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Physics Condensed Matter Mesoscale and Nanoscale Physics

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Friday 4 September

Mesoscale and Nanoscale Physics

Electrostatic splitting of an Edge Magnetoplasmon Resonator

Sloän Kouamé, Elric Frigerio, Giacomo Rebora et al. (+10 more)

Edge-magnetoplasmon resonators have been proposed as a powerful tool to detect anyons by introducing a quantum point contact into an isolated quantum Hall system probed via radiofrequency radiation. In this paper, we study the effect of a quantum point contact embedded within an edge-magnetoplasmon resonator and how its polarization influences the propagating magnetoplasmonic mode. Combining dc and rf measurements, we unambiguously evidence the signature of both integer ($\nu = 1$ and $2$) and fractional quantum Hall states ($\nu = 4/3$ and $2/3$) within the radiofrequency transmission signal. Using electrostatic gating, we determine the physical parameters characterizing the electrostatic edge of an AlGaAs/GaAs based two-dimensional electron gas. We extract the dependence of the cavity perimeter with the gate voltage of the quantum point contact and fully characterize the path followed by edge magnetoplasmons in this system. Finally, we provide a geometric model in good agreement with experimental results.
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All authors Sloän Kouamé, Elric Frigerio, Giacomo Rebora, Suvankar Purkait, Yong Jin, Ulf Gennser, Antonella Cavanna, Jean-Marc Berroir, Emmanuel Baudin, Pascal Degiovanni, François D. Parmentier, Gwendal Fève, Gerbold C. Ménard

Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.supr-con

Transparency-engineered SQUID cells for Kerr-free three-wave-mixing Josephson metamaterials

Claudio Guarcello, A. Mert Bozkurt, Carlo Barone et al. (+3 more)

We introduce a transparency-engineered rf-SQUID cell for Kerr-free three-wave-mixing Josephson metamaterials. This design replaces the conventional tunnel-junction element with an effective Josephson element formed by two junctions in series, yielding a non-sinusoidal energy-phase relation that can be used as a tunable nonlinear design resource. We show that the asymmetry between the two series junctions and the applied flux bias provide independent control over the local expansion of the rf-SQUID potential, enabling operating points where the leading quartic Kerr term is suppressed while the cubic nonlinearity remains finite. We derive the corresponding Kerr-free condition, identify the resulting operating ridge in parameter space, and analyze the local stability and passive-matching constraints that bound its physically accessible portion. Our results provide a compact unit-cell design principle for three-wave-mixing Josephson metamaterials and suggest a route toward Kerr-suppressed Josephson traveling-wave parametric amplifiers.
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All authors Claudio Guarcello, A. Mert Bozkurt, Carlo Barone, Giovanni Filatrella, Alessandro Bruno, Sergio Pagano

Mesoscale and Nanoscale Physics

Engineering Giant Thermoelectric Performance through Electrode-Coupling Geometry and Magnetic Flux in Quasiperiodic Su-Schrieffer-Heeger Rings

Sridhar, Souvik Roy and Malay Bandyopadhyay

We investigate coherent thermoelectric transport in magnetic-flux-threaded quasiperiodic Su-Schrieffer-Heeger (SSH) rings with engineered multi-site electrode couplings using the nonequilibrium Green's function formalism within the Landauer-Büttiker framework. We demonstrate that the electrode-coupling geometry serves as a powerful control parameter for tailoring quantum interference, thereby reshaping the transmission spectrum and thermoelectric response. In the absence of magnetic flux, the trivial dimerized phase ($t_1>t_2$) exhibits the highest thermoelectric efficiency, with asymmetric coupling producing a substantially larger figure of merit than the symmetric geometry. Magnetic flux further reconstructs the transmission spectrum through Aharonov-Bohm interference, driving a crossover of the optimal thermoelectric regime from the trivial to the topological dimerized phase. Under optimal flux conditions, the thermoelectric figure of merit reaches $ZT \approx 12$ for symmetric coupling and is dramatically enhanced to $ZT \approx 90$ for asymmetric coupling through enhanced energy filtering and suppressed electronic thermal transport. We further establish a clear correlation between the enhancement of thermoelectric efficiency and the violation of the Wiedemann-Franz law. Our results demonstrate that the combined interplay of quasiperiodicity, topology, magnetic flux, and electrode-coupling geometry provides a versatile strategy for engineering high-performance coherent thermoelectric devices.
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Mesoscale and Nanoscale Physics

ANT:UI: An interactive 3D tool for preparing ANT.Gaussian molecular junction geometries

A. Martinez-Garcia, J. J. Palacios and C. Sabater

ANT.UI is a Python graphical interface that automates the construction of molecular-junction geometries for NEGF-DFT quantum transport calculations. Through a real-time 3D viewer, users interactively position electrodes and molecules and generate complete, ready-to-run input files for Gaussian and ANT.Gaussian without manual scripting. Dedicated Pull, Grid, and Rotation assistants further automate electrode-pulling sequences, surface scans, and step-wise rotation studies, with optional geometry-optimisation chaining across each sequence. By replacing a process that previously demanded days of custom scripting with a point-and-click workflow, ANT.UI accelerates research in theoretical molecular electronics and lowers the barrier to entry for new users. The software also exports all constructed geometries in standard XYZ format, allowing direct reuse in molecular dynamics codes or third-party visualization tools without manual reformatting.
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Mesoscale and Nanoscale Physics

Bias-field control of the Neel skyrmion nonlinearity in a confined nanostructure

A.V. Valkov, A.A. Matveev, O.Yu. Arkhipova et al. (+3 more)

We study the nonlinear dynamics of a cylindrical skyrmion-based oscillator within the framework of a generalized Thiele model. We demonstrate the influence of an bias magnetic field applied perpendicular to the plane of the nanocylinder on the oscillation frequency and on the nonlinearity coefficient. It is shown that the field tunes the response frequency, while also producing a substantial change in the nonlinear frequency shift. We find that the nonlinearity coefficient reverses its sign as the field crosses a certain critical value. The variation of the nonlinearity coefficient with the field is clearly illustrated by the observed qualitative changes in nonlinear amplitude-frequency responses. Controlling the nonlinear properties of a skyrmion oscillator by changing the bias magnetic field opens up prospects for creating tunable computational elements for neuromorphic applications.
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All authors A.V. Valkov, A.A. Matveev, O.Yu. Arkhipova, R.V. Shcherbakov, A.R. Safin, S.A. Nikitov

Mesoscale and Nanoscale Physics

Nonreciprocal plasmonic response of drift-biased two-dimensional metals

Gonzalo Álvarez-Pérez and Joel D. Cox

We develop a nonlocal electrodynamic framework for drift-biased two-dimensional electron gases (2DEGs) with Dirac (linear) and parabolic (quadratic) dispersions, deriving closed-form drift-dependent conductivity tensors from the Boltzmann transport equation. We obtain the plasmon dispersion and near-field emission of a point dipole, revealing nonreciprocal propagation in both systems. At equal drift parameter, the parabolic 2DEG exhibits stronger nonreciprocity than the Dirac system, although we find that a larger drift parameter does not by itself produce stronger nonreciprocity: the response is set by the interplay of drift and plasmon nonlocality. As such, the combination of strong nonlocality and experimentally accessible drift velocities of semiconductor 2DEGs identifies parabolic systems as a promising platform for tunable, nonreciprocal plasmonics.
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Mesoscale and Nanoscale Physics

Cascade spin dynamics of excitons localized in indirect-band-gap (In,Al)As/AlAs quantum dots with type-I band alignment

S. V. Nekrasov, I. V. Kalitukha, A. A. Golovatenko et al. (+5 more)

We investigate the spin dynamics of excitons localized in type I (In,Al)As/AlAs quantum dots with an indirect in momentum space band structure. Polarized selective photoluminescence spectroscopy, i.e. fluorescence line narrowing, under magnetic fields up to 5 T applied in the Faraday geometry is employed. The experiment reveals a cascade spin evolution process of excitons in the indirect band-gap quantum dots: an initial short term spin dynamics associated with excited direct exciton states possessing a large oscillator strength is followed by electron relaxation into the X valley of the Brillouin zone and subsequent long term spin dynamics of indirect excitons. The two step mechanism manifests itself in the distinct features of the magnetic field dependences of photoluminescence: two component recovery of optical orientation, two component linear to circular polarization conversion and the presence of the linear polarization plane rotation. At the same time, suppression of the optical alignment shows one-component behavior governed by the spin dynamics of the indirect exciton states. Within the pseudospin formalism, we derive analytical expressions that quantitatively describe the observed dependences and yield estimates for the anisotropic exchange splitting: 210 {\mu}eV for direct excitons and 1.3 {\mu}eV for indirect excitons. Further analysis using the density matrix formalism agrees well with the pseudospin model calculations and shows that the finite optical orientation at zero magnetic field is due to comparable magnitudes of the anisotropic splitting of the indirect exciton states and the splitting of the X-valley electron states caused by the hyperfine interaction with nuclei.
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All authors S. V. Nekrasov, I. V. Kalitukha, A. A. Golovatenko, Ya. A. Kuznetsova, N. O. Mikhailenko, M. D. Ragoza, T. S. Shamirzaev, Yu. G. Kusrayev

Mesoscale and Nanoscale Physics

Spin-Point-Group Classification of Multipoles for Nonrelativistic Collinear Magnets

Yuuki Ogawa and Satoru Hayami

Multipole moments provide a unified symmetry language for describing electronic degrees of freedom and their associated physical responses. Although active multipoles have been systematically classified for crystallographic and magnetic point groups, their classification in spin point groups, which naturally describe magnetic systems in the absence of spin-orbit coupling, has remained unexplored. In this work, we present a complete classification of active orbital and spin multipoles for all 32 nonmagnetic and 122 collinear spin point groups. Treating orbital and spin degrees of freedom independently, we identify the symmetry-allowed multipoles associated with nonmagnetic and collinear magnetic orderings and clarify their hierarchy through comparisons among the corresponding spin point groups. The resulting classification provides a symmetry-based database that distinguishes structural and magnetic contributions to active multipoles and directly identifies microscopic order parameters, including those responsible for $d$-, $g$-, and $i$-wave altermagnetism. Furthermore, by classifying response tensors within the same framework, we establish a correspondence between active multipoles and symmetry-allowed physical responses. This correspondence systematically distinguishes nonrelativistic responses that survive without spin-orbit coupling from those requiring relativistic effects, providing a unified framework for understanding and predicting spin-dependent electromagnetic and transport phenomena in magnetic materials.
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Mesoscale and Nanoscale Physics

Excitation caging in a vertex-frustrated quasiperiodic Einstein artificial spin ice

T. Wang, F. Museur, G. M. Macauley et al. (+5 more)

Naturally occurring bulk quasicrystals are rare, and magnetic instances are rarer still, with chemical constraints typically permitting the synthesis of approximants rather than true quasicrystalline magnets. Here, we present an artificial spin ice based on a recently discovered Einstein lattice, the Hat tiling, which is built from the first known shape - the hat - that tiles the plane only aperiodically. The Einstein artificial spin ice has long-range structural order with no translational symmetry, and low-connectivity vertices with well-defined local ground states and excitations. Together, these properties provide a model two-dimensional quasicrystalline magnet, with magnetic correlations that we probe with magnetic force microscopy and parallel-tempered Monte Carlo simulations. We identify a two-stage partial ordering process, driven by the competition between two possible positions for magnetic excitations. This competition is resolved in the ground-state manifold, where exactly one magnetic excitation is caged on each antihat, yet the manifold remains macroscopically degenerate. This yields an unusual type of medium-range order, where the underlying quasiperiodic long-range order is randomly modulated by a strictly constrained disorder. Our findings establish the Einstein artificial spin ice as a blueprint for understanding quasicrystalline magnetism, demonstrating how quasiperiodic monotile geometries can be exploited to engineer unconventional magnetic phases with no direct equivalent in periodic systems.
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All authors T. Wang, F. Museur, G. M. Macauley, J. Colbois, L. Berchialla, F. Flicker, P. M. Derlet, L. J. Heyderman

Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci

Challenges in orbital current-driven domain wall motion in light metal/ferrimagnet heterostructures

Min-Gu Kang, Jaerin Kim, Benjamin J. Jacot et al. (+2 more)

Recent advances in spintronics suggest that orbital Hall currents generated by charge injection in light metals can provide nonequilibrium angular momentum without relying on strong spin-orbit coupling (SOC). Here, we examine whether such orbital currents can drive domain wall (DW) motion in an amorphous ferrimagnetic alloy, Gd$_{25}$(Fe$_{9}$Co$_{1}$)$_{75}$ (GFC), where the rare-earth sublattice offers strong SOC for orbital-to-spin conversion. We compare three representative heterostructures: Pt/GFC as a spin Hall reference, light-metal (Mn or Ti)/GFC for direct orbital-current injection, and light-metal/Pt/GFC incorporating an ultrathin Pt layer for orbital-to-spin conversion. Whereas Pt/GFC exhibits robust and reproducible spin-orbit-torque-driven DW motion, no current-driven DW motion is detected in Mn/GFC or Ti/GFC. Second-harmonic Hall measurements nevertheless reveal finite damping-like torques in both Mn/GFC and Ti/GFC, demonstrating that angular-momentum transfer into GFC does occur but is far weaker than in Pt/GFC. Inserting a 1-nm-thick Pt conversion layer strongly enhances the damping-like torque and restores DW motion. Thickness-dependent analysis further shows that DW mobility and depinning thresholds correlate with the interfacial Dzyaloshinskii-Moriya interaction and domain-wall width, highlighting weak torque conversion and insufficient interfacial stabilization of chiral DWs as key challenges for orbital-driven DW motion in light-metal/ferrimagnet heterostructures.
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All authors Min-Gu Kang, Jaerin Kim, Benjamin J. Jacot, Laura Van Schie, Pietro Gambardella

Mesoscale and Nanoscale Physics

Interlayer Exciton Condensate Stiffness Is Non-Monotonic in Quantum Metric

Bo Zou, Yitong Zhang, Siddhartha Sarkar et al. (+3 more)

Identifying the origin of the superfluid stiffness of electron-electron and electron-hole pair condensates is an important issue in flat-band physics. Here, we study the stiffness of bilayer exciton condensates using exact diagonalization and realistic Coulomb interactions across a wide variety of flat Chern band systems, including Landau levels, mixed Landau levels, and moiré bands. We find that stiffness is non-monotonic in the trace of the quantum metric and that it develops peaks when the band wavefunctions are engineered to be similar to those of Landau levels. The stiffness predicted by mean-field theory agrees quantitatively with exact diagonalization in these optimal cases, but systematically overestimates it otherwise. Flat bands with identical quantum geometry tensors can exhibit substantial differences in stiffness. The stiffness of condensates formed between moiré flat bands, which typically have strong variations in Berry curvature and quantum metric across their Brillouin zones, tends to be larger when the bands have non-zero Chern numbers and can be larger than that of Landau levels. Our results reveal a behavior that is richer than that suggested by simple geometric bounds and provide new guiding principles for the design of robust flat-band condensates with large superfluid stiffness.
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All authors Bo Zou, Yitong Zhang, Siddhartha Sarkar, Shi-Zeng Lin, Allan H. MacDonald, Kai Sun

Mesoscale and Nanoscale Physics

Evidence of Crystal-Field-Mediated Anisotropic Orbital Rashba Effect in Epitaxial Ru/FM Heterostructure

Yu Zhang, Wenhao Niu, Yumin Yang et al. (+5 more)

Electrical generation of orbital angular momentum provides a promising route to current-induced torques, yet effective control of orbital Rashba textures still remains challenging, particularly because the role of the interfacial crystal field remains largely unexplored. Here, we report experimental evidence for a crystal-field-mediated interfacial anisotropic orbital Rashba effect (AORE) in epitaxial Ru/ferromagnet heterostructures. Total orbital torque was disentangled into an isotropic bulk contribution and an in-plane anisotropic interfacial contribution. The latter was strongly suppressed by degrading the crystallinity of either constituent and by inserting a Cu spacer, highlighting the essential roles of coherent interfacial orbital hybridization and direct Ru/ferromagnet contact. These results identify interfacial crystal-field coherency as a key ingredient in manipulating orbital Rashba textures and establish a route toward engineering the symmetry and directionality of orbital torques.
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All authors Yu Zhang, Wenhao Niu, Yumin Yang, Wenqi Xu, Gengchen Meng, Hailong Wang, Na Lei, Dahai Wei

Mesoscale and Nanoscale Physics · Cross-listed from physics.optics

Band Gaps and Localization of Surface Waves at Hyperbolic Material and Topological Insulator Interfaces

Andrei I. Maimistov, Ildar R. Gabitov and Ilia Kuk

We develop analytical criteria for surface electromagnetic waves at interfaces between hyperbolic materials and topological insulators. The analysis identifies propagation conditions, field penetration depths, and spectral band gaps. In the lossless model, the band edge is governed primarily by dielectric contrast, while the bulk topological coupling produces only a small shift and a weak correction to the dispersion. For structures combining hexagonal boron nitride with bismuth selenide, a thin topological insulator film on a dielectric substrate with low permittivity can substantially broaden the accessible propagation window. We also analyze a dissipative titanium and silicon hyperbolic effective medium interfaced with bismuth selenide. To make the complex branch structure visible, this lossy calculation uses an intentionally enhanced interface response and is therefore illustrative rather than a quantitative prediction for a conventional topological insulator. In the lossy case, a root of the dispersion relation represents a physical guided mode only when the fields decay away from the interface, attenuate consistently along the propagation direction, have finite penetration depths, and exhibit a consistent energy flow profile. Apparent gaps and jumps can occur when the complex quantities controlling transverse decay approach square root branch cuts. These results provide design guidelines for controlling dispersion, confinement, band gaps, and propagation loss in mid-infrared photonic structures.
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Thursday 3 September

Mesoscale and Nanoscale Physics

Quantum oscillations of helical edge states of periodically deformed 2D topological insulator in magnetic field

A. V. Tsvetkova, P. D. Grigoriev and Ya. I. Rodionov

We study edge-state transport in a two-dimensional topological insulator with a periodically deformed edge subjected to a uniform magnetic field. Zeeman coupling breaks time-reversal symmetry and enables elastic backscattering, producing oscillations of the forbidden-band widths. In the strong-field regime, the gaps can close completely at discrete field values. In the weak-field regime, we identify an important class of periodic deformations for which the dominant semiclassical scattering is controlled by complex infinity rather than by the nearest turning points. We develop a semiclassical treatment of this process and establish its agreement with perturbation theory and direct numerical calculations. The gap modulation should produce observable oscillations of the edge conductance. Unlike conventional magnetic quantum oscillations, which are periodic in inverse field, the predicted oscillations are periodic in the magnetic field itself, with a period determined by the Fermi velocity and effective g-factor
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Mesoscale and Nanoscale Physics

The influence of quantum geometry on the phase boundary and collective excitations of electron liquids and crystals

Paul Froese, Mark R. Hirsbrunner and Yong Baek Kim

Recent experiments on multilayer graphene systems have reinvigorated the study of electron crystallization, now with the inclusion of quantum geometry. In this work, we apply time-dependent Hartree-Fock (TDHF) to the $\lambda$-jellium model to analyze the impact that quantum geometry has on the electronic liquid–crystal phase diagram and how it modifies the collective modes and responses of the liquid and crystal phases. In agreement with recent results utilizing neural quantum states, we find that quantum geometry favours electron crystallization, shifting the transition to higher densities. We also study the instabilities revealed by TDHF in the Fermi liquid ground state at low densities, providing insight into the fluctuations driving the crystallization transition. We further find that quantum geometry reduces the dispersion of the plasmon mode and suppresses Friedel oscillations deep in the liquid phase. Resolving the density response in terms of individual orbitals, we find that this suppression is caused by spectral weight transfer to an out-of-phase inter-orbital mode. Finally, we show that an analogous mode that emerges in the crystal phase corresponds to the breathing mode of an emergent real-space pseudospin skyrmion lattice.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.str-el

Wavefunctions for Anyon Superconductors

Donghae Seo, Taegon Lee and Gil Young Cho

Anyon superconductivity arises from the condensation of mobile anyons rather than from a conventional Cooper instability, yet a systematic wavefunction description remains lacking. We develop a hierarchy-wavefunction construction for superconducting states derived from parent topological orders and identify their off-diagonal long-range order, condensate charge, chiral central charge, and residual topological order through the plasma analogy and topological field theories. We construct Abelian and non-Abelian examples descending from the semion state, a $\nu=2/3$ hierarchy state, the $\nu=1/3$ Laughlin state, $\nu=1$ integer quantum Hall state, and Pfaffian state. Remarkably, for the semion case, the superconducting many-semion wavefunction is equivalent to a state of fermionized anyons filling two effective Landau levels, recovering Laughlin's original construction of semion superconductor. Finally, we show that hierarchy wavefunctions emerge naturally in the dilute, long-distance limit of the anyon-Hilbert-space formulation, which applies to ideal Chern bands and moiré bands of twisted bilayer MoTe$_2$. Our results establish a unified wavefunction-level framework linking anyon condensation, superconducting order, and topological field theory.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.str-el

HyperDet Wavefunction: A Phase-Agnostic Ansatz for Strongly Correlated Systems

Xiaodong Hu, Guan-Lin Lin, Ying Ran et al. (+1 more)

Competing phases of strongly correlated systems are often described by trial wavefunctions built on phase-specific assumptions. We propose the hyperdeterminant (HyperDet) wavefunction as a phase-agnostic ansatz for both bosonic and fermionic quantum many-body systems exhibiting spontaneous symmetry-breaking, fractionalization, and/or topological order. The HyperDet structure emerges by fusing auxiliary fermionic parton Slater determinants into physical orbitals through a learnable \emph{fusion tensor $\mathcal F$}. Optimized using variational Monte Carlo, a single HyperDet architecture achieves overlaps exceeding $99.9\%$ with exact-diagonalization ground states for nearly all sampled parameters across fractional Chern insulator (FCI) phases and their neighboring competing phases in both bosonic and fermionic models. Beyond its variational expressiveness, the optimized fusion tensor also provides rich interpretability. We show that, (i) the singular-value spectra of the bipartite fusion matrix can be used to track phase transitions; (ii) the reconstructed Bott indices reproduce the parton Chern numbers expected for the FCI states without parton-Hamiltonian input; and (iii) faithful lifts of physical translations to the parton degrees of freedom recover the expected translation fractionalization in the bosonic FCI without projective symmetry class assignment. These results establish HyperDet wavefunction as a promising framework for both variational ground-state searches and phase-diagram explorations across strongly correlated phases, and for providing theoretical insights by connecting the optimized wavefunction with parton microscopics and field-theory descriptions.
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All authors Xiaodong Hu, Guan-Lin Lin, Ying Ran, Di Xiao

Mesoscale and Nanoscale Physics

Hydrodynamics of two-dimensional electrons due to scattering by disorder

D. R. Raskulov, K. A. Baryshnikov and P. S. Alekseev

The hydrodynamic regime of electron transport, induced by fast inter-electron collisions, was discovered in high-quality nanostructures in recent ten years. However, signs of hydrodynamic transport, primarily, the giant negative magnetoresistance, were observed even at very low temperatures, when electron-electron scattering is too weak to affect the transport. To address this puzzle, here we develop a theory of mixed, hydrodynamic and non-Markovian, magnetotransport of two-dimensional electrons at zero temperature in samples with weak but still important disorder. Namely, we account for both the memory effects at electron scattering by localized defects in magnetic field and an unconventional viscosity effect due to electron scattering by defects in bulk and by rough sample edges. Solution of the model yields a strong negative magnetoresistance, which exhibits at zero magnetic field a sharp maximum in narrower samples or a blunt maximum in wider samples. This and other our results explain various properties of the giant negative magnetoresistance observed on ultra-high-quality GaAs quantum wells, thereby we apparently reveal the nature of low-temperature magnetotransport in these systems.
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Mesoscale and Nanoscale Physics

Extrinsic orbital Edelstein effect from asymmetric scattering

Sankar Sarkar, Koushik Ghorai and Amit Agarwal

The generation and manipulation of orbital angular momentum (OAM) by an external electric field constitute one of the central themes of orbitronics. In particular, the electrically induced nonequilibrium OAM polarization, known as the orbital Edelstein effect (OEE), has attracted considerable attention in recent years. While the intrinsic band-geometric mechanism and the role of conventional symmetric impurity scattering in the OEE are well understood, the contribution from disorder-induced asymmetric scattering remains unclear. Here, we develop a semiclassical theory that separates the OEE into intrinsic, Drude, side-jump, and third- and fourth-order skew-scattering channels. Unlike the Drude channel, the intrinsic, side-jump, and skew-scattering responses survive only in systems with broken time-reversal symmetry. We find that in a magnetized Rashba two-dimensional electron gas (2DEG), these disorder-induced mechanisms can substantially exceed the intrinsic contribution. Remarkably, we find that for a system with Rashba coupling of $1$ $eV \AA$, the orbital magnetization is about one order of magnitude larger than the spin magnetization for the chosen parameters, highlighting the crucial role of orbital degrees of freedom in the Edelstein effect.
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Mesoscale and Nanoscale Physics

Strongly anisotropic non-Kramers electron spin as a quantum coherence probe of angular fluctuations

Achuthan Manoj Kumar, Remy Dassonneville, Guillaume Gerbaud et al. (+5 more)

Strongly anisotropic non-Kramers rare-earth ions combine giant longitudinal g-factors with a vanishing transverse component imposed by time-reversal symmetry, a combination that makes their spin transitions exquisitely sensitive to the orientation of the applied magnetic field. We show that this sensitivity carries a dual identity: it is simultaneously an overlooked decoherence channel and the basis for a spin-coherence-based angular probe. Using pulsed electron paramagnetic resonance at X-band, we report the first measurements of the quantum coherence of Tb$^{3+}$ in a native-doped CaWO$_4$ crystal (15 ppb) and map the Hahn-echo coherence time $T_2$ as a function of temperature (2 to 10 K) and resonant field ($10^3$ to $10^4$ G). A parameter-free model combining spin-lattice relaxation, instantaneous diffusion and spectral diffusion from all independently quantified impurities overestimates $T_2$ by an order of magnitude at low temperature and wrongly predicts the field dependence of $T_2$, inconsistent with the observed monotonic decrease of $T_2$ with $B_r$. A two-parameter extension, including dynamical angular fluctuations of the crystal axis, reproduces the full dataset across multiple setups and laboratories. Two controlled experiments nominally identical except for different mechanical configuration of the setup establish the mechanical origin of the dominant contribution. The two-parameter extension corresponds to an angular amplitude noise spectral density of overall order 36 n{\deg}/$\sqrt{Hz}$ from global external vibrations (ranging from 10 to 66 n{\deg}/$\sqrt{Hz}$ depending on the exact setup mechanical configuration) estimated at $\sim$ 2.5 kHz plus a temperature-dependent contribution assumed to come from local phonon-driven angular jitter. It identifies and highlights a decoherence pathway of practical relevance to any anisotropic solid-state spin system.
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All authors Achuthan Manoj Kumar, Remy Dassonneville, Guillaume Gerbaud, Nolwenn Le Breton, Athanassios K. Boudalis, Patrice Bertet, Philippe Goldner, Sylvain Bertaina

Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Spin-to-polarization mapping with a coherent quantum dot-cavity receiver

Adrià Medeiros, Vincent Vinel, Eliott Rambeau et al. (+12 more)

Coherent light-matter interfaces controllably modifying the state of a photon upon interaction with a stationary qubit are a key resource for implementing deterministic entangling gates for optical quantum technologies. This requires a one-to-one mapping between the state of the scattered photon and that of the embedded qubit. Here, we present an experimental signature of such a bijection by leveraging the spin-induced Kerr rotation present in a low-noise charged quantum dot-micropillar cavity device. Through time-resolved polarization measurements, we project the electron spin to one of its eigenstates with $95\pm2\%$ fidelity with a single reflected photon detection, and follow the subsequent spin relaxation through the detection of a second reflected photon. We demonstrate that, after a transient regime governed by the trion radiative lifetime, two orthogonal polarization states can be produced, each associated to a given spin eigenstate. While the current results are limited by a timescale competition between electron spin relaxation and trion radiative lifetime, they could be improved using hole spins displaying increased relaxation times. Our work paves the way towards deterministic logic gates exploiting this one-to-one mapping between a spin and the polarization of a scattered photon.
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All authors Adrià Medeiros, Vincent Vinel, Eliott Rambeau, Petr Steindl, Elham Mehdi, Manuel Gundín, Clément Millet, Petr Stepanov, Niccolo Somaschi, Aristide Lemaître, Isabelle Sagnes, Olivier Krebs, Pascale Senellart, Dario A. Fioretto, Loïc Lanco

Mesoscale and Nanoscale Physics

Hierarchy of topological superconductivity generated via heterostructures of unconventional $p$-wave magnets

Koushik R. Das and Arijit Saha

A theoretical framework is proposed to engineer both first and second-order topological superconducting phases in a two-dimensional (2D) heterostructure, consisting of a quantum spin Hall insulator (QSHI) and an unconventional $p$-wave magnet in presence of proximity-induced $s$-wave superconducting pairing. Our analysis establishes that the transitions between the trivial and topological superconducting (TSC) phases can be regulated though the parameters of $p$-wave magnet. Presence of chiral symmetry leads to the characterization of both types of TSC phases by the respective invariants, one-dimensional winding number and quadrupolar winding number. These results are supplemented by an analytical effective low-energy edge theory that yields a deeper insight into the emergence of the different topological phases of the system. Bulk pairing analysis reveals the competition between the effective $(p_x+p_y)$ and $(p_x+ip_y)$ type pairings that are governed by the intrinsic spin-orbit coupling inherited to the QSHI and spin-split bands of the $p$-wave magnet, respectively.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.supr-con

Tunable Chern superconductivity of PtBi$_2$ in slab geometry

Luca Ketmaier, Jeroen van den Brink and Ion Cosma Fulga

Recent experiments indicate that PtBi$_2$ is a Weyl semimetal whose surfaces become topological superconductors with i-wave gap symmetry at low temperature. The bulk hosts 12 Weyl cones while in the superconducting state each of the two surfaces hosts in addition 6 Majorana cones. We study a simplified model in a slab geometry, where the finite thickness gaps out the bulk Weyl cones and leaves the surface Majorana cones as the low-energy degrees of freedom. We identify two competing mechanisms that gap these cones: inter-cone hybridization opens a trivial gap, whereas a Zeeman field opens a nontrivial one. In the nontrivial regime, chiral Majorana edge modes connect the gapped cones. We determine their wavefunction profile and relate it to the momentum-space distribution of the cones. Mapping out the phase diagram, we find both trivial and nontrivial regions in the quasi-two-dimensional limit.
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Mesoscale and Nanoscale Physics

The Casimir free energy of peptide films on a silicon substrate: Impact of dielectric-to-metal transition in silicon and nanoparticles in peptide

G. L. Klimchitskaya and V. M. Mostepanenko

Using the Lifshitz theory of the van der Waals and Casimir forces, we calculate the Casimir free energy of thin peptide films deposited on silicon substrates. The Casimir free energy is found as a function of film thickness for different fractions of water in the film, in the presence of either nonmagnetic or magnetic nanoparticles, and under the impact of irradiation of a silicon substrate with laser pulses or dopants resulting in the dielectric-to-metal phase transition. It is shown that for a dielectric silicon there is the borderline value of the film thickness, such that the Casimir free energy is negative and contributes to the film stability for thicker films, but is positive and makes the film less stable for thinner ones. According to our results, the borderline value of peptide film thickness decreases with increasing volume fractions of water and in the film. This decrease is more pronounced for the magnetic nanoparticles and becomes stronger with increasing their radius. The borderline value of peptide film thickness is found as a function of the fraction of water in the film. If the silicon substrate is in metallic state, the Casimir free energy of peptide coating is always positive, which makes it less stable. Possible applications of the obtained results in organic electronics and biomedicine are discussed.
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Mesoscale and Nanoscale Physics

Unravelling the Li-Haldane Conjecture with the Projected Ensemble

Daniel Spasic-Mlacak, Qi Camm Huang, Wen Wei Ho et al. (+1 more)

The entanglement spectra of fractional quantum Hall states contain universal fingerprints of their underlying topological order, as posited by the Li-Haldane conjecture. In this work, we uncover a finer universal structure within the entanglement spectra unravelled by projective measurements. Concretely, we study the projected ensemble of fractional quantum Hall states, defined as the collection of quantum states on a subsystem conditioned on measurement outcomes of its complement. We find that this ensemble exhibits a hidden hierarchy inside the Li-Haldane edge manifold: by conditioning on measurement outcomes, the entanglement spectrum's support is split into measurement-dependent sectors whose ranks we demonstrate are fixed by conformal field theory counting, an observation we dub the measurement-resolved Li-Haldane conjecture. For the non-Abelian Moore-Read state, this hierarchy is particularly rich: each parity-resolved edge manifold contains internal subspaces whose dimensions reproduce the conformal field theory counting of the opposite-parity sector. This structure persists even in realistic Coulomb-interacting ground states, establishing the projected ensemble as a sharp new probe of topological order beyond what the entanglement spectrum alone can detect.
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All authors Daniel Spasic-Mlacak, Qi Camm Huang, Wen Wei Ho, Nigel R. Cooper

Mesoscale and Nanoscale Physics · Cross-listed from math-ph

The conductivity matrix at the topological phase transition

Simone Fabbri, Giovanna Marcelli and Alessandro Giuliani

For a general class of two-dimensional non-interacting semi-metallic electron systems on a lattice, we derive an explicit formula for the whole conductivity matrix, by using Euclidean many-body formalism. The semi-metallic phase takes place whenever two Bloch bands touch at the Fermi energy with conical intersections and generally occurs at the transition between distinct integer quantum Hall phases. Unlike the longitudinal conductivity (which depends solely on the shape of the cones at the Fermi level), the transverse conductivity is remarkably determined both by the conical structures of the bands and by the nature of the two nearby topological phases. Generically, in the semi-metallic state, neither the longitudinal nor the transverse conductivities are quantized in integer multiples of a universal conductivity quantum; however, universality of the conductivity matrix is restored under the assumption of emergent rotational symmetry of the linearized Hamiltonian at the Fermi points. Using our formula, we compute the conductivity matrix for several physically relevant models of quantum Hall fluids at the topological phase transition, exhibiting cases where the transverse conductivity is quantized in half-integer multiples of $e^2/h$ and cases where it depends continuously on an external strain parameter, thus shedding light on its universality or non-universality features.
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Mesoscale and Nanoscale Physics

Coherent interaction of WS$_2$ and quasi-2D perovskite excitons over micrometer distances via a cavity field

Marti Struve, Hamid Pashaei Adl, Jamie M. Fitzgerald et al. (+13 more)

The coherent coupling of cavity-confined photons and excitonic matter resonances leads to the formation of cavity polaritons, hybrid light-matter quasi-particles. If multiple exciton resonances couple to the same photonic mode, the resulting polariton constitutes a coherent interaction between matter resonances that can be spatially separated without any direct electronic coupling. In this work, we demonstrate the formation of such a coherent coupling at room temperature using an open optical cavity containing two distinct van der Waals materials - monolayer WS2 and layered quasi-2D halide perovskites (HaPs) - separated by $1.5 \mu\rm m$. The system forms three polariton branches, with the middle branch possessing nearly equal fractions of both excitons and the photonic mode. White-light reflectivity and luminescence measurements are in good agreement with simulations using a coupled harmonic oscillator and a microscopic Wannier-Hopfield framework. Our results lay the foundation to combine highly complementary degrees of freedom in 2D materials in an in-situ tunable fashion to enable new polaritonic functionalities.
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All authors Marti Struve, Hamid Pashaei Adl, Jamie M. Fitzgerald, Oliwia Janikowska, Maciej Śmiertka, Alessandro Surrente, Sven Stephan, Christoph Lienau, Falk Eilenberger, Zdeněk Sofer, Watcharaphol Paritmongkol, William A. Tisdale, Paulina Plochocka, Ermin Malic, Christian Schneider, Martin Esmann

Mesoscale and Nanoscale Physics

Real-space Floquet topology written by the orbital angular momentum of light

Mohammad Shafiei and Milorad V. Milošević

Floquet engineering usually treats light as a uniform control field that changes the topology of an entire driven material. Here we show that structured light carrying orbital angular momentum (OAM) enables a different regime, in which topology is written directly in real space. For ultrathin topological insulator films, circularly polarized Laguerre–Gaussian beams generate a radial Floquet mass whose sign changes define a topological annulus bounded by two concentric chiral ring modes. The transition is helicity selective: below a thickness-dependent critical frequency, left-circularly polarized light drives mass inversion, whereas right-circularly polarized light increases the gap and leaves the film trivial. Independently, the OAM quantum number shifts and reshapes the annulus without changing the frequency, intensity, or helicity. In the decoupled-surfaces limit, the same mechanism produces a purely Floquet-induced topological mass and a vortex-core zero mode. These results identify photon OAM as a control parameter for nonequilibrium topology and provide a route to programmable topological landscapes in quantum materials.
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Mesoscale and Nanoscale Physics

Generalized s-d model for Wannier-Mott excitons in layered magnetic semiconductors

Sonu Verma, Bashab Dey and Akashdeep Kamra

The recent discovery of excitons coupled to the magnetic order, and the consequent strong magneto-optic responses, in some van der Waals magnetic semiconductors has triggered intense activity at the interface of magnetism and semiconductor optics. Here, we present an analytically tractable minimal model that describes magnetic order, electrons, holes, and excitons within a unified framework, thereby capturing a wide range of phenomena. It treats the magnetic order and itinerant carriers to be comprised by distinct electronic orbitals that are mutually coupled via orbital-dependent onsite exchange, similar to the treatment of metallic magnets using an s-d model. Investigating CrSBr bilayer as a case study, we benchmark our model and its predictions against recent experimental and ab-initio results finding good agreement as well as new insights enabled by the model's simplicity. Examining the optical selection rules, we find the conservation of a quantum number formed from a combination of spin and layer pseudospin to be a useful guiding principle, even in noncollinear magnetic configurations. Our analysis finds a series of bright and dark excitonic states in such layered A-type antiferromagnets. The presented framework should be valuable in achieving intuitive understanding of recently discovered excitonic phenomena and guiding the discovery of other excitonic states in layered magnetic semiconductors.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci

Multimodal and Multiscale Interrogation of a Mechanically Tough Glass Forming Copper-Based Metal-Organic Framework

Mounir El Skafi, Guo-Qiang Li, Sophie R. Thomas et al. (+8 more)

A copper-based metal-organic framework, Cu(Im)2, was synthesized using a sol-gel process and subsequently melt-quenched into glass upon heating above 240 {\deg}C. In this paper, we present a multimodal, multiscale interrogation of the MOF nanocrystals and the resulting glasses. Structural characterization using X-ray diffraction, atomic force microscopy, and electron microscopy was performed to understand the morphology and size of the synthesized nanocrystals and glasses. Thermogravimetric analysis and differential scanning calorimetry were employed to understand the melting process of the crystals to form the glass. Synchrotron pair distribution function analysis was performed to verify that the framework structure is maintained upon melting, and nearfield infrared nanospectroscopy provided insight into the local chemical structure of the materials. The mechanical characterization via nanoindentation revealed that the resulting glasses exhibit an appreciably high elastic modulus (~10 GPa) and the highest fracture toughness (K_1c ~ 0.5 MPa m^1/2) yet reported for MOF glasses. This development is central to the emerging field of MOF-based materials processing and shaping, while upholding mechanical robustness and resistance to cracking.
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All authors Mounir El Skafi, Guo-Qiang Li, Sophie R. Thomas, James D. Taylor, Mark Frogley, Gianfelice Cinque, Marc Pignitter, Michael Reithofer, Jia-Min Chin, Sebastian Henke, Jin-Chong Tan