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Physics Condensed Matter Mesoscale and Nanoscale Physics

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

Sunday 27 September

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

In-plane optimal qubit operation with control fidelities exceeding 99 %

Yu-Chen Zhou, Zhenzhen Kong, Rong-Long Ma et al. (+9 more)

Hole spin qubits based on semiconductor quantum dots are promising for building future large-scale quantum computers owing to their all-electrical manipulation. However, abundant physical mechanisms of valence band holes lead to anisotropic qubit properties. There is an opportunity to prolong the coherence time and achieve high-fidelity qubit manipulations. Here, we report a single-hole spin qubit in a planar germanium quantum dot and investigate its anisotropic susceptibility to charge noise under an in-plane magnetic field. By correlating the longitudinal spin-electric susceptibility with qubit coherence and control performance, we identify an optimal operating point where the sensitivity to charge noise is minimized. We find that optimizing the magnetic-field orientation reduces the spin-electric susceptibility, resulting in a five-fold enhancement of the Hahn-echo coherence time and a nearly tenfold suppression of control infidelity. At the optimal operating point, gate set tomography demonstrates the maximum gate fidelity of 99.82 %. Our finding enhances the prospects of hole spin qubits for scalable quantum information processing.
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All authors Yu-Chen Zhou, Zhenzhen Kong, Rong-Long Ma, Hao-Tian Jiang, Ao-Ran Li, Yang Zhong, Zhi-Tao Wu, Rui Zheng, Gui-Lei Wang, Gang Cao, Hai-Ou Li, Guo-Ping Guo

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

Unifying Magnetic, Electrical, and Thermoelectric Responses in a Non-Collinear Antiferromagnet

André José, Adrielson Dias, Carlos Eduardo et al. (+6 more)

Non-collinear antiferromagnets offer unconventional routes for controlling magnetic, electrical, and thermoelectric responses through their complex spin configurations and interfacial symmetry. Here, we detect exceptional interfacial properties arising from a non-collinear antiferromagnet by demonstrating a robust and quantitatively consistent exchange-bias response in an IrMn$_3$/Py heterostructure. The system consists of a 10 nm IrMn$_3$ layer coupled to a 5 nm permalloy (Py) film. Longitudinal magneto-optical Kerr effect (MOKE), anisotropic magnetoresistance (AMR), and anomalous Nernst effect (ANE) measurements independently reveal the same unidirectional field shift of approximately 50 Oe, together with a consistent cosine angular dependence. The simultaneous observation of these signatures establishes a direct correspondence between the interfacial magnetic symmetry imposed by the non-collinear antiferromagnet and the responses of the adjacent ferromagnet. This symmetry is manifested consistently in magnetization reversal, charge transport, and thermally driven voltage generation, demonstrating that the exchange-bias imprint is not restricted to a single experimental observable. Our results reveal a coherent multifunctional response of IrMn$_3$/Py and extend the conventional understanding of exchange bias beyond collinear antiferromagnetic systems. More broadly, they demonstrate the potential of non-collinear antiferromagnets as platforms for coupling magnetic, electrical, and thermoelectric functionalities in spintronic and spin-caloritronic devices.
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All authors André José, Adrielson Dias, Carlos Eduardo, Giovanna Celly, Luiza Paffer, José Araújo, José Laurentino, Monalisa Cavalcante, José Holanda

Saturday 26 September

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

Electro-Thermal Origins of Enhanced Performance and Scalability in Disc-Type Phase-Change Memory

Ghazi Sarwat Syed, Loris Coccia, Siddharth Gautam et al. (+2 more)

Disc-type phase-change memory is a promising device architecture for analog in-memory computing, enabled by the unique physical properties of ultra-thin phase-change materials and the device geometry. In this study, we develop a comparative analytical framework using compact electro-thermal models to examine the state dependent readout and programming behavior of these devices. The framework provides insight into the fundamental physical mechanisms responsible for their enhanced functionality and highlights promising directions for further device optimization and performance improvement.
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All authors Ghazi Sarwat Syed, Loris Coccia, Siddharth Gautam, Vara Prasad Jonnalagadda, Abu Sebastian

Mesoscale and Nanoscale Physics

Finite-temperature phase transitions across spin symmetries in two-dimensional magnets

Chen Chen, Moritz A. Goerzen, Megha Arya et al. (+3 more)

Recent advances in intrinsic two-dimensional (2D) magnets have created a need for a unified understanding of finite-temperature phase transitions across different spin-symmetry classes. Here, we investigate finite-temperature magnetism in the classical 2D Heisenberg model using large-scale Monte Carlo simulations, continuously spanning the easy-plane, isotropic, and easy-axis regimes. We find that characteristic temperatures are strongly affected by the interplay of finite-size effects and spin symmetry, induced by magnetocrystalline anisotropy, being most pronounced in the isotropic Heisenberg regime and substantially reduced toward the easy-plane and easy-axis limits. Examining Berezinskii–Kosterlitz–Thouless (BKT) physics in the easy-plane regime, we find that the characteristic temperatures independently estimated from the magnetization and heat capacity deviate significantly from those proposed by BKT theory, but match a previously reported anomaly in the XY-model. We report that characteristic temperatures instead are correlated with the proliferation of vortex-antivortex pairs, suggesting the gain in entropy by their accelerated nucleation as the origin of the anomaly. Establishing this connection both theoretically and numerically, we argue that the thermodynamic characteristic temperature in finite easy-plane Heisenberg magnets, including the deviation from BKT theory, is subject to the interplay between finite-size spin correlations and vortex proliferation. These results clarify how experimental and technologically relevant temperature scales evolve with magnetic anisotropy, spin symmetry, and system size in finite 2D magnets.
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All authors Chen Chen, Moritz A. Goerzen, Megha Arya, Lionel Calmels, Yongping Du, Dongzhe Li

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

Wide-Mass-Scanning-Range Setup and Phase-Resolved Protocol for Axion Dark Matter Detection

A. Cottet and T. Kontos

We propose a paradigm for quantum enhanced axion dark matter search, which does not rely on power measurements. We propose to measure directly the axion amplitude and phase in an interferometric protocol at the quantum limit, using a non-linear cavity. In addition, we introduce gyromagnetic modes as wide mass range transducers for axion signals compatible with standard haloscope designs. We expect this scheme to offer an improvement of at least 4 orders of magnitude in figure of merit and at least 2 orders of magnitude in mass window with respect to standard haloscopes. Owing to its generality, our proposed protocol has the potential to speed up axion search but also the search for dark photons or other cosmological objects, such as galactic masers.
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Mesoscale and Nanoscale Physics · Cross-listed from math-ph

Absolute and relative invariants for low-dimensional topological insulators

Federico Manzoni, Domenico Monaco and Gabriele Peluso

[An extended abstract is provided in-text] Motivated by topological insulators, this paper analyzes classification schemes for projection-valued maps on $d$-dimensional tori, $d \le 2$, subject to Altland-Zirnbauer-Cartan (AZC) symmetries (time-reversal, particle-hole, and chiral). The main objective is to compare three notions of equivalence for these maps: Murray-von Neumann, unitary, and homotopy equivalence. The analysis relies on constructing symmetric bases for the projection ranges under a pseudo-periodicity constraint, where select basis vectors pick up a phase when looped around the torus. If $d=1$, fully periodic symmetric bases exist across all AZC classes. If $d=2$, topological obstructions appear as non-trivial phases characterized by $\mathbb{Z}$ (Chern number) or $\mathbb{Z}_2$ (Fu-Kane-Mele) invariants. These serve as absolute invariants that classify both Murray-von Neumann and unitary equivalences. For homotopy equivalence, the behavior depends on the ambient Hilbert space: if this has non-minimal dimension, homotopy equivalence reduces directly to unitary equivalence, while in minimal ambient spaces additional relative homotopy invariants emerge. Their precise values change under unitary conjugation, leaving only relative topological phases between maps well-defined. Ultimately, this provides a unified geometric framework for gapped quantum systems in low dimensions, demonstrating how distinct equivalence relations generate specific absolute and relative topological invariants.
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Mesoscale and Nanoscale Physics

Electrically switchable one-dimensional quadrupolar excitons in lateral double heterojunctions

Ryo Kitaura

Two neighboring lateral interfaces provide a spatial degree of freedom for controlling one-dimensional charge-transfer excitons within a single semiconductor monolayer. We investigate a type-II WS2-MoS2-WS2 double heterojunction using an effective-mass two-particle Hamiltonian with a screened Coulomb interaction. For equivalent left and right interfaces at zero electric field,inter-interface coupling produces energetically split even- and odd-parity exciton states, each with zero permanent dipole. An electric field perpendicular to the interfaces continuously converts the lower state from a quadrupolar superposition with a quadratic Stark shift into a predominantly single-interface dipolar exciton with an approximately linear shift. The spatially resolved calculation gives binding energies of approximately 104 and 100 meV, a doublet splitting of 4.6 meV, and a crossover field of 0.87 V/um for a representative 1.5-nm MoS2 strip. Projection tests show that the lowest doublet controls the response near this crossover. Strip width tunes the coupling much more strongly than the binding energy, providing geometric control of the low-field Stark sensitivity. These results establish a continuum-model route to electrically reconfigurable one-dimensional quadrupolar excitons.
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Mesoscale and Nanoscale Physics

Helicity-Controlled Hall Transport in Hybrid Topological Magnetic Textures

Anton V. Hlushchenko, Julia Kharlan, Mykhailo I. Bratchenko et al. (+3 more)

Topological magnetic textures can serve as information carriers driven by spin currents. However, their motion is generally accompanied by a Hall effect that deflects them from the current direction, limiting transport efficiency and controllability. We develop a unified spin-space transformation framework enabling a systematic study of hybrid spin textures with different helicities, such as skyrmions, antiskyrmions, bimerons, and antibimerons. Combining analytical theory with micromagnetic simulations, we establish the relation between helicity and current-driven transport. An analytical solution of the generalized Thiele equation identifies helicity as a geometric control parameter and yields a simple expression for the Hall angle, enabling its continuous tuning, complete suppression, and deterministic steering along arbitrary in-plane directions. Micromagnetic simulations confirm that the generated spin textures remain stable under Landau–Lifshitz–Gilbert dynamics and validate the analytical predictions. These results establish helicity as a versatile control parameter for programmable transport of topological magnetic textures.
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All authors Anton V. Hlushchenko, Julia Kharlan, Mykhailo I. Bratchenko, Aleksei V. Chechkin, Jarosław W. Kłos, Oleg A. Tretiakov

Mesoscale and Nanoscale Physics

Enhancing magnonic frequency combs via geometric nonlinearity

Yushun Fang and Weichao Yu

Magnonic frequency combs (MFCs) generated via internal magnetic nonlinearities have exhibited rich physics beyond their optical counterparts. However, existing approaches rely on dynamic nonlinearity, which typically demands high power thresholds and stringent momentum conservation. Here we show that the geometric nonlinearity intrinsic to magnetic systems, originating from the unit-norm constraint of the magnetization vector, can serve as an independent nonlinear resource for MFC generation. Through transverse Floquet engineering, this geometric constraint converts a transverse drive into a longitudinal parametric modulation. In the low-frequency limit, the four-particle process reduces to an effective two-magnon modulation, enabling low-threshold comb generation in the linear regime, with the modulation amplitude scaling quadratically with the driving field and enhanced flatness arising from geometric harmonics. These results provide a deeper understanding of frequency combs and magnon nonlinear interactions, and offer a new theoretical foundation for enhancing MFC performance.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics

Geometry-Controlled Polarization Photocurrents in Scalable PtSe2 Infrared Pixels

Eunice Y. Paik, Owen A. Vail, Madaline R. Marland et al. (+11 more)

Polarization-sensitive photodetectors provide multi-dimensional optical information beyond the capabilities of traditional intensity-based detectors. The noble metal dichalcogenide PtSe2 presents unique opportunities for tunable polarization detection due to its strong spin-orbit coupling, material stability, customizable broadband polarization responses, and direct compatibility with a wide range of substrates for back-end-of-line silicon integration. In this work, we demonstrate room-temperature near-infrared to mid-wavelength infrared polarization photoresponses using scalable, as-grown, wide-area PtSe2 films, and we show that the measured polarization response is reshaped by device geometry. Finite-element current-flow simulations reproduce the observed spatial redistribution of the polarization-sensitive response and localize the transverse polarization response near the pixel center. This geometry-enabled separation allows wavelength-dependent laser spot scans to distinguish symmetry-allowed photocurrents from contact-proximate, dichroism-mediated photothermal contributions. At near-infrared wavelengths, we observe spatial response that is consistent with linear-dichroic photothermoelectric currents, whereas mid-wavelength infrared measurements reveal a helicity-dependent photothermal contribution under oblique illumination. These results identify pixel boundary engineering as both a design lever and a diagnostic tool for scalable PtSe2 polarization-sensitive infrared pixels.
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All authors Eunice Y. Paik, Owen A. Vail, Madaline R. Marland, William A. Beck, Antonio Llopis-Jepsen, Wendy L. Sarney, Jeffery H. Leach, Stefan Heiserer, Nikolas Dominik, Cormac Ó Coileáin, Paul B. Seifert, Georg S. Duesberg, Blair C. Connelly, George J. de Coster

Mesoscale and Nanoscale Physics

In-Memory AM Demodulation Using an All-Silicon Independent-Dual-Gate Gain-Cell Memory with $<10^{-22}$ A Leakage Determined by Single-Electron Counting

Katsuhiko Nishiguchi, Toshiaki Hayashi, Kensaku Chida et al. (+3 more)

Ultra-low-leakage memories are attracting increasing attention for in-memory sensing and computing. However, achieving sufficiently long retention in silicon memories for analog signal processing remains challenging because of leakage through the access transistor. In this work, we demonstrate an all-silicon independent-dual-gate memory whose leakage current, inferred from single-electron counting statistics, is below $10^{-22}$ A, giving a measured retention time exceeding 1000 s. Owing to the extremely low leakage, the subthreshold nonlinearity of the access transistor can be exploited without disturbing the stored charge, enabling in-memory amplitude-modulation (AM) demodulation. The proposed memory provides a CMOS-compatible platform for ultra-low-power signal processing and in-memory sensing.
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All authors Katsuhiko Nishiguchi, Toshiaki Hayashi, Kensaku Chida, Takase Shimizu, Gento Yamahata, Seiya Kasai

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

Temperature Dependent Evolution of the Electronic Structure in EuZn2As2 across the Neel Transition

Milo Sprague, Anup Pradhan Sakhya, Barun Ghosh et al. (+8 more)

Magnetoresistive materials have been tremendously important for the development of magnetic memory storage and spintronic devices. Recently, the antiferromagnetic EuX2Pn2 compounds, with X being a transition metal and Pn being a pnictogen, have seen intensive research interest due to their unusual anomalous Hall effect behavior and pronounced resistive anomaly near the Neel temperature (TN). These magnetotransport phenomena have been interpreted in the context of shortranged ferromagnetic Structuations, magnetic polaron formation, canted spin configurations, and temperature dependent metal insulator transitions in the electronic structure. Here, we report the observation of such a pronounced resistivity anomaly in EuZn2As2 near TN = 19 K. We demonstrate the suppression of this anomaly using applied magnetic fields, both in plane and out of plane. To further interpret the origin of the observed transport behavior, we studied the temperature dependent electronic structure using combined angle resolved photoemission spectroscopy (ARPES) and first principles density functional theory (DFT) calculations, which exhibits limited modifications to the bands across TN away from the Fermi energy. This lack of involvement of the electronic structure indicates a spin-scattering origin of the aforementioned transport properties, rather than a reconstruction of the Fermi surface.
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All authors Milo Sprague, Anup Pradhan Sakhya, Barun Ghosh, Mazharul Islam Mondal, Arun K. Kumay, Himanshu Sheokand, Kapil Gope, Tetiana Romanova, Dariusz Kaczorowski, Arun Bansil, Madhab Neupane

Friday 25 September

Mesoscale and Nanoscale Physics

Magnetic Q-balls

A.J. Balseyro Sebastian, Keisuke Ohashi and Muneto Nitta

We study charged soliton branches in quasi-one-dimensional chiral magnetic systems with Dzyaloshinskii–Moriya (DM) interaction, easy-axis anisotropy, and Zeeman coupling. The same static magnetic functional is equipped with two different dynamical completions: an antiferromagnetic model with second-order time derivatives and a ferromagnetic model with Berry-phase dynamics. On the helical branch selected by the static DM interaction, the problem reduces to an analytically tractable one-dimensional system for the polar angle of the order parameter. We derive the existence conditions for polar Q-balls from the curvature of the reduced effective potential and the presence of a nonzero turning point. In the antiferromagnetic case, the allowed frequency window is symmetric and can be completely closed by the combined effect of the DM coupling and the Zeeman field. At zero Zeeman field, the same reduction also supports antiferromagnetic Q-kinks, for which we obtain explicit profiles, charges, energies, and reduced-sector fission criteria. In the ferromagnetic case, the Berry phase makes the rotation frequency act as a shifted Zeeman field. As a result, north- and south-pole charged droplets are selected by opposite signs of the shifted rotation. We also show that a formal pole-to-pole solution of the ferromagnetic mechanical problem does not generally correspond to a finite-energy magnetic soliton, because the Berry term does not renormalize the physical Hamiltonian. These results clarify how charged-soliton mechanisms depend on the underlying magnetic dynamics, even when the static chiral energy is the same.
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Mesoscale and Nanoscale Physics

Nanodiamond Sensing of Stray Fields during Domain Reversal

Kin On Ho, Hamza Abudayyeh, Andrew Perez et al. (+6 more)

Quantitative measurement of nanoscale stray magnetic fields during domain reversal is important for understanding and optimizing magnetic memory and logic devices. Yet, achieving high spatial resolution with minimally invasive probes remains challenging. Here we demonstrate nanodiamonds (NDs) hosting an ensemble nitrogen vacancy (NV) centers as local quantum sensors of domain-reversal stray fields in a CoFeB strip. During magnetic-field-driven reversal, the ND sensors resolve three distinct local responses depending on their positions relative to the strip: a positive frequency jump at the edge, an unexpected negative jump just outside the strip, and a negligible change near the center. These contrasting signals are quantitatively explained by magnetostatic boundary fields from micromagnetic simulations. We further implement a fully constrained fitting procedure for optically detected magnetic resonance spectra, enabling robust field extraction even when resonances are partially resolved. Together, these results establish NV-ND magnetometry as a simple, transferable, and quantitative approach for characterizing spatially heterogeneous magnetic fields in thin-films and spintronic devices.
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All authors Kin On Ho, Hamza Abudayyeh, Andrew Perez, Hui-Ping Chang, Liang Juan Chang, Junwei Tong, Can Cui, Jean Anne C. Incorvia, Xiaoqin Li

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

Quantum Geometric Origin of Yu-Shiba-Rusinov States

Rui-Xing Zhang

In this work, we revisit the classic Yu-Shiba-Rusinov (YSR) problem of magnetic impurities in $s$-wave superconductors and uncover a quantum geometric origin of the YSR bound-state structure. The key geometric quantity is the momentum-space average of Bloch band projector over low-energy electrons, whose matrix rank, positive eigenvalues, and corresponding eigenvectors directly control the number, energies, and symmetry representations of the YSR states, respectively. As a result, a superconductor with nontrivial normal-state quantum geometry can host more bound states than its trivial counterpart, even if they share the same electronic dispersion. We apply our theory to monolayer $1H$-NbSe$_2$ and find that the geometric texture of its single superconducting band enforces three symmetry-distinct YSR channels for a magnetic point impurity at Nb or Se sites. Our work opens a route to probing normal-state wavefunction geometry through local YSR spectroscopy.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.str-el

Emergent low-energy many-body Hilbert spaces in Chern bands

Chen-Xin Jiang, Zi-Xiang Hu and Bo Yang

We show that in Landau levels and more generic Chern bands, the most relevant many-body subspace selected by realistic two-body interactions alone (e.g., in the limit of vanishing bandwidth and band gap) depends strongly on the particle density and can be constructed systematically. Using the well-defined hierarchical structure of conformal Hilbert spaces (CHS), each with a highest-density vacuum state, we compute, for both fermionic and bosonic systems, the many-body quantum metric that quantifies the interaction energy scales of these subspaces. For a large family of short-range, Coulomb-based interactions, particles preferentially occupy the many-body states in the smallest accommodating CHS. This allows us to describe the low-energy physics of the interacting system in terms of the appropriate anyonic degrees of freedom. Our results also explain why, in any Chern band (in lattice or continuum systems), band mixing tends to be suppressed even in the limit of strong interaction; this suppression is stronger when the band deviates less from the ideal trace condition and when the two-body interaction is shorter-ranged.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.str-el

Quantum Representation Selects Neutral Skyrmion Molecules

Vishnu Jejjala

Skyrmions experience a sideways gyroscopic force when they move. Bound molecules can cancel this force; we call them gyroscopically neutral. We show that the quantum states available on each site of a magnet select the composition needed for cancellation. In two models of $SU(3)$ magnetism, this composition changes from a pair to a trimer. Both models assign exactly the same energy to every configuration of their common classical order parameter, isolating the effect of the local quantum states. Neutral molecules can also unwind when additional local states are allowed. Mean field calculations nevertheless find both compositions bound and locally stable, with the neutral trimer surviving sampled interaction changes. Comparing their motion reveals the changed cancellation rule, and prepared neutral molecules translate over short distances with little deformation.
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Mesoscale and Nanoscale Physics

Emergent frustrated magnetism in strain-patterned graphene

Yu-Chiang Hsieh, Wen-Han Kao, Christophe De Beule et al. (+18 more)

Geometrically frustrated magnetism conventionally arises from pre-existing magnetic moments on lattices whose geometry prevents their interactions from being simultaneously satisfied, giving rise to highly degenerate states and rich collective behavior. Creating such frustration in an intrinsically non-magnetic material presents a fundamentally different challenge, requiring both the magnetism and the competing interactions to emerge from correlated electrons. Here we show that this can be realized in graphene through lithographically programmable strain engineering. Patterning strain and the associated pseudo-magnetic field (PMF) into superlattices creates a correlated electronic system with flat bands and strong interactions. Transport measurements reveal interaction-driven insulating behavior, anisotropic magnetic hysteresis, and slow relaxation dynamics reminiscent of spin freezing, qualitatively captured by Monte Carlo simulations of competing magnetic moments on the PMF-defined ruby superlattice. Cryogenic magnetic force microscopy further reveals magnetic textures associated with the PMF landscape. These observations demonstrate frustrated magnetism emerging from correlated electrons in otherwise non-magnetic graphene. Our results establish lithographic strain engineering as a general and scalable route to flat bands and correlated states in van der Waals materials, providing a versatile platform for programmable quantum matter.
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All authors Yu-Chiang Hsieh, Wen-Han Kao, Christophe De Beule, Sheng-Zhu Ho, Ru-Long Gou, Bo-Nian Chen, Kuan-Yu Chou, Kuo-En Chang, Chin-Chia Chang, Ying-Mei Yang, Ching-Hua Kao, Hao-Chien Chiang, Jyun-Lin Chen, Sheng-Chin Ho, Kenji Watanabe, Takashi Taniguchi, Ming-Hao Liu, Ching-Hao Chang, Yi-Chun Chen, Ying-Jer Kao, Tse-Ming Chen

Mesoscale and Nanoscale Physics

Rydberg excitons in core-shell nanostructures II. Plasmon-exciton interaction and enhancement

David Ziemkiewicz, Gerard Czajkowski and Sylwia Zielińska-Raczyńska

Interaction between Rydberg excitons in core-shell Cu$_2$O nanostructures and surface plasmons is investigated. An enhancement of a quadrupole transitions to the Rydberg exciton states in copper oxide plasmonic nanaostructures is examined. A possibility of a modification of plasmonic enhancment (i.e., an average amplification factor) of electric field distributions in the vicinity of nanostructures, which depends on its shape and geometrical size, is also discussed.
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Mesoscale and Nanoscale Physics

Maximal Chern Numbers from Finite-Range Hopping

Christopher Arriagada Cortés and Vladimir Juričić

Finite-range hopping constrains both the number of Dirac points and the masses that gap them. We determine the maximal absolute Chern numbers of an isotropic finite-range extension of the Qi–Wu–Zhang model on a square lattice through thirteenth-neighbor hopping. Algebraic zero counting and mass-weighted sum rules yield global bounds, and we construct explicit Hamiltonians that saturate them. We find $|C|_{\max}=36,40,51$ for eleventh-, twelfth-, and thirteenth-neighbor hopping. Equal numbers of Dirac points can produce different maxima because finite-range mass harmonics distinguish opposite vortex charges differently. Twice the squared hopping radius bounds every maximum through twelfth-neighbor hopping and is saturated at the eleventh and twelfth, but the thirteenth-neighbor maximum exceeds it. Thus finite-range hopping constrains the maximal Chern number in two complementary ways: through the number of Dirac vortices it can generate and through the mass-sign patterns it can assign to them. This geometric viewpoint provides a design principle for high-Chern bands and a route to analogous bounds in moiré and other lattice systems.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci

A quantitative phase-field model for grain boundary trapping and diffusion of hydrogen

Vincent Feyen, Martin Diehl and Nele Moelans

Grain boundaries influence hydrogen transport in polycrystalline metals by acting as both trapping sites and interconnected diffusion pathways. Conventional interpretations of thermal desorption spectroscopy (TDS) and permeation experiments often treat traps as isolated defects, neglecting grain boundary connectivity and potentially misinterpreting experimental data. Here, we develop a quantitative phase-field model for hydrogen diffusion, grain boundary trapping, and grain boundary-assisted transport. The formulation preserves the physical grain boundary volume independently of the numerical interface thickness and accounts for anisotropic diffusion parallel and perpendicular to grain boundaries. Benchmark simulations verify quantitative behavior under interface upscaling. The model shows that grain boundary diffusion can significantly shift TDS peaks, making Kissinger-type analyses unreliable when grain boundary transport is significant. Effective diffusion coefficients are also shown to depend strongly on grain size, trapping free energy, temperature, and grain boundary mobility. These results highlight the coupled role of trapping thermodynamics, bulk diffusion, and grain-boundary transport.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Quantum environment afterglow from broadband excitation spectroscopy in superconducting qubits

J. R. Guimarães, Y. Liu, Y. Gao et al. (+10 more)

Understanding the qubit environment is central to fault-tolerant superconducting quantum computation. Characterization typically relies on relaxation, leaving excitation largely underexplored. Here, we access this information with time-resolved broadband excitation spectroscopy. The resulting qubit excitation spectrum reveals a highly structured landscape, interspersed with cold regions. Combined with postselection, this technique enables full reconstruction of the noise power spectral density (PSD) and separates quantum from classical noise. With feed-forward, it exposes long-lived two-level-systems (TLSs), whose relaxation times span tens of microseconds to milliseconds - uncovering an intrinsic link between the qubit-TLS coupling and TLS relaxation. The data suggest that the long-lived TLSs are intrinsic to the qubit environment, and can cause excitation that lasts for many qubit operation cycles. Consequently, the environment retains a memory of prior dynamics, and properties like gate fidelity become non-Markovian and protocol-dependent. The presented approach enables identifying and bypassing the hidden roadblocks formed by long-lived TLSs in fault-tolerant quantum computation.
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All authors J. R. Guimarães, Y. Liu, Y. Gao, Y. Haddad, A. Galicia, D. A. Volkov, J. T. Schmieder, H. Bhardwaj, M. Neis, J. Cereijo, M. Jerger, P. A. Bushev, R. Barends

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

Steady–State Current Signatures of Strong Light–Matter Coupling in Single–Molecule Junctions

Kritanjan Polley and Norah M. Hoffmann

Strong light-matter coupling offers exciting opportunities for controlling molecular properties, yet resolving single-molecule behavior from collective effects remains a challenge. Recent experiments in scanning tunneling microscope break junctions (STM-BJs) have demonstrated strong light-matter coupling at the single-molecule level. Because STM-BJs provide direct access to molecular-junction currents, we investigate whether strong coupling leaves a measurable fingerprint in transport, potentially probing polaritonic states beyond optical spectroscopy. Using a semiclassical mapping approach for nonequilibrium quantum transport, we find that steady-state current indeed carries a direct signature of single-molecule strong coupling. We test the robustness of this signature against electrode connectivity, nuclear motion, spatially structured electromagnetic modes, and solvent effects. While environmental factors and nuclear motion reshape the signature, the current is not a passive response but is actively influenced by coupled molecular dynamics. Our work establishes current as a tool to interpret and control strong light-matter interactions in nanoscale junctions.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.chem-ph

A General Non-Markovian Electronic Friction and Langevin Dynamics Framework for Nonequilibrium Systems

S. L. Rudge, R. J. Preston, D. S. Kosov et al. (+1 more)

We present a general framework for simulating the nonequilibrium vibronic dynamics of molecules interacting with metal surfaces, which utilizes non-Markovian electronic friction and the corresponding generalized Langevin equation. The method employs a Markovian embedding scheme to sample coordinate-dependent quantum colored noise, with the underlying memory kernels represented systematically by exponential decompositions obtained directly from the electronic forces. In doing so, the approach extends the widely used electronic friction and Langevin dynamics formalism beyond the conventional Markovian approximation while retaining the coordinate dependence of the electronic back-action. We demonstrate the method for nonequilibrium charge transport through a vibrationally coupled molecular junction, where comparisons with numerically exact hierarchical equations of motion simulations show that the non-Markovian formulation is both more accurate and more robust than its Markovian counterpart. In particular, we find that non-Markovian electronic forces play a decisive role in the nonequilibrium vibrational dynamics, stabilizing regimes in which the conventional Markovian approximation fails.
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All authors S. L. Rudge, R. J. Preston, D. S. Kosov, M. Thoss

Mesoscale and Nanoscale Physics

Orbital photoinduced Faraday effect in a lattice of conducting disks

A. A. Gunyaga and M. V. Durnev

We present a theoretical study of pump-induced Faraday and Kerr rotation in a two-dimensional lattice of conducting disks. We propose a mechanism of Faraday and Kerr responses in which a circularly polarized pump directly induces a high-frequency Hall component $\sigma_{xy}=-\sigma_{yx}$ of the electron conductivity tensor at the probe frequency. Microscopically, $\sigma_{xy}$ originates from the third-order nonlinear response of the electron gas rather than from the real magnetic field created by solenoidal charge currents in the inverse Faraday effect. We show that the Faraday and Kerr rotation angles are significantly enhanced when the pump and probe frequencies are tuned close to the plasmon resonance of the disks, reaching $\sim 0.1^\circ$ per 1~kW/cm$^2$ of incident pump intensity in the terahertz range. This mechanism can explain recently observed giant pump-induced Faraday rotation in graphene disk lattices.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci

Modern triad for magnetic material science: geometric shape, electronic bands and spin textures

Denys Makarov, Oleksandr Pylypovskyi, Rui Xu et al. (+1 more)

To enable novel concepts in nanotechnologies, it is insightful to design materials with qualitatively new performances originating from recent discoveries in fundamental material science and physics. Curvilinear magnetism emerged as a tool to design chiral and anisotropic responses of materials at the nanoscale using the effects of the geometric shape and topology of the object. This concept is distinct yet complementary to material screening, which is primarily based on the optimization of intrinsic microscopic properties to modify magnetic textures for specific applications. Contemporary curvilinear magnetism focuses on mean-field micromagnetics, while the explicit contribution of the lattice structure and electronic degrees of freedom remains beyond consideration. In this review, we will emphasize on the effects which appear when this coupling is accounted for and that have resulted in novel concepts for the design of “metageometric” materials. Further development of this field will provide appealing technological prospects for fundamental understanding of curvilinear magnetic nanostructures and their applications in energy efficient and scalable nanoelectronics.
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All authors Denys Makarov, Oleksandr Pylypovskyi, Rui Xu, Carmine Ortix

Mesoscale and Nanoscale Physics

Plasmonic Modes in hybrid Josephson Junction Arrays

Alex Kirchner, Simon Feyrer, Vjeko Dimić et al. (+9 more)

We present microwave characterization measurements of Josephson junction arrays (JJAs) based on epitaxial Al-InAs quantum well heterostructure. The Josephson inductance of the constituent planar junctions can be derived by probing the low-energy plasmon modes of these devices. Applying an out-of-plane magnetic field gives rise to a Fraunhofer-like diffraction pattern, from which the current-phase relation and the effective transparency can be extracted. JJAs can be used to achieve high inductances, suitable for the implementation of quantum circuits. They also provide an excellent test-bed for studying the microscopic excitations of hybrid superconductor-semiconductor devices associated with the presence of Andreev states. Here, we demonstrate their tunability over a broad range of out-of-plane magnetic fields.
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All authors Alex Kirchner, Simon Feyrer, Vjeko Dimić, Johanna Berger, Davide Curcio, Giorgio Biasiol, Michael Prager, Matthias Kronseder, Dominique Bougeard, Nicola Paradiso, Christoph Strunk, Leandro Tosi

Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.stat-mech

The renormalization group for a slab model of the spin reorientation transition

D. Pescia

In 1975, Polyakov invented a renormalization group algorithm for treating the problem of a classical isotropic planar Heisenberg ferromagnet. Here we define a tool - "parallel transport of frames" - that extends Polyakov's original renormalization group method to local magnetic anisotropies and, most significantly, the non-local dipolar interaction. We apply this tool to the problem of the spin reorientation transition in an ultrathin ferromagnetic slab with finite thickness. We find that integrating out the short wavelength spin wave fluctuations generates two local anisotropies that are absent from the microscopic dipolar energy Hamiltonian. Taking them into account yields the correct topology of the spin reorientation transition line, as observed experimentally and in numerical simulations.
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Mesoscale and Nanoscale Physics

Measurement protocol for non-adiabatic geometric phases of Floquet states

Carlos Martín-Fernández, Gloria Platero and Sigmund Kohler

Periodically time-dependent quantum systems have Floquet solutions. They consist of a phase factor and a Floquet mode which shares the periodicity of the driving. Consequently, any such solution possesses a non adiabatic geometric phase known as the Aharonov-Anandan (AA) phase. It is gauge-invariant and, therefore, is experimentally accessible. We propose a protocol for the measurement of AA phases based on the adiabatic change of the phase of the non-adiabatic driving. We argue that the experimental requirements of the protocol are those of previous measurements of adiabatic phases.
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Mesoscale and Nanoscale Physics

Electrically controlled spin-splitting and asymmetric tunnel magnetoresistance in anti-altermagnets

Abhiram Soori

Anti-altermagnets (AAMs) are a recently identified class of layered magnetic materials where opposite spin-splitting in adjacent layers creates a globally spin-degenerate band structure, rendering conventional spectroscopic detection highly difficult. In this paper, we theoretically demonstrate an all-electrical method to manipulate and probe this hidden magnetic order using a dual-gated transport junction. By applying a perpendicular displacement field, we break the spatial inversion symmetry of the lattice, explicitly lifting the global spin degeneracy. We attach ferromagnetic (FM) leads on either side of the AAM. Using quantum transport calculations, we show that this gate-induced spin-splitting manifests as a strongly asymmetric tunnel magnetoresistance (TMR) as a function of the lead magnetization. We identify specific crystallographic orientations where the TMR retains its symmetry despite the fully split bands, a direct consequence of exact momentum-space compensation. We further reveal that Rashba spin-orbit coupling guarantees robust, highly directional transport asymmetries even in the absence of an explicit chemical potential mismatch between the layers. Our findings establish a clear, electrically tunable framework for exploiting AAMs in next-generation spintronic architectures.
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