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Physics Condensed Matter Mesoscale and Nanoscale Physics

cond-mat.mes-hall Watch Mesoscale and Nanoscale Physics

Monday 28 September

Mesoscale and Nanoscale Physics

Topological Band Theory for High-Dimensional Parameter Spaces

Vivek Chakrabhavi, Walt Chavarria, Jonathan J. Heckman et al. (+1 more)

We study the topological band theory of quantum Hall systems in which the adiabatic flux parameters of an external gauge potential form a high-dimensional manifold. This situation arises both for strongly correlated matter on spatial Riemann surfaces of genus $g > 1$, as well as in the formal study of matter on compact oriented manifolds of dimension $4\ell+2 = 2p$ coupled to $p$-form gauge potentials. In these cases, the underlying topological invariants defined over the parameter space are significantly richer than the low-dimensional (i.e., two-dimensional) case and involve both the curvature (i.e., first Chern class) as well as higher order curvature invariants. These higher curvature invariants correspond to topologically protected contributions to Kubo-like formulae, constructed from correlation functions of the physical current operators. We illustrate these general considerations with an explicit example from hyperbolic band theory based on the genus-two Bolza Riemann surface, a case which has recently been simulated on a synthetic-dimension platform.
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All authors Vivek Chakrabhavi, Walt Chavarria, Jonathan J. Heckman, Steven Rayan

Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.str-el

Advancing Fuzzy-Sphere CFTs: $\mathrm{SO}(3)$-Rotation-Resolving Exact Diagonalization, 3D Ising Heavy Primaries, and Quasi-Hole-Space Projection

Zheng Zhou and Yin-Chen He

Fuzzy-sphere regularization has recently emerged as a powerful framework for studying three-dimensional conformal field theories (CFTs). In this work, we exploit symmetry and Hilbert-space structures to substantially advance this framework. We develop an exact-diagonalization algorithm that resolves the full $\mathrm{SO}(3)$ rotational symmetry, reducing computational costs by factors of several hundred. For the three-dimensional Ising CFT, we identify around 100 primary operators, including a large number of previously unknown heavy scalar primaries up to scaling dimension $\Delta\approx16.5$. We also resolve the tension between previous fuzzy-sphere and bootstrap results regarding the parity-odd scalar primary. Furthermore, we identify a branch of scalar primaries associated with $\phi^n$ operators in the $\phi^4$ Lagrangian description, beginning with the identity, $\sigma$, $\epsilon$, $\epsilon'$, and $\sigma'$. Their wave functions exhibit a semi-classical structure closely related to states invariant under area-preserving diffeomorphisms of the sphere. Finally, we show that critical points involving fractional quantum Hall states can be studied within a substantially reduced Hilbert space spanned by quasi-hole states of the corresponding model quantum Hall wave functions like the Laughlin state. This suggests a general strategy for exploring CFTs intertwined with topologically ordered phases.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci

AI-Assisted Identification of Magnetic Orders and Skyrmions

Haowen Yang, Sophia Huerta and Yingying Wu

Exotic magnetic orders in two-dimensional (2D) materials are attracting huge interest for energy-efficient spintronic applications, yet realizing robust high-temperature van der Waals antiferromagnets and topological magnetic states remains challenging. In this work, we develop a machine-learning framework for identifying magnetic orders and predicting magnetization using structural, compositional, and electronic information derived from the Materials Project. Fixed-length descriptors are constructed for two complementary tasks: ferromagnetic (FM) versus antiferromagnetic (AFM) classification and quantitative magnetization prediction. Magnetic order is classified using a LightGBM model trained on structure-derived descriptors without explicitly including magnetic descriptors. Five-fold cross-validation grouped by chemical system is used to reduce chemical leakage, together with hyperparameter and classification-threshold optimization. On an isolated test set, the classifier achieves a balanced accuracy of 93.6% in the testing set. Magnetization is predicted using a residual multilayer perceptron with compositional, structural, electronic, and task-specific initial-state descriptors. A logarithmic target transformation and robust weighted loss are used to account for the broad magnetization distribution, while three independently trained models are combined into a final ensemble. The model achieves a mean absolute error of 0.686 {\mu}B/formula unit. For selected magnetic candidates, simulated magnetic imaging and phase-reconstruction analysis are further used to investigate magnetization textures and skyrmion-like features through normalized magnetization profiles and topological charge. This framework provides an efficient approach for screening 2D magnetic materials and prioritizing candidates for antiferromagnetic and topological spintronic applications.
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Mesoscale and Nanoscale Physics

Superfluid Spin Transport in the Van der Waals Antiferromagnet CrCl$_3$

Peisen Yuan, Xiaomin Guo, Vincent Flynn et al. (+3 more)

Over the past decade, the quest for spin superfluidity has moved to the forefront of spintronics, driven by the promise of phase-gradient-driven, ultra-low-loss spin transport. However, experimental investigations remain limited, primarily due to the lack of suitable material systems. Here, we report on the discovery and control of a superfluid spin transport in the easy-plane van der Waals antiferromagnetic (AFM) insulator CrCl$_3$ by a nonlocal device structure. Combining nonlocal magnon transport measurements with theoretical modelling, we demonstrate that spin superfluidity emerges in CrCl$_3$ under canted AFM spin configurations, where it gives rise to ultra-long range (around 90 $\mu$m), weakly decaying spin transport. We also provide direct evidence that strong magnetic fields and elevated temperatures suppress the superfluid state, restoring the rapid exponential decay with distance of incoherent magnons. These findings underscore the potential of spin superfluidity in two-dimensional magnetic insulators and establish CrCl$_3$ as a promising platform for energy-efficient, long-distance spin transport in next-generation spintronic applications.
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All authors Peisen Yuan, Xiaomin Guo, Vincent Flynn, Benedetta Flebus, Fèlix Casanova, Luis E. Hueso

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

Electron decoherence in cylindrical holes and circular apertures

Cruz I. Velasco and F. Javier García de Abajo

The coherence of free electrons sets fundamental limits on the resolution and contrast of phase-sensitive electron microscopy because coherence is lost whenever the electron leaves a distinguishing excitation in its environment. We develop a quantitative theory of fast-electron decoherence in two canonical geometries: a cylindrical hole drilled through a realistic metal and a circular aperture in a thin perfectly conducting film. By combining an electromagnetic Green-tensor formulation with the fluctuation–dissipation theorem while fully retaining retardation, we obtain the decoherence probability and elastic phase as functions of the electron trajectory, temperature, and material response. For the cylindrical hole, we obtain a closed-form, azimuthally resolved expression that separates the dependences on path position, temperature, and conductivity. In the high-conductivity and high-temperature limits, this result reduces to a universal expression that is linear in temperature and independent of both conductivity and electron velocity. For the circular aperture, which we solve using a cylindrical-wave modal expansion, the energy-loss probability diverges as $1/\omega$ at low frequency, whereas the decoherence probability remains finite and reaches a maximum when the aperture radius is comparable to the relevant electromagnetic wavelength. Because the interaction is spatially localized, aperture-induced decoherence is generally weaker than that produced by a cylindrical hole, except for sufficiently large apertures at high temperature. Finally, we show that, for sufficiently large holes, decoherence can dominate the spatial broadening of a focused electron probe and must therefore be incorporated into the design of coherent electron-beam instruments.
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Mesoscale and Nanoscale Physics

Dynamical transition in non-Hermitian Chern insulator

Zhi-Qiang Zhang, Yuan-Hang Ren, Ming Lu et al. (+1 more)

We unveil a peculiar dynamical transition for the propagation of wave packets in non-Hermitian Chern insulators, where the evolution of the topological wave packets at the edge is not solely determined by the topological Chern number. Unlike the Hermitian Chern insulator, where a wave packet initiated at the edge propagates along the system boundary, here it may instead penetrate into the bulk. This behavior is attributed to the competition between the localization induced by conventional topology and the non-Hermitian skin effect. Specifically, when the former dominant, the wave packet will evolve along the boundary; otherwise, it will spread into the bulk. These features demonstrate that while the generalized-Brillouin zone framework reliably predicts topological phase transitions, it does not on its own specify the dynamical transitions.
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All authors Zhi-Qiang Zhang, Yuan-Hang Ren, Ming Lu, Hua Jiang

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

Improving the Stability of the Hierarchical Equations of Motion for Open Quantum Systems with Strong Coupling to Structured Bosonic Baths

Salvatore Gatto, Samuel L. Rudge, Bokang Hou et al. (+2 more)

The hierarchical equations of motion (HEOM) approach is one of the most powerful methods avail- able to simulate the dynamics of open quantum systems. Although the HEOM approach has been shown to be stable and efficient in many parameter regimes and physical scenarios, it is also well known that the unavoidable finite truncation of the hierarchy can lead to fundamental numeri- cal instabilities for bosonic environments. In this work, we apply recently developed techniques to analyze these issues. We use an auxiliary Fock-space picture of the hierarchy to first identify the unbalanced hierarchy-raising terms responsible for the strong transient amplification associated with the non-normal algebraic structure of the HEOM generator. We then apply a non-unitary similarity transformation that converts these terms into balanced combinations of hierarchy-raising and hierarchy-lowering terms, thereby suppressing their numerical impact. We first demonstrate the efficacy of this approach via a spin-boson model with a simple Brownian oscillator spectral den- sity and subsequently extend the analysis to a structured spectral density, showing for both cases that the transformed HEOM approach allows simulations of much larger system-bath coupling than would otherwise be possible.
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All authors Salvatore Gatto, Samuel L. Rudge, Bokang Hou, Eran Rabani, Michael Thoss

Mesoscale and Nanoscale Physics

Extracting the anyonic exchange phase from co-tunneling through an open quantum dot

Felix Puster, Matthias Thamm and Bernd Rosenow

The elementary excitations of fractional quantum Hall states obey anyonic statistics, described by an exchange phase $\theta$ intermediate between the bosonic and fermionic values. We study an interferometer in which three chiral edge segments are pairwise connected by three quantum point contacts, so that, depending on the applied voltages, one of the segments acts as an open quantum dot: its spectrum is continuous, and tunneling through it is resonant without any gate tuning. This setup realizes the co-tunneling mechanism of a recently proposed antidot interferometer in a particularly simple setting. Using a non-equilibrium Keldysh calculation to third order in the tunneling amplitudes, we show that the interference current contains a co-tunneling contribution in which two quasiparticles are exchanged, so that for Laughlin states the exchange phase $\theta=\pi\nu$ appears as the phase shift between the Aharonov-Bohm oscillations measured in two voltage configurations. We obtain a closed analytic expression for the interference current at finite temperature and finite separation between the quantum point contacts and show that, provided voltage-induced changes of the enclosed area are sufficiently screened, the exchange phase can be extracted from a robust phase-plateau difference. Alternatively, simultaneous measurements of the interference currents at two drains avoid this screening assumption and time-of-flight phases can be quantified analytically, allowing the exchange phase to be extracted by a controlled extrapolation with a few-percent systematic error.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics

Plasmon-Enhanced Second-Harmonic Generation in Atomically Thin Crystalline Silver Nanostructures

Saad Abdullah, Philipp K. Jenke, Andrew P. Weber et al. (+8 more)

The intrinsically weak nonlinear optical response of existing materials, further constrained by symmetry-forbidden second-order processes in centrosymmetric media, severely limits efficient frequency conversion in deeply subwavelength, ultrathin volumes. Addressing this challenge is crucial for the development of nonlinear nanophotonics. Here, we show that atomically thin, epitaxially grown crystalline silver films circumvent these restrictions through the interplay of vertical electronic quantum confinement and lateral plasmonic enhancement. We fabricate atomically thin films that exhibit an enhanced nonlinear response associated with electronic quantum wells, and subsequently pattern them into periodic nanoribbon and nanotriangle arrays sustaining infrared localized surface plasmon resonances. Strong near-field confinement in these structures further boosts second-harmonic generation compared to unpatterned films. Precise control over nanostructure geometry enables spectral tuning of the plasmonic resonance, and consequently, the enhanced harmonic frequency. Our findings establish an approach for activating robust second-order nonlinearities in quantum-confined metals, where intrinsic size effects and plasmonic resonances act synergistically. The compatibility of high-quality epitaxial growth with microchip fabrication technology offers a scalable route toward ultracompact nonlinear optical components for on-chip frequency conversion, sensing, and quantum photonic applications.
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All authors Saad Abdullah, Philipp K. Jenke, Andrew P. Weber, Álvaro Rodríguez Echarri, Vahagn Mkhitaryan, Fadil Iyikanat, Frederik Schiller, Philip Walther, J. Enrique Ortega, Lee A. Rozema, F. Javier García de Abajo

Mesoscale and Nanoscale Physics

Plasmon modes in tilted three-dimensional nodal-ring semimetals. I. $\mathcal{PT}$-symmetric nodal ring and its gapped cousin

Ipsita Mandal

We study collective charge excitations in three-dimensional $\mathcal{PT}$-symmetric nodal-ring semimetals (PTNRs) and their gapped counterparts (GNRs) in the presence of band tilt, together with Weyl semimetals (WSMs). Within a low-energy two-band description, we consider untilted systems as well as in-plane and axial tilts. Using the random-phase approximation, we obtain the density of states, Drude weights, dielectric functions, and plasmon dispersions at low doping and in the intrinsic limit. The mass gap and the two inequivalent tilt directions generate distinct Fermi-surface topologies and thereby control the formation and damping of plasmons. By comparing the collective modes with the particle-hole continuum, we identify the regimes in which plasmons remain well defined. We also calculate the response of untilted and tilted WSMs and contrast it with that of PTNRs and GNRs. The two classes of semimetals differ in the carrier-density dependence and isotropy of the plasmon frequency as well as in interband screening and their response to tilt. These differences reflect their distinct Fermi-surface geometries and interband structures. Our results establish how mass and tilt govern collective charge dynamics through their interplay with intraband spectral weight and interband particle-hole excitations.
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Mesoscale and Nanoscale Physics

Capacitance sensing in bilayer graphene with gate reflectometry

Tamás Kalmár, Gergő Fülöp, Bálint Szentpéteri et al. (+5 more)

In the search for topological states in bilayer graphene, capacitance measurement methods are widely utilized in bridge type readouts or source-drain reflectometry setups. In this paper we demonstrate an alternative readout method based on gate reflectometry. We probe the capacitance of a BLG flake encapsulated between hBN and WSe$_2$ through a lumped-element LC resonator coupled to the top gate electrode of the heterostructure. The microwave readout reliably tracks the opening of a displacement field-induced band gap in the device. Compared to simultaneous DC transport measurements, the RF signal proves to be less affected by the percolating transport channels caused by sample disorder. Furthermore, we use the gate based readout to identify a small-angle alignment between the hBN and BLG flake. From the fixed frequency microwave readout, we extract the device capacitance change between the insulating and metallic state of the bilayer and utilize a comprehensive capacitance network model to explain its origin. Finally, we propose an advanced, multiplexed double-resonator readout scheme capable of simultaneously measuring top and bottom gate capacitances to extract the layer polarizability of the system. This work establishes gate reflectometry as a highly scalable and powerful methodology for exploring topological phases and internal charge dynamics in van der Waals heterostructures.
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All authors Tamás Kalmár, Gergő Fülöp, Bálint Szentpéteri, Olivér Kürtössy, Kenji Watanabe, Takashi Taniguchi, Szabolcs Csonka, Péter Makk

Mesoscale and Nanoscale Physics

Moiré Quantum Layer Hall Effect

Jin-Xin Hu, Wen-Bo Dai and X. C. Xie

Even-layer topological antiferromagnetic thin films such as MnBi$_2$Te$_4$ exhibit an unconventional layer Hall effect (LHE) arising from a layer-locked Berry curvature. This effect manifests as a layer-polarized anomalous Hall effect that can be controlled by a vertical displacement field. However, achieving a quantized version of the LHE remains experimentally challenging. In this work, we propose that moiré engineering, using an electrostatic superlattice potential from control layers, can realize the quantum layer Hall effect (QLHE). Specifically, by placing moiré control layers in close proximity to the surfaces of a MnBi$_2$Te$_4$ thin film without breaking $PT$ symmetry, the resulting system exhibits a vanishing net Hall conductance but a quantized layer Hall conductance of $e^2/h$. A weak gate electric field then breaks $PT$ symmetry and drives the system into a layer-polarized quantum anomalous Hall (QAH) phase. Furthermore, when a single control layer is introduced on only one surface, the layer-polarized QAH emerges even in the absence of an external electric field. We identify the microscopic origin of the QLHE as an emergent layer-$U(1)$ gauge field generated by the scalar moiré potential, which in turn produces opposite periodic pseudomagnetic fields on the top and bottom layers. Our work provides a feasible pathway toward realizing the QLHE in antiferromagnetic thin films.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci

Optimization of InAs/InAlGaAs/InP quantum dots for O-band laser applications

Anna Penkała, Paweł Podemski, Vinayakrishna Joshi et al. (+3 more)

The O-band telecommunication spectral range combines minimal chromatic dispersion with low transmission loss, making it highly suitable for optical communications. Semiconductor telecom lasers utilizing low-dimensional active regions, such as quantum dots, offer low threshold power and high thermal stability. However, long-wavelength quantum dot emitters often suffer from thermal carrier escape through excited states when the energy separation between the ground and excited states is insufficient. Here we demonstrate the optimization of InAs quantum dot emitters grown on InP by molecular-beam epitaxy for O-band laser active regions. By optimizing the design for better carrier capture efficiency and tuning the emission wavelength to the O-band, we show ways of improving the carrier confinement. Absorption spectroscopy on the finalized structure confirms substantial energy separation between the quantum dot ground and excited states, effectively suppressing thermal carrier escape even at elevated temperatures. These results highlight critical design for improving carrier capture and retention in long-wavelength quantum dot lasers.
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All authors Anna Penkała, Paweł Podemski, Vinayakrishna Joshi, Vitalii Sichkovskyi, Johann P. Reithmaier, Grzegorz Sęk

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

Phase compositions of Si oxynitride: A comprehensive thermodynamic modeling study

Andrey Sarikov, Mariia Babiichuk, Mariia Voitovych et al. (+1 more)

In this work, a comprehensive thermodynamic description of the formation of phases in amorphous SiOxNy (0 <= x <= 2, 0 <= y <= 4/3) films as a function of the film chemical composition and fabrication temperature is presented. Two possible phase states, namely homogeneous single-phase Si oxynitride and two-phase mixture of Si oxide and Si nitride phases, are analyzed in terms of the lowest values of the Gibbs free energy. The characters of the modification of the phase composition upon changing the SiOxNy stoichiometry indices and fabrication temperature are determined. Moreover, characteristic features of the chemical composition of the Si oxide and Si nitride phases in two-phase Si oxynitrides are revealed. Particular attention is given to the thermodynamic origin of the boundaries between different phase states of the SiOxNy films and to determining the critical stoichiometry values separating them. A comprehensive phase diagram indicating single- and two-phase SiOxNy regions as functions of the fabrication temperature is constructed. The peculiarities of the transitions between different SiOxNy phase states, along with underlying mechanisms, are discussed with reference to this phase diagram. The obtained results extend our understanding of the fundamental properties of Si oxynitride films and their dependence on the film fabrication conditions, and may be used for tailoring SiOxNy characteristics for practical applications.
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All authors Andrey Sarikov, Mariia Babiichuk, Mariia Voitovych, Sergii V. Mamykin1

Mesoscale and Nanoscale Physics

Sub-20 nm spin textures with arbitrary topological charge stabilized by higher-order interactions

Zhen Sun, Shiwei Zhu, Moritz A. Goerzen et al. (+3 more)

Topological magnetization textures play a central role in modern magnetism. For many applications, spin textures with different topological charges $Q$ in the same system are particularly attractive. Although the coexistence of skyrmions and antiskyrmions ($|Q| = 1$) has been reported in inversion-symmetric magnets, extending this to high-$Q$ ($|Q| > 1$) textures with arbitrary charge remains elusive. Here, using an atomistic spin model parameterized from first-principles calculations, we predict the emergence of sub-20 nm high-$Q$ textures in Janus monolayers, van der Waals magnets of growing interest. We explore skyrmion and antiskyrmion rings as well as skyrmion bags with $|Q|$ up to 5, and characterize their nucleation mechanisms, thermal stability, and collapse pathways. We find that higher-order spin interactions (HOI), which extend the conventional bilinear-exchange Hamiltonian, are essential for stabilizing these high-$Q$ spin textures. The rings remain thermally stable at zero magnetic field. HOI substantially enhance their energy barriers while leaving their size nearly unchanged and stabilize them even in the absence of Dzyaloshinskii-Moriya interaction. Skyrmion bags, in contrast, nucleate only in the presence of HOI. In particular, the four-spin three-site interaction is the key ingredient preventing high-$Q$ textures from collapsing into the ferromagnetic state. Finally, we identify previously unreported parity-dependent collapse mechanisms for high-$Q$ textures. Our results establish HOI as an overlooked mechanism for high-$Q$ nucleation.
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All authors Zhen Sun, Shiwei Zhu, Moritz A. Goerzen, Megha Arya, Changsheng Song, Dongzhe Li

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

Trotterisation Thresholds and Dissipative Quantum Chaos in Open-System Digital Quantum Simulation

Angsar Manatuly, Lukas M. Sieberer, Cahit Kargi et al. (+1 more)

Digital quantum simulation (DQS) is one of the most promising applications of quantum computing. Trotterised DQS models quantum dynamics by decomposing the evolution into a sequence of gate-based Trotter steps. Using larger Trotter steps reduces the required gate count, but it is now understood that the Trotterisation step size cannot be increased beyond a certain threshold value, beyond which there is a sudden breakdown in simulation accuracy, due to the onset of quantum chaos. To date, this behaviour has only been studied for closed systems not subjected to the environmental noise and decoherence to which real-world quantum computers are highly sensitive. In this work, we study a range of experimentally relevant open-system quantum simulator models and show that Trotterisation thresholds persist even when open-system effects are included, even in the long-time, steady-state limit, once all coherence has been lost. We show that open DQS can accurately reproduce the dynamics of open target systems prior to the threshold, but still exhibits a sudden performance breakdown beyond it. We introduce new, statistical techniques to rigorously characterise the onset of quantum chaos beyond the Trotterisation threshold for both approximately unitary and genuine dissipative quantum chaos, based on random matrix theory (RMT), building on techniques developed for closed systems. Finally, we demonstrate that dissipative quantum chaos emerges when the dissipation is in balance with the presence of underlying unitary quantum chaos; the dissipation must be strong enough to induce genuinely dissipative behaviour, yet not so strong as to suppress the underlying chaotic structure.
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All authors Angsar Manatuly, Lukas M. Sieberer, Cahit Kargi, Nathan K. Langford

Mesoscale and Nanoscale Physics

Probing hydrodynamics in graphene and quark matter via Seebeck coefficient

Subhalaxmi Nayak, Jayanta Dey and Sabyasachi Ghosh

We investigate the Seebeck coefficient as a probe of collective transport behavior in graphene and quark-gluon plasma using a kinetic-theory approach in the hydrodynamic regime. The Seebeck coefficient is obtained by solving the Boltzmann transport equation in the relaxation-time approximation. At high-charge-carrier density, corresponding to the Fermi-liquid domain, our result approaches the behavior expected from the conventional Mott relation. In contrast, significant deviations from the Mott relation are observed in the low-carrier-density regime, corresponding to the Dirac fluid domain. These facts are in good agreement with experimental Seebeck coefficient data for graphene. This behavior indicates the emergence of collective hydrodynamic transport in graphene. The enthalpy per particle plays a key role for the Seebeck coefficient in the Dirac fluid regime. We extend our formalism to the ultra-relativistic quark-gluon plasma. A similar deviation from the Mott relation is observed, supporting a similar fluid response in the Seebeck coefficient across two markedly different strongly correlated quantum systems - graphene and quark matter.
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Mesoscale and Nanoscale Physics

Observing Colossal and Tunable Near-field Thermal Radiation with A Highly Sensitive Annular Micro-thermocouple Junction

Ken Araki, Wei Han Won and Liping Wang

Near-field radiative heat transfer between two objects has been theoretically predicted and experimentally demonstrated to exceed far-field blackbody limit across nanoscale vacuum gap distance enabled by evanescent surface waves coupling, while significant enhancement by more than 100 times usually requires sub-50-nm vacuum gaps around room temperature. This is challenging for parallel-plate configuration with millimeter sample sizes due to intrinsic wafer bow and contaminant particles. Sphere-plate configuration with a microsphere attached to bimaterial cantilevers or micro-thermocouple tips has been used to experimentally demonstrate near-field radiative heat transfer down to 30-nm gaps, but it is much less developed because of the challenges in the sophisticated sensor fabrication, low sensitivity and weak signals. In this work, we overcome these challenges by an annular micro-thermocouple junction fabricated at the end of a glass fiber with straightforward thin-film deposition to achieve high measurement accuracy with large Seebeck coefficient 25 uV/K and thermal resistance 8.7e6 K/W. With a silica microsphere attached underneath the micro-thermocouple junction, we report experimental observation of colossal near-field radiation heat transfer over blackbody limit down to 10-nm gap up to 2600 times with quartz and 900 times with doped silicon. Upon phase transition of VO2 thin film emitter, tunable near-field heat transfer up to 430-fold enhancement is experimentally demonstrated at 15-nm gap with 64% reduction. Experimental data agrees well with rigorous modeling based on fluctuational electrodynamics and Derjaguin approximation, and underlying mechanism is understood by energy transmission calculations. The results will advance the experimental study and fundamental understanding of energy transport at nanoscale gaps.
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Mesoscale and Nanoscale Physics

(Sub)nanoscale Visualization of Reconstruction-Driven Moiré Exciton Localization and Delocalization

Medha Dandu, Sriram Sankar, Giovanny Espitia et al. (+12 more)

Spectral fingerprints in optical absorption and emission have typically been used as a signature of exciton localization in twisted moiré bilayers. However, the mechanism by which excitons become confined to specific stacking sites and their associated optical signature is experimentally unresolved. Here, we directly visualize in real space how tuning the change in extent of structural reconstruction leads to localization and delocalization of moiré excitons in the WSe2/WS2 moiré superlattice. Using cryogenic monochromated electron energy loss spectroscopy, together with first-principles GW-Bethe Salpeter equation calculations and optical spectroscopy, we uncover the physical mechanism that drives the correlation between twist-angle-dependent structural transformations, the real-space localization of moiré excitons, and their optical signatures. Surprisingly, and in contrast to the prevailing understanding, we show that the emergence of new moiré exciton resonances in the optical spectra alone is insufficient to establish exciton localization. Instead, the extent of structural reconstruction and external strain drives exciton localization, leading to new design principles for engineering moiré excitons and strain-aware quantum optoelectronic devices.
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All authors Medha Dandu, Sriram Sankar, Giovanny Espitia, Rwik Dutta, Patrick J. Hays, Daria Blach, Takashi Taniguchi, Kenji Watanabe, James R. Chelikowsky, Seth Ariel Tongay, Peter Ercius, Jordan A. Hachtel, Mit H. Naik, Archana Raja, Sandhya Susarla

Mesoscale and Nanoscale Physics · Cross-listed from cs.LG

FLARE: Flow Matching with Local Axis-Angle Representations for Stochastic Micromagnetic Evolution

Pengyu Li, Renjie Tong, Xuanlue Jiang et al. (+2 more)

Long-horizon micromagnetic simulation remains expensive because conventional and learned solvers typically propagate Landau–Lifshitz–Gilbert (LLG) dynamics step by step. Existing learned approaches generally retain stepwise integration or model deterministic evolution, leaving full-field, direct-horizon stochastic prediction largely unexplored. We propose FLARE, a flow-matching framework that recasts stochastic finite-time magnetization prediction as conditional transport over anchor-relative local axis-angle rotations. This rotation-space formulation respects the intrinsic geometry of magnetization dynamics and preserves pointwise unit norm by construction. By explicitly conditioning on the physical prediction horizon, FLARE directly generates full-field stochastic endpoints across multiple target times without stepwise integration. Against the strongest single-checkpoint external baseline on each metric, FLARE achieves 29.9% lower angular energy distance ($15.30^\circ$), and a 37.3% lower fair energy score (0.393). On a representative composed 5-ns two-segment protocol, FLARE achieves a $3{,}062\times$ best-batch speedup over the widely used GPU micromagnetic solver MuMax$^3$ on a single GPU.
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All authors Pengyu Li, Renjie Tong, Xuanlue Jiang, Jianmin Li, Yuanyuan Zhou

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

Multimode oscillation and its route to chaos in transverse-mode-coupled optomechanical resonators

Motoki Asano, Lalit Maharjan and Hiroshi Yamaguchi

Nonlinear oscillators exhibit rich collective phenomena including synchronization, bifurcation, and chaos. Experimentally accessing multimode nonlinear dynamics, however, remains challenging because low-order internal resonances readily induce mode locking and suppress stable multimode oscillation. Here, we demonstrate a transverse-mode-coupled optomechanical platform that combines engineered collective mechanical modes with optically controllable nonlinear interactions. The engineered transverse mechanical modes enable stable two- and three-mode self-sustained oscillations while suppressing trivial low-order internal resonances. By varying the laser frequency, we observe successive beat-frequency fractionalization ({\Delta}f/2 and {\Delta}f/3), followed by a broadband state exhibiting enhanced trajectory divergence consistent with deterministic chaos. These results establish transverse-mode-coupled optomechanical resonators as a scalable and tunable platform for exploring high-dimensional nonlinear dynamics in interacting mechanical networks.
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Sunday 27 September

Mesoscale and Nanoscale Physics

Magnetic localization and spectral asymmetry of a charged particle at a screw dislocation

Claudio Furtado, Omar Mustafa, Hassan Hassanabadi et al. (+1 more)

We study a charged particle moving outside a spiral (screw) dislocation in a uniform magnetic field. Although the geometry is locally Euclidean, its global screw identification couples the conserved axial and azimuthal quantities through the combination \(\mathcal{J}=\ell-\beta k\) After eliminating the cyclic coordinates, the radial motion is governed by an inverse-square term determined by $\mathcal{J}$ and a harmonic confining term generated by the magnetic field. The corresponding reduced quantum problem is exactly solvable for $q\mathcal{B}_0\neq0$, yielding an equally spaced spectrum with an orientation-dependent energy shift. The radial probability density depends on $\mathcal{J}$, and opposite values of the screw-modified quantum number have identical spatial profiles but different energies for a fixed magnetic-field orientation. The radial size scales as \(\sqrt{\langle r^2\rangle_n}\propto |q\mathcal{B}_0|^{-1/2}\), with the magnetic length setting the localization scale. At $q\mathcal{B}_0=0$, the confining term vanishes, and the problem reduces to a scale-free inverse-square system. Thus, the screw parameter enters the dynamics through the global coupling of the conserved axial and azimuthal quantities, whereas the magnetic field provides radial confinement and its orientation determines the spectral asymmetry.
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All authors Claudio Furtado, Omar Mustafa, Hassan Hassanabadi, Abdullah Guvendi

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

Correlation Between Dopant Atom Evaporation Field and Measured Site Preference in Atom Probe Tomography

Kasper A. Hunnestad, Constantinos Hatzoglou, Frida H. Danmo et al. (+6 more)

Complex oxides possess a wide range of electric, magnetic, and optical properties that can be precisely tuned by chemical doping. The atomic-scale analysis of the property-controlling dopants, however, becomes increasingly difficult towards low doping levels. Atom probe tomography (APT) offers chemical sensitivity and spatial resolution to image individual dopant atoms down to a few parts per million. To reliably extract such information, detailed knowledge about the atom-specific field evaporation processes is required. Here we demonstrate a first insight into the APT-measured atomic position of dopant atoms and the field evaporation conditions, using Zr-doped ErMnO3 as a model system. Our analysis reveals a substantial preferential retention of both matrix and dopant atoms which strongly affects the dopant site determination and can lead to an incorrect interpretation. The retention effect is determined by intrinsic and extrinsic parameters, such as the dopant's evaporation field and concentration and the analysis temperature, respectively, as we explain based on field-evaporation simulations. Our results are important for the APT-based analysis of individual dopant atoms in solid systems and the understanding of field evaporation dynamics at the atomic level in general.
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All authors Kasper A. Hunnestad, Constantinos Hatzoglou, Frida H. Danmo, Zewu Yan, Edith Bourret, Francois Vurpillot, Antonius T. J. van Helvoort, Sverre Selbach, Dennis Meier

Mesoscale and Nanoscale Physics

Topological chiral edge modes in the continuum of a trivial bulk

Li Ge

Chiral edge modes in topological states of matter are routinely found inside band gaps, which may be deformed and shifted as a function of the lattice momentum. Here we show that they can exist inside a bulk band instead, i.e., in the continuum. These chiral edge modes in the continuum (CEMICs) are induced by introducing an imaginary magnetic flux to an otherwise topologically trivial two-dimensional system, realized by imposing asymmetric couplings along the edge. While the stronger couplings provide a preferred circulation direction, we find that the edge localization of CEMICs does not originate from the non-Hermitian skin effect, which is typically associated with systems featuring asymmetric couplings and the open boundary condition. Instead, this edge localization is due to the energy exchange between the system and the environment at the asymmetric coupling junctions, which leads to a parity-time (PT) transition in the Brillouin zone. Intriguingly, the onset of CEMICs is independent of the system size in the macroscopic limit, which is given by the golden ratio between the asymmetric couplings and their geometric average.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.supr-con

Superconducting Pairing Symmetry on Geometric-Algebra Foundations via the Scalar-Projection Method

Youping Dai

We formulate the low-energy theory of superconducting pairing in the geometric algebra $Cl_{3,0}$. Conventional BCS mean-field theory and its extensions ($s$-, $p$-, $d$-wave, etc.) have algebraic counterparts in an eight-dimensional real multivector space. The construction is a two-level projection: matrix blocks are represented as Clifford multivectors, and their grade-0 projected geometric products extract the scalar blocks from which Hamiltonians are built. The result is an algebraic reconstruction, physically equivalent to the standard complex-matrix formulation. In this reconstruction, the dichotomy of pairing channels acquires an algebraic root: it follows from the fermionic identity $B^\dagger(V)=-B^\dagger(V^{\mathsf T})$, and the Fierz rearrangement is realized by the map $\Phi:G\mapsto Ge_{31}$ (with $e_{31}^2=-1$). This yields a kernel/matrix dictionary: at the effective-kernel level grades $0\oplus3$ correspond to spin singlets and grades $1\oplus2$ to triplets; at the pairing-matrix level the singlet plane is $\mathrm{span}\{e_2,e_{31}\}$. The BCS limit has a double grade identity: kernel grade 0 (scalar glue) and vertex grade 2, a bivector ($i\sigma_2\leftrightarrow e_{31}$). We state three algebraic results: (i) a decomposition theorem for BdG quantum geometry with a null-texture criterion, applied to the chiral-state controversy in CsV$_3$Sb$_5$; (ii) a Fierz sign duality in the four-dimensional Minkowski algebra, with a chirality-reversal extension to two-node Weyl-semimetal models; (iii) an error bound and condition-number structure for tomographic reconstruction under a linear-response probe model. Illustrations include a glue-generation mechanism, a one-loop algebraic renormalization flow whose feeding constant coincides in magnitude with the $\mathfrak{su}(2)$ Casimir, closed-form $\mu=0$ inter-node spectra, and a UTe$_2$ two-phase analysis.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.stat-mech

Quantum Dynamics of Full Counting Statistics in Fermionic Lattices with Localized Gain

Bijay Kumar Agarwalla and Manas Kulkarni

We investigate the dynamics of full counting statistics (FCS) of the growth of the total number of fermions in a one-dimensional non-interacting lattice subjected to a localized particle gain (source) at one edge. The dynamics of the setup is modeled by the Gorini–Kossakowski–Sudarshan–Lindblad (GKSL) quantum master equation. We recast the counting problem that involves counting particle number at every lattice site to a problem where only the local injected site is involved. We employ the Schwinger-Keldysh path integral formalism within the GKSL framework and derive an analytical expression for the cumulant generating function at arbitrary times and obtain a Levitov-Lesovik type formula in the long-time limit, earlier derived for boundary driven setups in the steady-state. For clean lattices with either short- or long-range hopping, supporting single-particle delocalized eigenstates, we show that all cumulants grow linearly with time in the asymptotic regime. Our analytical results are in excellent agreement with direct numerical simulations. These findings establish a general framework for characterizing FCS and quantum fluctuations in driven open fermionic systems with localized particle injection.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci

Placement-driven reversal of preferred spin alignment in monolayer hBN vacancy pairs

Daniel Hashemi

The negatively charged boron vacancy is an optically addressable spin centre in hexagonal boron nitride (hBN), but bringing two vacancies together introduces electronic interactions absent from the isolated-defect picture. Here we use density-functional theory at total charge q = -2 to show that atomic-scale placement reverses the preferred collinear spin alignment in monolayer hBN. Among seven configurations, the closest pair, separated by 4.3 angstrom, favours parallel alignment by 27.6 meV within the semilocal approximation. Moving one vacancy by a single lattice vector reverses the preference, and a 7.5 angstrom pair favours antiparallel alignment by 50.7 meV. Numerical controls change these two reference splittings by less than 1 meV; hybrid-functional calculations retain their signs while substantially changing their magnitudes. Local distortions connect the antiparallel preference at 7.5 angstrom to changes in vacancy-state hybridization along an intervening atomic chain. The closest pair instead exhibits a contact-localized spin-density contrast and constrained angular energies that depart from the bilinear Heisenberg form. These results identify a placement-sensitive regime of interacting defects and provide a microscopic foundation for investigating coupled spin centres in atomically thin materials.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Engineering Defect-Phonon Interactions Through Heterophase-Interfaces in Silicon Carbide Membranes

Kirlie Iulius Figuera Michal, Jin Hee Lee, Keiju Sato et al. (+2 more)

Point defects in wide-bandgap semiconductors offer spin and photonic qubits in a solid-state platform, making them important building blocks for quantum information processing, communication, and sensing. While these systems have the strong advantage of room-temperature operation, intrinsic electron-phonon interaction induces broad phonon-sideband emission and weak zero-phonon-line transitions, limiting efficient spin-photon interfaces and scalable photon-mediated interaction. Here, we introduce a controlled heterophase interface based on the remote epitaxy technique as a crystal heterogeneity-engineering strategy. While stacking faults are treated as imperfections to be eliminated, our results instead show that crystal-phase interfaces can provide an additional degree of freedom to engineer defect-phonon interaction beyond the intrinsic properties of a single crystal. In comparison with single-phase 4H-silicon carbide (SiC) membranes, Vsi in 3C/4H heterointerface SiC exhibits a drastic enhancement of zero-phonon optical transitions, with a substantially narrower zero-phonon linewidth of 4.71 meV even at room temperature. These results establish heterophase-interface engineering as an effective route for tailoring defect-phonon interactions and realizing bright room-temperature quantum emitters with enhanced zero-phonon optical transitions.
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All authors Kirlie Iulius Figuera Michal, Jin Hee Lee, Keiju Sato, Takuji Maekawa, Je-Hyung Kim

Mesoscale and Nanoscale Physics

Bare-Die Antiferromagnetic Computing

Yu Liu, Zhuoting Han, Zexin Feng et al. (+15 more)

Semiconductor electronic devices are increasingly constrained by fundamental quantum tunneling effects and charge-based mechanisms, which severely limit further miniaturization, write-speed scaling, and environmental robustness of silicon-based technologies. These limitations are particularly prohibitive for deep-space exploration, where extreme temperatures, ultra-strong magnetic fields, and intense radiation rapidly incapacitate conventional electronics without massive shielding. Here, we present an intrinsically resilient, strain-mediated antiferromagnetic MnIr/PMN-PT edge processor that operates reliably as a bare die under temperatures up to 500 K, magnetic fields of 55 T, and radiation doses of 1.5 Mrad. By exploiting an input-modulated in situ self-refreshing encoding mechanism, the device performs nonlinear feature extraction and classification directly from raw analog signals, enabling an analog computing architecture that requires no time-frequency transformation. This architecture achieves 99.8% accuracy in speech recognition without digital preprocessing and 100% accuracy in astronaut visual object recognition. Furthermore, an all-hardware integrated drone vision system demonstrates real-time in situ command execution and autonomous navigation, delivering a terahertz-level response frequency and an ultra-low energy consumption of approximately 0.2 fJ per operation. This work expands the functional scope of antiferromagnetic devices beyond memory and logic, establishing them as a promising materials platform for energy-efficient physical computing and autonomous intelligence in extreme environments.
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All authors Yu Liu, Zhuoting Han, Zexin Feng, Peixin Qin, Zhiyuan Duan, Yuhao Ye, Zengwei Zhu, Chengyan Zhong, Li Liu, Guojian Zhao, Wenbin Shen, Jingyu Li, Sixu Jiang, Xiaoyang Tan, Xiaoning Wang, Ziang Meng, Chengbao Jiang, Zhiqi Liu

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

High-fidelity geometric quantum gates exceeding 99.9% in germanium quantum dots

Yu-Chen Zhou, Rong-Long Ma, Zhenzhen Kong et al. (+11 more)

Achieving high-fidelity and robust qubit manipulations is a crucial requirement for realizing faulttolerant quantum computation. Here, we demonstrate a single-hole spin qubit in a germanium quantum dot and characterize its control fidelity using gate set tomography. The maximum control fidelities reach 97.48%, 99.81%, 99.88% for the I, X/2 and Y /2 gate, respectively. These results reveal that off-resonance noise during consecutive I gates in gate set tomography sequences severely limits qubit performance. Therefore, we introduce geometric quantum computation to realize noiseresilient qubit manipulation. The geometric gate control fidelities remain above 99% across a wide range of Rabi frequencies. The maximum fidelity surpasses 99.9%. Furthermore, the fidelities of geometric X/2 and Y /2 (I) gates exceed 99% even when detuning the microwave frequency by +-2.5 MHz (+-1.2 MHz), highlighting the noise-resilient feature. These results demonstrate that geometric quantum computation is a potential method for achieving high-fidelity qubit manipulation reproducibly in semiconductor quantum computation.
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All authors Yu-Chen Zhou, Rong-Long Ma, Zhenzhen Kong, Ao-Ran Li, Chengxian Zhang, Xin Zhang, Yang Liu, Hao-Tian Jiang, Zhi-Tao Wu, Gui-Lei Wang, Gang Cao, Guang-Can Guo, Hai-Ou Li, Guo-Ping Guo