arXiv subjects

Ryotaro Sano

Publications and source records attributed to Ryotaro Sano.

13 recordsLinked to original sources

arXiv2026

Quantum Geometric Origin of Hall Viscosity and Nonlocal Hall Conductivity in Lattice Bands

We show that Hall viscosity in lattice bands is governed by a band-projected electric quadrupole encoded within the quantum geometry: Berry curvature sets the projected-coordinate algebra, while the quantum metric determines the quadrupolar spread of a wave packet. The same structure enters the quadratic wave-vector coefficient of the nonlocal Hall conductivity, yielding a lattice viscosity-conductivity relation. In ideal bands, the deviation from the Landau-level form is quantified by Berry curvature fluctuations. Our results establish the nonlocal Hall response as an electrical signature of the quantum geometry underlying Hall viscosity and as a transport diagnostic of geometric idealness.

cond-mat.mes-hall↗

arXiv2026

Gyromagnetic Quantum Friction in Rayleigh Vorticity Baths

We identify an intrinsic zero-temperature relaxation channel for near-surface spins gyromagnetically coupled to Rayleigh-wave vorticity. This surface-mode contribution requires no thermal phonons, unlike Raman relaxation, and is fixed by Rayleigh vorticity rather than material-specific $g$-factor modulation. The Rayleigh-vorticity bath is super-Ohmic and evanescent with depth, producing field and depth scalings of spin relaxation. These scalings establish shallow spin sensors and hybrid surface-acoustic-wave spin interfaces as detectors of Rayleigh-wave acoustic quantum friction in solids.

cond-mat.mes-hall↗

arXiv2026

Hanbury Brown-Twiss interferometry at the $\nu=2/5$ fractional quantum Hall edge

We propose a Hanbury Brown-Twiss interferometer for a $\nu=2/5$ fractional quantum Hall edge system, in which quasiparticles tunnel between two co-propagating edge modes. In contrast to the previously studied anyonic Fabry-P\'{e}rot and Mach-Zehnder interferometers, the proposed setup relies purely on two-particle interference rather than single-particle interference. In the weak-tunneling regime, we employ a bosonized edge theory together with Keldysh perturbation theory to evaluate the cross-correlation of the tunneling currents. In the large-device limit, we obtain an analytic expression for the flux-dependent noise, whose structure closely resembles that of an electronic HBT interferometer, but with the electron charge replaced by the fractional charge $e^{\star}=e/3$ and with scaling dimensions characteristic of the fractional edge modes. In this limit, the explicit anyonic exchange phases cancel, whereas when the device size becomes comparable to the thermal length, the cross-correlation may recover a more explicit dependence on the anyonic statistical angle.

cond-mat.mes-hall↗

arXiv2026

Microwave response of fractional quantum Hall droplets with quasiparticle tunneling

We theoretically study microwave absorption spectroscopy of fractional quantum Hall droplets in the presence of quasiparticle tunneling across a quantum point contact. This contact-free probe provides access to collective edge dynamics beyond conventional transport measurements. We develop a nonperturbative path-integral Monte Carlo approach that enables computation of the frequency-dependent response at finite temperature and for arbitrary droplet geometries, and benchmark the method against analytical results in the weak-tunneling regime. We find that tunneling produces measurable shifts and broadening of resonance peaks, with systematic dependence on tunneling strength and device geometry. Such shifts and broadenings are not obtained in perturbative treatments acting directly on the response function, but emerge when interaction-kernel effects are properly incorporated. Our results indicate experimentally accessible signatures of edge-mode interference and tunneling-induced renormalization of collective excitations, and support the use of microwave spectroscopy as a quantitative probe of quasiparticle dynamics in mesoscopic quantum Hall structures.

cond-mat.mes-hall↗

arXiv2025

Valley Hall Viscosity in Gapped Graphene with and without a Magnetic Field

Hall viscosity is conventionally defined through the stress response to time-dependent strain, a perturbation that is difficult to implement in solid-state experiments. We formulate a related viscoelastic response to static, spatially inhomogeneous electric fields and compare it with the strain-based response. For gapped graphene in a perpendicular magnetic field, the two formulations give the same Landau-level response, whose Hall viscosity is asymmetric between the two valleys. At zero magnetic field, a valley-even quantum-metric coefficient combines with the valley-odd Hall conductivity to produce equal and opposite valley-resolved responses; global time-reversal symmetry therefore forces the net Hall viscosity to vanish. In an insulating state, exact particle--hole symmetry eliminates this zero-field response, whereas particle--hole-symmetry breaking generates a cutoff-dependent geometric contribution from the occupied Fermi sea. These results connect valley-dependent viscoelasticity with electromagnetic response in gapped Dirac materials and clarify the conditions under which a valley Hall viscosity can arise.

cond-mat.mes-hall↗

arXiv2025

Superconducting Acoustogalvanic Effect in Twisted Transition Metal Dichalcogenides

Two-dimensional van der Waals superconductors are attracting much attention owing to their rich phase diagrams including possible unconventional superconductivity. However, they suffer from a lack of reliable methods for identifying their nontrivial pairing symmetries and quantum geometry. In this study, we propose nonlinear responses driven by surface acoustic waves as a novel probe to access exotic Bogoliubov quasiparticles in such superconductors. Our approach is particularly suitable for addressing the superconducting gap structure as the gap energies in these systems typically lie within the frequency range of surface acoustic waves, and thus paves the way toward the experimental identification of exotic superconducting states especially in low-$T_c$ superconductors.

cond-mat.supr-con↗

arXiv2025

Directional propagation of quantum Hall viscous fluid by nano-structural engineering

We present a microscopic theory of the viscous electron fluid in the quantum Hall state based on the nonequilibrium Green's function method and the von Neumann lattice representation. This approach permits the formulation of hydrodynamic equations in the strong field regime that accommodates arbitrary boundary conditions. We demonstrate nonreciprocal transport resulting from the interplay between magnetic field-induced viscosity and device geometry in a notched system. Our results will offer a powerful tool for studying the nonperturbative effects of magnetic fields on electron viscous fluids.

cond-mat.mes-hall↗

arXiv2024

Unveiling the origin of diffusion suppression of hydrogen isotopes at the α-Al2O3(0001)/α-Cr2O3(0001) interfaces

It has been reported that the α-Al2O3, a promising tritium permeation barrier material for a fusion reactor, can be grown at low temperatures on the α-Cr2O3 template, and that α-Al2O3/α-Cr2O3 composite films have more efficiently suppress the hydrogen isotope permeation than the single α-Al2O3 film. In this study, we investigated the diffusion properties of hydrogen isotopes at the α-Al2O3(0001)/α-Cr2O3(0001) interfaces using first-principles calculations based on density functional theory. In the α-Al2O3 region near the interfaces, O-H covalent bonds, which are not observed in the bulk α-Al2O3, are formed, and hydrogen isotopes become stable. Such chemical bonds induced by the interfaces are the origin of hydrogen isotope trapping and result in a larger diffusion barrier than in the α-Al2O3 and the α-Cr2O3. It was also found that the suppression of hydrogen isotope diffusion does not occur at the interface site but at sites adjacent to the interfaces. In addition, the interface enhances the oxygen vacancies, which may also suppress hydrogen isotope permeation.

cond-mat.mtrl-sci↗

arXiv2024

Acousto-magnonic spin Hall effect in honeycomb antiferromagnets

The recently discovered van der Waals antiferromagnets have suffered from the lack of a comprehensive method to study their magnetic properties. Here, we propose a dissipationless magnon spin Hall current driven by surface acoustic waves as a novel probe for such antiferromagnets. Our results pave the way towards mechanical detection and manipulation of the magnetic order in two-dimensional antiferromagnets. Furthermore, they will overcome the difficulties with weak magnetic responses inherent in the use of antiferromagnets and hence provide a building block for future antiferromagnetic spintronics.

cond-mat.mes-hall↗

arXiv2024

Chirality-induced spin selectivity by variable-range hopping along DNA double helix

We here present a variable-range hopping model to describe the chirality-induced spin selectivity along the DNA double helix. In this model, DNA is considered as a one-dimensional disordered system, where electrons are transported by chiral phonon-assisted hopping between localized states. Owing to the coupling between the electron spin and the vorticity of chiral phonons, electric toroidal monopole appears in the charge-to-spin conductances as a manifestation of true chirality. Our model quantitatively explains the temperature dependence of the spin polarization observed in experiments.

cond-mat.mes-hall↗

arXiv2023

Breaking down the magnonic Wiedemann-Franz law in the hydrodynamic regime

Recent experiments have shown an indication of a hydrodynamic magnon behavior in ultrapure ferromagnetic insulators; however, its direct observation is still lacking. Here, we derive a set of coupled hydrodynamic equations and study the thermal and spin conductivities for such a magnon fluid. We reveal the drastic breakdown of the magnonic Wiedemann-Franz law as a hallmark of the hydrodynamics regime, which will become key evidence for the experimental realization of an emergent hydrodynamic magnon behavior. Therefore, our results pave the way towards the direct observation of magnon fluids.

cond-mat.mes-hall↗

arXiv2022

Valley hydrodynamics in gapped graphene

Recent experiments have revealed that novel nonequilibrium states consistent with the hydrodynamic description of electrons are realized in ultrapure graphene, which hosts the valley degrees of freedom. Here, we formulate a theory of electron hydrodynamics including dissipation processes of the valley angular momentum by employing the concept of micropolar fluids. As a result, our theory proposes a novel strategy to generate a valley polarization by the microrotation. We uncover that the rotational viscosity induces longitudinal valley currents which are second order in electric fields.

cond-mat.mes-hall↗

arXiv2021

Nonreciprocal electron hydrodynamics under magnetic fields: applications to nonreciprocal surface magnetoplasmons

Recent experiments have elucidated that novel nonequilibrium states inherent in the so-called hydrodynamic regime are realized in ultrapure metals with sufficiently strong momentum-conserving scattering. In this letter, we formulate a theory of electron hydrodynamics with broken inversion symmetry under magnetic fields and find that novel terms emerge in hydrodynamic equations which play a crucial role for the realization of the nonreciprocal responses. Specifically, we clarify that there exist a novel type of nonreciprocal collective modes dubbed nonreciprocal surface magnetoplasmons arising from an interplay between magnetic fields and the orbital magnetic moment. We reveal that these nonreciprocal collective modes indeed give rise to the nonreciprocity in magneto-optical responses such as the reflectivity. The physics discussed here will bridge the two important notions of magnetoplasmonics and nonreciprocity in electron hydrodynamic materials with inversion symmetry breaking and magnetic fields.

cond-mat.mes-hall↗