Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Exact modes, hybridization and polarization rotation of electromagnetic fields propagating in topological insulating slab
Sebastián Filipini, Mauro Cambiaso, Alberto Martín-Ruiz et al. (+1 more)
We study electromagnetic waves in slab waveguides with a topological
insulator core characterized by a topological magnetoelectric parameter (ME). TIs are electrically insulating in the bulk with robust conducting states at their boundaries. Their electromagnetic response is described by an
axion-like $\Theta$ term that modifies Maxwell's electrodynamics, leading to rich and unconventional phenomena, as the topological ME effect. All supported modes are exact hybrid modes with nonvanishing longitudinal field components. This hybridization is a consequence of the boundary conditions produced by the $\Theta$ term and is absent in topologically trivial, reciprocal and non-
chiral slab waveguides. Modifications to the propagation condition and modes are shown for the asymmetric slab. The detailed solution of the exact modes, coupling of modes and the dispersion relations is made for the symmetric slab. By solving the full $\Theta$-electrodynamics nonperturbatively, we derive the modal dispersion relations and explore polarization rotation and power transfer between modes. Our approach reveals qualitative and quantitative deviations from standard coupled-mode theory and captures new signatures of the topological ME response. Due to the smallness of the $\Theta$-effects, we perform a perturbative analysis of mode propagation, based on writing a general solution as a superposition of exact modes of $\Theta$-ED but expanding to first non-vanishing order. Also, we apply coupled-mode theory, that is predicated on building solutions as superpositions of modes of ordinary electrodynamics that fail to satisfy the boundary conditions imposed by the $\Theta$-term but compensate at the expense of modifying the field profiles. These findings provide a comprehensive framework for light control in topological photonics and potential routes to experimentally probe the ME effect in guided settings.
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All authors Sebastián Filipini, Mauro Cambiaso, Alberto Martín-Ruiz, Luis F. Urrutia
Strongly Correlated Electrons
Fractional phase slips across the charge-density-wave domain walls in 1-T TiSe2
Haotian Zhang, Zihao Song, Zhongchen Xu et al. (+9 more)
The microscopic origin of the charge density wave (CDW) in 1T-TiSe$_2$ remains controversial, with competing scenarios based on
phonon-driven
lattice instability and electronically driven excitonic correlations. Here, we combine low-temperature scanning tunneling microscopy with two-dimensional lock-in phase analysis to directly resolve the local CDW phase in real space and track its
evolution across individual domain walls. In homogeneous regions, the CDW phase remains uniform; by contrast, across domain walls we uncover a robust and reproducible $2\pi/3$ phase shift that occurs collectively in all three
symmetry-related CDW components. This nontrivial and correlated phase-slip configuration places stringent constraints on the order-parameter
manifold and challenges the simplest purely
phonon-driven commensurate lock-in picture, which would instead predict a $\pi$ phase shift. A minimal free-energy model incorporating both electron-
phonon and electron-hole interactions reproduces the observed phase behavior and indicates that electronic interactions play an important role in shaping the local phase structure of the CDW order. These results establish domain walls as direct real-space probes of the microscopic interactions underlying multicomponent order and provide a general phase-resolved framework for constraining competing ordering mechanisms in correlated materials.
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All authors Haotian Zhang, Zihao Song, Zhongchen Xu, Jun Shu, Zhongxu Wei, Zunming Lu, Jun Liu, Zengyi Du, Jinxing Zhang, Youguo Shi, Ge He, Jun Shen
Mesoscale and Nanoscale Physics
High-Performance Nanophononic Resonators in Self-Suspended WSe$_2$ Domes and Drums
Jens-Christian Drawer, Bo Han, Edson Rafael Cardozo de Oliveira et al. (+7 more)
Van der Waals materials are ideally suited for the implementation of high-frequency nanophononic resonators with atomically flat interfaces. Here, we present two versatile van der Waals-based nanophononic architectures: First, we introduce self-supporting nano-domes of WSe$_2$ as a scalable platform for the simultaneous generation of hundreds of high-quality nanoacoustic resonators with resonance frequencies in the 100 GHz range. Second, we engineer self-supporting nano-drums that reach record-high working frequencies for 2D-
semiconductor transducers beyond 1 THz. Through optical pump-probe spectroscopy experiments and photoelastic linear chain model calculations, we gain a detailed understanding of the intricate interplay between phononic mode hybridization across
heterostructures, the differences between modes close to the center and edge of the acoustic Brillouin zone, and the temporal structure of the photoelastic response. Both architectures have potential applications in low-cost nanoacoustic probing and the ultrafast modulation of
quantum emitters in two-dimensional
semiconductors. While nano-drums surpass the THz frequency barrier, nano-domes appear as an accessible, low-cost alternative for developing scalable nanophononic technologies.
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All authors Jens-Christian Drawer, Bo Han, Edson Rafael Cardozo de Oliveira, Chushuang Xiang, Vita Solovyeva, Kenji Watanabe, Takashi Taniguchi, Norberto Daniel Lanzillotti-Kimura, Christian Schneider, Martin Esmann
Materials Science
Impact of sintering conditions on the dielectric properties of TiO2 ceramics for metamaterialsapplications at terahertz frequencies
Djihad Amina Djemmah, Delphine Gourdonnaud, Faycal Bouamrane et al. (+3 more)
Titanium dioxyde (TiO2) is a promising dielectric material for the realization of metamaterials operating in the terahertz (THz) range. Indeed, these necessitate a high permittivity and low loss material. In this paper, we compare the processes of fabrication and the results of characterisation of bulk TiO2 pellets. From the results of this characterization, we have numerically designed 2D all dielectric metamaterials (ADM) showing that they may exhibit negative or near-zero effective index. Our previous simulations show that the relative permittivity epsilon has to be around 100, while the loss tangent has to be lower than 0.02. We have thus compared conventional sintering (CS) vs spark
plasma sintering (SPS), and investigated the effect of post-sintering annealing on the loss to satisfy these two criteria. The samples were characterized by THz Time Domain Spectroscopy (THz-TDS). One of the samples exhibits a loss tangent as low as 0.006, with a permittivity epsilon = 103. These results highlight the importance of the fabrication process on the EM properties of bulk TiO2, and demonstrate that it is a promising material for the development of metamaterial in the THz band.
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All authors Djihad Amina Djemmah, Delphine Gourdonnaud, Faycal Bouamrane, Jean-Francois Roux, Pierre-Marie Geffroy, Eric Akmansoy
Disordered Systems and Neural Networks
Spectral properties and phase diagrams of sparse antagonistic random matrices with diagonal disorder and Jacobian-like structure
Luca Giammanco, Pietro Valigi and Chiara Cammarota
Complex interacting systems are often modelled by random
matrices whose spectral properties dictate stability. In sparse antagonistic
matrices without diagonal disorder, low connectivity gives rise to a characteristic reentrance effect in the spectral boundary near the real axis, which disappears via a continuous transition as the connectivity increases. The reentrance effect implies the presence of a complex leading
eigenvalue, which suggests the existence of a phase characterized by oscillatory dynamics around
equilibrium. Here, we expand the investigation to
matrices featuring diagonal disorder and a Jacobian-like structure. In these settings, the spectrum also develops a segment of
eigenvalues accumulating on the real axis, which can trigger a discontinuous jump of the complex leading
eigenvalue to a purely real value. The interplay between connectivity and disorder produces a rich variety of spectral behaviours. Employing the cavity method and a an adaptation of the Population Dynamics
algorithm, we map a phase diagram with five distinct spectral phases. Finally, we show that the
algorithm underestimates the spectral support under strong disorder, motivating future technical developments to handle this limit.
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Statistical Mechanics
Macroscopic Fokker-Planck equation from microscopic Glauber dynamics for the Nagle-Kardar model
Jean-François de Kemmeter, Stefano Ruffo and Stefano Gherardini
In the companion Letter we have highlighted the dynamical universality class of the Nagle-Kardar model, where a mean-field interaction is added to the one-dimensional nearest-neighbor Ising model. Starting from the microscopic Glauber dynamics, this paper provides a complete derivation of the Fokker-Planck equation that describes the time
evolution of the macroscopic variables (magnetization and defect density) appearing in the model's
Hamiltonian. The study of the Langevin equation, associated with the Fokker-Planck equation, allowed us to prove that the model belongs to the universal class of systems with diffusive dynamics and non-conserved order parameter (model A). To this goal, we used several features of the model at
equilibrium, including the phase diagram and the fluctuations of macroscopic variables, which are here discussed for completeness. The derivation of the Fokker-Planck equation requires the solution of some combinatorial problems that appear in the counting of configurations at an intermediate level between the microscopic Glauber dynamics and the macroscopic Fokker-Planck one. Finally, we apply both the Glauber and the Langevin dynamics to the study of the average first passage time between local
equilibrium states. We confirm that this time obeys an exponential Arrhenius law in terms of system's size, offering a direct link between microscopic energy landscapes and macroscopic relaxation mechanisms.
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Materials Science
Orientation Mapping via Dictionary Indexing of AC-STEM Kikuchi patterns using Open-source Software
Shamail Ahmed, Johannes Haust, Felix Gruber et al. (+5 more)
The properties of polycrystalline materials are strongly influenced by the spatial arrangement and orientations of individual grains within the microstructure, making nanoscale characterization of grain orientation essential. This is also often the case for small grains in the nm regime explored using scanning transmission electron microscopy (STEM). Automated
crystal orientation mapping (ACOM) is traditionally performed using spot-like diffraction patterns. In contrast, orientation mapping based on transmission Kikuchi diffraction (TKD) using an aberration-corrected (AC) convergent STEM probe remains relatively underexplored, despite its superior orientation sensitivity and higher spatial resolution. In this work, we present an open-source software-based template-matching approach for orientation mapping using AC-STEM TKD. A master pattern (a simulated angular distribution of Kikuchi band intensities on the unit sphere) is first generated through a dynamical simulation implemented in open-source software. This resulting pattern is subsequently imported into another open-source package for
geometric simulations and orientation indexing. We demonstrate the capability of the proposed method by applying it to orientation mapping in BaZr0.4Ce0.4Y0.1Yb0.1O3-{\delta} (BZCYYb4411) fuel-
cell material and LiNiO2 (LNO) lithium-ion battery cathode material. The best-matched simulated patterns exhibit strong agreement with experimental data, even under the challenging conditions with limited diffraction space available for matching.
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All authors Shamail Ahmed, Johannes Haust, Felix Gruber, Celina Becker, Juergen Belz, Andreas Beyer, Laura-Alena Schaefer, Kerstin Volz
Materials Science
The interplay of interfaces, supramolecular assembly, and electronics in organic semiconductors
Belinda J. Boehm, Huong T.L. Nguyen and David M. Huang
Organic
semiconductors, which include a diverse range of carbon-based small molecules and
polymers with interesting optoelectronic properties, offer many advantages over conventional inorganic
semiconductors such as silicon and are growing in importance in electronic applications. Although these materials are now the basis of a lucrative industry in electronic displays, many promising applications such as photovoltaics remain largely untapped. One major impediment to more rapid development and widespread adoption of organic
semiconductor technologies is that device performance is not easily predicted from the chemical structure of the constituent molecules. Fundamentally, this is because organic
semiconductor molecules, unlike inorganic materials, interact by weak non-covalent forces, resulting in significant structural disorder that can strongly impact electronic properties. Nevertheless, directional forces between generally anisotropic organic-
semiconductor molecules, combined with translational
symmetry breaking at interfaces, can be exploited to control supramolecular order and consequent electronic properties in these materials. This review surveys recent advances in understanding of supramolecular assembly at organic-
semiconductor interfaces and its impact on device properties in a number of applications, including transistors, light-emitting diodes, and photovoltaics. Recent progress and challenges in computer simulations of supramolecular assembly and orientational anisotropy at these interfaces is also addressed.
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Superconductivity
First-Principles Quantum-Spectral framework for Elementary Vortex Pinning in superconductors
Haozhe Shi, Yuncheng Xie, Tong Zhang et al. (+2 more)
The critical current of a type-II
superconductor is controlled by
vortex pinning, whose microscopic input is the elementary pinning force. Scanning tunneling spectroscopy has shown that a defect pins a
vortex by reorganizing the Caroli–de Gennes–Matricon (CdGM) states in its core, but why this spectral reorganization amounts to a pinning force has lacked a
quantum-mechanical, first-principles account. Here we establish a transferable first-principles computational framework for elementary
vortex pinning, in which defect-resolved DFT/Wannier electronic structures are embedded into a finite-box projected Bogoliubov–de Gennes free-energy formalism to convert quasiparticle spectral reorganization into
vortex-pinning energies and forces. Using this framework, we confirm that the defect-induced reorganization of the
vortex-core spectrum is the microscopic origin of the elementary pinning force. The force is evaluated as a finite-box
vortex-insertion free energy whose four-configuration subtraction isolates the meV-scale interaction from much larger backgrounds. With the superconducting gap scale and
vortex-core profile fixed from experiments, the FeSe Fe-site vacancy reproduces the microscopic STM force scale together with the measured spectral reorganization. All five point defects in FeSe and FeTe pin attractively, with FeTe Fe-site vacancy strongest. Elementary
vortex pinning thereby becomes a computable electronic-structure quantity, opening the first-principles screening of point defects toward higher critical currents.
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All authors Haozhe Shi, Yuncheng Xie, Tong Zhang, Weibin Chu, Xin-Gao Gong
Materials Science
Sensitivity-optimal coplanar waveguide design for broadband magnetic resonance spectroscopy: a Beer–Lambert framework
Scott Dietrich and Artur Solodovnyk
Coplanar waveguide (CPW) transmission spectroscopy is used to probe
spin dynamics,
ferromagnetic resonance, and complex conductivity across a wide range of materials, yet no systematic framework connects waveguide geometry to measurement sensitivity when sample volume and concentration are fixed. We show that the shared
geometric scaling of sample coupling and conductor loss maps CPW design onto the Beer–Lambert optimization problem of optical spectrophotometry, reducing it to a universal one-parameter problem whose solution depends only on sample geometry and the dominant noise source – not on sample properties, operating frequency, or system losses. The framework predicts a near-universal $1\,\mathrm{Np}$ optimum across the full range of sample thicknesses and design geometries. Benchmarking against seven published broadband FMR instruments reveals two fabrication-delimited classes: PCB-milled designs are bounded by a ceiling imposed by their minimum slot width, while photolithographic designs approach the additive-noise optimum. For large-area PCB samples a meander geometry offers a direct path to near-optimal sensitivity without interferometric compensation; for sub-millimeter samples, a single lithographic straight pass suffices.
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Materials Science
A Combined Tight Binding with Machine Learning Potential Model for Magnesium Compounds
Jiwen Yu, Arash A. Mostofi and Andrew Horsfield
We present a model for magnesium-based systems that combines density functional tight binding (DFTB) with MACE, a machine learning interatomic potential (DFTB+MACE). In this model, the conventional repulsive potential, pair potential, is replaced by a many-body MACE potential. The MACE component of the model is trained on the difference between density functional theory (DFT) energies and forces and the corresponding DFTB values, but neglecting the pair potential contribution. Using this model we performed structural relaxation of MgO-CO2 adsorption systems, molecular dynamics calculations of water clusters and
phonon spectrum calculations of stable fcc-MgO and metastable bcc-MgO structures. We compare the performance of our model with a pure MACE model and with DFT. We demonstrate that the DFTB+MACE model achieves improved accuracy relative to DFTB with a pair potential, in many cases with only a moderate increase in computational cost. In addition, it can provide electronic structures that most of the machine learning potentials cannot. The training
dataset, originally developed for MACE, may not fully represent all regions of the potential surface we may encounter during simulations. Expanding the
dataset for a wider potential surface is expected to further enhance predictive accuracy of DFTB+MACE model. Overall, the resulting DFTB+MACE framework enables simulations at length and time scales beyond the reach of first-principles methods while retaining an explicit description of electronic structures, making it particularly attractive for studying charge-transfer in materials.
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Materials Science
Harnessing electrostatics through temperature modulations to control ferroelectrics
Cameron A.M. Scott, Xabier Diaz de Cerio and Jorge Íñiguez-González
Temperature modulations provide an alternative method for dynamically controlling the ferroelectric state. In this paper, we use scale-independent Landau potentials and predictive atomistic simulations to explore how temperature modulation can harness the depolarizing field to obtain non-electrical poling. We further predict that temperature gradients can be combined with strain to induce persistent polar textures such as multidomain states.
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Materials Science
Spontaneous spin splitting and tunable valley polarization in a two-dimensional fully compensated ferrimagnet
Hongyan Lv, Yueli Li, Yunfan Zhang et al. (+3 more)
Materials with controllable valley polarization and anomalous valley
Hall (AVH) effect are highly desired in valleytronic applications. While current AVH studies primarily focus on
ferromagnetic materials, two-dimensional (2D) antiferromagnets are more attractive for valleytronics since they possess zero net magnetization, negligible stray fields, and ultrafast
spin dynamics. Nevertheless, the joint space-inversion and time-reversal ($PT$)
symmetry in conventional collinear antiferromagnets prohibits the occurrence of AVH response. The recently proposed fully compensated ferrimagnets break $PT$
symmetry, and the
spin-opposite sublattices are not related by
crystal symmetry, providing a natural platform for the coexistence of spontaneous
spin splitting, valley polarization, and anomalous-
Hall compatible
symmetry. Herein, we demonstrate that such compensated ferrimagnetism can be realized in a Janus Mn$_{2}$BrI monolayer, with a Néel temperature above room temperature. Spontaneous
spin splitting is observed due to the built-in layer-dependent electrostatic potential. When SOC is considered, valley polarization emerges for an out-of-plane Néel vector. Moreover, proper hole doping stabilizes the perpendicular
magnetic anisotropy and the two valleys exhibit markedly different Berry
curvatures, thereby making AHE responses allowed. Furthermore, the valence band extrema of Mn$_{2}$BrI monolayer can be effectively tuned by external biaxial strain and
giant piezomagnetism can be achieved. Our results identify Janus Mn$_{2}$BrI monolayer as a promising fully compensated ferrimagnetic platform for 2D valleytronics and spintronics.
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All authors Hongyan Lv, Yueli Li, Yunfan Zhang, Jiayu Dai, Zhongjun Li, Ding-Fu Shao
Other Condensed Matter
Brillouin Light Scattering Spectroscopy of Propagating Magnons at Sub-Kelvin Temperatures
David Schmoll, Nikolai Kuznetsov, Phillip Rehberger et al. (+8 more)
Coupling light to
magnetic excitations in the form of
spin waves underpins both the optical study of magnetism and emerging schemes for
quantum transduction, positioning the quanta of these excitations,
magnons, as promising carriers for hybrid
quantum networks. However, exploiting them in the
quantum regime requires millikelvin temperatures to suppress thermal
magnon populations, thereby confining such experiments to dilution refrigerators. There,
magnons can already be excited and read out electrically, yet an optical interface required for microwave-to-optical
photon conversion has been missing. Here, we demonstrate the first optical detection of coherently driven, propagating
spin waves via Brillouin Light Scattering (BLS) spectroscopy inside a dilution refrigerator. By simultaneously recording the optical and electrical responses of the same
spin-wave mode in a yttrium iron garnet film, we find that the BLS spectra track the electrically measured transmission across a range of applied
magnetic fields. For the lowest optical power of 7.9 {\mu}W that still enabled
spin-wave detection, we measured a global
equilibrium sample temperature of 510 mK via a resistance thermometer, while numerical modelling of the
laser-induced heating yields a maximum local temperature of 900 mK at the focal spot. This brings free-space optical access to
magnons into the sub-kelvin regime, representing a milestone towards
magnon-mediated
quantum transduction in hybrid
quantum systems.
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All authors David Schmoll, Nikolai Kuznetsov, Phillip Rehberger, Franz Vilsmeier, Roman Verba, Denys Slobodianiuk, Rostyslav O. Serha, Khrystyna O. Levchenko, Sebastiaan van Dijken, Andrii V. Chumak, Sebastian Knauer
Disordered Systems and Neural Networks
Weight geometry governs functional memory in complex systems
Elkaïoum M. Moutuou and Habib Benali
Complex systems, from gene regulatory networks to neural
circuits and ecological food webs, exhibit rich functional behaviour that
topology alone does not capture. Yet functional complexity remains difficult to quantify independently of structural organisation. Here we introduce a thermodynamic framework in which functional complexity is characterised through the hierarchical organisation of functional
memory, quantifying how the influence of past interactions is distributed and progressively compressed across scales. Across thirty-four empirical networks spanning biological, ecological, social, technological, and biophysical systems and several orders of magnitude in size and density, real interaction strengths organise functional
memory at greater hierarchical depth than random weight assignment on the same
topology in every domain studied. The framework further reveals that functional
memory occupies a remarkably low-dimensional space, collapsing onto four recurrent dynamical organisations. Comparisons with null models that selectively perturb weighted transport geometry, mesoscale wiring, and directionality show that these structural ingredients play distinct roles: weighted transport geometry systematically governs
memory depth, whereas mesoscale wiring organises
memory across scales and directionality modulates the response of the cascade to structural perturbation. The same comparisons provide an operational criterion for determining whether network weights encode functionally meaningful structure beyond
topology. These results establish weighted transport geometry as a primary organiser of functional
memory and provide a quantitative framework for studying functional complexity in directed weighted networks.
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Disordered Systems and Neural Networks
Kinetic metric for basins of attraction of RNA secondary structures and analysis of the ultrametricity of the energy landscape
A.P. Zubarev
A method for testing the hypothesis of an ultrametric organization of the energy landscape of RNA secondary structures is proposed, based on the analysis of the kinetics of transitions between basins of attraction. The method is based on a kinetic metric constructed from the spectral decomposition of the symmetrized Kramers transition rate
matrix and the Mahalanobis distance, and it is not an ultrametric by construction. A computational scheme has been developed that includes automatic filtering of noise eigenmodes and a procedure for analyzing disconnected structure graphs. The performance of the method is demonstrated on a sample of reference and random RNAs.
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Superconductivity · Cross-listed from quant-ph
Benchmarking Dark Matter Search using a Parity-Check Protocol with Machine-Learning Optimized Pulses
Yu-Han Chang, Ilya Moskalenko, Marko Kuzmanović et al. (+7 more)
We report on an improved microwave detection protocol for dark matter candidates such as the
axion and the dark
photon. We employ a superconducting transmon
qubit dispersively coupled to a double-cavity system, enabling
quantum non-demolition measurements of the
photon occupation in a relatively short-lived storage cavity. To reduce the experimental cycle time and enhance sensitivity for
axion and dark-
photon searches, we operate this detector in a regime of increased
qubit-cavity coupling, resulting in Stark shifts of 4.6 MHz. In this regime, conventional control pulses suffer from strong frequency-detuning sensitivity and
photon-number-dependent errors. We address this limitation by implementing frequency-detuning-robust $\pi/2$ pulses (obtained by machine-learning optimization) that preserve high-fidelity
qubit control over a bandwidth of approximately 20 MHz. We experimentally validate this protocol and demonstrate single-
photon detection performance comparable to previous implementations, despite significantly reduced
qubit coherence times and storage-cavity lifetimes. Using parity-based measurement sequences combined with a Hidden Markov Model (HMM) analysis, we achieve background rates on the order of $\mathcal{O}(20)$ Hz. In the absence of a
magnetic field, we derive exclusion limits on the dark
photon model for dark matter, reaching a sensitivity to the kinetic mixing angle of $\epsilon_{95\%} \sim 1\times10^{-14}$ at 5.051 GHz. These results establish machine-learning robust control as a key enabler for faster, more scalable microwave
quantum sensors for dark-matter searches.
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All authors Yu-Han Chang, Ilya Moskalenko, Marko Kuzmanović, Ognjen Stanisavljević, Isak Björkman, David Díez-Ibáñez, Yikun Gu, Akash V. Dixit, Igor G. Irastorza, Gheorghe Sorin Paraoanu
Quantum Gases · Cross-listed from quant-ph
Sp(2N, R) interferometry in multi-mode Gaussian bosonic systems for optimal metrology and quantum control
Chenwei Lv and Renbao Liu
Multi-mode interferometers for
bosons in Gaussian states are important systems for
quantum metrology with precision beyond the standard
quantum limit and for bosonic
quantum computing. However, there is a lack of theoretical foundation for generic $N$-mode Gaussian interferometry. In this work, we study
quantum metrology and
quantum control in multi-mode bosonic systems with quadratic
Hamiltonians, exploiting the fundamental Sp$(2N,R)$
symmetry of such interferometers. We show that the optimal
quantum control to maximize sensitivity requires aligning squeezing and displacement in the same direction. We propose Sp$(2N,R)$ echo, a multi-mode generalization of the SU$(1,1)$ interferometry, to achieve the sensitivity of phase estimation set by the
quantum Fisher information. In addition, we introduce a geometrical means for reversing many-body dynamics with Sp$(2N,R)$ dynamical
symmetry, such as dynamics of the bosonic Kitaev chain. Our schemes are readily realizable in optical, atomic, and mechanical platforms.
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Materials Science
Thermoelectric response of a ferroelectric insulator
Ryo Iguchi, Takashi Teranishi, Sakyo Hirose et al. (+4 more)
Thermoelectric effects enable the conversion between heat and electricity without moving parts. While conventionally associated with mobile charges, we report thermoelectricity caused by bound charges in the form of temperature changes measured by multi-harmonic lock-in thermography of a ferroelectric under an ac electric field. The observed temperature gradient depends on the field-induced displacement current, a Peltier effect in a dielectric material. Its coefficient exceeds 100 V around the ferroelectric-paraelectric phase transition, which is several orders of magnitude greater than reported values in conductors. Our findings uncover previously hidden functionalities of ferroelectric materials for thermal management by directional heat transport in ferroelectrics.
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All authors Ryo Iguchi, Takashi Teranishi, Sakyo Hirose, Ping Tang, Jun Kano, Gerrit E.W. Bauer, Ken-ichi Uchida
Materials Science
Barocaloric phase transformation from data efficient fine-tuning of machine learned interatomic potentials
Ludwig Hedin and Johan Klarbring
Solid-state cooling based on the barocaloric (BC) effect has emerged as promising environmentally friendly prospective alternative to conventional vapor-compression refrigeration. The search for suitable BC materials relies on efficient atomistic simulations of their phase behavior. Machine-learned interatomic potentials (MLIPs) enable such simulations at near density functional theory (DFT) accuracy, but generating the required DFT training data remains computationally demanding, which motivates development of strategies that reduce the amount of data needed to train accurate models. In this work, we use a prototypical BC material, ammonium sulfate, as a model system and investigate how small a training set can be while still reproducing the temperature-driven structural phase transformation that underlies its BC response. We train a series of MLIPs based on the MACE architecture using three strategies: training from scratch, and naive- and multihead replay fine-tuning of the MACE-MPA-0 foundation model. These strategies are evaluated on their ability to reproduce the phase transformation of ammonium sulfate in molecular dynamics simulations across a range of training-set sizes. We find that, while the MACE-MPA-0 foundation model itself fails to reproduce the transformation, and models trained from scratch break down for small
datasets, fine-tuned models reproduce the transformation using as few as 5 to 10 60-atom DFT configurations. Both fine-tuning protocols yield similarly accurate results for ammonium sulfate, but we also find some indications that multihead replay fine-tuning is more robust on configurations outside the fine-tuning domain. Exploiting this data efficiency, we further show that models can be trained on small
datasets and the hybrid-DFT level, and that some form of inclusion of dispersion correction is necessary to describe the phase behavior correctly.
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Quantum Gases
Effect of Two-Body Interactions on Floquet topological phases
Arijit Dutta, Souradeep Roy Choudhury, Tao Qin et al. (+1 more)
We study the circularly driven Falicov-Kimball model on a honeycomb
lattice within real space Floquet dynamical mean field theory (DMFT). The noninteracting version of this model has been realized experimentally. The noninteracting system hosts an effective Haldane phase at large driving frequencies, while at intermediate frequencies it hosts an anomalous topological phase. We study the effect of two-body interactions $U$ on the stability of these phases. We find that charge pumping does not remain quantized upon increasing $U$, despite the presence of edge modes in the spectrum. This can be attributed to the broadening of the edge modes due to interaction. We also calculate the rate of energy dissipation into the bath and find remarkably different behaviour in the two regimes.
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All authors Arijit Dutta, Souradeep Roy Choudhury, Tao Qin, Walter Hofstetter
Soft Condensed Matter
Asymmetry-Induced Chiral Dynamics in Coupled Self-Propelled Robots: Spinning and Circular Motion
Priyanka, Nitin Kumar and Harsh Soni
Motivated by the
chiral motility of microswimmers, we investigate how
geometric asymmetry in a system of two self-propelled active Brownian
robots coupled by a spring gives rise to rich collective dynamics. We demonstrate that asymmetry in the propulsion directions of the
robots generates net torques that induce persistent rotational motion. Depending on the choice of propulsion angles $\alpha_1$ and $\alpha_2$, the system exhibits three distinct dynamical regimes – run-and-tumble motion, circular trajectories, and spinning – with the
geometric configuration primarily determining the realized regime. We further show that spring stiffness and rotational noise act as additional tuning parameters governing the stability of these regimes. These results demonstrate how the interplay of mechanical coupling and activity produces diverse self-organized dynamics in simple robotic dimers, providing a bridge between artificial active systems and biological microswimmers such as bacteria, Chlamydomonas reinhardtii, and spermatozoa.
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Quantum Gases
Self-Organized Stabilization of Straight Dark Solitons in Stripe Supersolids
Koushik Mukherjee and Hiroki Saito
Straight dark
solitons in two-dimensional (2D)
quantum fluids usually decay by transverse modulational instability, with no intrinsic suppression in contact-interacting Bose–Einstein condensates (BECs). We theoretically show that anisotropic long-range interactions in a quasi-2D dipolar BEC stabilize an embedded straight
soliton, with spontaneous stripe order providing stronger pinning. The excitation spectra show that the lowest transverse solitonic branch remains gapped, while stripe-supersolid density modulation further hardens this branch and increases the
soliton bending stiffness, penalizing transverse deformation. Accessible in current $^{166}$Er and $^{164}$Dy platforms, these results establish interaction-driven protection for straight dark
solitons in structured
quantum fluids.
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Materials Science
Rate Programmable Ionic-Redox Switching with Tunable Volatility in CuCrP2S6
Suzanne Lancaster, Francesco Calavalle, Mayank Sharma et al. (+8 more)
Metal thiophosphates are emerging as a multifunctional material platform for neuromorphic electronics due to their accessible polar phases and ion dynamics on biologically relevant timescales. While resistive switching in these materials is frequently attributed to ferroelectric or antiferroelectric polarization, the intrinsic role of ion dynamics remains underexplored. Here, we isolate and demonstrate purely ion-driven resistive switching in paraelectric CuCrP2S6. Robust and reproducible resistive switching is observed in the absence of measurable ferroelectricity. The conductance can be tuned through both voltage amplitude and sweep rate, revealing a rate dependence characteristic of ion dynamics. The resulting resistance states exhibit controllable
volatility, where switching rate determines the decay time constant of the readout current, attributed to ionic relaxation. Using either inert or reactive electrodes, we observe electrical evidence of solid-state redox activity associated with the interfacial reduction of native Cu+ ions, enabling controlled formation of filamentary conduction pathways. Analysis of this process allows extraction of the Cu+
diffusion coefficient, providing quantitative insight into the underlying transport kinetics. The understanding of ionic-redox based resistive switching in CuCrP2S6 is crucial for unleashing its full potential as a material platform for dual- or multi-mode operation.
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All authors Suzanne Lancaster, Francesco Calavalle, Mayank Sharma, Lucia Olano-Vegas, Garen Avedissian, Tanweer Ahmed, Marco Gobbi, Beatriz Martin-Garcia, Beatrice Fraboni, Felix Casanova, Luis E. Hueso
Statistical Mechanics · Cross-listed from quant-ph
Exact Leg-Cut Influence Functional and Emergence of Gaussian Entanglement Theory in a Statistical-Dressing Ladder Model
Babatunde Moses Ayeni
The emergence of Gaussian effective field theories in low-dimensional
quantum systems is traditionally understood through top-down frameworks such as bosonization and Luttinger-
liquid theory. However, these approaches typically focus on the long-wavelength degrees of freedom in ways that do not directly track how non-Gaussian
lattice-scale correlations are progressively discarded under coarse-graining. In this work, we present an exact
lattice formulation from which this phenomenon emerges analytically. We analyze a two-leg hard-core ladder under a leg bipartition, where non-local statistical strings cross the
entanglement cut. We construct an exact
lattice influence-functional representation showing that the reduced state factorizes strictly into a product-state amplitude and a full-counting-statistics functional. By introducing a commuting linked-cluster superoperator hierarchy that bypasses Baker-Campbell-Hausdorff ordering ambiguities, we prove that the first mixedness-generating sector is strictly density-density in character. Under a specific systematic coarse-graining procedure, we analytically derive the suppression of higher-order corrections, providing a controlled, closed-form framework showing how highly non-Gaussian
lattice states evolve toward their quadratic continuum form under coarse-graining. We corroborate these analytical predictions through finite-size exact diagonalization and
entanglement-spectrum diagnostics.
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Statistical Mechanics
Eric Vernier, Yuan Miao and Masahito Yamazaki
Conventional
quantum integrability is encoded in a commuting
algebra of transfer
matrices. By contrast, several models possess additional non-commuting conserved charges with important physical consequences, yet the nature of the corresponding
symmetry has remained elusive. Focusing on the XXZ
spin chain at roots of unity, we show that the non-Abelian analogue of the commuting transfer-
matrix algebra is governed by quadratic relations following from a new class of unbalanced Yang–Baxter/RLL relations. This quadratic
algebra is shown to encode precisely the Onsager
algebra, for which we construct explicit
matrix-product representations of both its generators and its duality defect line. The latter obeys $\mathbb{Z}_N$ Tambara–Yamagami fusion rules, thereby providing a
lattice realization of the topological defect lines of the compactified
boson conformal field theory. Our results identify non-Abelian transfer-
matrix algebras as a microscopic origin for Onsager
symmetry and dualities in
lattice models.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Long-lasting Topological Entanglement in a Monitored Rashba Nanowire
Emanuele Guida, Giulia Salatino, Gianluca Passarelli et al. (+2 more)
We study the topological properties of a monitored Rashba chain along
quantum-jump trajectories, investigating the persistence of the initial topological value of the disconnected
entanglement entropy (DEE). We find that the DEE persists in its topological value for a time linear in the system size, even if the dissipation acts on the boundary and affects the topological Majorana modes. The reason for this phenomenon lies in the absence of particle conservation and in the degeneracy of the topological
manifold, allowing the monitoring to let the system switch between different topological states – alternatively creating and annihilating a Majorana mode – while producing a poisoning of finite-energy ballistically propagating quasiparticles that eventually destroy the topological
entanglement structure.
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All authors Emanuele Guida, Giulia Salatino, Gianluca Passarelli, Angelo Russomanno, Procolo Lucignano
Soft Condensed Matter
Bath-modes quantitatively capture the nonlinear microrheology of micellar solutions
Pierre Champagnac, Clemens Bechinger, Juliana Caspers et al. (+3 more)
Active microrheology experiments, in which a probe is driven through a complex fluid, often exhibit nonlinear responses that cannot be captured by generalized Langevin equations. Models that couple the probe to a Gaussian field reproduce such nonlinear effects qualitatively, but their large number of parameters hinders direct comparison with experiments. Here, we restrict these models to a small number of field modes and demonstrate that this reduced description quantitatively reproduces a broad range of active microrheology experiments in a micellar solution using a single set of parameters. We further show that the same framework extends naturally to multi-probe systems, such as colloidal dumbbells.
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All authors Pierre Champagnac, Clemens Bechinger, Juliana Caspers, Pierre Illien, Matthias Krüger, Vincent Démery
Disordered Systems and Neural Networks
Critical Universality of the SU (2) Gauge Glass Model Analyzed by the Dynamical Scaling Method
Yosei Takada, Yusuke Terasawa, Yuma Osada et al. (+1 more)
We investigate the critical phenomena of the three-dimensional (3D) $SU(2)$ gauge glass model, which can be regarded as the $O(4)$
spin-glass model with gauge
symmetry. Using Monte Carlo simulations and the non-
equilibrium relaxation method, we examine the critical behavior along phase boundaries across various degrees of disorder. Consistent with previous studies, we verify that weak disorder is irrelevant to the universality class; the critical behavior of the
ferromagnetic-paramagnetic transition remains in the 3D $O(4)$ universality class of the pure
ferromagnetic system. Additionally, we demonstrate that the paramagnetic-
spin glass transition exhibits universal critical behavior independent of the disorder. Our findings provide valuable insights into the fundamental properties and universality of gauge glass models.
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All authors Yosei Takada, Yusuke Terasawa, Yuma Osada, Yukiyasu Ozeki
Materials Science
Valence-change-driven reduction of antiphase boundaries in spinel ferrite epitaxial films
Kouki Takeo, Eiji Kita and Hideto Yanagihara
Antiphase boundaries (APBs) formed in thin films sometimes cause severe degradation of their physical properties. In particular, a high density of APBs in spinel ferrite films generates a non-negligible
magnetic dead layer near the interface. In this study, we examined the effect of post-oxidation annealing in an oxygen
plasma atmosphere on Co$_{0.125}$Fe$_{2.875}$O$_4$(001) thin films grown on MgO(001) as a model system. The thickness of the
magnetic dead layer was found to be significantly reduced after post-oxidation, resulting in an increase in the saturation magnetization and an improved squareness ratio. Dark-field transmission electron microscopy analysis revealed that the post-oxidation process increased the antiphase domain size, indicating a substantial reduction in APB density. Furthermore, reflection high-energy electron diffraction and x-ray diffraction measurements confirmed that the spinel
crystal structure and epitaxial strain were preserved after post-oxidation. These results suggest that post-oxidation proceeds through a topotactic solid-state reaction in which Fe$^{2.5+}$ ions are oxidized to Fe$^{3+}$, accompanied by cation rearrangement across APBs, thereby reducing APB density without degrading crystallinity and leading to improved
magnetic properties in spinel ferrite epitaxial films.
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