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Physics Condensed Matter Mesoscale and Nanoscale Physics

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

Sunday 4 October

Mesoscale and Nanoscale Physics

From Nested Soliton Crystals to Skyrmion Crystals in Chiral Magnets

Sven Bjarke Gudnason and Muneto Nitta

We perform an exhaustive study of the parameter space of the chiral magnetic model with a Dzyaloshinskii-Moriya interaction, an in-plane anisotropy term and an out-of-plane Zeeman magnetic field. We map out the phase diagram for the model and find a chiral soliton lattice hosted on a chiral soliton lattice as the ground state in a particular corner of the phase diagram. There is a smooth crossover, as opposed to a phase transition, to the skyrmion crystal lattice phase. Finally, we also discover excited composite soliton states such as an anti-skyrmion coexisting with a bimeron or an anti-bimeron.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics

Deep learning enables large-scale inverse design of free-form metasurfaces

Viktor A. Lilja, Khosro Zangeneh Kamali, Mikael Käll et al. (+1 more)

Metasurfaces are ultrathin optical elements that control light through carefully engineered structures smaller than the wavelength of light, enabling compact devices with functionalities that are difficult to achieve with conventional optics. However, exploiting their full design freedom over large areas has been prohibited by the large computational cost of repeated electromagnetic simulations required for inverse design. Here we introduce a physics-tailored deep-learning surrogate model that exploits the locality and symmetries of electromagnetic interactions to generalize from small-scale simulations to metasurfaces orders of magnitude larger. The model captures nonlocal interactions while predicting optical fields more than four orders of magnitude faster than the conventional electromagnetic solver it is trained on, enabling gradient-based topology optimization under arbitrary illumination. We validate the approach through the inverse design and experimental realization of free-form metagratings with diffraction angles up to 75 degrees, as well as a millimeter-scale free-form holographic metasurface more than 1,000 wavelengths across and comprising 1.6 billion degrees of freedom. By decoupling the scale of electromagnetic simulation from the scale of inverse design, our approach enables system-scale free-form photonic devices that retain nanoscale design freedom.
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All authors Viktor A. Lilja, Khosro Zangeneh Kamali, Mikael Käll, Philippe Tassin

Mesoscale and Nanoscale Physics

Multi-bit Ferroelectric-NAND for High-throughput Massive Database Search

Prasanna Venkatesan, Tanvir H. Pantha, Po-Kai Hsu et al. (+28 more)

The growing demand for large-scale database search in data-intensive applications, ranging from proteomics to autonomous systems, has exposed fundamental limitations in von Neumann architectures due to memory bandwidth and energy constraints. Hyperdimensional (HD) computing offers a robust and parallelizable framework for such tasks, but its practical implementation remains challenged by high memory demands. Ultra-high-density, energy-efficient ferroelectric NAND (FE-NAND) memory provides a potential solution by enabling in-situ computation. We fabricate quad-level FE-NAND strings with wide memory windows, disturb resilience, and robust retention. Using these planar FE-NAND strings as building blocks, we experimentally demonstrate in-situ multi-level cell (MLC) dot product operations at the single-cell level and, using experimentally calibrated physics-based simulations, demonstrate Hamming similarity calculations between reference and query hypervectors (HV). This platform leverages the inherent error tolerance of HD computing to achieve >90% search accuracy even at high logic levels (TLC, QLC). When benchmarked on Open Modification Search (OMS) tasks in proteomics with TB-scale datasets, our system shows nearly 1,000x speedup and over 10,000x energy efficiency improvement compared to incumbent solutions. These results establish FE-NAND as a viable in-storage compute architecture for large-scale, high-dimensional data processing.
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All authors Prasanna Venkatesan, Tanvir H. Pantha, Po-Kai Hsu, Sumukh Pinge, Zheyu Li, Chinsung Park, Priyankka Ravikumar, Hari Jayasankar, Lance Fernandes, Weihong Xu, Zihan Xia, Flavio Ponzina, Keming Fan, Amrit Garlapati, Huy Tran, Taeyoung Song, Mengkun Tian, Hang Chen, Winston Chern, Kijoon Kim, Kwangyou Seo, Suhwan Lim, Kwangsoo Kim, Wanki Kim, Daewon Ha, Duygu Kuzum, Shimeng Yu, Mingu Kang, Tajana Rosing, Sourav Dutta, Asif Khan

Mesoscale and Nanoscale Physics

Nonlinearity-induced Topological Phase Transitions in One-dimensional Systems with Chiral Symmetry: A Real-Space Treatment

Liu Bi Tao, Shilpi Roy and Jiangbin Gong

Nonlinearity can induce topological phase transitions in periodic systems. It is hence of considerable interest to examine if such transitions persist in the absence of translational symmetry. We address this question directly in real space, using the periodic Su-Schrieffer-Heeger (SSH) chain as a reference for understanding the effect of quasiperiodicity. How nonlinearity drives a chain towards a topological phase transition is found to depend strongly on the strength of the quasiperiodic potential. As the nonlinearity strength increases, we find that weak quasiperiodicity supports a transition from a trivial to a topological phase, whereas the intermediate regime does not have a topological phase transition. Under strong quasiperiodicity, pronounced boundary localization can develop well before a nonlinearity-induced topological transition. Our results show how nonlinearity may interplay with a quasiperiodic potential in inducing topological phase transitions and that boundary localization of nonlinear eigenstates alone may not be taken as a clear signature of topological edge states.
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Saturday 3 October

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

Site-Specific Orbital Symmetry Breaking in Epitaxial Graphene on Silicon Carbide

Vinod K. Paidi, Yves Joly, Alex Taekyung Lee et al. (+5 more)

The epitaxial graphene grown on SiC interface has been the subject of tremendous research efforts to control its electronic transport properties in the quest for graphene electronic applications. The electronic structure of the epitaxial graphene buffer layer on SiC(0001) is investigated at the atomic scale using monochromated electron energy loss spectroscopy (EELS) in an aberration-corrected scanning transmission electron microscope (STEM). The C $K$-edge reveals spectral fine structures distinctly different from free-standing graphene layer, providing direct experimental evidence of a modified bonding environment. Ab initio calculations providing a site-resolved probe of orbital character to elucidate the origin of these spectral features: covalent bonding between one-quarter of the buffer-layer carbon atoms and the substrate silicon atoms induces partial $\mathrm{sp}^3$ hybridization, quenching the out-of-plane $\pi$ states and disrupting $\pi$-conjugation across the interfacial layer. Substrate-imposed symmetry breaking further lifts the in-plane orbital degeneracy. This orbital-engineering framework, rooted in $\pi$-state quenching and site-specific symmetry breaking, establishes a quantitative basis for tailoring graphene-substrate interfaces toward next-generation low-energy transistor applications.
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All authors Vinod K. Paidi, Yves Joly, Alex Taekyung Lee, Guillaume Radtke, Vlado K. Lazarov, Demie Kepaptsoglou, Quentin M. Ramasse, Matthieu Bugnet

Mesoscale and Nanoscale Physics

Anisotropic Friedel oscillations and isoperimetric transport in two-dimensional free lattice Fermi seas

Guillermo R. Zemba

Two physical consequences of the recent topological classification of 2d Fermi seas for free particles based on flat orbifolds $\mathbb{R}^2/\Gamma$ of discrete symmetry $\Gamma$, are explored. The first is a study of the spatial density behavior inside the mesoscopic window enclosed by the Fermi and (infinite) thermal lengths. It is shown that the single-particle density matrix exhibits a sharp directional anisotropy, encoding a real space diffraction pattern, i.e., a Fraunhofer-like diagram of the Fermi sea, that reveals the point-group symmetries of the background lattice $\Gamma$ in the form of anisotropic Friedel oscillations. As examples, the special cases of the $p4m$ and $p6m$ crystallographic flat orbifolds are treated in some detail. The second physical consequence is the establishment of an explicit geometric correspondence between momentum-space packing and electrical transport. A mean-field expression for the longitudinal electrical conductivity $\sigma_{xx}$ as a function of the isoperimetric parameter $\cal{I}$ of the occupied orbifold domain by utilizing geometric measure theory is presented, satisfiying the scaling law $ \sigma_{xx} \propto 1/\sqrt{\cal{I}}$. The topological transport formula naturally incorporates the vanishing conductivity ($\sigma_{xx} \to 0$) of the previously described “geometric insulators,” promoting the isoperimetric parameter as an efficient descriptor for topological and geometric phases in conductors.
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Mesoscale and Nanoscale Physics

Electron-phonon control of obstructed and quantum spin Hall topology in an altermagnet

Kuntal Bhattacharyya, Bilal Tanatar and Saurabh Basu

We theoretically demonstrate control over the interplay between obstructed atomic insulating and first-order topological phases via electron-phonon coupling (EPC) in a $d$-wave altermagnet (AM) that hosts nonrelativistic spin-split bands with zero net magnetization. By embedding a $d_{x^{2}-y^{2}}$-wave AM in a quantum spin Hall (QSH) insulator, we show that an altermagnetic order beyond a critical strength reconstructs the parent QSH state of a Bernevig-Hughes-Zhang (BHZ)-type topological insulator (TI) into an obstructed atomic insulator (OAI), characterized by nontrivial bulk polarization with quantized fractional corner charges, accompanied by characteristic in-gap boundary states, while the spin Chern number vanishes. Upon incorporating sufficiently strong EPC, the polaronic dressing reorganizes the Wannier centers and the associated effective edge topology, thereby weakening the altermagnetism-induced OAI phase and restoring the helical QSH edge modes. Further, EPC eventually drives the system into a trivial insulator. By uncovering a controllable switching mechanism between topologically distinct insulating phases in AMs, our study establishes a direct route toward phonon-tuned spintronic functionalities in unconventional magnetic platforms.
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Mesoscale and Nanoscale Physics

Spatiotemporal imaging of microwave magnetic fields via magnonic coherent splitting

C. K. Wei, Z. J. Chen, J. T. Song et al. (+7 more)

Spatiotemporal microwave magnetic-field imaging reveals current flow in high-frequency circuits and nonequilibrium spin dynamics, yet probes rarely combine calibrated spectral readout, optics-free operation and transient mapping at room temperature. Here ferrimagnetic order in yttrium iron garnet supports coherent coupling from a pump-induced magnon mode, converting target-field amplitude into a spectral splitting with all-microwave readout. Sampling the calibrated splitting over position and delay reconstructs spatiotemporal imaging of magnetic fields. Continuous-wave measurement reaches a sensitivity of 58 pT/$\sqrt{\mathrm{Hz}}$ and recovers phases across various powers. Combined with time-resolved frequency-comb spectroscopy, the method reconstructs transient fields with a 130-ns response time. Coplanar-waveguide imaging validates the magnetic selectivity of the mode-splitting readout, where measured maps agree with simulated magnetic-field distribution. In a microwave amplifier, our reconstruction resolves nonuniform switching dynamics and detects downstream field suppression from an open-contact fault. Magnonic coherent splitting provides a scalable route for optics-free imaging of spatiotemporal field evolution in functional devices.
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All authors C. K. Wei, Z. J. Chen, J. T. Song, S. H. Ma, W. H. Liu, J. H. Wu, Z. W. Huang, Jinwei Rao, Wei Lu, Bimu Yao

Mesoscale and Nanoscale Physics

Micromagnet engineering for enhanced addressability of donor-cluster arrays in silicon

Hao Wang, Baolong Zhao, Shihang Zhang et al. (+11 more)

Phosphorus donors in silicon are one of the promising platforms for fault-tolerant quantum computing, owing to their long coherence times and compatibility with complementary metal-oxide-semiconductor (CMOS) technology. However, a key bottleneck for scaling this platform lies in the independent addressability of individual spin qubits. Here, we present a scalable quantum processor architecture that integrates scanning tunneling microscope (STM)-defined phosphorus donor-cluster arrays with on-chip micromagnets. By generating magnetic field gradients, the micromagnets enable a broader addressable frequency range compared to the addressing scheme based solely on variations in hyperfine (HF) interactions, which arise from the randomness of intra-cluster configurations. Through micromagnetic simulations to optimize micromagnet geometry, we demonstrate that these structures are compatible with customized array designs, facilitating the integration of over 120 atomic spin qubits and enabling frequency multiplexing with a single microwave antenna, which greatly reduces the overhead of fan-out addressing lines. This design is further validated via magnetic measurements, which generally align with our micromagnetic simulations. These results establish a critical foundation for the development of scalable silicon quantum computing with atomic qubits.
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All authors Hao Wang, Baolong Zhao, Shihang Zhang, Ziliang Jin, Huan Shu, Peihao Huang, Guanyong Wang, Mingchao Duan, Tianluo Pan, Tao Xin, Guangchong Hu, Zhen Tian, Dapeng Yu, Yu He

Mesoscale and Nanoscale Physics · Cross-listed from hep-th

Wald entropy and Wen-Zee type gauge-curvature coupling in 2+1-dimensional gravity

Aryan Bhatia, Giandomenico Palumbo and Suraj S. Hegde

The Wen-Zee term is a mixed gauge-curvature coupling in the topological Chern-Simons description of a quantum Hall fluid, encoding the electric charge bound to spatial curvature. We investigate a Lorentz-covariant generalisation of this coupling, expanding its scope to black-hole spacetimes and determine its contribution to horizon entropy. Such a coupling arises naturally in three-dimensional Chern-Simons gravity based on the Maxwell algebra. We show that its Wald entropy contribution is a horizon boost charge, given by a loop integral of the additional gauge field projected along the tangent to the bifurcation circle. This contribution can be nonzero even when the mixed term vanishes on shell. We show that the integral admits an Abelian holonomy interpretation when the projection direction is covariantly constant. We evaluate the charge on a flat cosmological solution and, using smooth horizon fields and a specified thermal ensemble, on an AdS-Lorentz black hole. These results connect the geometric response familiar from quantum Hall physics to gravitational horizon thermodynamics.
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Friday 2 October

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

Distilling universal machine-learning potentials for moiré lattices across one million atoms

Thomas Huang, Yueyao Fan, Kaichen Xie et al. (+7 more)

Atomic reconstruction reshapes moiré materials across multiple scales, from local structure and polarization textures to global electronic topology, yet direct ab initio modeling becomes prohibitive for large superstructures such as marginal-twist-angle moirés and moiré-of-moirés. We develop MoiréMLIP by fine-tuning a universal atomistic model on the density functional theory labeled Moiré Kaleidoscope dataset, which spans transition metal dichalcogenide compositions, symmetries, stackings, and twist angles. MoiréMLIP reproduces ab initio reconstruction with force errors of 6–8\,meV/Å and transfers to smaller twist angles and unseen structures. Knowledge distillation yields MoiréMLIP-mini, which retains this accuracy while extending single-GPU inference to one million atoms. Applied to an alternate-twist MoTe$_2$ trilayer, it reveals a hierarchical polarization network spanning tens of nanometers arising from large moiré-cell distortions sharply localized along the moiré-of-moiré domain walls. These results overcome key accuracy, transferability, and scaling bottlenecks of existing atomistic models and enable predictive simulations across emergent moiré length scales.
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All authors Thomas Huang, Yueyao Fan, Kaichen Xie, Bolun Li, Kaijie Yang, Jenna A. Bilbrey, Eric Bylaska, Peter V. Sushko, Di Xiao, Ting Cao

Mesoscale and Nanoscale Physics

Exchange-controlled quantum beats and entanglement in an exciton–bimodal-cavity system

Cesar E. P. Villegas, Victor P. Brasil, Pedro A. S. Contri et al. (+2 more)

We theoretically demonstrate tunable population transfer and entanglement generation in a two-exciton system coupled to a bimodal optical cavity, including an exciton-exciton exchange interaction. By using dressed-state transformations and Löwdin partitioning, we derive effective Hamiltonians that identify three dynamical time scales: local polaritonic oscillations, long-period dressed-state beats, and direct excitonic exchange. We apply the framework to graphene nanoribbon excitons, using excitonic energies, transition dipoles, and lifetimes obtained from first-principles calculations to parameterize the model. In the small- and moderate-exchange regimes, the dynamics become multiscale, and the beat channel sustains sizable quantum entanglement over long dissipative time windows. In the large-exchange regime, the excitonic Hamiltonian dominates and drives nearly complete population transfer between excitonic states over many coherent cycles. The resulting analytical expressions provide direct design rules connecting the beat period, transfer amplitude, and coherent-cycle number to the exchange interaction, cavity detuning, and light–matter coupling. Our results establish a controllable route for engineering long-lived entanglement and coherent excitonic operations in exciton–bimodal-cavity systems.
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All authors Cesar E. P. Villegas, Victor P. Brasil, Pedro A. S. Contri, Kevin Lizárraga, Jonas Maziero

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

Studying the evolution of exchange and dipolar interactions and spin correlation in vdW magnet CrCl3 across magnetic phases

Prem B. Karki, Ayodimeji E. Aregbesola, Karishma Prasad et al. (+5 more)

Understanding quantum interactions in van der Waals magnets are critical to realizing their potential for next-generation magnetic, electronic, and spintronic applications. In this study, we investigated the evolution of exchange and dipole-dipole interactions in van der Waals magnet CrCl3 using multifrequency broadband (1-16 GHz) magnetic resonance on a bulk single-crystal CrCl3 sample. We found that the dipolar-broadened low-field resonance linewidth narrows due to exchange narrowing at higher resonance fields. Our findings show that the exchange interaction evolves exponentially as we lower the sample temperature from room temperature to 50 K. However, we found that the dipole-dipole interaction remains constant in the same temperature range. We have also detected the half-field magnetic resonance transition at room temperature, indicating a robust dipole-dipole interaction among spins. The measured inter-spin distance is 2.4(3) A at room temperature. The evolution of dipole interactions, the observation of half-field magnetic resonance, and the strong exchange interaction indicate short-range ordering/correlation in CrCl3 at temperatures far above the magnetic global ordering temperature. This study also demonstrates the significance and sensitivity of the multifrequency electron spin resonance technique for understanding quantum interactions and magnetic correlations in van der Waals magnetic materials.
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All authors Prem B. Karki, Ayodimeji E. Aregbesola, Karishma Prasad, Jonathan Skeels, Avani Inamdar, Pooja Kalal, Jian Wang, Kapildeb Ambal*

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

Energy-filtered readout preserves gap-enhanced sensing in interacting quantum dots

Shirwan Abdullah

A small excitation gap makes a quantum dot a sensitive probe of a weak electric field, but the charge detector that reads the probe can also excite it. We ask how much of this gap enhancement survives continuous readout, for two interacting electrons tuned through a confinement-driven crossover in a gate-defined quantum dot, using a weak-coupling, stationary two-level model. The answer depends on the energy structure of the detector, not only on its noise. A quantum point contact measures more strongly at higher bias, but once the bias energy exceeds the gap it also excites the probe. When this back-action dominates the probe's own relaxation, the optimised mean-current information rate grows only as the inverse of the gap. A sensor quantum dot with a narrow level instead reaches full measurement strength at a bias below the gap, where, for a non-interacting detector and to second order in the coupling, it cannot excite the probe at zero temperature. This energy-filtered readout keeps the inverse-square gap dependence of the quantum Fisher information, down to a gap set by the detector's level width and the electron temperature. Through such a detector the interacting pair gives about three times the information rate of a single electron with the same gap and detector, compared with 1.6-1.7 in the quantum Fisher information, for both contact and Coulomb-type interactions. These different gap dependences, and the different optimal biases of the two detectors, can be tested by bias and gate sweeps on suitably tuned charge-sensed double dots.
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Mesoscale and Nanoscale Physics

Escaping the Composite Fermi Sea: An Incompressible State at Half Filling in Graphene's Lowest Landau Level

Domagoj Perkovic, Ziwei Wang and Steven Herbert Simon

Recent experiments in monolayer and trilayer graphene have observed incompressible even-denominator fractional quantum Hall states within narrow regions of parameter space associated with crossings of zeroth Landau levels. This is surprising because at half filling the Coulomb interaction in the zeroth Landau level is expected to favour a compressible composite Fermi liquid. Here we provide the first quantitative energetic study of the candidate incompressible phases and of the microscopic mechanisms that can stabilise them near such Landau-level crossings. Using exact diagonalization and infinite density-matrix renormalisation group, we first study ultra-short-range corrections to the Coulomb interaction arising from finite layer separation, lattice-scale effects, and electron-phonon coupling. We find that a sufficiently strong attractive short-range interaction drives the composite Fermi liquid first into a weakly paired \(d\)-wave pseudospin-singlet state and subsequently into a strongly paired state. However, microscopic estimates of these short-range corrections are far too small to stabilise either incompressible phase. We then incorporate Landau-level mixing through screening within the random-phase approximation. Screening substantially reshapes the effective interaction, suppresses the weak-pairing regime, and strongly enhances the tendency toward strong pairing. For a realistic range of microscopic parameters, the strongly paired phase is stabilised over a substantial fraction of that range. Our results identify the interplay of Landau-level mixing and ultra-short-range interactions as a plausible microscopic mechanism for the experimentally observed incompressible states in monolayer and trilayer graphene and point toward a strongly paired composite-fermion phase as their candidate ground state.
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Mesoscale and Nanoscale Physics

Integrating spin glass dynamics into nanomechanical resonators

S.Y. Grebenchuk, T.M. Savilov, Y.W. Ho et al. (+15 more)

Spin glasses are non-equilibrium magnetic systems with pronounced slow relaxation, ageing, and chaotic, synaptic-like properties, whose unique history-dependent dynamics have remained difficult to harness in functional devices. Two-dimensional van der Waals spin-glass magnets offer a route to overcome this limitation by allowing controlled coupling between magnetic and mechanical degrees of freedom. Here, we demonstrate the integration of a spin-glass functionality in nanoelectromechanical systems (NEMS) using thin exfoliated NbFeTe$_2$ films, which establishes a robust spin-glass state down to a few tens of nanometer-thick layers. Using cryogenic magnetic force microscopy, we reveal characteristic slow, hour-scale macroscopic magnetic relaxation, associated with glassy reorganisation of its magnetic domain clusters. Incorporation of thin NbFeTe$_2$ into membrane resonators allows the transduction of this glassy magnetic domain relaxation into strain, shifting their mechanical resonance frequency. This provides a functional nanomechanical readout of spin-glass dynamics and establishes a versatile platform for integrating frustrated magnetism into NEMS.
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All authors S.Y. Grebenchuk, T.M. Savilov, Y.W. Ho, A.K. Grebenko, M. Kravtsov, J.M. Wolf, D.A. Litvinov, Z. Yang, P. Cai, S. Ramachandran, R. Duan, L. Zheng, B. Özyilmaz, G. Eda, E.J.G. Santos, M. Koperski, K.S. Novoselov, M. Šiškins

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

Layer-Asymmetry-Induced Topological Superconductivity in High-T$_c$ Bilayer Nickelates

Zhongyi Zhang, Congcong Le, Hoi Chun Po et al. (+3 more)

The recent discovery of high-T$_c$ superconductivity in bilayer nickelates has highlighted the crucial role of interlayer coupling and motivated proposals for dominant interlayer pairing. Whether such pairing can support topological superconductivity, however, remains unexplored. Here, we demonstrate that substrate-supported bilayer nickelate thin films can host an intrinsic time-reversal-invariant topological superconducting phase protected by diagonal mirror symmetry. Using a two-orbital model derived from first-principles calculations, we show that a modest layer-asymmetric potential and layer-staggered Rashba spin-orbit coupling drive the system into this topological phase over a broad parameter range with a dominant interlayer pairing. The nontrivial topology arises from a reversal of the pairing sign on one of the spin-split bonding Fermi surfaces and is characterized by a nonzero mirror winding number along the diagonal direction, as well as a Majorana Kramers pair at the [11] edge. The phase also features bulk gap nodes located slightly away from the diagonal directions, featuring chiral charge and zero-energy flat bands. We discuss experimental routes for realizing and tuning this phase. Our results establish high-T$_c$ bilayer nickelates as a promising platform for topological superconductivity, where tunable topological transitions and Majorana boundary modes can provide probes of unconventional pairing.
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All authors Zhongyi Zhang, Congcong Le, Hoi Chun Po, Jiangping Hu, Xianxin Wu, Shengshan Qin

Mesoscale and Nanoscale Physics

Electrostatic Doping of Moiré Superlattices Controls the Optical Fingerprint of a WSe_2 /Twisted Bilayer Graphene heterostructure

Houssem Eddine Hannachi and Sihem Jaziri

We theoretically investigate the optical response of the WSe2 monolayer vertically stacked on twisted bilayer graphene (tBG) under electrostatic doping. In this heterostructure, the doped moiré superlattice of tBG generates a spatially modulated electrostatic potential that couples to the electron and hole constituents of the WSe2 exciton through the screened Coulomb interaction, thereby providing a microscopic mechanism for exciton coupling to the charge-density landscape of the moiré Fermi sea. Focusing on twist angles below the magic angle (1.1{\deg}), where electronic correlations are strongly enhanced, we demonstrate that electrostatic doping induces pronounced modifications of the excitonic absorption spectrum, including the emergence of multiple satellite resonances. We show that these spectral features originate from the interplay between the exciton center-of-mass and internal degrees of freedom, together with doping-induced hybridization between Rydberg exciton states of different orbital symmetry. The calculated spectra are in good agreement with previously reported experimental observations and theoretical predictions. Our results establish electrostatic doping in tBG as an effective means of engineering excitonic states in adjacent semiconducting monolayers and provide a pathway toward novel optical sensor devices.
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Mesoscale and Nanoscale Physics

Complete Magnetic Hierarchy in Bichromatically Driven Unconventional Magnets

Pei-Hao Fu and Sayed Ali Akbar Ghorashi

We establish a general framework for engineering unconventional magnetism using bichromatic driving. We identify a sharp hierarchy: for a bichromatic drive with a generic even commensurate frequency ratio, the leading continuum $q$-wave magnet generates components only up to order $q-2$, whereas lattice higher-gradient terms supply the missing $q-1$ and $q$ parities and complete the hierarchy through order $q$. We explicitly illustrate this new revised hierarchy on a $d$-wave altermagnet irradiated by a circularly-linearly polarized light, and show that the asymmetry of the driving field is transferred to the light-dressed electronic structure, producing momentum-asymmetric dispersions beyond the static and single-frequency limits. We further show that this band asymmetry is absent in the leading continuum expansion and originates from higher-gradient lattice terms that are converted by the bichromatic drive into odd-in-momentum contributions. Extending the analysis to higher-order unconventional magnets, we further obtain complete magnetic hierarchies for all $q$-parity unconventional magnets. Our results establish bichromatic Floquet driving as a general route for generating mixed-parity magnetic hierarchies and dynamically engineering unconventional magnetism.
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Mesoscale and Nanoscale Physics

Beyond Pure Dephasing: Quantum Error Correction in Single Molecules Requires Multiple Spins

Matteo Mezzadri, Silvia Macedonio, Luca Lepori et al. (+5 more)

We propose multi-spin molecules as a viable architecture for fault-tolerant quantum computing. To this aim, we introduce a correction protocol handling both diagonal and off-diagonal errors, typically associated with dephasing and relaxation. The scheme is based on a hybrid encoding which combines dephasing-tolerant units suppressing the leading pure dephasing error into a multi-spin molecule implementing a multi-qubit code for residual off-diagonal errors. Our proposal leverages peculiar properties of molecular spins, i.e. the strong hierarchy between different errors and the possibility to engineer multi-spin molecules at the synthetic level. Moreover, it addresses the important issue of the loss of coherences in anharmonic systems subject to off-diagonal errors, which hampers their correction at the single spin level. Thanks to the huge suppression of dephasing by the first-level code, we numerically demonstrate the potential performance of this strategy even with a limited number of spins per logical unit.
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All authors Matteo Mezzadri, Silvia Macedonio, Luca Lepori, Emilio Macaluso, Francesco Albarelli, Richard E.P. Winpenny, Alessandro Chiesa, Stefano Carretta

Mesoscale and Nanoscale Physics

Plasmon modes in tilted three-dimensional nodal-ring semimetals. II. Vortex nodal ring

Ipsita Mandal

We investigate collective charge excitations in three-dimensional semimetals with dipole-like Berry-curvature (BC) profiles, focusing on vortex nodal-ring semimetals (VNRs) and Hopf semimetals (HSMs). The VNR hosts a continuous ring of dipole-like BC sources generated by its winding pseudospin texture, whereas the HSM hosts an ideal BC dipole. This allows us to examine how distinct realisations of dipole-like BC structure affect collective charge dynamics. While plasmon modes in $\mathcal{PT}$-symmetric nodal-ring semimetals (PTNRs) and their gapped cousins were studied in a companion work, arXiv:2609.35373, here we analyse the density response, Drude weights, dielectric function, and plasmon modes of VNRs and HSMs at low doping within the random-phase approximation. For VNRs, we consider untilted, in-plane tilted, and axially tilted systems. Although VNR and PTNR have identical energy dispersions, their distinct eigenstates introduce a toroidal-angle dependence in the band-overlap factor, yielding additional interband contributions for in-plane wavevectors and weak corrections to the screened plasmon frequencies. The toroidal Fermi surface also produces intrinsically anisotropic bare plasmons. In contrast, HSMs have isotropic bare plasmons, with anisotropy arising only through their interband response. Our results show that collective charge dynamics can distinguish different realisations of dipole-like BC structure and reveal pseudospin information beyond the single-particle dispersion.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Infrared Memory of a Majorana Shutter

Ali Vahedi

We study a finite-width Majorana shutter as a local, time-dependent scattering defect and determine which features of its infrared memory are insensitive to the microscopic spatial profile. For a smooth shutter, the zero-frequency scattering matrix is fixed by the integrated coupling, while finite-width corrections vanish in the long-wavelength limit. A time-dependent switch then produces an infrared Bogoliubov kernel whose singular part is controlled by the change in this scattering matrix. We examine the many-body response through three observables. The overlap of the pre- and post-shutter Gaussian vacua exhibits Anderson orthogonality, with an exponent set by the scattering angle. A lattice calculation of the post-quench quasiparticle number resolves its logarithmic infrared growth, reaching the predicted coefficient in the slow-switch test and reproducing the expected dependence on the scattering-angle change. When the entanglement cut passes through the shutter, the entropy follows the effective-central-charge description of a conformal defect, with parameter-free agreement at the percent level, improving for the wider shutter. When the shutter lies inside the interval, its contribution remains a subleading finite-size correction. A local bilinear correlator approaches the expected Majorana power law and shows no stable logarithmic amplitude. These results show that the same low-frequency scattering data control distinct global and spatial observables, while their infrared coefficients are not interchangeable. The remaining limits are also made explicit: the finite-memory correction to the continuum kernel and the controlled continuum limit of large-interval spatial entropy.
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Mesoscale and Nanoscale Physics

Evaluating Chern Topology in Discretized Brillouin Zones Using Bargmann Invariants

Swarup Sangiri and A Taraphder

We develop a finite-state geometric framework based on third-order Bargmann invariants for evaluating Chern numbers and characterizing local quantum-state geometry. Using gauge-invariant state overlaps, the framework evaluates the Chern number directly on discretized parameter spaces while retaining local geometric information through the phase-derived density and the complementary amplitude density, as well as signatures associated with changes in topological character. We apply the construction to the Qi–Wu–Zhang, $1/3$- and $1/4$-flux Hofstadter, SSH, and Rice–Mele models, including a rank-$2$ extension for isolated composite subspaces and applications to closed-loop and parameter-space topology. The resulting framework organizes Chern topology and local geometric information directly from finite-state data, providing a compact state-based description without relying on dynamical evolution.
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Mesoscale and Nanoscale Physics

Topological insulators on complex networks

Sunkyu Yu, Xianji Piao and Namkyoo Park

The landscape of topological insulators has expanded beyond its traditional domain of periodic lattices with short-range hopping. Related studies have explored topological phenomena under non-Euclidean geometries, disordered structures, and long-range hopping, progressively narrowing the gap between topological phases of matter and complex networks. Here we demonstrate that genuine complex networks, far beyond periodic lattices and their conventional variants, can themselves host topological insulating phases. By developing a nonconflicting design framework for multiple topological objectives, we realize topological insulators in high-degree Hofstadter lattices and across regular, small-world, and random networks. This generalization uncovers distinct network-specific features, including an expanded range of attainable topological characteristics, a degree-dependent transition from Hofstadter-type to Haldane-type Chern insulators, and, most notably, the superior robustness and reconfigurability of small-world topological insulators. Our graph-theoretic framework establishes network complexity as a resource for realizing high-capacity and reconfigurable topological insulators.
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Mesoscale and Nanoscale Physics

Extracting the anyon charge from shot noise in complex fractional quantum Hall edges

Jinhong Park and Christian Spånslätt

Shot-noise measurements with a quantum point contact provide a direct probe of the quasiparticle charge in Laughlin fractional quantum Hall (FQH) states. However, the interpretation of such measurements becomes more subtle for multichannel edges, where the point-contact tunneling noise coexists with noise generated by intermode equilibration and heating. We develop a general framework that incorporates both these contributions and apply it to the paradigmatic $\nu=2/3$ FQH edge. We derive expressions for the drain auto- and cross-correlations in a four-terminal QPC geometry and show that equilibration-induced heating affects the auto- and cross-correlations in parametrically different way than the intrinsic partition noise. This distinction permits us to propose a specific combination of the two correlations which strongly suppresses the heating contribution and fully recovers the tunneling quasiparticle charge. Our results thereby provide a systematic framework for interpreting shot-noise measurements in complex FQH edges and can be further extended to more general counterpropagating edge structures.
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Thursday 1 October

Mesoscale and Nanoscale Physics

Surface scalar plasmons on curved interfaces: a venue for analogue gravity

Matheus E. Pereira

We investigate whether the geometry of a curved conductor–dielectric interface can modify the effective mass and propagation of scalar surface plasmons (SSPs). In the hydrodynamic limit, we describe SSPs as density perturbations in a semiclassical jellium electron gas. Using a thin–layer dimensional reduction procedure, we derive a massive Klein–Gordon equation for SSPs on the curved interface with a geometric potential. We find that under specific conditions, the geometric potential allows SSP propagation with a vanishing effective mass. We then apply the formalism to a well known analogue black hole configuration, determining the corresponding quasinormal mode frequencies. Our results show that interface curvature provides a geometric handle on plasmon propagation and localization, suggesting new possibilities for plasmon transport and analogue gravity experiments with surface plasmons.
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Mesoscale and Nanoscale Physics

Quantum materials QED with van der Waals crystals

Suheng Xu, Brian Vermilyea, Ran Jing et al. (+19 more)

A central goal of the emerging field of materials QED is to harness subwavelength electromagnetic confinement in engineered cavities to tailor light-matter interactions. Here, we demonstrate that van der Waals multilayer cavities composed of stacked graphene and hexagonal boron nitride (hBN) provide unprecedented control over hybridization between their electromagnetic resonances. By magnetically tuning graphene inter-Landau-level transitions (ILTs) into resonance with hBN phonons, we witness broadband, mode-selective strong coupling in the mid-infrared. Our quantum-material QED framework shows that cavity geometry and layer placement jointly control both coupling strength and modal selectivity. For experimentally realistic cavity parameters, the predicted mode splitting exceeds the width of the hBN Reststrahlen band, providing a direct route to the ultrastrong coupling regime. Together, these results establish van der Waals multilayer cavities as a scalable platform for tunable multimode QED and broaden the design space for reconfigurable quantum materials.
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All authors Suheng Xu, Brian Vermilyea, Ran Jing, Lukas Wehmeier, Jihoon Park, Rafael A. Mayer, Xinzhong Chen, Samuel L. Moore, Fuyang Tay, Boyi Zhou, Wenjun Zheng, Dihao Sun, Birui Yang, Cory R. Dean, Daniel Cazorla, Xu Du, Milan Delor, Andrew J. Millis, Angel Rubio, Michael M. Fogler, Mengkun Liu, D. N. Basov

Mesoscale and Nanoscale Physics

Magnetic-field response of generalized Wigner crystals in twisted MoTe$_2$

F. K. Wolff, S. Jiao, H. Park et al. (+9 more)

We report a magnetotransport study of fractional hole-filling states in the layer-polarized regime of a twisted MoTe$_2$ homobilayer. A perpendicular magnetic field suppresses the resistance peak at the two-thirds filling while enhancing the one-third peak by several orders of magnitude. Both remain near their commensurate densities. We argue that these commensurate states are generalized Wigner crystals whose distinct charge configurations define different magnetic lattices, leading to contrasting responses to spin polarization. Near half filling, we observe a qualitatively different state whose resistance maximum shifts approximately quadratically with field and exhibits pronounced transport anisotropy consistent with a stripe phase. These results reveal a strong dependence of magnetotransport on fractional filling and open a route to magnetic control of transport in moiré charge-ordered states.
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All authors F. K. Wolff, S. Jiao, H. Park, J. Cai, E. Anderson, X. Liu, C. Wang, T. Taniguchi, K. Watanabe, X. Xu, D. Xiao, S. Vaitiekėnas

Mesoscale and Nanoscale Physics

Highly Tunable Photon-Magnon Coupling Governed by Collective-Mode Profiles in Reconfigurable Dielectric-Resonator Arrays

Shihao Zhou, Edward Kwao, Junming Wu et al. (+7 more)

The spatial structure of a microwave photon mode provides a degree of freedom for controlling its interaction with a localized magnetic excitation. We demonstrate site-selective magnon-photon coupling in modular arrays of discrete dielectric resonators mounted on a common microstrip line. The resonators can be added, removed, or rearranged on the same completed PCB, enabling post-fabrication geometrical reconfiguration of the collective photon modes and their nodal structure. A YIG sphere is positioned successively above individual resonators, while an in-plane magnetic field tunes its Kittel mode through the collective photon resonances. In a three-resonator array, modes with finite local microwave magnetic fields hybridize with the magnon at every measured site, whereas a mode containing a central field node exhibits no resolvable splitting when the sphere is positioned at that node. Full-wave simulations and a coupled-mode model show that the interaction is governed by the local amplitude of the collective photon mode rather than by spectral resonance alone. Extending this local-node selection rule to a five-resonator array successfully predicts the measured position-dependent coupling patterns. These results establish post-fabrication control of spatial magnon-photon hybridization and provide a route toward reconfigurable magnonic interfaces in future hybrid quantum microwave architectures.
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All authors Shihao Zhou, Edward Kwao, Junming Wu, Abhijit Shinde, Yin Lyu, Rene Lopez, Wencan Jin, Yi Li, Binbin Yang, Wei Zhang

Mesoscale and Nanoscale Physics

Chiral Vacuum Engineering of Quantum Hall Matter

Kiran M. Kulkarni, Andrey Baydin, Motoaki Bamba et al. (+3 more)

We reveal that a chiral cavity distinguishes the resonant and antiresonant interactions between a two-dimensional electron gas and the cavity vacuum. For co-rotating helicities, the modes anticross, exhibiting vacuum Rabi splitting, and retain a bare vacuum ground state. For counter-rotating helicities, the modes cross, acquiring vacuum-mediated energy shifts and a two-mode squeezed ground state. We trace the origin of these observations to the SU(2) and SU(1,1) symmetries of the respective Hamiltonians and present their spectroscopic signatures in chiral photonic crystal cavities. We further predict that cavity chirality produces a handedness-dependent correction to Hall resistivity at finite polariton broadening, while such a correction is not present in an achiral cavity. For the longitudinal resistivity, we find an asymmetric response of the Shubnikov–de Haas oscillations for the different helicities. Finally, we present an experimentally accessible route for detecting the squeezed ground state through current fluctuations. Parameters based on a recently demonstrated terahertz chiral cavity place these effects within experimental reach.
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All authors Kiran M. Kulkarni, Andrey Baydin, Motoaki Bamba, Junichiro Kono, Ceren B. Dag, Vasil Rokaj