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Physics Condensed Matter Mesoscale and Nanoscale Physics

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

Tuesday 18 August

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

Anomaly-Induced Phenomena with Massive Fermions: Higher-Landau-Level Dominance from Spatially Modulated Electric Fields

Koichi Hattori, Kazuya Mameda, Takeru Uchiyama et al. (+1 more)

We investigate the axial Ward identity for massive fermions under a constant magnetic field at arbitrary strength, maintaining an arbitrary spacetime configuration of a perturbative electric field. We show that a spatially modulated electric field prevents the exact cancellation between the anomaly and pseudoscalar terms, generating a local axial-charge source even in the adiabatic regime where the frequency is subthreshold to massive-fermion production. Remarkably, unlike conventional magnetic responses, this charge generation is dominated not by the contribution of the lowest Landau level, but by those of the higher Landau levels. Our findings provide a microscopic foundation for anomaly-induced transport and anomalous optical responses in gapped systems. In particular, we find that the spatially modulated chiral magnetic effect in weakly gapped Weyl semimetals that exhibits a linear suppression of the magneto-resistance by the magnetic-field strength instead of the renowned quadratic suppression.
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All authors Koichi Hattori, Kazuya Mameda, Takeru Uchiyama, Di-Lun Yang

Mesoscale and Nanoscale Physics

Flat band and Bulk-Boundary correspondence in a non-Hermitian trimerized lattice model with generic boundary conditions

Supriyo Ghosh, Pijush K. Ghosh and Shreekantha Sil

We consider a Su-Schrieffer-Heeger(SSH)-type trimer model with next-nearest-neighbor(NNN) interaction and balanced loss-gain(BLG) to study the combined effect of lattice symmetries, topology, non-hermiticity and general boundary conditions(GBC)on the existence of flat band and the nature of Bulk-Boundary correspondence(BBC). We derive the necessary and sufficient conditions for the existence of an entirely real spectrum under the periodic boundary condition(PBC). The exact expressions for the compact localized states(CLS) and energy eigenvalues corresponding to flat bands are derived analytically under the PBC. We establish topological phase transitions(TPT) for PT-symmetry and pseudo-chiral symmetry through the computation of the Zak phase and sub-lattice Zak phase, respectively. The Hamiltonian under the open boundary condition(OBC) is studied numerically, and edge states are observed in the topologically non-trivial phase, thereby establishing the non-hermitian BBC. The CLS exists in both bulk and the boundary for systems having only pseudo-chiral symmetry, and an additional PT-symmetry destroys the CLS at the boundary. We generalize a known formalism to study the same Hamiltonian under GBC, and derive analytic expressions for the energy and eigenstates for a class of boundary conditions in parametric ranges which admit flat band under the PBC. The edge states for these boundary conditions, including the OBC, are obtained analytically in the topologically non-trivial phase, thereby establishing BBC. The non-hermitian skin effect(NHSE) is seen in the model with reciprocal bulk interaction and strongly non-reciprocal boundary terms. The winding number based on spectral topology is computed analytically.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci

Giant Bandgap Pulsation Driven by Hotspot Breathing Phonons in a Flat-Band Solid

Wenjie Liu, Huaxin Wu and Jiyang Fan

The electronic bandgap of solids is conventionally viewed as a static property at a given temperature, with only weak and stochastic thermal fluctuations under equilibrium conditions. Here, using ab initio molecular dynamics and first-principles electron-phonon calculations, we reveal a pronounced room-temperature bandgap pulsation at about 7.8 THz in a perovskite-like flat-band solid, with a maximum peak-to-peak variation approaching 0.95 eV. This behavior originates from a dual selection mechanism: the A1g-like breathing branch couples much more strongly to the flat conduction-band edge than other phonon branches, while real-space phase selectivity distinguishes its hotspot gamma-point and finite-q components. Although finite-q modes retain appreciable microscopic coupling, their intercell phase shifts produce smaller-amplitude shorter-recurrence-period responses, leaving the unit-cell-synchronous gamma-point A1g component to dominate the fundamental-period bandgap pulsation. The resulting band-edge dynamics further modulates the optical response on femtosecond timescales. These findings demonstrate that an unexpectedly ordered electronic response can emerge from intrinsically disordered thermal lattice fluctuations.
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Mesoscale and Nanoscale Physics

Flux-tunable global and local superconductivity in a topological insulator nano-SQUID

Ella Nikodem, Jakob Schluck, Michał Papaj et al. (+5 more)

Topological systems are defined by global properties that enforce the existence of local boundary modes. Three-dimensional topological insulators (TIs) were among the earliest proposed systems for hosting topological superconductivity, but experimental focus subsequently shifted to other platforms. Here, we revisit bulk-insulating TIs using a columnar nano-superconducting quantum interference device (nano-SQUID) architecture. This geometry optimises the proximity effect on the TI surface and enables simultaneous probing of global superconducting properties - via the critical current through the nano-SQUID - alongside the local states at the ends of the nano-SQUID via tunnel junctions. We observe several global superconducting features that appear to show a flux-driven global phase transition consistent with entering the topological regime, including periodic critical current oscillations and a sign reversal in the superconducting diode effect. Simultaneously, tunnelling spectroscopy reveals spectral jumps in local and nonlocal conductance that align with these global features. However, zero-bias peaks (ZBPs) in local conductance are present both within the predicted topological range of magnetic fields and in theoretically trivial regimes, including at zero magnetic field. Ultimately, the lack of correlation between local ZBP signatures and global signatures emphasises that conclusively identifying Majorana bound states will necessitate a combined approach, integrating the establishment of global topological properties with the use of local and other, more advanced, probes.
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All authors Ella Nikodem, Jakob Schluck, Michał Papaj, Max Geier, Mahasweta Bagchi, Liang Fu, Henry F. Legg, Yoichi Ando

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

Second Harmonic Generation Spectroscopy of the Surface Charge Density Wave in the Weyl Semimetal CoSi

Awadhesh K. Das, Wesley E. Deeg, Sujan Subedi et al. (+3 more)

Using temperature-dependent rotational anisotropy second harmonic generation (RA-SHG), we identify a charge density wave (CDW) instability on the CoSi (001) face with an onset temperature at $90.0 \pm 0.8$ K. The SHG response tracks the order parameter amplitude, dominated by two nonlinear tensor elements, whose background-subtracted intensity evolves with temperature as a power law. The extracted critical exponent $\beta = 0.30 \pm 0.03$ is consistent with the 3D XY universality class, an unexpected result for a nominally two-dimensional surface layer. No corresponding anomaly is observed in the bulk response, establishing the transition as a purely surface-driven phase transition. We attribute this unexpected scaling to the coupling between surface Fermi-arc states and the bulk topology they are tied to, grounded in a previously observed intra-unit-cell phase relationship between surface sublayers that gives the order parameter intrinsic three-dimensional structure.
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All authors Awadhesh K. Das, Wesley E. Deeg, Sujan Subedi, Chandra Shekhar, Claudia Felser, Darius H. Torchinsky

Mesoscale and Nanoscale Physics

Zero Point Density Fluctuations and Electron Brownian Motion

L. H. Ford, G. O. Heymans and N. F. Svaiter

The fluctuations in the phonon vacuum state can lead to zero point density fluctuations in a material, which in turn lead to local zero point fluctuations of the dielectric properties of the material. We argue that the density fluctuations lead to a fluctuating force on a test charge, such as an electron, located a short distance outside of the material. This force is due to fluctuating dipole moments inside the material, and produces Brownian motion of the electron. We calculate the mean squared velocity of the electron in both the normal and transverse direction relative to the boundary of the material. The result is nonzero in both directions, but larger in the normal case. We estimate the magnitude of this quantum Brownian motion and find that, in some cases, it can exceed the effects of both thermal motion and quantum momentum uncertainty. This suggests that the effect may be observable, and could constitute a source of quantum noise in nanoscale devices. It also potentially offers a means to remotely sense zero point density fluctuations in a material.
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Monday 17 August

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

Demonstration of a scalable all-solid-state refrigerator exploiting diffusion geometries and limiting interfacial conductances at temperatures below 1 kelvin

Robert M. Young, Zachary Stegen, John X. Przybysz et al. (+32 more)

Solid-state refrigerators using Normal-metal/Insulator/Superconductor (NIS) junctions have previously demonstrated excellent electron cooling but limited ability to cool phonons. The energy gap of the superconductor is used as an energy filter to allow higher than average energy electrons to preferentially tunnel from the normal-metal through the insulator into the superconductor where they travel as quasi-particles. Typically, the heat is moved and work is done to deposit hot quasi-particles into a normal-metal quasi-particle trap for rejection to the next refrigeration stage. Realizing that (1) the quasi-particles flow diffusively, driven by a concentration gradient in the electric field-free superconductor, and (2) that the undesirable backwards leaking of heat from the hot-side trap can be reduced by engineering the geometry and materials at the superconductor-to-trap interface, enhanced cooling can be achieved. Fabrication of the refrigerator was accomplished using a tungsten and titanium-tungsten alloy as the cold-side normal-metal, aluminum oxide as the insulator, aluminum as the superconductor, and gold as the trap, with the cold-side NIS portion being attached to the hot-side gold trap by bump bonding. The refrigerator consisted of 1121 junction pairs, each pair being an SINIS unit, all electrically connected in series. Using this we have measured the effective phonon temperature of a 3.9 mm x 3.9 mm x 0.65 mm silicon chip driven down to 70 mK from a bath temperature of 120 mK, and down to 174 mK from a 271 mK rejection temperature (a cooling of -97 mK). This is the first demonstration of the sub 1 K cooling of an entire silicon chip using NIS junctions.
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All authors Robert M. Young, Zachary Stegen, John X. Przybysz, Edward R. Engbrecht, Aaron A. Hathaway, Justin C. Hackley, Kirby B. Myers, Christian C. Thorpe, Aurelius L. Graninger, Robert Miller, Diego A. Morales, Roberto D. Carcamo, Glen Walters, Jeric P. Sarad, Nicholas F. Pleim, Seth Whitsitt, Joshua T. Shipman, Anil Erol, Melissa G. Loving, Evan Donohue, Corey A. Kegerreis, Benjamin Dalfort, Moe S. Khalil, Christopher Pinion, Randi Jaramillo, John Milinichik, Sandro J. Di Giacomo, Thomas Zodda, Nilesh Tralshawala, Gregory R. Boyd, Jonathan M. Cochran, Katherine A. Maddock, Michael P. De Feo, Aaron A.Pesetski, Marc E. Sherwin

Mesoscale and Nanoscale Physics

Emissivity by Design: Geometric Mesh Inductance Governs Thermal Radiation in Metallic Nanowire Networks

Amaury Baret and Ngoc Duy Nguyen

The thermal infrared emissivity of metallic nanowire networks - the property that makes them candidate low-emissivity transparent electrodes - follows regularities that have resisted physical explanation: a strong wire-diameter dependence with no wire-length dependence, a correlation with sheet resistance that breaks down above ~15 ohm/sq, and an angular signature that turns from dielectric-like to metallic as the network densifies. We show that all of them follow from one local geometric length, the average inter-wire gap g, acting through the geometric inductance of a mesh finer than the thermal wavelength: $X_L = Z_0 (g/\lambda) \ln(2g/\pi D)$, a parameter-free reactance that exceeds the ohmic loss and, unlike the DC sheet resistance, stays finite instead of diverging at the percolation threshold. Since the gap is fixed by areal density and wire diameter alone, the optics is length-independent and decoupled from percolative transport; what has been read as a second, optical percolation is instead a smooth impedance crossing. With a single fitted parameter the theory reproduces 56 silver-nanowire samples across four diameters to a mean absolute error of 0.04, collapses them onto one universal curve, and - unchanged - predicts the emissivity-transmittance data of five independent groups and the measured spectral emissivity, including the silica phonon band. Because this reactance contains no material constant, the inter-wire gap emerges as the master design variable for the radiative properties of metallic nanowire transparent conductors.
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Mesoscale and Nanoscale Physics

Local magnetic resonance of scalar spin chirality

Mar Ferri-Cortés and Joaquin Fernández-Rossier

Quantum states with finite scalar spin chirality carry an orbital magnetic moment that has eluded direct measurement. We show that a local drive breaks the cyclic symmetry and activates chirality-changing transitions. We propose two complementary probes: direct chirality resonance and chirality-resolved spin resonance. Lindblad simulations demonstrate their feasibility in locally addressable spin platforms, including scanning tunneling microscopy, silicon donors, and quantum dots.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Multi-purpose quantum laboratories from superconducting circuits

Arpit Arora, Emily M. Been, William Munizzi et al. (+4 more)

Superconducting circuits (SCs) are the cornerstone of modern quantum technology, enabling scalable computing through coherent control of macroscopic quantum states. Through a legacy that predates modern quantum computing, SCs have emerged as high-precision instruments for discovery. In this review, we highlight the role of SCs as general-purpose quantum laboratories, outlining the emerging landscape of correlated matter-circuit science. We review and unify the capabilities of superconducting quantum hardware across condensed matter, high energy and quantum information sciences. We trace the technical evolution of these architectures, illustrating how their foundational development has culminated in a toolkit for resolving the complexities of macroscopic quantum states.
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All authors Arpit Arora, Emily M. Been, William Munizzi, Joel Wang, Taylor L. Patti, Aaron Chou, Prineha Narang

Mesoscale and Nanoscale Physics

Tuning single-molecule fluorescence by atomic-scale control of the local environment

Thiago G. L. Brito, Daniel Arribas, Sofia Canola et al. (+3 more)

Molecules that absorb and emit light play a central role in microscopy, light-emitting devices and photosynthesis. Their fluorescence arises from well-defined radiative transitions that are governed by the electronic states and their coupling to the nuclear motion that are influenced by the local environment. Yet the effect of controlled atomic-scale variations in the emitter surroundings remains unexplored. Here, we use scanning tunneling microscopy combined with optical spectroscopy to investigate the optical response of a single phthalocyanine to the change in the position of a nearby molecule, controlled with precision better than 100 pm. Upon decreasing the intermolecular distance, the molecular emission energy redshifts and its line profile evolves. Supported by theoretical calculations, we disentangle the electronic and nuclear contributions to the changes in fluorescence. We find that the redshift originates from the interaction between the excitations of the two molecules, while the lineshape changes reflect modifications of the molecular rotational degree of freedom and non-equilibrium dynamics. We extend this control to larger assemblies, where one molecule tunes the energies of two chromophores, mimicking the environmental tuning in photosynthetic systems. Our study provides atomic-scale insight into how the local environment affects the optical properties of molecular systems.
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All authors Thiago G. L. Brito, Daniel Arribas, Sofia Canola, Klaus Kuhnke, Tomáš Neuman, Anna Rosławska

Mesoscale and Nanoscale Physics

Surface weak ferromagnetism

Vladimir A. Zyuzin

This paper proposes a model of a Néel-ordered antiferromagnet exhibiting a weak ferromagnetic moment restricted to the crystal surface, generated by spin-orbit coupling induced by broken surface symmetries. Depending on crystal termination, the surface magnetic moment can align with identical or opposing signs on the top and bottom surfaces, resulting in a zero Faraday effect paired with a finite Kerr effect upon reflection for the latter configuration.
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Mesoscale and Nanoscale Physics

Classical Mechanics Exactly Yields the Full Bound-State Spectrum of the Two-Dimensional Coulomb Problem

Gang Zheng, Wenqi Xue, Mengli Wang et al. (+2 more)

High-lying Rydberg excitons in two-dimensional semiconductors universally exhibit a characteristic odd-integer energy scaling distinct from three-dimensional systems. While this hallmark of two-dimensional Coulomb interaction is well known from quantum mechanical solutions, its deeper classical geometric origin remains unclarified. Here we show that the complete bound-state spectral structure of the two-dimensional Coulomb problem—a central model for two-dimensional exciton physics—follows as an exact theorem from classical mechanics augmented by a single phase-scale parameter $\alpha$ with dimensions of action. We derive an amplitude-closure criterion as a necessary and sufficient condition for a classical propagator kernel to satisfy a linear evolution equation, and demonstrate that the singular Coulomb potential can be mapped shell-by-shell via Levi-Civita regularization into the class of quadratic Hamiltonians that obey this criterion exactly. The resulting spectrum bears odd-integer modal numbers, $1/N^2$ energy ratios and $N$-fold degeneracies, all independent of $\alpha$ and consistent with experimental observations of high-lying Rydberg excitons. This work provides a pure classical-geometry benchmark for two-dimensional exciton spectral analysis, allowing quantitative disentanglement of universal Coulomb effects from material-specific screening effects. No semiclassical, short-wavelength or $\hbar \to 0$ approximation is invoked at any stage. Our results invert the usual logical hierarchy for this integrable system: the wave equation emerges as a representation of the underlying classical geometry, rather than as an independent first principle.
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All authors Gang Zheng, Wenqi Xue, Mengli Wang, Peng Chen, Benniu Zhang

Mesoscale and Nanoscale Physics

Reduced vortex descriptors linking polycrystallinity in magnetic nanoparticles with polarized magnetic small-angle neutron scattering

M.P. Adams, J. Leliaert, A. Michels et al. (+1 more)

Analytical vortex models reduce polarized magnetic small-angle neutron scattering (SANS) from nanoparticle ensembles to a small set of texture descriptors. In this work, we apply this reduction to micromagnetic simulations of polycrystalline iron oxide nanoflowers at a fixed particle size and examine how a controlled parametrization of multigrain disorder is reflected in the remanent descriptors. The particles are represented by explicit Voronoi microstructures, and intraparticle disorder is varied through the intergrain exchange coupling and anisotropy-axis coherence. Fitting each remanent magnetization state to a hyperbolic vortex model reveals a predominantly two-channel organization: the intergrain exchange coupling is associated mainly with the radial vortex profile, whereas the anisotropy-axis coherence is associated mainly with the orientational moment of the vortex-axis distribution. The normalized spin-flip SANS cross sections are accurately represented by independent fits of the analytical linear-vortex SANS expression obtained from the first-order expansion of the hyperbolic profile. The fitted orientational descriptor agrees closely with its independent real-space estimate, whereas the corresponding radial descriptors exhibit a strong global nonlinear relation. This separation identifies which information from the micromagnetic vortex textures is robustly retained by the reduced analytical representation.
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All authors M.P. Adams, J. Leliaert, A. Michels, E.M. Jefremovas

Mesoscale and Nanoscale Physics

Engineering two-qubit gates via anisotropic exchange in germanium spin qubits

Leonardo Massai, Bence Hetényi, Eoin G. Kelly et al. (+14 more)

Germanium hole spin qubits are a promising and versatile platform for quantum computation and simulation. In this system, strong spin-orbit interaction (SOI) renders the single-qubit $g$-tensor anisotropic and electrically tunable, enabling operational sweet spots with reduced noise sensitivity. SOI also transforms the isotropic two-qubit exchange coupling into an anisotropic tensor whose geometry is inherited from the single-qubit $g$-tensors and spin-flip tunnelling. Here, using two hole spin qubits in a strained-germanium quantum well and full vector control of the magnetic field, we map this exchange tensor, separate it into longitudinal and transverse components, and show that they govern controlled-phase and SWAP-like dynamics, respectively. We find that the longitudinal exchange can be tuned via the magnetic field orientation from a conventional positive value, through zero, to an effectively negative one, as measured by inverted exchange-split spin transitions. The magnetic field direction thus provides continuous control over the interaction Hamiltonian: at a point of purely transverse exchange, we engineer a single-pulse baseband iSWAP, unattainable under isotropic exchange. Linking $g$-tensor geometry to exchange anisotropy establishes native Hamiltonian engineering, enabling spin-based quantum simulation and gate sets selected by the global field orientation alone.
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All authors Leonardo Massai, Bence Hetényi, Eoin G. Kelly, Inga Seidler, Konstantinos Tsoukalas, Michele Aldeghi, Alexei Orekhov, Lisa Sommer, Marta Pita-Vidal, Uwe von Lüpke, Stephan Paredes, Stephen W. Bedell, Felix J. Schupp, Matthias Mergenthaler, Gian Salis, Andreas Fuhrer, Patrick Harvey-Collard

Mesoscale and Nanoscale Physics

Proximity-induced superconductivity in a bilayer graphene quantum point contact

Clara Galante-Agero, Christoph Adam, Artem O. Denisov et al. (+9 more)

We report the realization of a gate-defined quantum point contact (QPC) in bilayer graphene proximitized by a single aluminum superconducting electrode. Superconducting correlations induced in the ballistic channel enhance the conductance plateaus beyond their normal-state values. In addition, we observe a pronounced above-gap conductance anomaly which serves as a spectroscopic signature of the loss of superconductivity and the associated collapse of the Andreev excess current. By reconstructing the nonlinear current-voltage characteristics, we find that the magnitude of the excess current increases as successive QPC modes are populated. Additionally, we find that the switching current associated with the loss of superconductivity follows the underlying mode structure of the QPC, exhibiting discrete levels consistent with a heat dissipation-driven transition. These results demonstrate that the one-dimensional transport modes of the QPC govern both the equilibrium proximity effect and the non-equilibrium dynamics of the hybrid system.
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All authors Clara Galante-Agero, Christoph Adam, Artem O. Denisov, Jonas D. Gerber, Markus Niese, Alexandra Mestre-Torà, Marta Perego, Jessica Richter, Takashi Taniguchi, Kenji Watanabe, Klaus Ensslin, Thomas Ihn

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

Time-optimal quantum gates with bang-bang control in multilevel systems

Valentín Reparaz, Santiago Ferreyra, María José Sánchez et al. (+2 more)

We determine the optimal quantum manipulation protocols for implementing high-fidelity, fast single-qubit gates. We demonstrate that the time-optimal pulse sequence is a “bang-bang” sequence: discrete pulses of either positive or negative maximum amplitude or zero. The non-adiabatic bang-bang pulse sequence minimizes gate duration providing a speedup for low-frequency architectures. We first derive the protocol for a transversally driven two-level system, extracting exact analytic expressions for minimum gate times. We then extend this framework to general multilevel architectures, identifying conditions that enable the coherent suppression of leakage errors. Using the fluxonium circuit as a representative case study, we optimize $X/2$ and $Y/2$ gates through a combination of discrete bang sequences and continuous waveform smoothing. This approach preserves near-optimal execution speeds while mitigating transitions outside the computational subspace. Open-system simulations demonstrate that these sequences outperform commensurate and resonant pulse schemes across different fluxonium regimes, achieving low-error manipulation significantly faster than standard resonant control, even in the presence of $1/f$ flux noise and dissipation.
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All authors Valentín Reparaz, Santiago Ferreyra, María José Sánchez, Daniel Domínguez, Leandro Tosi

Mesoscale and Nanoscale Physics

Topological insulator realization induced by fermionic interaction through BF mediators

G. B. de Gracia, R. da Rocha, A. A. Nogueira et al. (+1 more)

This paper demonstrates that ordinary fermions, interacting via a BF mediator, form a renormalized structure with non-trivial topological properties. We explore the analogy between the renormalized fermion and a subset of real three-dimensional topological insulators (TIs) in the vicinity of their single Dirac cones. Using the typical magnitude of TI lattice and gaps, we constrain model parameters. The topological structure induced by radiative corrections enters a class of modified Dirac equations, ensuring the existence of helical gapless near-boundary modes. We derive an effective potential for inter-quasi-particle interactions that incorporates finite-size effects in the axial direction, revealing signatures of spin-orbit coupling and time-reversal invariance. Remarkably, particles with different spins do not interact via the characteristic spin-orbit coupling, and a non-central spin-dependent force arises. We also address the behavior of the system in the phase transition associated with the thin-film limit.
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All authors G. B. de Gracia, R. da Rocha, A. A. Nogueira, M. A. C. de Barcelos

Mesoscale and Nanoscale Physics

Five-terminal quantized transconductance originating from symmetric quantum fluctuations

Klaiv Mertiri and Yuli V. Nazarov

We consider the renormalization of transport in a quantum contact by the external electromagnetic environment and show that weak quantum fluctuations from a symmetric environment can lead to a quantized transconductance in five-terminal contacts. This mechanism does not work for fewer terminals. We present an implementation of the environment and investigate several example quantum contacts where the quantization takes place.
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Mesoscale and Nanoscale Physics

Plexciton-mediated Raman scattering in strongly coupled systems

Danyang Liu, Meijuan Sun, Li Chen et al. (+1 more)

A series of experimental results demonstrate a distinctive Raman response in plasmon-exciton coupled systems. The enhancement of Raman scattering varies for different phonon modes. We describe the microscopic dynamical process of this Raman scattering using quantum many-body theory. Unlike conventional Raman scattering involving electron-phonon interactions, the process in plasmon-exciton coupled systems is characterized by inelastic scattering between phonons and plasmon-exciton polaritons-formed through the coupling of plasmons and excitons-acting as intermediate states. We derive analytical expressions for the Raman intensity and enhancement factors for various phonon modes, which show excellent agreement with experimental data. Furthermore, experimental fittings indicate a substantial disparity in the linewidths of the upper and lower polariton branches, for which we provide a comprehensive theoretical explanation. Based on linear response theory, we propose a microscopic mechanism for the formation of plasmon-exciton polaritons, enabling the analytical calculation of their dispersions and linewidths. This approach naturally accounts for the significantly asymmetry observed in the linewidths of the upper and lower polariton branches. By characterizing the polariton-phonon scattering process at the quantum level, we reveal the fundamental physical mechanism driving polariton-enhanced Raman scattering. Our work establishes a universal framework for describing the dynamical evolution of coupled systems, providing a versatile paradigm for exploring the interactions between plasmons and other quasiparticles.
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All authors Danyang Liu, Meijuan Sun, Li Chen, Hao Shen

Mesoscale and Nanoscale Physics

Raman-detected quantum dot microscopy for nanoscale electrostatic potential imaging

Jiří Doležal, Amandeep Sagwal, Rodrigo Cezar de Campos Ferreira et al. (+1 more)

Quantification of electrostatic potentials at the nanoscale is crucial for understanding the principles governing properties of materials across multiple length scales. Currently, one of the most successful approaches relies on the charging response of a molecular quantum dot, suspended on a tip of a scanning probe microscope and measured using dynamic force spectroscopy. We investigate the possibility of an optical detection, aiming to improve the speed and reduce the complexity of this measurement scheme. We show that the integrated tip-enhanced Raman scattering intensity strongly correlates with the charge state of the quantum dot, and use it to map the electrostatic potential of a single atom. A quantitative equivalence with the established force spectroscopy method is found. We address the underlying photophysical principle of this new method by measuring the Raman spectra as a function of excitation wavelength and the molecular quantum dot charge. We reveal that the observed Raman intensity variations are primarily driven by transitions between resonant and non-resonant Raman scattering regimes of the molecule.
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All authors Jiří Doležal, Amandeep Sagwal, Rodrigo Cezar de Campos Ferreira, Martin Švec

Mesoscale and Nanoscale Physics

Stability and optoelectronic properties of oligothiophene molecules confined in boron-nitride nanotubes : A many-body theoretical approach

Xavier Blase, Mauricio Rodriguez-Mayorga and Ivan Duchemin

We investigate the structural and optoelectronic properties of oligothiophene (nT) molecules encapsulated in boron-nitride (BN) nanotubes using density functional theory, many-body GW and Bethe-Salpeter equation approaches. We show that the binding energy is maximized for tube diameters of approximately 10 Å, decreasing gradually for larger diameters. The nT molecules can slide along the tube with a corrugation potential smaller than room temperature thermal energy, promoting their head-to-tail aggregation. Regarding the electronic properties, we find that hybridization with the tube electronic states has a much smaller effect than that of screening, which can close the nT photoemission gap by as much as an eV. A simple model for the polarization of the BN tube demonstrates how these polarization effects decrease with increasing nT molecule length and BN tube diameter. Compared to the gas phase optical properties, structural relaxation, hybridization, and screening can redshift the absorption onset by up to 250 meV for isolated intercalated nTs. Additionally, the study of a head-to-tail sexithiophene dimer reveals an exciton-exciton interaction that splits the absorption onset into a lowest bright exciton, separated by approximately 75 meV from a dark peak. This suggests possible collective effects upon the formation of nT chains inside BN tubes. Our results confirm and clarify experimental data, mitigating the conclusion that insulating BN tubes just act as a protecting environment for encapsulated molecules.
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Mesoscale and Nanoscale Physics

Field-controlled breaking and restoration of parity-time symmetry in Josephson interference

Yi-Chen Tsai, Yung-Yeh Chang, Tao-Yi Hsu et al. (+6 more)

Symmetry plays a fundamental role in determining the phases and physical properties of quantum matter. Controlling symmetry in mesoscopic superconducting devices provides a route to reconfigure their phase-coherent transport. Here we demonstrate symmetry-selective Josephson interferometry in lateral NbTi/PtTe$_{\text{2}}$/NbTi junctions by controlling the relative orientations of the current and magnetic field. From the supercurrent interference patterns, we construct a field-current symmetry map that identifies configurations exhibiting or violating the device-level parity ($\mathcal{P}$), time-reversal ($\mathcal{T}$) and their combined $\mathcal{PT}$ symmetry. In the absence of an in-plane field, the junction exhibits a symmetric Fraunhofer pattern. An in-plane field parallel to the current produces a pronounced side-lobe asymmetry, whereas reversing both the current and the complete magnetic-field configuration restores a generalized $\mathcal{T}$ relation. Remarkably, orienting the in-plane field perpendicular to the current restores the $\mathcal{PT}$-symmetric Fraunhofer response even at substantial field strengths. A microscopic model attributes this behavior to the interplay between disorder-induced potential variations and flux dipoles generated by in-plane-field Meissner focusing near the superconducting electrodes. Our results establish a reconfigurable Josephson interferometer in which the field-current geometry selects the symmetry operation being probed and switches the device between symmetry-broken and symmetry-restored interference states.
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All authors Yi-Chen Tsai, Yung-Yeh Chang, Tao-Yi Hsu, Thomas Kuo, Chia-Nung Kuo, Chin-Shan Lue, Kuei-Lin Chiu, Chen-Hsuan Hsu, Chung-Ting Ke

Mesoscale and Nanoscale Physics

A magnonic-optoelectronic reservoir for physical reservoir computing

Alexey B. Ustinov, Ivan Y. Tatsenko, Andrei A. Nikitin et al. (+1 more)

Physical reservoir computing is a promising approach for fast and energy efficient computer vision, natural language processing, and general pattern recognition. This work presents a physical reservoir based on magnonic-optoelectronic oscillator (MOEO). This approach allowed us to realize short-term memory and nonlinearity as separate system components. The device`s optical path uses a fiber-optic delay line as a short-term-memory element. The microwave path is responsible for nonlinear mapping of input data to a higher-dimensional space. The strong four-wave nonlinearity of spin waves propagating in an yttrium-iron garnet (YIG) ferrite film enables the process. The reservoir performance is evaluated by completing task-independent tests known as short-term memory (STM) and parity-check (PC) tasks. In addition, a numerical model of the MOEO based reservoir is developed. Results of the numerical simulation of the reservoir performance are in good agreement with the experimental data.
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All authors Alexey B. Ustinov, Ivan Y. Tatsenko, Andrei A. Nikitin, Mikhail P. Kostylev

Mesoscale and Nanoscale Physics

Tunable Fano Resonance and Frequency Locking in a Graphene-SiNx Hybrid Nanomechanical Resonator

Ateesh K. Rathi, Javed A. Mondal, Rajan Singh et al. (+3 more)

Fano resonances, arising from the interference between discrete and continuum states, are observed across a wide range of quantum and classical systems. Here, we report the experimental observation of Fano resonances in a graphene SiNx hybrid nanomechanical system modeled as coupled oscillators. The broad, low quality factor graphene mode plays the role of the continuum, while the dense comb of sharp, high quality factor SiNx modes provides the discrete states. The inter-mode detuning is tunable via a DC gate voltage, enabling dynamic control of the Fano resonance: we demonstrate gate controlled switching of both the sign and the magnitude of the Fano asymmetry parameter $q$, in quantitative agreement with a coupled oscillator theory that predicts $q=-\cot\phi$, with $\phi$ the phase of the continuum response. At strong drive, the graphene mode enters the Duffing regime and its jump-down frequency locks to successive SiNx modes, producing a staircase of drive insensitive frequency plateaus; a weak seeding tone deterministically switches the resonator between adjacent locked states. The dense SiNx mode thus acts, in the linear regime, as the discrete states of a tunable Fano interferometer and, in the nonlinear regime, as a frequency ruler that stabilizes and quantizes the graphene oscillation. This platform offers a controllable mechanical realization of Fano interference and opens new avenues for high resolution hybrid resonant sensors and stable nanomechanical frequency references.
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All authors Ateesh K. Rathi, Javed A. Mondal, Rajan Singh, Ryan J.T. Nicholl, Kirill I. Bolotin, Saikat Ghosh

Mesoscale and Nanoscale Physics

Helical Magnon Frequency Comb in Synthetic Antiferromagnetic Skyrmion Lattices

Liu Xuejuan, Zheng Xingen, Li Zhixiong et al. (+5 more)

Synthetic antiferromagnetic skyrmion lattices (SAF-SkLs), consisting of two ferromagnetic SkLs coupled antiferromagnetically with compensated magnetization, provide a promising platform for robust nonlinear magnonics. Here, we investigate helical magnon frequency comb (HMFC) generation in a SAF-SkL by combining analytical modeling with micromagnetic simulations. We show that nonlinear coupling between helical magnon edge states and the skyrmion gyration produces frequency combs with pronounced edge localization. The HMFC exhibits strong enhancement exclusively when the driving frequency lies within the helical edge-state band, whereas the interior response remains negligible. This frequency selectivity confirms the essential role of helical edge modes in localized nonlinear frequency conversion. We further demonstrate that the interlayer antiferromagnetic coupling reconstructs the magnon spectrum, thereby tuning the comb spacing and the number of comb teeth while also redistributing modal energy. Our results establish SAF-SkLs as a tunable platform for edge-localized HMFCs and suggest a route toward robust coherent magnonic signal processing.
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All authors Liu Xuejuan, Zheng Xingen, Li Zhixiong, Li Xiaoguang, Zhou Cangtao, Li Hui, Sun Haipeng, Yan Peng

Mesoscale and Nanoscale Physics

Chiral Damping-Induced Chirality Switching and Control of Domain Walls in Antiferromagnets

Collins Ashu Akosa, Mu-Kun Lee, Aurélien Manchon et al. (+1 more)

We investigate the impact of chiral damping (CD) on current-driven domain-wall (DW) dynamics in antiferromagnets (AFMs). Asymmetric CD between sublattices generates off-diagonal components in the DW mass tensor, thereby coupling translational and rotational modes. When CD is modulated by an ac gate voltage via the Rashba spin-orbit interaction (RSOI), symmetric and asymmetric contributions induce oscillations in the DW velocity and tilt angle, respectively. A perturbative analysis yields explicit expressions for the oscillation amplitudes, in quantitative agreement with numerical simulations. Remarkably, even in the absence of Dzyaloshinskii-Moriya interaction (DMI), asymmetric CD enables chirality switching between Néel- and Bloch-type DWs. Finally, by exploiting the relativistic Lorentz contraction of the DW width at high driving currents, we propose an experimentally viable protocol to qualitatively and quantitatively extract the CD contribution. These results establish clear experimental signatures of CD in antiferromagnetic DW dynamics and demonstrate its potential as a control parameter for magnetic textures.
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All authors Collins Ashu Akosa, Mu-Kun Lee, Aurélien Manchon, Masahito Mochizuki

Sunday 16 August

Mesoscale and Nanoscale Physics

Electrically Switchable Spintronics in a Multiferroic Altermagnet

Martin Latorre, Sebastian Allende and Alvaro S. Nunez

We introduce a minimal model of a two-dimensional lattice that, upon spontaneous symmetry breaking, simultaneously develops altermagnetic order, a finite electric polarization, and a spin-polarized transport response, all of which are controlled by an external electric field. By coupling a dimerized altermagnet to an external electric field, we show that the three order parameters are not merely compatible but dynamically entangled, so that switching one (for instance, reversing the polarization with an electric field) necessarily reconfigures the other two. We show that this model offers a clear physical blueprint for designing next-generation spintronic logic and pure spin current memdevices that merge the ultrafast, stray-field-free advantages of compensated magnets with the low-power switching architectures of ferroelectrics.
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Mesoscale and Nanoscale Physics

Morphology-Guided Deterministic Fabrication of Low-Noise High-Temperature Superconducting Quantum Interference Devices

Bingke Xiang, Wanjuan Tang, Shiqun Liu et al. (+9 more)

Reproducible bicrystal high-temperature superconducting quantum interference devices remain limited by local variability along the grain boundaries that form the Josephson junctions. Here, we develop a site-selective fabrication workflow in which atomic force microscopy maps the intended junction region before lithography, quantifies an apparent grain-boundary width, rejects pore-rich segments, and writes a nearby registration mark for site-specific pattern alignment. The apparent grain-boundary width provides a practical morphology metric, with narrower regions consistently yielding larger critical currents and characteristic voltages. Iterative optimization within this workflow further improves junction and device performance, reaching a liquid-nitrogen-temperature field-noise level of 40 fT Hz^(-1/2). This strategy turns local grain-boundary heterogeneity from an uncontrolled source of variability into a basis for site-selective fabrication, providing a route towards scalable manufacturing of low-noise HTS SQUIDs with high uniformity.
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All authors Bingke Xiang, Wanjuan Tang, Shiqun Liu, Lingtong Hou, Geming Zhang, Yibo Wang, Ruonan Wang, Zhiqiang Cao, Jiaqi Wei, Xueshen Wang, Xueying Zhang, Xiaoyang Lin

Mesoscale and Nanoscale Physics

The Hodge structure of Berry-phase transport: topology, geometry, and noise

Zhi-Wei Wang and Samuel L. Braunstein

We show that the Hodge-de Rham decomposition of the Berry curvature organises the transport of a Bloch band and its fluctuations within a single geometric structure. Splitting the curvature into $L^2$-orthogonal harmonic, exact, and co-exact sectors yields a dictionary for both moments of the current. In the mean response the harmonic sector carries the topological anomalous-Hall conductivity, the exact sector the Fermi-surface geometry and the antisymmetric Berry-curvature dipole of polar metals, and, in three dimensions, the co-exact sector the chiral anomaly, quantised by the Weyl-node charges. In the fluctuations, described by a particle-conserving stochastic Boltzmann equation constrained by the fluctuation-dissipation theorem (FDT), the harmonic sector is silent, so topological transport is noiseless, while the field-driven noise is sourced by the geometric sectors (solely the exact sector in two dimensions); current-noise spectroscopy therefore separates global band topology from local band geometry. We prove that the harmonic null-space protection is dimension-independent, and we settle the remaining sector: the co-exact (monopole) sector carries no conservation law and, under the thermal sampling measure, mixes with the exact sector at $\mathcal{O}(1)$, so it furnishes no clean noise observable. The separation the noise provides is therefore two-way, topology versus geometry, in both two and three dimensions.
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