arXiv subjects

Takahiro Anan

Publications and source records attributed to Takahiro Anan.

6 recordsLinked to original sources

arXiv2026

Emergent induction in magnetic Weyl semimetals

We theoretically study emergent electromagnetic responses in Weyl semimetals. Focusing on magnetic Weyl semimetals, we develop a general theory of emergent induction driven by magnetic dynamics. We show that magnetoelectric (ME) responses in Weyl semimetals give rise to emergent induction mediated by magnetization dynamics. Using effective two-band models for magnetic Weyl semimetals, we derive a formula for the ME response that includes both intraband and interband contributions. The resulting formula shows that the intraband contribution is proportional to the relaxation time $τ$, whereas the interband contribution is associated with the separation of the Weyl nodes. Applying the general formula to a model of polar Weyl ferromagnets, we demonstrate that the dynamics of the toroidal moment is closely related to the emergent inductive response in polar Weyl ferromagnets, as recently discovered by Suzuki et al. [Y. Suzuki et al. arXiv:2607.12322]. The chemical-potential dependence of the inductance indicates that the emergent electromagnetic response is enhanced in the energy range of the Weyl dispersion, reflecting the topological nature of Weyl semimetals.

cond-mat.mes-hall↗

arXiv2026

Emergent toroidal induction in a polar Weyl ferromagnet

Spin-orbit coupling (SOC) underpins modern spintronics by enabling the electrical generation of spin torques. Its reciprocal counterpart, in which magnetization dynamics produce electromotive forces through a spin-dependent Berry phase, is known as emergent electromagnetic induction (EEMI). However, this effect has previously been observed only in magnetic textures with spatial gradients, such as domain walls, helices, and skyrmions. Here, we demonstrate that even a spatially uniform ferromagnet can host EEMI through a previously unrecognized Berry-phase mechanism inherent to noncentrosymmetric conductors. In the polar Weyl ferromagnet PrAlGe, an applied alternating current generates spin-orbit torques that drive collective magnetization dynamics. The resulting emergent toroidal moment (T = P \times M), where (P) is the crystal's polar axis and (M) is the net magnetization, acts as a gauge potential whose time derivative (dT/dt) induces a Hall voltage. This contribution appears specifically in the out-of-phase component of the AC Hall response and scales linearly with frequency, providing direct evidence for EEMI. First-principles calculations further reveal that this toroidal vector encodes the collective motion of Weyl nodes in momentum space. These findings establish "emergent toroidal induction" as a new manifestation of spin-orbit entanglement, unifying Berry phase, topology, and spin dynamics while opening a pathway toward intrinsic and energy-efficient spin-charge interconversion.

cond-mat.mtrl-sci↗

arXiv2026

Quantum-geometric shift of quasiequilibrium: Origin of nonreciprocal current driven by quantum-metric dipole

We study nonlinear DC electric transport of quantum-metric origin by combining adiabatic perturbation theory with the nonequilibrium Green function approach. The adiabatic ansatz provides a basis for directly treating a DC electric field in the velocity gauge, rather than introducing it as the zero-frequency limit of an AC field. The resulting adiabatic-basis Hamiltonian takes the same form as in the length gauge, enabling a systematic comparison across different formulations. Applying this fully quantum formulation, we find a longitudinal nonreciprocal current governed by the quantum-metric dipole. The essential ingredient is a quantum correction to the distribution function that is absent in semiclassical treatments. We trace this correction to the finite spread of an electron wave packet during relaxation under a bias field, thereby identifying shifted quasiequilibrium as the physical origin of quantum-metric nonreciprocal transport.

cond-mat.mes-hall↗

arXiv2026

Nonreciprocal current induced by dissipation in time-reversal symmetric systems

We study nonreciprocal current response in noncentrosymmetric crystals under time-reversal symmetry. We reveal that the nonreciprocal current appears in a dissipative system through interband processes. We derive a formula for the nonreciprocal current using the Green's function technique. The nonreciprocal current of the present mechanism turns out to be of $O(1/τ)$ ($τ$: the lifetime of Bloch electrons) and arises from the shift of the electron wave packet during the interband processes which has a geometric origin. We present a numerical simulation of the nonreciprocal current in the one-dimensional Rice-Mele model and give its order estimation for nonmagnetic polar semiconductors.

cond-mat.mes-hall↗

arXiv2025

Emergent inductors in non-helical magnets

The emergent inductor, which is a concept of an inductor employing quantum mechanics on helical magnets, has been studied actively from both theoretical and experimental aspects. Interestingly, finite inductance has been observed not only in spiral magnetic phases but also across various other magnetic phases although the underlying mechanism behind emergent inductance in non-helical magnets remains unresolved. In this study, we broaden the concept of emergent inductance to encompass non-helical magnets and establish a comprehensive formalism of the emergent inductance generated by magnetization dynamics. Using a diagrammatic approach, we derive the linear response of current density mediated by magnetization dynamics and formulate impedance and inductance for general magnetic materials. We reveal that the emergent inductance is composed of two distinct components, each contributing positively or negatively. Notably, the positive inductance arises from Ohmic dissipation including the effect of the emergent electric field (Berry phase in real space) while the negative inductance arises from the polarization of itinerant electrons (Berry curvature in $k$-$t$ space). We also apply the present method to quasi 1D models and show the numerical results of the inductance, the spin dynamics, the impedance, and the Q-value.

cond-mat.str-el↗

arXiv2023

Time-dependent Gutzwiller simulation of Floquet topological superconductivity

Periodically driven systems provide a novel route to control the topology of quantum materials. In particular, Floquet theory allows an effective band description of periodically-driven systems through the Floquet Hamiltonian. Here, we study the time evolution of $d$-wave superconductors irradiated with intense circularly-polarized laser light. We consider the Floquet $t$-$J$ model with time-periodic interactions, and investigate its mean-field dynamics by formulating the time-dependent Gutzwiller approximation. We observe the development of the $id_{xy}$-wave pairing amplitude along with the original $d_{x^2-y^2}$-wave order upon gradual increasing of the field amplitude. We further numerically construct the Floquet Hamiltonian for the steady state, with which we identify the system as the fully-gapped $d+id$ superconducting phase with a nonzero Chern number. We explore the low-frequency regime where the perturbative approaches in the previous studies break down, and find that the topological gap of an experimentally-accessible size can be achieved at much lower laser intensities.

cond-mat.str-el↗