arXiv subjects

Minoru Kanega

Publications and source records attributed to Minoru Kanega.

8 recordsLinked to original sources

arXiv2026

Floquet Theory for Light-Driven Rotation of Dipolar and Multipolar Particles

Nano- or micro-particle rotation driven by light has been well known in the fields of optical manipulation and optical physics since the end of the last century. It is viewed as a sort of angular-momentum transfer from light to material, but its microscopic analysis based on the Hamiltonian or the equation of motion has been less developed. We model this rotation with a simple setup of an electrically dipolar or multipolar particle irradiated by circularly polarized laser and comprehensively analyze the Langevin-type equation of motion by using the Floquet theory for dissipative classical systems and the mode separation method. Furthermore, we numerically compute the time evolution of the particle. As a result, we accurately estimate the dependence of the laser-frequency, laser-intensity, particle mass, temperature, and friction (dissipation) on the laser-driven rotation. We determine the ``nonequilibrium phase diagram'' of the laser-driven rotation in a broad parameter regime, which consists of three regimes: the rotation frequency $\Omega\propto\omega^{-1}$, $\Omega\propto\omega^{-3}$, or $\Omega=\omega$ ($\omega$ is the laser frequency). Comparing our theoretical result with some experiments, we show that the result of the overdamped Langevin equation is qualitatively consistent with the experiments.

cond-mat.mes-hall↗

arXiv2026

Magnon harmonic generation in antiferromagnets: Dynamical symmetry enriched by symmetry breaking

In recent years, techniques of intense THz laser have enabled us to experimentally observe nonlinear spin dynamics in antiferromagnets since the elementary excitations such as magnons reside on a THz to GHz range in antiferromagnets and THz laser thus can directly excite them. We numerically and theoretically investigate THz-laser or GHz-wave driven harmonic generations in typical ordered phases of antiferromagnets: N\'eel, canted and weak ferromagnetic phases. The radiation waves (harmonic generations) are created by the incident-wave driven magnon dynamics. We point out that magnetic orders and phase transitions can change the spectra of harmonic generations, differently from those of metallic, semiconductor, or atomic-gas systems without (spontaneous) symmetry breakings. We consider both the magnon harmonic generation driven by standard single-color laser and that by two-color laser in the antiferromagnets, and find several dynamical symmetries and the corresponding selection rules of the harmonic generations. These results indicate that the magnon harmonic generation spectra provide new information about symmetry or symmetry breaking of antiferromagnets.

cond-mat.str-el↗

arXiv2025

Generation of magnetic chiral solitons, skyrmions, and hedgehogs with electric fields

Electric-field controls of Dzyaloshinskii-Moriya interactions (DMIs) have recently been discussed from the microscopic viewpoint. Since the DMI plays a critical role in generating topological spin textures (TSTs) such as the chiral soliton, the magnetic skyrmion, and the magnetic hedgehog, electric-field controls of these TSTs have become an important issue. This paper shows that such electric-field-induced DMI indeed creates and annihilates TSTs by numerically solving the Landau-Lifshitz-Gilbert (LLG) equation for many-body spin systems at finite temperatures. We show that when a strong electric field is applied in a proper way to one- or two-dimensional ferromagnets, the Hamiltonians are changed into the well-known spin models for the chiral soliton or the skyrmion lattice, and the TST states emerge. We utilize a machine-learning method to count the number of generated TSTs. In the three-dimensional (3D) case, we demonstrate the electric-field induction of a magnetic hedgehog structure as follows: Applying a strong enough electric field along a proper direction to a skyrmion-string state (a triple-$\boldsymbol{q}$ state) at low but finite temperatures, we find that the field-induced DMI can drive a quadruple-$\boldsymbol{q}$ state with hedgehog-antihedgehog pairs. This result indicates that we have succeeded in constructing a simple 3D short-range interacting spin model hosting a magnetic hedgehog structure.

cond-mat.str-el↗

arXiv2024

Two-color laser control of photocurrent and high harmonics in graphene

We comprehensively investigate two-color-laser-driven photocurrent and high harmonic generation (HHG) in graphene models. By numerically solving the quantum master equation, we uniformly explore a broad parameter regime including both the weak (perturbative) and intense-laser (nonperturbative) cases while considering the dissipation effects. We demonstrate that the HHG spectra can be drastically altered by tuning the real-space path traced by the laser electric field. This controllability is explained by the dynamical symmetry argument. We also show that both the magnitude and the direction of photocurrent (zeroth order harmonics) can be controlled by varying the frequency, intensity, ellipticity, and relative phase of the two-color laser. Furthermore, the nature of photocurrent is shown to be classified into shift- or injection-current types, depending on the phase of two-color laser. Our findings indicate that even in centrosymmetric electron systems, photocurrent and HHG can be quantitatively controlled by adjusting various external parameters if we utilize multicolor laser with a lower spatial or temporal symmetry.

cond-mat.mes-hall↗

arXiv2024

High-harmonic generation in graphene under the application of a DC electric current: From perturbative to nonperturbative regimes

We theoretically investigate high-harmonic generation (HHG) in honeycomb-lattice graphene models when subjected to a DC electric field. By integrating the quantum master equation with the Boltzmann equation, we develop a numerical method to compute laser-driven dynamics in many-electron lattice systems under DC electric current. The method enables us to treat both the weak-laser (perturbative) and intense-laser (nonperturbative) regimes in a unified way, accounting for the experimentally inevitable dissipation effects. From it, we obtain the HHG spectra and analyze their dependence on laser frequency, laser intensity, laser-field direction, and DC current strength. We show that the dynamical and static symmetries are partially broken by a DC current or staggered potential term, and such symmetry breakings drastically change the shape of the HHG spectra, especially in terms of the presence or absence of $(2n+1)$th-, $2n$th-, or $3n$th-order harmonics ($n\in \mathbb Z$). The laser intensity, frequency, and polarization are also shown to affect the shape of the HHG spectra. Our findings indicate that HHG spectra in conducting electron systems can be quantitatively or qualitatively controlled by tuning various external parameters, and DC electric current is used as such an efficient parameter.

cond-mat.mes-hall↗

arXiv2024

TopologicalNumbers.jl: A Julia package for topological number computation

TopologicalNumbers.jl is an open-source Julia package designed to calculate topological invariants, mathematical quantities that characterize the properties of materials in condensed matter physics. These invariants, such as the Chern number and the $\mathbb{Z}_2$ invariant, are crucial for understanding exotic materials like topological insulators and superconductors, which have potential applications in advanced electronics, spintronics, and quantum computing. This package provides researchers and educators with an easy-to-use and efficient toolset to compute these invariants across various dimensions and symmetry classes, facilitating the exploration and discovery of new topological phases of matter.

cond-mat.mes-hall↗

arXiv2023

Signature of BKT-like spin transport in a quasi-2D antiferromagnet BaNi$_2$V$_2$O$_8$

In two-dimensional (2D) spin systems, the augmentation of spin fluctuations gives rise to quasi-long-range order; however, how they manifest in spin transport remains unclear. Here we investigate the spin Seebeck effect (SSE) in a quasi-2D antiferromagnet, BaNi$_2$V$_2$O$_8$, which has been reported to exhibit the Berezinskii-Kosterlitz-Thouless (BKT) transition owing to its distinct 2D nature. We found that the SSE in Pt / BaNi$_2$V$_2$O$_8$ persists well above the N\'eel temperature, significantly different from the behavior of 3D ordered magnets. Our numerical analysis for a 2D microscopic spin model supports the hypothesis that the observed SSE is linked to strong magnetic correlations in the BKT-like phase.

cond-mat.str-el↗

arXiv2021

Linear and Nonlinear Optical Responses in Kitaev Spin Liquids

We theoretically study THz-light-driven high-harmonic generation (HHG) in the spin-liquid states of the Kitaev honeycomb model with a magnetostriction coupling between spin and electric polarization. To compute the HHG spectra, we numerically solve the Lindblad equation, taking account of the dissipation effect. We find that isotropic Kitaev models possess a dynamical symmetry, which is broken by a static electric field, analogous to HHG in electron systems. We show that the HHG spectra exhibit characteristic continua of Majorana fermion excitations, and their broad peaks can be controlled by applying static electric or magnetic fields. In particular, the magnetic-field dependence of the HHG spectra drastically differs from those of usual ordered magnets. These results indicate that an intense THz laser provides a powerful tool to observe dynamic features of quantum spin liquids.

cond-mat.str-el↗