arXiv subjects

Gen Tatara

Publications and source records attributed to Gen Tatara.

At least 19 recordsLinked to original sources

arXiv2026

Josephson phase shift and diode effect due to the inverse spin Hall effect

We theoretically study the direct and inverse spin Hall effects in a superconductor-normal metal-uperconductor junction induced by a spin-orbit interaction that is invariant under spatial inversion. We show that a supercurrent induces a spin Hall effect, leading to a static spin accumulation with opposite polarizations at the two edges, analogous to that in normal conductors. For the inverse effect, we consider a spatially inhomogeneous static magnetic field and show that it induces an anomalous phase shift, which, in the presence of higher harmonics, results in a diode effect. Unlike Rashba systems studied previously, the present mechanism does not require broken structural inversion symmetry, since an inhomogeneous magnetic field, equivalent to a spin current, breaks the inversion symmetry extrinsically.

cond-mat.mes-hall↗

arXiv2024

A quantum picture of light-suppressed photosynthetic charge transfer

We propose a dynamic mechanism for the reversible regulation of photosynthesis in varying light environments. We employ a three-level quantum model to take into account the correlations between charge donors and charge acceptors immediately before photoexcitation, and show that under continuous illumination, the transfer efficiency of a single charge is inversely proportional to the intensity of light, which can be suppressed so severely that it becomes a limiting factor on linear electron transport. This result is used to derive a set of analytical expressions that characterize the light response curves of photosynthetic parameters, including that of gross photosynthetic rate which saturates in high light and has long been assumed to obey a Michaelis-Menten function. We discuss the implications of thermal fluctuation in the light source, and argue that at a given intensity of light, the quantum yields measured with an incandescent lamp may be higher than those measured with a laser, a manifestation of thermal fluctuation in lamp illumination. Our new picture helps understand the observed plastocyanin-dependent electron transport in photosystem I and provides a donor-side scheme for the onset of irreversible damage to photosystem II by visible light.

physics.bio-ph↗

arXiv2022

Intrinsic orbital and spin Hall effect in bismuth semimetal

We investigate the intrinsic orbital Hall conductivity (OHC) and spin Hall conductivity (SHC) in a bismuth semimetal, by employing an sp-orbital tight-binding model. We report a notable difference between the anisotropy of OHC and SHC whose orbital and spin polarizations lie within the basal plane. We do not observe a substantial correlation between the orbital and spin Berry curvatures with spin-orbit coupling (SOC) at the Fermi energy, disproving the correlation between OHC and SHC in a strong SOC regime. We argue the huge SHC in a Bi semimetal is attributed to its gigantic SOC which strongly affects the hybridization of the p orbitals, despite its relatively small magnitude of OHC. We hope the distinct anisotropy of OHC and SHC provides a feasible means to differentiate between the two effects in experiments.

cond-mat.str-el↗

arXiv2022

Inverse Faraday effect in massive Dirac electrons

We study the inverse Faraday effect (IFE) in a Dirac Hamiltonian with random impurities using Keldysh formalism and diagrammatic perturbation theory. The mass term in the Dirac Hamiltonian is essential for IFE, where the spin magnetic moment induced by circularly polarized light is proportional to the frequency of the incident light within the THz regime. For massive Dirac electrons, the corrections due to short-range impurities on spin magnetic moment vertex exhibits mixing of the spin magnetic moment vertex and spin angular momentum vertex. The spin magnetic density response is divergently enhanced by the vertex corrections near the band edge, indicting a long-range diffusion of spin density profile in massive Dirac electrons.

cond-mat.str-el↗

arXiv2022

Calculation of magnon drag force induced by an electric current in ferromagnetic metals

Magnon drag effect induced by an applied electric field in ferromagnetic metals is theoretically studied by a microscopic calculation of the force on magnons arising from magnon emission/absorption and scattering due to driven electrons. It is shown that magnon scattering contribution dominates over the emission/absorption one in a wide temperature regime in good metals with long elastic lifetime $\taue$, as the latter has a relative suppression factor of $(\Deltasd\taue)^{-2}$ due to the electron spin flip by the magnon, where $\Deltasd$ is the $sd$ exchange interaction energy. Spin-transfer efficiency is discussed including the magnon drag effect.

cond-mat.mes-hall↗

arXiv2022

Nonlocality of electrically-induced spin accumulation in chiral metals

Spin accumulation induced by an electric field in chiral electron system is investigated based on a linear response theory. It is shown that the spin response function has a spatially uniform component due to the chiral angular momentum generation effect, resulting in a nonlocal spin generation. The result suggests a scenario for nonlocal long-range spin transport in chiral metals reported experimentally recently.

cond-mat.mes-hall↗

arXiv2022

Spin accumulation without spin current

The spin Hall (SH) effect is a phenomenon in which the spin current flows perpendicular to an applied electric field and causes the spin accumulation at the boundaries. However, in the presence of spin-orbit couplings, the spin current is not well defined. Here, we calculate the spin response to an electric-field gradient, which naturally appears at the boundaries. We derive a generic formula using the Bloch wave functions and the phenomenological relaxation time. We also calculate the response for the uniform Rashba model with $δ$-function nonmagnetic disorder within the first-order Born approximation and corresponding vertex corrections. We find the nonzero spin accumulation, although the SH conductivity exactly vanishes.

cond-mat.mes-hall↗

arXiv2021

Spin Hall response at finite wave vector in ferromagnets

Spin Hall effect at finite wave vector in a ferromagnetic conductor is theoretically studied by calculating the spin density as the linear response to an applied electric field. The cases of a spin-orbit interaction due to random impurities and a localized Rashba interaction are considered. It is shown that the spin Hall effect has a broad response for the wave vector $q\lesssim 2\kf$ where $\kf $ is the Fermi wave vector. This fact confirms the local nature of the spin-charge conversion effects.

cond-mat.mes-hall↗

arXiv2021

Hydrodynamic theory of vorticity-induced spin transport

Electron spin transport in a disordered metal is theoretically studied from the hydrodynamic viewpoint focusing on the role of electron vorticity. The spin-resolved momentum flux density of electrons is calculated taking account of the spin-orbit interaction and uniform magnetization, and the expression for the spin motive force is obtained as the linear response to a driving electric field. It is shown that the spin-resolved momentum flux density and motive force are characterized by troidal moments expressed as vector products of the applied external electric field and the spin polarization and/or magnetization. The spin-vorticity and magnetization-vorticity couplings studied recently are shown to arise from the toridal moments contribution to the momentum flux density. Spin motive force turns out to have a nonconservative contribution besides the conventional conservative one due to the spin-vorticity coupling. Spin accumulation induced by an electric field is calculated to demonstrate the direct relation between vorticity and induced spin, and the spin Hall effect is interpreted as due to the spin-vorticity coupling. The spin-vorticity coupling is shown to give rise to a vorticity-induced torque and a spin relaxation. The vorticity-induced torque is a linear effect of the spin-orbit interaction and is expected to be larger than the second-order torques such as nonadiabatic ($β$) current-induced torque due to magnetization structure. The intrinsic inverse spin Hall effect is argued to correspond to the antisymmetric components of the momentum flux density in the hydrodynamic context.

cond-mat.mes-hall↗

arXiv2021

Vorticity-induced anomalous Hall effect in electron fluid

We develop a hydrodynamic theory for an electron system exhibiting the anomalous Hall effect, and show that an additional anomalous Hall effect is induced by a vorticity generated near boundaries. We calculate the momentum flux and force proportional to the electric field using linear response theory. The hydrodynamic equation is obtained by replacing the local electric field with the electric current, focusing on a scale that is sufficiently larger than the mean free path. It is demonstrated that there is a coupling between a vorticity of an electric current and a magnetization which generates a pressure from non-uniform vorticity. Taking into account Hall viscosity and relaxation forces, a non-uniform flow near a boundary and an additional Hall force are calculated. The additional anomalous Hall force is opposite to conventional anomalous Hall force, resulting in a sign reversal in thin systems.

cond-mat.mes-hall↗

arXiv2020

Skew-scattering-induced giant antidamping spin-orbit torques: Collinear and out-of-plane Edelstein effects at two-dimensional material/ferromagnet interfaces

Heavy metal/ferromagnet interfaces feature emergent spin-orbit effects absent in the bulk materials. Because of their inherent strong coupling between spin, charge and orbital degrees of freedom, such systems provide a platform for technologically sought-after spin-orbit torques (SOTs). However, the microscopic origin of purely interfacial antidamping SOT, especially in the ultimate atomically thin limit, has proven elusive. Here, using two-dimensional (2D) van der Waals materials as a testbed for interfacial phenomena, we address this problem by means of a microscopic framework accounting for band structure effects and impurity scattering on equal footing and nonperturbatively. A number of unconventional and measurable effects are predicted, the most remarkable of which is a giant enhancement of antidamping SOT in the dilute disorder limit induced by a robust skew scattering mechanism, which is operative in realistic interfaces and does not require magnetic impurities. The newly unveiled skew scattering mechanism activates rich semiclassical spin-charge conversion effects that have gone unnoticed in the literature, including a collinear Edelstein effect with nonequilibrium spin polarization aligned with the direction of the applied current.

cond-mat.mes-hall↗

arXiv2020

Hydrodynamic theory of chiral angular momentum generation in metals

We present a hydrodynamic theory to describe a chiral electron system with a Weyl spin-orbit interaction on a field-theoretic basis. Evaluating the momentum flux density as a linear response to a driving electric field, we derive an equation of motion for the orbital angular momentum. It is shown that the chiral nature leads to a dynamic bulk angular momentum generation by inducing a global torque as a response to the applied field. The steady state angular momentum is calculated taking account of rotational viscosity.

cond-mat.mes-hall↗

arXiv2020

Pair emission from a relativistic domain wall in antiferromagnets

Magnon emission and excitation by a relativistic domain wall at a constant velocity in antiferromagnet is theoretically studied. A pair emission due to a quadratic magnon coupling is shown to be dominant. The emission corresponds in the comoving frame to a vacuum polarization induced by a zero-energy instability of the Lorentz-boosted anomalous response function. The emission rate is sensitive to the magnon dispersion and wall profile, and is significantly enhanced for a thin wall with velocity close to the effective light velocity. The Ohmic damping constant due to magnon excitation at low velocity is calculated.

cond-mat.mes-hall↗

arXiv2020

Optical responses induced by spin gauge field at the second order

Optical responses of ferromagnetic materials with spin gauge field that drives intrinsic spin curren is theoretically studied. The conductivity tensor is calculated based on a linear response theory to the applied electric field taking account of the non-linear effects of the spin gauge field to the second order. We consider the case where the spin gauge field is uniform, realized for spiral magnetization structure or uniform spin-orbit interaction. The spin gauge field, or an intrinsic spin current, turns out to give rise to anisotropic optical responses, which is expected to be useful to experimental detection of magnetization structures.

cond-mat.mes-hall↗

arXiv2020

Collective coordinate study of spin wave emission from dynamic domain wall

We study theoretically the spin wave emission from a moving domain wall in a ferromagnet. Introducing a deformation mode describing a modulation of the wall thickness in the collective coordinate description, we show that thickness variation couples to the spin wave linearly and induces spin wave emission. The dominant emitted spin wave turns out to be polarized in the out-of wall plane ($ϕ$)-direction. The emission contributes to the Gilbert damping parameter proportional to $\hbarω_ϕ/K$, the ratio of the angular frequency $ω_ϕ$ of $ϕ$ and the easy-axis anisotropy energy $K$.

cond-mat.mes-hall↗

arXiv2020

Topological Hall signatures of magnetic hopfions

Magnetic hopfions are topologically protected three-dimensional solitons that are constituted by a tube which exhibits a topologically nontrivial spin texture in the cross-section profile and is closed to a torus. Here we show that the hopfion's locally uncompensated emergent field leads to a topological Hall signature, although the topological Hall effect vanishes on the global level. The topological Hall signature is switchable by magnetic fields or electric currents and occurs independently of the anomalous and conventional Hall effects. It can therefore be exploited to electrically detect hopfions in experiments and even to distinguish them from other textures like skyrmion tubes. Furthermore, it can potentially be utilized in spintronic devices. Exemplarily, we propose a hopfion-based racetrack data storage device and simulate the electrical detection of the hopfions as carriers of information.

cond-mat.mes-hall↗

arXiv2019

Spin backflow: a non-Markovian effect on spin pumping

The miniaturization of spintronic devices, specifically, nanoscale devices employing spintronics, has attracted intensive attention from a scientific as well as engineering perspective. In this paper, we study non-Markovian effect on spin pumping to describe spin current generation driven by arbitrary precession frequency of magnetization in a quantum dot attached to an electron lead. Although the Markovian approximation can be used when driving is sufficiently slow compared with relaxation times in electron tunneling, recent developments in nano-spintronic devices show that we need to include non-Markovian effects. In contrast to the one-way-only nature of the spin current generation under the Markovian dynamics, we find that the non-Markovian dynamics exhibits a temporal backflow of spin, call spin backflow for brevity. We capture the phenomenon by introducing its quantifier, and show that the backflow significantly reduces the amount of spin current when the frequency exceeds the relaxation rate. This prevents unphysical divergence of the spin current in the high frequency limit that occurs under the Markovian approximation. We believe our analysis provides an understanding of the spin pumping particularly in regard to producing a more efficient spin current generation over shorter time scales by going beyond the conventional Markovian approximation.

cond-mat.mes-hall↗

arXiv2019

Theory of spin transport through antiferromagnetic insulator

A theoretical formulation for spin transport through an antiferromagnetic (AF) insulator is presented in the case driven/detected by direct/inverse spin Hall effect in two heavy metal contacts. The spin signal is shown to be transferred by the ferromagnetic correlation function of the antiferromagnet, which is calculated based on a magnon representation. To cover high temperature regimes, we include an auxiliary field representing short AF correlations and a temperature-dependent damping due to magnon scattering. The diffusion length for spin is long close to the degeneracy of the two AF magnons, and has a maximum as function of temperature near the Néel transition.

cond-mat.mes-hall↗