Mesoscale and Nanoscale Physics
Discrete holography and density of states in the crossover from hyperbolic to Euclidean lattices
Mireia Tolosa-Simeón and Igor Boettcher
We study tight-binding models in the crossover from
hyperbolic to Euclidean
lattices, realized through the successive insertion of Euclidean defects into
hyperbolic lattices. We analyze how the
holographic two-point boundary correlation function and bulk density of states evolve as defects are gradually introduced. We find that bulk properties are strongly affected by the presence of Euclidean defects, whereas boundary observables remain remarkably robust even at high defect fractions. This robustness indicates that essential features of boundary physics on
hyperbolic lattices, which capture aspects of anti de-Sitter/conformal field theory (AdS/CFT)-like dualities in discrete systems, can be reproduced both experimentally and numerically without requiring perfectly
hyperbolic lattices, thereby reducing the system size needed for implementation.
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Statistical Mechanics
Topological Defects from Quantum Reset Dynamics
R. Jafari, Henrik Johannesson and Sebastian Eggert
We analyze mechanisms for universal out-of-
equilibrium dynamics near criticality by exploring the effect of randomized
quantum resetting (QR) under a finite-time quench across a
quantum phase transition. Using the transverse-field Ising chain as a generic model and exploiting its exact solution, QR is found to cause a crossover of the scaling of the topological defect density with the time scale $\tau$ of the quench, from Kibble-Zurek to anti-Kibble-Zurek scaling as $\tau$ increases. This reflects a competition between non-adiabatic quench-driven excitations and QR, giving rise to local minima of the defect densities at optimal annealing times. These times and the corresponding local minima are shown to scale as universal power laws with the rate of QR. Additional results for the scaling of the mean excess energy suggest that a system driven across a
quantum critical point exhibits the same scaling behavior under a linear quench with QR as with uncorrelated noise.
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Statistical Mechanics · Cross-listed from quant-ph
Signatures of coherent initial ensembles on all work moments
Pranay Nayak, Sreenath K. Manikandan, Tan Van Vu et al. (+1 more)
Standard treatments of
quantum work using projective energy measurements erase initial coherence and alter the dynamics, thereby failing to capture the thermodynamic effects of coherent superpositions of energy eigenstates in an ensemble of initial states. In this article, we use an operational work definition that is non-intrusive, applying it to the case of a driven dissipative
qubit, where the
qubit's initial preparation comprises coherent superposition states, while the driving is coherence-less. We derive an
evolution equation for the moment generating function for this work, faithfully capturing the thermodynamic signature of coherent superpositions in the initial ensemble. We demonstrate that different initial ensembles that correspond to the same density
matrix upon ensemble average, while having the same average work, display different work fluctuations. For monotonic driving, we show that fluctuations are maximum for coherence-less initial ensembles. As an application, we consider
quantum bit-erasure in finite time and demonstrate significantly different work statistics for erasing a classical bit of information versus a Haar random initial ensemble. Our results indicate that coherence in the initial ensemble can be utilized as a resource for thermodynamic precision without incurring additional dissipative work costs. We also obtain a generalized fluctuation
theorem that establishes a new
quantum lower bound on the mean dissipated work. This bound, counterintuitively, is also applicable to a "classical" initial ensemble with the same initial density
matrix and is connected to
quantum absolute irreversibility.
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All authors Pranay Nayak, Sreenath K. Manikandan, Tan Van Vu, Supriya Krishnamurthy
Materials Science
QUASAR: A Universal Autonomous System for Atomistic Simulation and a Benchmark of Its Capabilities
Fengxu Yang and Jack D. Evans
The integration of large
language models (LLMs) into materials science offers a transformative opportunity to streamline computational workflows, yet current agentic systems remain constrained by rigid, carefully crafted domain-specific tool-calling paradigms and narrowly scoped
agents. In this work, we introduce
QUASAR, a universal autonomous system for atomistic simulation designed to facilitate production-grade scientific discovery.
QUASAR autonomously orchestrates complex multi-scale workflows across diverse methods, including density functional theory, machine learning potentials, molecular dynamics, and Monte Carlo simulations. The system incorporates robust mechanisms for adaptive planning, context-efficient
memory management, and hybrid knowledge
retrieval to navigate real-world research scenarios without human intervention. We
benchmark QUASAR against a series of three-tiered tasks, progressing from routine tasks to frontier research challenges such as photocatalyst screening and novel material assessment. These results suggest that
QUASAR can function as a general atomistic
reasoning system rather than a task-specific automation framework. They also provide initial evidence supporting the potential deployment of agentic AI as a component of computational chemistry research workflows, while identifying areas requiring further development.
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Soft Condensed Matter
Dynamical density functional theory for dense odd-diffusive fluids
Iman Abdoli, René Wittmann and Hartmut Löwen
Odd
diffusion breaks time-reversal
symmetry in overdamped systems through transverse probability currents while preserving
equilibrium steady states. In this work, we develop a dynamical density functional theory (DDFT) for dense interacting odd-diffusive fluids and apply it to ultrasoft particles in two dimensions. In bulk, odd
diffusion qualitatively reshapes collective relaxation by generating transient circulating current patterns which do not exist in normal fluids. Under harmonic ring confinement, the circulation of probability current induces an angular redistribution of density along the ring during relaxation. This unique footprint of odd
diffusion opens up a shorter pathway to
equilibrium. Repulsive interactions significantly enhance these effects. Excellent agreement with Brownian dynamics simulations confirms that our odd-DDFT framework quantitatively captures all essential nonequilibrium aspects of the nontrivial odd transport and collective redistribution for dense fluids in both bulk and confined geometries.
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Mesoscale and Nanoscale Physics
Analytical topological invariants for 2D non-Hermitian phases using Morse theory
Cameron Gibson and Evelyn Tang
As energy dissipation and gain are ubiquitous in the real world, such phenomena demand the generalization of Hermitian methods such as the analysis of topological properties for non-Hermitian systems. However, as non-Hermitian systems typically contain more degrees of freedom, this poses a challenge for analytical approaches to understand their
topology and invariants. In this work, we analytically calculate the 2D Zak phase for a 2D non-Hermitian SSH-type
Hamiltonian that supports a rich structure and edge currents. Closed-form expressions for eigenstates and divisions of the phase diagram are obtained, including for regions in the phase diagram where different types of exceptional points exist. We use Morse theory to determine the
topology of exceptional points in momentum space. Although the band structure breaks down at exceptional points, we show that a specific phase-based topological invariant remains well-defined. Furthermore, our work yields an analytic derivation for counting edge states in the Hermitian limit. These results provide new conceptual and analytical tools for the study of complex topological systems.
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Mesoscale and Nanoscale Physics
Weight-four parity checks with silicon spin qubits
Brennan Undseth, Nicola Meggiato, Yi-Hsien Wu et al. (+7 more)
Recent advances in coherent
spin shuttling have made sparse
semiconductor spin qubit arrays an appealing solid-state platform to realize
quantum processors. The dynamic and long-range connectivity enabled by shuttling is also essential for many
quantum error-correction (QEC) schemes. Here, we demonstrate a silicon
spin-
qubit device that comprises a shuttling bus for coherently transporting
qubits that can interact at four isolated locations we call bus stops. We dynamically populate the array and tune all single- and two-
qubit operations using shuttling and
quantum non-demolition (QND)
spin measurements, without access to charge sensing in most of the device. We achieve universal control of the effective five-
qubit processor and select the connectivity required to form a surface-code stabilizer plaquette that supports X- and Z-type parity checks up to weight-four. We use the parity checks to generate multi-
qubit entanglement between all
qubit combinations in the array and report the genuine
entanglement of a five-
qubit Greenberger-Horne-Zeilinger (GHZ) state, constituting the largest such state ever constructed with gate-defined
semiconductor spins. This work opens immediate opportunities to pursue QEC experiments with
spin qubits, and the protocols developed here lay the groundwork for the modular calibration and operation of sparse
spin qubit arrays.
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All authors Brennan Undseth, Nicola Meggiato, Yi-Hsien Wu, Sam R. Katiraee-Far, Larysa Tryputen, Sander L. de Snoo, Davide Degli Esposti, Giordano Scappucci, Eliška Greplová, Lieven M. K. Vandersypen
Disordered Systems and Neural Networks
When low-loss paths make a binary neuron trainable: detecting algorithmic transitions with the connected ensemble
Damien Barbier
We study the connected ensemble, a statistical-mechanics framework that characterizes the formation of low-loss paths in rugged landscapes. First introduced in a previous paper, this ensemble allows one to identify when a network can be trained on a simple task and which minima should be targeted during training. We apply this new framework to the symmetric binary perceptron model (SBP), and study how its typical {connected} minima behave. We show that {connected} minima exist only above a critical threshold $\kappa_{\rm connected}$, or equivalently below a critical constraint density $\alpha_{\rm connected}$. This defines a parameter range in which training the network is easy, as local
algorithms can efficiently access this connected
manifold. We also highlight that these minima become increasingly robust and closer to one another as the task on which the network is trained becomes more difficult.
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Statistical Mechanics
Riccardo Travaglino, Federico Rottoli and Pasquale Calabrese
We investigate the dynamics of
Entanglement Hamiltonians (EHs) in dissipative free-fermionic systems using a recent operator-based formulation of the quasiparticle picture. Focusing on gain and loss dissipation, we study the post-quench
evolution and derive explicit expressions for the EH at the ballistic scale. In the long-time and weak-dissipation regime, the EH is shown to take the form of a time-dependent Generalized Gibbs Ensemble (t-GGE), with a structure that is universal across different initial states of the quench protocol. Within this framework, the emergence of the t-GGE is fully accounted for by the quasiparticle picture, and we argue that this description remains valid whenever the Lindbladian admits an appropriate coarse-grained representation.
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Mesoscale and Nanoscale Physics
SpinWaveToolkit: Python package for (semi-)analytical calculations in the field of spin-wave physics
Jan Klíma, Ondřej Wojewoda, Jakub Krčma et al. (+4 more)
We present an open-source Python package, SpinWaveToolkit (SWT), for (semi-)analytical modeling of
spin-wave dynamics in thin
ferromagnetic films and exchange-coupled
magnetic bilayers. SWT combines analytical models based on the Kalinikos-Slavin theory with a semi-analytical dynamic-
matrix approach, enabling the calculation of dispersion relations, group velocities, decay lengths, mode profiles, and static
equilibrium magnetization states. In addition, SWT implements a quantitative model of micro-focused Brillouin light scattering (BLS) that incorporates vectorial optical focusing,
spin-wave Bloch functions, magneto-optical coupling, and Green-function propagation to simulate experimentally measured BLS spectra. The package is validated against finite-element dynamic-
matrix simulations performed with TetraX for Damon-Eshbach, backward-volume, forward-volume, and oblique-field geometries, showing excellent agreement while reducing computation times by nearly two orders of magnitude in comparison to the numerical simulations. Thanks to the easiness of the use and fast calculation times, SWT can be used not only for exploratory mapping of the parameter space, but also for the fitting of the measured dispersion relations and related parameters. Thus, it provides a versatile and efficient framework for experiment design, interpretation, and parameter optimization for magnonics research.
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All authors Jan Klíma, Ondřej Wojewoda, Jakub Krčma, Martin Hrtoň, Dominik Pavelka, Jakub Holobrádek, Michal Urbánek
Mesoscale and Nanoscale Physics
In-situ Straining of Epitaxial Freestanding Ferroic Films by a MEMS Device
Simone Finizio, Tim A. Butcher, Maria Cocconcelli et al. (+10 more)
Mechanical strain can be used to control physical properties in materials. The experimental investigation of strain-induced effects at the nanoscale is of importance not only for its fundamental aspects, but also for the development of device applications. Transmission X-ray microscopy is a particularly well-suited technique for nanoscale imaging of
magnetic materials, but its compatibility with in-situ mechanical straining of samples is limited. In this work, we present a setup for applying tailored in-situ mechanical strains to freestanding thin films by means of a micro electromechanical system (MEMS) actuator. We then present a proof-of-concept experiment in which a freestanding 80 nm thick (001) BiFeO3 multiferroic thin film is strained with the MEMS device, allowing us to control the coupled ferroelectric/
spin cycloidal configuration.
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All authors Simone Finizio, Tim A. Butcher, Maria Cocconcelli, Elisabeth Müller, Lauren J. Riddiford, Jeffrey A. Brock, Chia-Chun Wei, Li-Shu Wang, Jan-Chi Yang, Shih-Wen Huang, Federico Maspero, Riccardo Bertacco, Jörg Raabe
Materials Science · Cross-listed from astro-ph.EP
Direct simulations of H-He mixtures at planetary interior conditions: demixing, insulator-metal transition and miscibility boundaries
Valentin V. Karasiev, S. X. Hu, Joshua P. Hinz et al. (+4 more)
Accurate knowledge of the electrical and thermal conductivities and structural properties of hydrogen-helium mixtures under thermodynamic conditions within and beyond the immiscibility range is very important to predict the thermal
evolution and internal structure of gas
giant planets like Jupiter and Saturn. Here, we propose a novel method to determine the immiscibility boundary accurately without the need for free energy calculations, while providing consistent insights into structural and transport properties of mixtures. We show with direct large-scale ab initio simulations that the
insulator-metal transition (IMT) of the hydrogen subsystem is strongly affected by an admixture with a small fraction of helium and occurs at temperatures significantly higher than those of pure hydrogen. At pressures below 150 GPa, the IMT boundary is not related anymore to the H2 subsystem dissociation, the system remains insulating even after the full dissociation of H2 molecules and its transition to an H-He mixture. The offset of the IMT in the H-He mixture relative to the dissociation region in the hydrogen subsystem and the significant reduction of static electrical and thermal conductivity by a factor between two and a few thousand relative to pure hydrogen found in mixtures have consequences for Jupiter and Saturn's thermal
evolution, internal structure, and dynamo action, affecting a large fraction of the interior of both
planets.
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All authors Valentin V. Karasiev, S. X. Hu, Joshua P. Hinz, R. M. N. Goshadze, Shuai Zhang, Armin Bergermann, Ronald Redmer
Strongly Correlated Electrons · Cross-listed from quant-ph
Compact U(1) Lattice Gauge Theory in Superconducting Circuits with Infinite-Dimensional Local Hilbert Spaces
J. M. Alcaine-Cuervo, S. Pradhan, E. Rico et al. (+2 more)
We propose a superconducting-
circuit architecture that realizes a compact U(1)
lattice gauge theory using the intrinsic infinite-dimensional
Hilbert space of phase and charge variables. The gauge and matter fields are encoded directly in the degrees of freedom of the rotor variables associated with the
circuit nodes, and Gauss's law emerges exactly from the conservation of local charge, without auxiliary stabilizers, penalty terms, or
Hilbert-space truncation. A minimal gauge-matter coupling arises microscopically from Josephson nonlinearities, whereas the
magnetic plaquette interaction is generated perturbatively via virtual matter excitations. Numerical diagonalization confirms the emergence of compact electrodynamics and coherent
vortex excitations, underscoring the need for large local
Hilbert spaces in the continuum regime. The required
circuit parameters are within the current experimental capabilities. Our results establish superconducting
circuits as a scalable, continuous-variable platform for analog
quantum simulation of non-perturbative gauge dynamics.
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All authors J. M. Alcaine-Cuervo, S. Pradhan, E. Rico, Z. Shi, C. M. Wilson
Strongly Correlated Electrons
Magnetic field control of the excitonic transition in Ta$_2$NiSe$_5$
Giacomo Mazza
The formation of excitonic
insulator phases in
quantum materials is often masked by structural distortions caused by the coupling between electronic and phononic order parameters. Here we show that the candidate material Ta$_2$NiSe$_5$ is characterized by a metastable excitonic insulating phase that is decoupled from the
lattice, and that can be stabilized for sufficiently high applied
magnetic fields. By considering the interplay between the excitonic and structural instabilities, we predict a
magnetic field induced transition from the low-temperature structurally distorted semiconducting phase to an undistorted excitonic
insulator phase with ground state loop currents. Before the transition, the existence of a latent excitonic phase can be detected by the
magnetic field softening of the
phonon mode associated with the structural distortion. These results highlight an unbiased route towards the disentanglement of the coupled excitonic-structural transition in Ta$_2$NiSe$_5$, and uncover a general mechanism for
magnetic field control of competing phases in
quantum materials.
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Mesoscale and Nanoscale Physics
Loop-gap resonators achieving strong magnon-photon coupling in magnetic insulator thin films
Francesca Zanichelli, Davit Petrosyan, Hanchen Wang et al. (+4 more)
Magnon-
photon hybrid systems consisting of a three-dimensional electromagnetic resonator and a bulk
magnetic insulator constitute the standard experimental platform in cavity magnonics. Here, we demonstrate a modular loop-gap resonator design optimized to couple with thin films of
magnetic insulators. We achieve the strong-coupling regime using this loop-gap resonator coupled to a 75~nm-thick epitaxial film of yttrium iron garnet at room temperature. We further show how to perform field-differential spectroscopy of the hybrid
magnon-
photon system, which eliminates the unwanted signal from other loop-gap modes uncoupled to the
magnetic film. In addition to the uniform
ferromagnetic resonance mode, the loop-gap resonator enables an hybridization with the standing
spin-wave modes forming across the thickness of the film. Our approach unlocks the use of epitaxial films and multilayers of
magnetic insulators to tune the
magnon band structure in cavity magnonics experiments.
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All authors Francesca Zanichelli, Davit Petrosyan, Hanchen Wang, Patrick Helbingk, Richard Schlitz, Pietro Gambardella, William Legrand
Mesoscale and Nanoscale Physics
Andreev bound states in a superconducting qubit at odd parity
Manuel Houzet, Julia S. Meyer and Yuli V. Nazarov
The
quantum mechanics of the Josephson effect is the core ingredient for
quantum technologies with superconducting
circuits. A new avenue was recently opened in this field by predicting that the Josephson
quantum mechanics in the odd parity sector, when a quasiparticle in trapped in an Andreev bound state, is fundamentally different from the conventional one in the even sector. The focus was then on a Josephson junction surrounded by an electromagnetic environment formed of a collection of bosonic modes, including the case of an ohmic environment. Here we consider the distinct case of a superconducting
qubit made of a single Josephson junction whose environment reduces to a capacitance. We find a novel structure for the low-lying discrete states in the odd sector, which is altogether different from the one that appears in the even sector. Our study of the bound-state spectrum ranges from the Coulomb-dominated (Cooper pair box) to the Josephson-dominated (transmon) regime. Our prediction could be tested in forthcoming experiments with
superconductor/
semiconductor/
superconductor junctions, which have been studied intensively in recent years, both using nanowires as well as two-dimensional electron gases.
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Soft Condensed Matter
Spatial self-organization driven by temporal noise
Satyam Anand, Guanming Zhang and Stefano Martiniani
The counterintuitive emergence of order from noise is a central phenomenon in science, ranging from pattern formation and synchronization to order-by-disorder in frustrated systems. While large-scale spatial self-organization induced by local spatial noise is well studied, whether temporal noise can also drive such organization remains an open question. Here, by studying interacting particle systems, we show that temporally correlated noise can lead to a self-organized state with suppressed long-range density fluctuations, or hyperuniformity. Further, we develop a fluctuating hydrodynamic theory that quantitatively explains the origin of this phenomenon. Finally, by casting the dynamics as a
stochastic optimization problem, we show that temporal correlations lead to better solutions, akin to perturbed gradient descent in neural networks – where noise is injected during training to escape poor minima. This reveals a striking correspondence between perturbed gradient descent dynamics on the energy landscapes of particle systems and the loss landscapes of neural networks. Our study establishes temporal correlations as a novel mechanism for noise-driven self-organization, with broad implications for self-assembling materials, biological systems, and optimization
algorithms that leverage temporal noise for applications like differentially private learning.
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Materials Science
Rotating Magnetocaloric Effect in Sintered La(Fe,Mn,Si)$_{13}$H$_z$ Plates
Rafael Almeida, Tomás Ventura, Ricardo Moura Costa Pinto et al. (+6 more)
La-Fe-Si-based
alloys are among the most application-ready magnetocaloric materials for room-temperature
magnetic refrigeration. Powder metallurgy methods have been previously demonstrated to successfully produce structures with sub-mm features for
magnetic refrigerators in a scalable method. In this work, we explore the rotating magnetocaloric effect (RMCE) present in a 0.27 mm thin plate of sintered and hydrogenated La(Fe,Mn,Si)$_{13}$. The high aspect ratio ($\sim$50) of the thin plate leads to an anisotropic magnetocaloric effect (MCE), dependent on the relative orientation of the external
magnetic field, and an RMCE when the external field is rotated. We find a maximum rotating adiabatic temperature change ($\Delta T_{ad}^{rot}$) of 1.17 K with the rotation of a 1 T
magnetic field and 1.12 K when rotating a 0.6 T
magnetic field, a reduction of only 4% for a 40% reduction in applied field strength. Magnetostatic computations revealed a considerable rotating isothermal
entropy change ($\Delta S_{iso}^{rot}$), comparable to the conventional MCE of Gd for similar fields, reaching 3.97 J K$^{-1}$ kg$^{-1}$ for 1 T and 3.68 J K$^{-1}$ kg$^{-1}$ for 0.6 T (7% reduction), highlighting La-Fe-Mn-Si
alloys as high potential candidates for a
magnetic refrigerator based on the RMCE utilizing relatively low external
magnetic field amplitudes, such as 0.6 T.
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All authors Rafael Almeida, Tomás Ventura, Ricardo Moura Costa Pinto, João Oliveira Silva, Konrad Loewe, Rodrigo Kiefe, João Sequeira Amaral, João Pedro Araújo, João Horta Belo
Superconductivity
Theory of Little-Parks oscillations by vortices in two-dimensional superconductors
Ying-Ming Xie and Naoto Nagaosa
The Little-Parks (LP) effect is a
quantum phenomenon in which the superconducting transition temperature of a superconducting cylinder (or ring) oscillates periodically as a function of the
magnetic flux threading the loop. Recently, multiple experiments have observed half-
quantum flux shifts in measurements of LP oscillations, where the oscillations are globally shifted by half a flux
quantum compared to conventional cases, a behavior referred to as a $\pi$-ring. Such observations are commonly linked to unconventional pairing
symmetries. In this work, we demonstrate that half-
quantum flux shifts can arise in two-dimensional (2D) superconducting rings without invoking unconventional pairing
symmetry, provided that
vortices near the Berezinskii-Kosterlitz-Thouless (BKT) transition are taken into account. Specifically, based on the
vortex-charge duality theory near the BKT transition, we map the problem onto a Coulomb gas model, in which the
magnetic flux is represented as a pair of opposite boundary charges (or
vortices) at the two edges. The screening of these boundary charges by thermally excited
vortex-antivortex pairs is investigated through explicit Monte Carlo simulations. Importantly, we demonstrate that the oscillation of the free-
vortex density as a function of
magnetic flux can exhibit an anomalous half-
quantum flux shift. Our work thus predicts the LP oscillations induced by
vortices in 2D superconducting rings near the BKT transition, which provides a new mechanism for generating $\pi$-rings.
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Mesoscale and Nanoscale Physics
Charging energy effects on a single-edge anyon braiding detector
Noé Demazure, Flavio Ronetti, Benoît Grémaud et al. (+4 more)
We investigate the influence of capacitive coupling on the detection of anyon braiding in a single-edge interferometer realized in the fractional
quantum Hall regime. In this setup, a
quantum point contact bends a single edge into a loop, where tunneling occurs at the open end and is controlled by the QPC voltage. In contrast with previously studied two-edge geometries, the weak backscattering regime is dominated by the first-order perturbative term, allowing
quantum transport quantities to factorize into a non-universal prefactor and a braiding-induced contribution that provides direct access to the universal statistical angle $\pi\lambda$. While previous analyses neglected edge-to-edge capacitance, we show that capacitive effects, which are known to play a crucial role in mesoscopic capacitors, modify both the current and the current cross-correlations. Using a two-point Green's function formalism augmented by Dyson's equation to include the charging energy, we quantify how the fluctuations of the cross-correlations depend simultaneously on $\lambda$ and on the capacitance of the loop. Our results indicate that a reliable extraction of the statistical angle requires a parallel measurement of the loop capacitance, which can be implemented via a charged gate coupled to the junction.
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All authors Noé Demazure, Flavio Ronetti, Benoît Grémaud, Laurent Raymond, Masayuki Hashisaka, Takeo Kato, Thierry Martin
Strongly Correlated Electrons
Conical Magnetic Structure and Atomic Displacements in Chiral Helimagnet Yb(Ni,Cu)$_3$Al$_9$ in Magnetic Fields along the Helical $c$ Axis
Takeshi Matsumura, Mitsuru Tsukagoshi, Shota Nakamura et al. (+1 more)
We investigated the conical
magnetic state of a uniaxial
chiral helimagnet Yb(Ni$_{1-x}$Cu$_x$)$_3$Al$_9$ induced in
magnetic fields applied along the $c$ axis, which coincides with the helical axis at zero field. Using resonant X-ray diffraction, we clearly observed the disappearance of
magnetic satellite peaks, corresponding to the transition from the conical to the field-induced
ferromagnetic state. The critical fields were determined to be 4 T for $x=0$ and 7 T for $x= 0.05$, which were hardly discernible in the magnetization curves. We also found that atomic displacements with the same propagation vector emerge simultaneously with the onset of the conical order. The transition temperature $T_{\text{N}}$ and the critical fields for $H \parallel c$ ($H_{\text{c}}^{z}$) and $H\perp c$ ($H_{\text{c}}^{x}$) are discussed on the basis of a mean-field calculation for a simple $q=1$ model of the
magnetic structure. We propose that $T_{\text{N}}$ and $H_{\text{c}}^{z}$ primarily reflect the dominant intralayer exchange interactions within the honeycomb Yb-layer, whereas $H_{\text{c}}^{x}$ is governed by the much weaker interlayer coupling.
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All authors Takeshi Matsumura, Mitsuru Tsukagoshi, Shota Nakamura, Shigeo Ohara
Superconductivity
Infinite Magnetoresistance and Vortex Coupling in the Pb/BSCCO Heterostructure
Weifan Zhu, Jiamin Yao, Shuntianjiao Ling et al. (+11 more)
Combining superconductivity with spintronics provides exciting opportunities to realize low-dissipation
quantum devices. Here we report the synthesis, characterization and magnetotransport measurements of the Pb/Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (BSCCO) superconducting
heterostructures, where an insulating PbO$_{x}$ layer spontaneously forms at the interface. Non-volatile switching between superconducting (logical "0") and normal ("1") states in Pb films by an external field, i.e., infinite magnetoresistance (IMR), can be realized and are attributed to the strong trapping and pinning of
vortices in BSCCO. Furthermore, butterfly-shaped hysteresis loops in magnetoresistance, pronounced resistance dips/jumps and thermal reset to superconducting states can be observed and are direct manifestations of the peculiar
vortex dynamics in BSCCO and
vortex coupling across the Pb/BSCCO interface. Our work demonstrates a simple and effective way to realize IMR through superconducting
vortices and opens up new opportunities to study the
vortex interactions across the superconducting interfaces.
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All authors Weifan Zhu, Jiamin Yao, Shuntianjiao Ling, Shanyin Fu, Yifu Xu, Pengyue Xiong, Jiawen Zhang, Mengwei Xie, Yanan Zhang, Ye Chen, Huiqiu Yuan, Xin Lu, Qing-Hu Chen, Yang Liu
Materials Science
Atomic-scale Imaging of Iodide-Gold Interactions in Nanoconfined Liquid-Solid Interfaces
Oliver R. Waszkiewicz, Yuxiang Zhou, Baptiste Gault et al. (+3 more)
Functionalization of nanoporous metallic materials enables the tailoring of surface chemistry and morphology in nanostructured materials, optimising their performance for electrocatalytic and sensor applications.
Liquid phase chemical functionalization is governed by
liquid solid interfaces. Yet, these interfaces remain poorly understood due to the challenges of characterising the
liquid phase at high spatial and chemical resolutions. To elucidate pathways for functionalizing nanoscale metals, it is crucial to measure the distribution of species, including light elements, across the
liquid solid interface, capturing both reactants and products. Here, we employ cryogenic atom probe
tomography to directly analyse frozen
liquid solid reaction interfaces at near atomic resolution. Focusing on the interaction of iodide and sodium ions with nanoporous gold, we observe the formation of iodine containing complexes on gold nanoligament surfaces and subsurfaces. These findings reveal aspects of the gold iodide system that were previously hidden, including the reaction mechanism between iodide and gold atoms on the surface, and the multiple gold iodide complexes forming. Our work demonstrates that cryogenic atom probe
tomography can provide unprecedented visualisation and characterisation of nanoscale interfaces during chemical and electrochemical reactions, with potential implications for modern manufacturing, energy technologies, and sustainable materials development.
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All authors Oliver R. Waszkiewicz, Yuxiang Zhou, Baptiste Gault, Finn Giuliani, Mary P. Ryan, Ayman A. El-Zoka
Mesoscale and Nanoscale Physics
Quasiperiodic Skin Criticality in an Exactly Solvable Non-Hermitian Quasicrystal
Zhangyuan Chen, Muhammad Idrees, Ying Yang et al. (+2 more)
Critical states in quasiperiodic systems defy the conventional dichotomy between extended and localized states. In this work, we demonstrate that non-Hermiticity fundamentally reshapes this paradigm by giving rise to an exactly solvable quasiperiodic critical phase with no energy selectivity. We introduce a non-Hermitian quasiperiodic
lattice based on a modulated Hatano-Nelson model and uncover a new universality class of quasiperiodic skin criticality, in which all eigenstates share an identical multifractal spatial structure. Through a nonunitary gauge transformation, the system is mapped onto a disorder-free
lattice, enabling exact analytical solutions for the full spectrum and eigenstates. As a consequence, the inverse participation ratio is strictly energy-independent and controlled solely by a global phase. We further show that this criticality persists in multiband
lattices, establishing a general and analytically controlled framework for non-Hermitian quasiperiodic critical phenomena.
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All authors Zhangyuan Chen, Muhammad Idrees, Ying Yang, Xianqi Tong, Xiaosen Yang
Materials Science
Unlocking the Power of Orbital-Free Density Functional Theory to Explore the Electronic Structure Under Extreme Conditions
Cheng Ma, Qiang Xu, Zhenhao Zhang et al. (+8 more)
Recent advances in X-ray free-electron
laser diagnostics have enabled direct probing of the electronic structure under extreme pressures and temperatures, such as those encountered in
stellar interiors and inertial confinement fusion experiments, challenging theoretical models for interpreting experimental data. Kohn-Sham density functional theory (KSDFT) has been successfully applied to analyze experimental X-ray scattering measurements, but its high computational cost renders routine application impractical. Orbital-free DFT (OFDFT) is a substantially more efficient alternative, with computational cost scaling linearly with system size and a weak temperature dependence, yet it often lacks the accuracy required for electronic structure description. Overcoming this limitation, we present a non-empirical Kohn-Sham-assisted orbital-free density functional framework for calculations at extreme conditions, which enables efficient OFDFT simulations with KSDFT-level accuracy for electron densities, electron-ion structure factors, and equations of state across a broad range of conditions.
Benchmark comparisons with
quantum Monte Carlo data for dense hydrogen and validation against Rayleigh weight measurements of hot dense beryllium demonstrate the reliability of the framework and speedups of up to several hundred times compared with KSDFT. We further show that even at temperatures on the order of 100 eV,
quantum non-locality remains essential for correctly describing the electronic structure of dense hydrogen.
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All authors Cheng Ma, Qiang Xu, Zhenhao Zhang, Ke Wang, Ying Sun, Wenhui Mi, Zhandos A. Moldabekov, Tobias Dornheim, Jan Vorberger, Sebastian Schwalbe, Xuecheng Shao
Materials Science
Hydrogen at GaN(0001) surface control of Fermi level pinning: Mg activation of p-type conductivity – Nakamura process deciphered
Konrad Sakowski, Pawel Strak, Pawel Kempisty et al. (+2 more)
Ab initio calculations were used to disentangle the mystery of Nakamura activation of p-type in Mg doped MOVPE grown gallium nitride, the key process leading to the 2014 Nobel Prize in Physics. Calculations were used to obtain the
equilibrium state of the hydrogen atom deep in the GaN bulk and at the GaN(0001) surface. It was shown that the H position within bulk GaN depends on the
Fermi level: in n-type GaN, it is located in the channel, whereas in p-type GaN, it is attached to the N atom, breaking one of the GaN bonds. In contrast, at the GaN(0001) surface, H is attached in the on-top position for any hydrogen coverage; for low and high H-coverage, the
Fermi level is pinned at the Ga - broken bond state and at the valence band maximum (VBM), respectively. The
diffusion path from the bulk to the surface was obtained when the
Fermi level was high and low, the barrier was zero, and $\Delta E_{bar} \approx 1.717 eV$, which effectively blocked hydrogen escape into the vapor. Thus, high H coverage, that is, high hydrogen pressure in the vapor, prevents H from escaping from the bulk to the surface, whereas at low coverage (low hydrogen pressure), the process is barrierless. It is therefore proven that the hydrogen escape control step in the Nakamura process is the transition of hydrogen from the bulk to the surface, which is controlled by the position of the
Fermi level at the surface. Molecular hydrogen desorption from the surface is easy for high H coverage and difficult for low, thus opposite to observed experimentally thus this process is not the determining step in activation. A full thermodynamic estimate of the maximal partial pressure of hydrogen in the vapor, corresponding to the transition of the
Fermi level from the Ga-broken bond state to the VBM, was used to establish the maximal hydrogen pressure limit for the p-type Mg activation process.
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All authors Konrad Sakowski, Pawel Strak, Pawel Kempisty, Izabella Grzegory, Stanislaw Krukowski
Mesoscale and Nanoscale Physics
Probing Interfacial Spin Dynamics and Temperature Dependent Asymmetry in Spin Pumping Across Ni80Fe20/Cu/Cr1.12Te2 Interfaces
Mahammad Tahir, Swati Pandey, Sourabh Manna et al. (+3 more)
Spin transfers in
magnetic multilayers offers a promising pathway toward ultrafast, energy-efficient spintronic devices. In this study, we investigate the interfacial
spin pumping and temperature-dependent
spin current exchange in a Cr1.12Te2/Cu/Ni80Fe20 (Py)(FM1/NM/FM2) trilayer structure. Using broadband and cryogenic
ferromagnetic resonance (FMR) measurements, we investigate key magnetization dynamical parameters, including the effective Gilbert damping factor, effective
magnetic fields, interfacial
spin mixing conductance, and
spin current density. Efficient
spin angular momentum transfers from Py to Cr1.12Te2 are observed at room temperature. At lower temperatures, the enhanced linewidth reflects temperature dependent
spin pumping effects occurring at distinct precession frequencies of the
ferromagnetic layers. Notably, the absence of interfacial Damping indicates that
spin pumping can be modulated by controlling the net
spin current flow. These findings offer critical insight into temperature-dependent tunable
spin transport mechanisms in
magnetic multilayers, highlighting their potential for next-generation spintronic applications.
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All authors Mahammad Tahir, Swati Pandey, Sourabh Manna, Rajdeep Singh Rawat, Rohit Medwal, Soumik Mukhopadhyay
Materials Science
Role of quasi-Fermi levels in Si- and Mg-related optical absorption in nitride laser diodes (LDs): material context
Konrad Sakowski, Cyprian Sobczak, Pawel Strak et al. (+5 more)
Optical absorption and reabsorption of light emitted from active regions in nitride
laser diodes (LDs) have been shown to reduce the light extraction efficiency of these devices. It was proven that the presence of Si and Mg may considerably increase the optical absorption. This effect is much stronger in the high-energy (short-wavelength) range of the spectrum. The absorption increase is directly related to the ionization of the Si donor and Mg acceptor levels, which are controlled by the electron and hole quasi-
Fermi levels. It is shown that the absorption may be increased because of the higher ionization of Mg caused by the compensation in the p-type region and the high ionization of Si in the n-type region. It was explained theoretically why optical efficiency is increased by removal of doping in waveguides. It was also shown that good material quality leads to a low absorption level, especially in the Mg-doped p-type part of the device.
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All authors Konrad Sakowski, Cyprian Sobczak, Pawel Strak, Izabella Grzegory, Robert Czernecki, Jacek Piechota, Agata Kaminska, Stanislaw Krukowski
Soft Condensed Matter · Cross-listed from q-bio.PE
How adaptation to food resources and death rates shape oscillatory dynamics in a microbial population
Benedetta Ciarmoli and Sophie Marbach
Microbes constantly interact with their environment by depleting and transforming food sources. Theoretical studies have mainly focused on Lotka-Volterra models, which do not account for food source dynamics. In contrast, consumer-resource models, which consider food source dynamics, are less explored. In particular, it is still unclear what physical mechanisms control oscillatory dynamics at a single population level, a phenomenon which can only be captured by a consumer-resource model. Here, we present a minimalistic consumer-resource model of a single microbial population with growth and death dynamics, consuming a continuously replenishing substrate. Our model reveals that decaying oscillations can occur around steady state if and only if the timescale of microbial adaptation to food supply changes exceeds the death timescale. This interplay of timescales allows us to rationalize the emergence of oscillatory dynamics when adding various biophysical ingredients to the model. We find that microbial necromass recycling or complementary use of multiple food sources reduces the parameter range for oscillations and increases the decay rate of oscillations. Requiring multiple simultaneous food sources has the opposite effect. Essentially, facilitating growth reduces the likelihood of oscillations around a fixed point. We further demonstrate that such damped oscillatory behavior is correlated with persistent oscillatory behavior in a noisy environment. We hope our work will motivate further investigations of consumer-resource models to improve descriptions of environments where food source distributions vary in space and time.
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Soft Condensed Matter
Gradient dynamics model for chemically driven running drops
Justus Niehoff, Florian Voss and Uwe Thiele
We present a thermodynamically consistent model for chemically driven running drops on a solid substrate with reversible substrate adsorption of a wettability-changing chemical species. We consider drops confined to a vertical gap, thereby allowing us to first obtain a gradient dynamics description of the closed system, corresponding to a set of coupled dynamical equations for the drop profile and the chemical concentration profiles of species on the substrate and in both fluids (drop, ambient medium). Chemostatting the species in the drop and the ambient medium, we then derive a reduced model for the dynamics of the drop and the adsorbate on the substrate. When the externally imposed chemical potentials are distinct, the system is driven away from thermodynamic
equilibrium, allowing for sustained drop self-propulsion across the substrate due to a wettability contrast maintained by chemical reactions. We numerically study the resulting running drops and show how they emerge from drift-pitchfork bifurcations.
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