Searcharxiv⌕ Search

arXiv subjects

Takeo Kato

Publications and source records attributed to Takeo Kato.

At least 37 records · Page 2Linked to original sources

Probing anyon statistics on a single-edge loop in the fractional quantum Hall regime

We propose a setup to directly measure the anyonic statistical angle on a single edge of a fractional quantum Hall system, without requiring independent knowledge of non-universal parameters. We consider a Laughlin edge state bent into a closed loop geometry, where tunneling processes are controllably induced between the endpoints of the loop. To illustrate the underlying physical mechanism, we compute the time-dependent current generated by the injection of multiple anyons, and show that its behavior exhibits distinctive features governed by the anyonic statistical angle. The measured current reflects quantum interference effects due to the time-resolved braiding of anyons at the junction. To establish experimental relevance, we introduce a protocol where anyons are probabilistically injected upstream of the loop via a quantum point contact (QPC) source. Unlike in Fabry-Perot interferometers, where phase jumps occur spontaneously due to stochastic quasi-particle motion, here the phase jumps are deliberately induced by source injections. These events imprint measurable signatures in the cross-correlation noise, enabling a controlled statistical analysis of the braiding phase. We further show that, by varying the magnetic field while remaining within the same fractional quantum Hall plateau, the statistical angle can be extracted without relying on the knowledge of other non-universal system parameters. Our results provide a minimal and accessible platform for probing anyonic statistics using a single chiral edge.

cond-mat.mes-hall↗

Light-induced inverse spin Hall effect and field-induced circular photogalvanic effect in GaAs revealed by two-dimensional terahertz Fourier analysis

The electromotive force transverse to a bias field under irradiation of circularly polarized light, namely the photovoltaic Hall response or light-induced anomalous Hall effect, has attracted considerable attention to investigate the topologically nontrivial states in Floquet engineering and the inverse spin Hall effect of spin-polarized carriers in spintronics. However, taking into account inversion symmetry breaking by the bias field, the circularly polarized light can excite photocarriers with asymmetric momentum distribution, which generates injection current transverse to the bias field. Therefore, the field-induced circular photogalvanic effect (FI-CPGE) should also emerge in the very same experimental configuration for light-induced anomalous Hall effect but has been overlooked in literature. In this work, using terahertz pulses as a bias field for a semiconductor GaAs, we conduct two-dimensional Fourier analysis and demonstrate that FI-CPGE can play a major role in the photovoltaic Hall response. Counterintuitively, FI-CPGE is significantly enhanced when the photocarriers are excited near the bandgap with small density of states and low group velocity, which can be explained by a three-level resonant nonlinear interaction near the band degeneracy point. We also clarified that FI-CPGE would be further largely detected in the contact-type measurement using electrodes because of the absence of a filtering effect inherent to terahertz pulses. This work provides a comprehensive, generalized view of the photovoltaic Hall response in biased materials, paving a new avenue for detecting topological monopoles in momentum space hidden in equilibrium using third-order nonlinear responses.

cond-mat.mtrl-sci↗

Spin pumping into quantum spin nematic states

We theoretically study spin pumping into a spin-nematic state in a junction system composed of a ferromagnetic insulator and a spin-nematic insulator, described by using the spin-1 bilinear-biquadratic model. We analyze an increase of the Gilbert damping in ferromagnetic resonance (FMR) due to an interfacial exchange coupling within a mean-field theory based on the Schwinger boson method. We find that the two Schwinger bosons contribute in distinct ways to spin pumping. We report a detailed dependence of the spin pumping on a resonant frequency, a magnetic field, and an interface type.

cond-mat.mes-hall↗

Microscopic theory of Rashba-Edelstein magnetoresistance

We theoretically study Rashba-Edelstein magnetoresistance (REMR) in a two-dimensional electron gas (2DEG) system with Rashba and Dresselhaus spin-orbit interactions. We consider a microscopic model of a junction system composed of a ferromagnetic insulator and a 2DEG, and derive analytic expressions for the spin and current densities in the 2DEG using the Boltzmann equation, while taking into account dynamical contributions from magnons. Our findings reveal that the sign of the REMR varies depending on the type of interface. We also discuss the experimental relevance of our results.

cond-mat.mes-hall↗

Fluctuations in Spin Dynamics Excited by Pulsed Light

We theoretically investigate nonequilibrium spin fluctuations in a ferromagnet induced by a light pulse. Using a Lindblad equation consistent with the Landau-Lifshitz-Gilbert equation, we compute the autocorrelation function of magnetization. Our analysis reveals that this function comprises both thermal and nonequilibrium components. To examine the latter in detail, we introduce a Fano factor similar to nonequilibrium current noise in electronic circuits. We demonstrate that this factor encapsulates insights into the transfer of spin units to the environment. Our findings lay the groundwork for nonequilibrium spin noise spectroscopy, offering valuable insights into spin relaxation dynamics.

cond-mat.mes-hall↗

TeNeS-v2: Enhancement for Real-Time and Finite Temperature Simulations of Quantum Many-Body Systems

Quantum many-body systems are challenging targets for computational physics due to their large degrees of freedom. The tensor networks, particularly Tensor Product States (TPS) and Projected Entangled Pair States (PEPS), effectively represent these systems on two-dimensional lattices. However, the technical complexity of TPS/PEPS-based coding is often too much for researchers to handle. To reduce this problem, we developed TeNeS (Tensor Network Solver). This paper introduces TeNeS-v2, which extends TeNeS with real-time and finite temperature simulations, providing deeper insights into quantum many-body systems. We detail the new algorithms, input/output design, and application examples, demonstrating TeNeS-v2's applicability to various quantum spin and Bose models on two-dimensional lattices.

cond-mat.str-el↗

Theory of spin pumping and inverse Rashba-Edelstein effect in a two-dimensional electron gas

We theoretically investigate spin transport in a junction system composed of a ferromagnetic insulator (FI) and a two-dimensional electron gas (2DEG) with both Rashba and Dresselhaus spin-orbit interactions. We briefly present our findings on spin pumping into the 2DEG under microwave irradiation and subsequent current generation via the inverse Rashba-Edelstein effect. We highlight the crucial role of vertex corrections in the theoretical description of these effects.

cond-mat.mes-hall↗

Chirality-induced Phonon-Spin Conversion at an Interface

We consider spin injection driven by nonequilibrium chiral phonons from a chiral insulator into an adjacent metal. Phonon-spin conversion arises from the coupling of the electron spin with the microrotation associated with chiral phonons. We derive a microscopic formula for the spin injection rate at a metal-insulator interface. Our results clearly illustrate the microscopic origin of spin current generation by chiral phonons and may lead to a breakthrough in the development of spintronic devices without heavy elements.

cond-mat.mes-hall↗

Spin pumping into quantum spin chains

We theoretically investigate spin pumping into a quantum easy-plane ferromagnetic spin chain system. This quantum spin chain is effectively described by the Tomonaga-Luttinger (TL) liquid despite the ferromagnetic exchange interaction because of the easy-plane magnetic anisotropy. This TL liquid state has an extremely strong interaction that is hardly realized in other quantum antiferromagnetic chain systems or weakly interacting electron systems. We show how the strongly interacting TL liquid affects the ferromagnetic resonance that occurs in the ferromagnetic insulator. In particular, we discuss the dependence of the Gilbert damping on the temperature and the junction length. The Gilbert damping allows us to extract information about the above-mentioned strong interaction within the quantum ferromagnetic spin chain. We also point out that a well-known compound CsCuCl$_3$ will be suitable for the realization of our setup.

cond-mat.str-el↗

Theory of the inverse Rashba-Edelstein effect induced by thermal spin injection

We theoretically consider a junction composed of a ferromagnetic insulator (FI) and a two-dimensional electron gas (2DEG) with Rashba- and Dresselhaus-type spin-orbit interactions. Using the Boltzmann equation, we calculate an electric current in 2DEG induced by the inverse Rashba-Edelstein effect when imposing the temperature difference between FI and 2DEG. We clarify how the induced current depends on the magnetization direction of FI, spin texture on the Fermi surface of 2DEG, and temperature. Our result provides an important foundation for an accurate analysis of the inverse Rashba-Edelstein effect induced by thermal spin injection.

cond-mat.mes-hall↗

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↗

What is a proper definition of spin current? -- Lessons from the Kane-Mele Model

Spin current, a key concept in spintronics that carries spin angular momentum, has a non-unique definition due to the non-conservation of spins in solids. While two primary definitions exist -- conventional spin current and conserved spin current -- their validity has not been quantitatively examined. Here, we examine the validity of these definitions of spin current by comparing their spin Hall conductivities to the spin accumulation on edges of materials calculated in a real-time evolution simulation. Employing the Kane-Mele model with the Rashba term, which explicitly violates spin conservation, we reveal that the spin Hall conductivities calculated under both definitions fail to reproduce the simulated results of spin accumulation when the Rashba term is large. Our results suggest that the standard definitions of spin current and the associated spin Hall conductivity do not give an accurate quantitative estimate of spin accumulation. This conclusion indicates that real-time simulations are necessary to accurately estimate spin accumulation on edges/surfaces of materials.

cond-mat.mes-hall↗

H-wave -- A Python package for the Hartree-Fock approximation and the random phase approximation

H-wave is an open-source software package for performing the Hartree--Fock approximation (HFA) and random phase approximation (RPA) for a wide range of Hamiltonians of interacting fermionic systems. In HFA calculations, H-wave examines the stability of several symmetry-broken phases, such as anti-ferromagnetic and charge-ordered phases, in the given Hamiltonians at zero and finite temperatures. Furthermore, H-wave calculates the dynamical susceptibilities using RPA to examine the instability toward the symmetry-broken phases. By preparing a simple input file for specifying the Hamiltonians, users can perform HFA and RPA for standard Hamiltonians in condensed matter physics, such as the Hubbard model and its extensions. Additionally, users can use a Wannier90-like format to specify fermionic Hamiltonians. A Wannier90 format is implemented in RESPACK to derive ab initio Hamiltonians for solids. HFA and RPA for the ab initio Hamiltonians can be easily performed using H-wave. In this paper, we first explain the basis of HFA and RPA, and the basic usage of H-wave, including download and installation. Thereafter, the input file formats implemented in H-wave, including the Wannier90-like format for specifying the interacting fermionic Hamiltonians, are discussed. Finally, we present several examples of H-wave such as zero-temperature HFA calculations for the extended Hubbard model on a square lattice, finite-temperature HFA calculations for the Hubbard model on a cubic lattice, and RPA in the extended Hubbard model on a square lattice.

cond-mat.str-el↗

Observation of Terahertz Spin Hall Conductivity Spectrum in GaAs with Optical Spin Injection

We report the first observation of the spin Hall conductivity spectrum in GaAs at room temperature. Our terahertz polarimetry with a precision of several $μ$rads resolves the Faraday rotation of terahertz pulses arising from the inverse spin Hall effect of optically injected spin-polarized electrons. The obtained spin Hall conductivity spectrum exhibits an excellent quantitative agreement with theory, demonstrating a crossover in the dominant origin from impurity scattering in the DC regime to the intrinsic Berry-curvature mechanism in the terahertz regime. Our spectroscopic technique opens a new pathway to analyze anomalous transports related to spin, valley, or orbital degrees of freedom.

cond-mat.mtrl-sci↗

Minimal alternating current injection into carbon nanotubes

We study theoretically the effect of electronic interactions in 1d systems on electron injection using periodic Lorentzian pulses, known as Levitons. We consider specifically a system composed of a metallic single-wall carbon nanotube, described with the Luttinger liquid formalism, a scanning tunneling microscope (STM) tip, and metallic leads. Using the out-of-equilibrium Keldysh Green function formalism, we compute the current and current noise in the system. We prove that the excess noise vanishes when each Leviton injects an integer number of electrons from the STM tip into the nanotube. This extends the concept of minimal injection with Levitons to strongly correlated, uni-dimensional non-chiral systems. We also study the time-dependent current profile, and show how it is the result of interferences between pulses non-trivially reflected at the nanotube-lead interface.

cond-mat.mes-hall↗

Spin Pumping into Carbon Nanotubes

We theoretically study spin pumping from a ferromagnetic insulator (FI) into a carbon nanotube (CNT). By employing the bosonization method, we formulate the Gilbert damping induced by the FI/CNT junction, which can be measured by ferromagnetic resonance. We show that the increase in the Gilbert damping has a temperature dependence characteristic of a Luttinger liquid and is highly sensitive to the Luttinger parameter of the spin sector for a clean interface. We also discuss the experimental relevance of our findings based on numerical estimates, using realistic parameters.

cond-mat.mes-hall↗

Twisted bilayer graphene reveals its flat bands under spin pumping

The salient property of the electronic band structure of twisted bilayer graphene (TBG), at the so-called magic angle (MA), is the emergence of flat bands around the charge neutrality point. These bands are associated with the observed superconducting phases and the correlated insulating states. Scanning tunneling microscopy combined with angle resolved photoemission spectroscopy are usually used to visualize the flatness of the band structure of TBG at the MA. Here, we theoretically argue that spin pumping (SP) provides a direct probe of the flat bands of TBG and an accurate determination of the MA. We consider a junction separating a ferromagnetic insulator and a heterostructure of TBG adjacent to a monolayer of a transition metal dichalcogenide. We show that the Gilbert damping of the ferromagnetic resonance experiment, through this junction, depends on the twist angle of TBG, and exhibits a sharp drop at the MA. We discuss the experimental realization of our results which open the way to a twist switchable spintronics in twisted van der Waals heterostructures.

cond-mat.mes-hall↗

Nonequilibrium noise as a probe of pair-tunneling transport in the BCS--BEC Crossover

The detection of elementary carriers in transport phenomena is one of the most important keys to understand non-trivial properties of strongly-correlated quantum matter. Here we propose a method to identify the tunneling current carrier in strongly interacting fermions from nonequilibrium noise in the Bardeen-Cooper-Schrieffer to Bose--Einstein condensate crossover. The noise-to-current ratio, the Fano factor, can be a crucial probe for the current carrier. Bringing strongly-correlated fermions into contact with a dilute reservoir produces a tunneling current in between. The associated Fano factor increases from one to two as the interaction becomes stronger, reflecting the fact that the dominant conduction channel changes from the quasiparticle tunneling to the pair tunneling.

cond-mat.quant-gas↗