSs) whose support includes both the flux-threaded plaquettes and auxiliary sites introduced by the
unitary transformations. In these TRS-broken constructions, the CLSs host localized circulatory currents whose magnitude depends on the applied flux. We further extend the framework to
lattices with coexisting flat and dispersive bands, illustrating cases with both orthogonal and non-orthogonal CLSs. Our results provide a controlled route for generating dispersionless
lattices supporting flux-induced local currents.
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All authors Rohit Kishan Ray, Carlo Danieli, Alexei Andreanov, Sergej Flach
Statistical Mechanics
Refinements of the Eigenstate Thermalization Hypothesis under Local Rotational Invariance via Free Probability
Elisa Vallini, Laura Foini and Silvia Pappalardi
The Eigenstate Thermalization Hypothesis (ETH) was developed as a framework for understanding how the principles of statistical mechanics emerge in the long-time limit of isolated
quantum many-body systems. Since then, ETH has shifted the
attention towards the study of
matrix elements of physical observables in the energy eigenbasis. In this work, we revisit recent developments leading to the formulation of full ETH, a generalization of the original ETH ansatz that accounts for multi-point correlation functions. Using tools from free probability, we explore the implications of local rotational invariance, a property that emerges from the statistical invariance of observables under random basis transformations induced by small perturbations of the
Hamiltonian. This approach allows us to make quantitative predictions and derive an analytical characterization of subleading corrections to
matrix-element correlations, thereby refining the ETH ansatz. Moreover, our analysis links the statistical properties of
matrix elements under random basis changes to the empirical averages over energy windows that are usually considered when dealing with a single instance of the ensemble. We validate our analytical predictions through comparison with numerical simulations in non-integrable Floquet systems.
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Other Condensed Matter · Cross-listed from cs.RO
Field-programmable dynamics in a soft magnetic actuator enabling true random number generation and reservoir computing
Eduardo Sergio Oliveros-Mata, Oleksandr V. Pylypovskyi, Eleonora Raimondo et al. (+12 more)
Complex and even chaotic dynamics, though prevalent in many natural and engineered systems, has been largely avoided in the design of electromechanical systems due to concerns about wear and controlability. Here, we demonstrate that complex dynamics might be particularly advantageous in soft robotics, offering new functionalities beyond motion not easily achievable with traditional actuation methods. We designed and realized resilient
magnetic soft actuators capable of operating in a tunable dynamic regime for tens of thousands cycles without fatigue. We experimentally demonstrated the application of these actuators for true random number generation and
stochastic computing. {W}e validate soft
robots as physical reservoirs capable of performing Mackey–Glass time series prediction. These findings show that exploring the complex dynamics in soft robotics would extend the application scenarios in soft computing, human-
robot interaction and collaborative
robots as we demonstrate with biomimetic blinking and randomized voice modulation.
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All authors Eduardo Sergio Oliveros-Mata, Oleksandr V. Pylypovskyi, Eleonora Raimondo, Rico Illing, Yevhen Zabila, Lin Guo, Guannan Mu, Mónica Navarro López, Xu Wang, Georgios Tzortzinis, Angelos Filippatos, Gilbert Santiago Cañón Bermúdez, Francesca Garescì, Giovanni Finocchio, Denys Makarov
Mesoscale and Nanoscale Physics
Electric circuit analog of Landau-Zener tunneling using time-varying elements
Enhong Cheng, Zheng Lian, Zezhou Chen et al. (+1 more)
Landau-Zener tunneling (LZT) is a fundamental dynamical phenomenon, ubiquitous in various
quantum systems. Here, we propose a time-varying electric
circuit to address the question of whether the
quantum LZT can occur in classical systems. Although the underlying differential equation of motion is quite different from the Schrödinger equation and the instantaneous frequency spectrum of the proposed
circuit is not linear, the probability of the LZT in
circuits (
circuit LZT for short), based on our generalized definition for norm-unconserved systems, still follows the laws of the LZT in
quantum systems, codetermined by the linear sweeping rate $\alpha'$ and the frequency gap $\Delta$, i.e., approaching the analytical value $\exp(-\pi\Delta^2/2\alpha')$, regardless of whether the coupling is reciprocal or nonreciprocal. The deep relationship between the
circuit LZT and its
quantum counterpart can be established through a linearization and block-diagonalization process. Our proposal provides a general method for simulating time-dependent
quantum models using time-varying electric
circuits, which has been lacking in previous studies, and paves the way for studying more complicated LZT and other dynamical phenomena in
circuits and other classical systems.
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All authors Enhong Cheng, Zheng Lian, Zezhou Chen, Li-Jun Lang
Mesoscale and Nanoscale Physics
Chiral cavity-induced quantum phase transitions in a quantum ring
Loic Remolif and Ivan Iorsh
We consider a
quantum ring placed in a gyrotropic cavity characterized by the energy splitting between the left and right circularly polarized modes. We show that despite the absence of constant
magnetic field penetrating through the ring, in the regime of the ultrastrong light matter coupling, the total current in the ground state changes discontinuously with the light matter coupling in the direct analogy with the Aharonov-Bohm ring. We consider the driven-dissipative of the system and show that the discontinuous change of the total angular momentum can be directly probed via the spectral and statical properties of the radiation emitted by the system under weak coherent drive.
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Statistical Mechanics
A thermodynamic framework for the thermal conductivity of dense fluids
Miguel Hoyuelos
A thermodynamic framework that predicts the thermal conductivity $\lambda$ of simple fluids beyond the dilute-gas limit is introduced. By generalizing the transition-rate approach of particles on a
lattice to conserved quantities in continuous space, an expression for the ratio $\lambda/\lambda_{\rm id}$ is derived, where $\lambda_{\rm id}$ is the dilute-gas value; the ratio depends solely on
equilibrium thermodynamic properties and is therefore directly computable from any equation of state. The resulting formula quantitatively reproduces simulation data for hard spheres throughout almost the entire fluid range, and captures the behavior of Lennard-Jones fluids in the supercritical region where thermodynamic fluctuations remain moderate. Comparison with experimental data for argon, reported by other authors, also shows good agreement. These results provide evidence that transport coefficients of dense fluids can be expressed as their dilute-gas values multiplied by a universal function of
equilibrium thermodynamic properties.
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Soft Condensed Matter
Diffusion through complex confining environments: fluctuating triply periodic minimal surfaces
Jakob Mihatsch and Andreas M. Menzel
The transport of individual entities through interconnected structures is a process of practical relevance both in biology and technology. Examples are given by diffusive dynamics of molecules in porous structures. In soft environments, this transport can be strongly influenced by fluctuations of the porous structure itself. Here, we focus on triply periodic membrane structures found both in
cell organelles and in synthetic amphiphilic systems. We theoretically study the effect of a complex three-dimensional fluctuating environment on the diffusive motion of a test object, using a phase field approach. The rigid spherical test object is energetically forced to not penetrate the membrane. Generally, the pores of the membrane structure can be smaller than the diffusing object. Yet, fluctuations of the membrane can intermittently widen its pores, still allowing for the motion of the larger particles through them. Thus, the object stays trapped for a while inside one cavity formed by the membrane, before an appropriate fluctuation event widens a membrane pore in the right moment so that the object can jump into the next cavity. The process is reflected by a pronounced plateau in the time
evolution of the mean squared displacement. We think that the described scenario should be directly observable, for instance, in
protein diffusion through biological environments.
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Strongly Correlated Electrons
Electronic Structure and Dynamical Correlations in Antiferromagnetic BiFeO$_3$
Yihan Wu, Mario Caserta, Tommaso Chiarotti et al. (+1 more)
We study the electronic structure and dynamical correlations in
antiferromagnetic BiFeO$_3$, a prototypical room-temperature multiferroic, using a variety of static and dynamical first-principles methods. Conventional static Hubbard corrections (DFT+$U$, DFT+$U$+$V$) incorrectly predict a deep-valence Fe $3d$ peak (around $-7\,\text{eV}$) in
antiferromagnetic BiFeO$_3$, in contradiction with hard-X-ray photoemission. We resolve this failure by using a recent generalization of DFT+$U$ to include a frequency-dependent screening – DFT+$U(\omega)$ – or using a dynamical Hubbard functional (dynH). The screened Coulomb interaction $U(\omega)$, computed with
spin-polarized RPA and projected onto maximally localized Fe $3d$ Wannier orbitals, is expressed as a sum-over-poles, yielding a self-energy that augments the Kohn–Sham
Hamiltonian. This DFT+$U(\omega)$ approach predicts a fundamental band gap of $1.53\,\text{eV}$, consistent with experiments, and completely eliminates the unphysical deep-valence peak. The resulting simulated HAXPES spectrum reproduces the experimental lineshape with an accuracy matching or exceeding that of far more demanding DFT+DMFT calculations. Our work demonstrates the critical nature of dynamical screening in complex
oxides and establishes DFT+$U(\omega)$ as a predictive, computationally efficient method for correlated materials.
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All authors Yihan Wu, Mario Caserta, Tommaso Chiarotti, Nicola Marzari
Materials Science
Surface oxidation of Pt and PtPd alloys during NO conversion investigated by Atom Probe Tomography
Yoonhee Lee, Daniel Dobesch, Patrick Stender et al. (+3 more)
In this study, the dynamic oxidation state changes of pure Pt and 50at% PtPd
alloy catalysts were investigated during a temperature ramp from 80 to 450 C under a reactive gas mixture of 500 ppm NO and 3 % Oxygen in Nitrogen atmosphere. These changes are closely correlated with variations in NO conversion efficiency. Sharp tip specimens were prepared from Pt and PtPd
alloy wires by electrochemical polishing and Focused Ion Beam annular milling, with the hemispherical apex serving as a model for nanoscale catalyst surfaces. The samples were exposed to the reactive atmosphere in a dedicated reaction chamber and subsequently analyzed using atom probe
tomography. Effective
oxide thicknesses and three-dimensional surface morphology were quantitatively evaluated. A pronounced decrease in
oxide thickness was observed during the first cooling and second heating cycles, particularly below 200 C, indicating reversible redox behavior on both Pt and PtPd
alloy surfaces. This behavior correlates with the inverse hysteresis of NO conversion measured for both systems, suggesting that the redox reversibility is driven primarily by reaction kinetics rather than thermodynamic stability.
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All authors Yoonhee Lee, Daniel Dobesch, Patrick Stender, Ute Tuttlies, Ulrich Nieken, Guido Schmitz
Soft Condensed Matter · Cross-listed from physics.bio-ph
Nature of frontier quasi-particle states in nitrogen-base systems
Raul Quintero-Monsebaiz, Per Hyldgaard and Elsebeth Schröder
Understanding photophysical properties of DNA is important: It can help us elucidate and probe the impact of charges and free radicals in the cellular environment. For example, a photoemission at a given nucleobase means that we both charge it and place an electron right next to a neighboring part of the genetic code. Inverse photoemission means that we trap a free electron (at some empty state or resonance), and instead emit a low-energy
photon. This may reduce the damage if it happens at an already charged base, but it can cause extra damage if it arises somewhere else. Predicting the nature of sudden optically-driven excitations, termed quasi-particles (QPs), help us detail interactions and possibly control the damage that might follow. Also, these QPs contain information on the larger DNA assembly because they reflect the fingerprints of nucleobase polarity, the hydrogen bonding in Watson-Crick pairs, and the van der Waals (vdW) interactions in the Watson-Crick-pair stacking that makes up the genome. In this study, we utilize the recently developed (optimally tuned) range-separated hybrid vdW density functional, AHBR-mRSH* [JPCM 37, 211501 (2025)] to analyze the electron-attached and ionized QP states of these DNA components, with a particular focus on dipole- and multipole-trapped empty states (bound or resonances). We also evaluate critical properties such as dipole and quadrupole moments, QP HOMO-LUMO energy gaps, and transition-dipole moments. Finally, we classify the Watson-Crick stacked dimers based on their QP nature. This classification provides the foundation for proposing a model of DNA reactivity and photo-physical activity.
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Mesoscale and Nanoscale Physics
Reservoir neuromorphic computing based on spin-orbit coupling in an organic crystal resonator
Teng Long, Yibo Deng, Xuekai Ma et al. (+5 more)
Neuromorphic computing is at the basis of the recent progress in artificial intelligence. But the progress is accompanied with increasing demands in computational resources and power supply. Reservoir neuromorphic computing uses a non-linear physical system to replace a part of a large neural network. The advantages can include reduced power consumption and faster learning. We show that the interference in an organic
crystal waveguide resonator leads to efficient separation of optical patterns, allowing a significant reduction of the size of the neural network and an acceleration of the learning process. For more complex symbols, extending the reservoir output dimension thanks to
spin-orbit coupling, we achieve a 10-times reduction of the network size and a 3-fold speedup. Our work suggests a general path for the performance improvement of photonic reservoir computing systems.
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All authors Teng Long, Yibo Deng, Xuekai Ma, Chunling Gu, Guillaume Malpuech, Qing Liao, Hongbing Fu, Dmitry Solnyshkov
Disordered Systems and Neural Networks · Cross-listed from cs.LG
A Differentiable Measure of Algebraic Complexity: Provably Exact Discovery of Group Structures
Dongsung Huh, Lior Horesh and Halyun Jeong
Discovering discrete algebraic rules from data is a fundamental challenge in machine learning. We formalize this problem through Cayley-table completion – an algebraic counterpart to classical
matrix completion – where the degree of associativity violation replaces linear rank as the intrinsic measure of complexity. We provide a rigorous landscape analysis of HyperCube, an operator-valued tensor factorization, on the fully observed target table $\delta$, proving that its global infimum $H_{\inf}(\delta) := \inf_{\Theta \in F_\delta} H(\Theta)$ implicitly defines an exact differentiable measure for this complexity. We show that HyperCube's native objective $H(\Theta)$ decomposes into two components:
geometric alignment (collinearity) and an inverse $\ell_2$ penalty. We establish that these continuous variational pressures induce core discrete properties: collinearity enforces associativity (Collinearity–Associativity Equivalence), and the inverse $\ell_2$ penalty reduces to an exact inverse rank penalty within the collinear
manifold, driving the parameters toward full-rank unitarity. Consequently, we derive an absolute lower bound $H(\Theta) \ge H_{\inf}(\delta) \ge 3 \, |\delta|$, where $|\delta|$ is the target table size. We prove this absolute floor is attained if and only if the target is isotopic to a group, and characterize the global minimizer as the regular representation of the underlying group (up to
unitary gauge), resolving the central open
conjecture of Huh (2025). This work serves as an existence proof that certain discrete algebraic structures can be exactly characterized by differentiable measures, enabling gradient-based discovery without the need for combinatorial search. All theoretical results are mechanically verified in Lean 4 and confirmed via small-scale experiments.
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Superconductivity
Nonequilibrium Quasiparticle Dynamics in a MoRe-Based Superconducting Resonator under IR Excitation
O. A. Kalenyuk, S. I. Futimsky, I. A. Martynenko et al. (+5 more)
The response of a MoRe-based superconducting resonator operating near 5 K to pulsed infrared irradiation is investigated, and the underlying physical mechanisms are analyzed. The device exhibits a pronounced nonlinear response dominated by nonequilibrium quasiparticle dynamics rather than uniform thermal heating. Infrared pulses produce strong distortions of the resonance curve and a transient decrease in the resonance frequency, consistent with increased kinetic inductance caused by quasiparticle generation. The frequency shift scales approximately linearly with absorbed power, whereas the dissipation response saturates at higher powers, indicating the formation of a nonequilibrium steady-state quasiparticle population. These observations demonstrate a transition from a linear pair-breaking regime to a saturated dissipation regime, likely associated with a quasiparticle relaxation bottleneck or partial suppression of the smaller superconducting gap in MoRe. The results highlight the relevance of nonequilibrium processes in MoRe and confirm its potential for microwave kinetic-inductance detector applications.
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All authors O. A. Kalenyuk, S. I. Futimsky, I. A. Martynenko, A. P. Shapovalov, O. O. Boliasova, V. I. Shnyrkov, A. L. Kasatkin, A. A. Kordyuk
Strongly Correlated Electrons
Trion gas on the surface of a failed excitonic insulator
Yuval Nitzav, Abigail Dishi, Himanshu Lohani et al. (+15 more)
Trions, three-body bound states composed of an
exciton and an additional charge, are typically fragile and require external excitation to form. Here, we report the spontaneous emergence of a stable trion gas at the surface of the layered
semiconductor Ta2NiS5, revealed through angle-resolved photoemission spectroscopy. We observe a sharp, highly localized in-gap feature that cannot be explained by conventional band-theory. Instead, we argue that it arises from the formation of negative trions, stabilized by surface-induced band bending and the material's quasi-one-dimensional geometry. Unlike
excitons, these trions form without optical pumping and persist at
equilibrium, marking a rare example of an interaction-driven surface state in a nominally conventional
semiconductor. Our findings establish Ta2NiS5 as a unique platform for exploring many-body physics at surfaces and open new avenues for studying and controlling collective excitations in low-dimensional systems.
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All authors Yuval Nitzav, Abigail Dishi, Himanshu Lohani, Ittai Sidilkover, Noam Ophir, Roni Anna Gofman, Avior Almoalem, Ilay Mangel, Nitzan Ragoler, Francois Bertran, Jaime Sánchez-Barriga, Dmitry Marchenko, Andrei Varykhalov, Nicholas Clark Plumb, Irena Feldman, Hadas Soifer, Anna Keselman, Amit Kanigel
Mesoscale and Nanoscale Physics
Irina Heinz, Jeroen Danon and Guido Burkard
Spin qubits have proven to be a feasible candidate for
quantum computation, and some realizations of
spin qubits already benefit from advanced device manufacturing in the
semiconductor industry. Compared to superconducting platforms,
spin qubits can operate at higher temperatures from tens of millikelvin up to a few kelvin. However, recent experiments show a non-trivial and often non-monotonic dependence of the
spin qubit frequency on the temperature, featuring a region of decreased sensitivity to temperature fluctuations. In this work, we aim to gain insight into the physics behind such temperature shifts in the low-temperature limit. Investigating the
spin qubits' interaction with
phonon modes of the host material, we can explain some of the key features of the observed behavior and estimate the temperature sweet spot for the
qubit frequency shift.
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Materials Science
A cascade model for the defect-driven etching of porous GaN distributed Bragg reflectors
Ben Thornley, Maruf Sarkar, Saptarsi Ghosh et al. (+4 more)
Fabrication of porous GaN distributed Bragg reflectors (DBRs) via the selective electrochemical etching (ECE) of conductive Si-doped layers, separated by non-intentionally doped (NID) layers, provides a straightforward methodology for producing highly reflective DBRs suitable for device overgrowth and integration, which has otherwise proven difficult in the III-nitride epitaxial system via conventional alloying. Such photonic materials can be fabricated by a lithography-free defect-driven etching process, where threading dislocations intrinsic to heteroepitaxy form nanoscale channels that facilitate etchant transport through NID layers. Here, we report the first three-dimensional characterisation of porous GaN-on-Si DBRs fabricated in this methodology with different ECE voltages, using serial-section
tomography in a focused ion beam scanning electron microscope (FIB-SEM). These
datasets reconstruct the pore morphology as etching proliferates through the alternating Si-doped/NID layer stack. Volumetric reconstruction enabled us to enhance the established `kebab' model for defect-driven etching by proposing a `cascade' model where etchant cascades through the material via vertical etching down nanopipes and horizontal etching across pores, forming complex networks directly related to the pathways taken. This accounts for premature nanopipe termination and discontinuities in nanopipe formation, where dislocations are observed to activate and deactivate individually. Statistical analysis of individual etching behaviour, across all dislocations for each tomograph, revealed a greater tendency to form continuous structures that follow conventional kebab behaviour at higher ECE voltages. We propose that higher ECE voltages alter the probability of dislocation etching relative to doped layer etching, thereby empowering morphological optimization through improved mechanistic understanding of ECE.
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All authors Ben Thornley, Maruf Sarkar, Saptarsi Ghosh, Martin Frentrup, Menno J. Kappers, Thom R. Harris-Lee, Rachel A. Oliver
Mesoscale and Nanoscale Physics
Non-magnetic spin splitting driven by spin-valley-layer coupling in multilayer WSe2
Min-Gue Kim, Min-Sik Kim, Kenji Watanabe et al. (+3 more)
Transition metal dichalcogenides provide a platform for exploring
spin-valley physics, offering a promising approach to electric-field-driven
spin control for low-power spintronic and
quantum devices. Here, we demonstrate electric-field-induced
spin splitting in the Q and Q' valleys of multilayer n-type WSe2 using
quantum-point-contact spectroscopy. Systematic modulations in four distinct conductance quantization steps, providing direct evidence of
spin-valley-layer coupling-driven
spin-resolved density of states, are achieved by tuning the out-of-plane gate voltage. Notably, the electric-field-induced
spin splitting significantly dominate the
magnetic-field-induced valley-Zeeman effect (i.e., ~7 meV for a displacement field change of ~0.08 V/nm vs. ~2 meV for a
magnetic field of B = 9 T), demonstrating a powerful, non-
magnetic manipulation of
spin states. This ability to manipulate
spin states by gate voltage is crucial for advancing next-generation low-power spintronic and
quantum information technologies.
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All authors Min-Gue Kim, Min-Sik Kim, Kenji Watanabe, Takashi Taniguchi, Ju-Jin Kim, Myung-Ho Bae