Chiral gauge field in fully spin-polarized magnetic Weyl semimetal with magnetic domain walls

Ozawa, Akihiro*; Araki, Yasufumi; Nomura, Kentaro*

Journal of the Physical Society of Japan, 93(9), p.094704_1 - 094704_9, 2024/09

https://doi.org/10.7566/JPSJ.93.094704

Modulation of magnetization in magnetic Weyl semimetals leads to the shift of Weyl points in momentum space, which effectively serves as the chirality-dependent gauge field for the Weyl fermions. Here, we theoretically study such a magnetization-induced chiral gauge field, in a fully spin-polarized Weyl ferromagnet CoSnS. From a tight-binding model of CoSnS on stacked kagome lattice with magnetism, we calculate the magnetization-dependent evolution of the Weyl points in momentum space, resulting in the chiral gauge field. In the presence of the magnetic domain wall structure, we evaluate the chiral magnetic field arising from the spatial profile of the chiral gauge field. We find that a magnetic domain wall in CoSnS gives rise to a giant chiral magnetic field for the Weyl fermions, which reaches the order of a few hundred tesla to induce the Landau quantization. Such a giant chiral magnetic field may also influence the novel transport phenomena, such as the charge pumping by the domain wall motion, compatible with the spinmotive force.

Non-Hermitian Casimir effect of magnons

Nakata, Koki; Suzuki, Kei

npj Spintronics (Internet), 2, p.11_1 - 11_6, 2024/06

https://doi.org/10.1038/s44306-024-00017-4

To explore and utilize even dissipation is a crucial issue of spintronics. Here, we shed light on this problem by using a quantum effect, called the magnonic Casimir effect. We show that the dissipation caused by the Gilbert damping decreases the magnon energy gap, and it enhances the magnonic Casimir energy. Then, we find that this magnonic non-Hermitian Casimir effect exhibits an oscillating behavior as a function of the film thickness, and the oscillation is characterized by the exceptional point. Our result suggests that dissipation can serve as a key ingredient of Casimir engineering. Microfabrication technology can control the thickness of thin films and realize the manipulation of the magnonic non-Hermitian Casimir effect. Thus, we pave the way for magnonic Casimir engineering.

Persistent magnetic coherence in magnets

Makiuchi, Takahiko*; Hioki, Tomosato*; Shimizu, Hiroki*; Hoshi, Kojiro*; Elyasi, M.*; Yamamoto, Kei; Yokoi, Naoto*; Serga, A. A.*; Hillebrands, B.*; Bauer, G. E. W.*; et al.

Nature Materials, 23(5), p.627 - 632, 2024/05

https://doi.org/10.1038/s41563-024-01798-z

Fast Magnons modulated by slow mechanical rotation

Yamamoto, Kei

JPSJ News and Comments (Internet), 21, p.07_1 - 07_2, 2024/04

https://doi.org/10.7566/JPSJNC.21.07

Valley-selective phonon-magnon scattering in magnetoelastic superlattices

Liao, L.*; Puebla, J.*; Yamamoto, Kei; Kim, J.*; Maekawa, Sadamichi*; Hwang, Y.*; Ba, Y.*; Otani, Yoshichika*

Physical Review Letters, 131(17), p.176701_1 - 176701_6, 2023/10

https://doi.org/10.1103/PhysRevLett.131.176701

Emergence of inductance and capacitance from topological electromagnetism

Araki, Yasufumi; Ieda, Junichi

Journal of the Physical Society of Japan, 92(7), p.074705_1 - 074705_9, 2023/06

https://doi.org/10.7566/JPSJ.92.074705

Topological electromagnetism owing to nontrivial momentum-space topology of electrons in insulators gives rise to diverse anomalous magnetoelectric responses. While conventional inductors and capacitors are based on classical electromagnetism described by Maxwell's equations, here we show that topological electromagnetism in combination with spin dynamics in magnets also generates an inductance or a capacitance. We build a generic framework to extract the complex impedance on the basis of topological field theory, and demonstrate the emergence of an inductance or a capacitance in several heterostructure setups. In comparison with the previously-studied emergent inductances in metallic magnets, insulators highly suppress the power loss, because of the absence of Joule heating. We show that the inductance from topological electromagnetism is achieved at low current and high frequency, and is also advantageous in its power efficiency, as characterized by the high quality factor (Q-factor).

Effect of vertex corrections on the enhancement of Gilbert damping in spin pumping into a two-dimensional electron gas

Yama, Masaki*; Matsuo, Mamoru; Kato, Takeo*

Physical Review B, 107(17), p.174414_1 - 174414_15, 2023/05

https://doi.org/10.1103/PhysRevB.107.174414

Magnonic Casimir effect in ferrimagnets

Nakata, Koki; Suzuki, Kei

Physical Review Letters, 130(9), p.096702_1 - 096702_6, 2023/03

https://doi.org/10.1103/PhysRevLett.130.096702

Quantum fluctuations of quantum fields induce a zero-point energy shift under spatial boundary conditions. This quantum phenomenon, called the Casimir effect, has been attracting much attention beyond the hierarchy of energy scales, whereas its application to spintronics has not yet been investigated enough, particularly to ferrimagnetic thin films. Here we fill this gap. Using the lattice field theory, we investigate the Casimir effect induced by quantum fields for magnons and find that the magnonic Casimir effect can arise not only in antiferromagnets but also in ferrimagnets (e.g., YIG). Thus, we pave the way for magnonic Casimir engineering.

Nonlinear magnon polaritons

Lee, O.*; Yamamoto, Kei; Umeda, Maki; Zollitsch, C. W.*; Elyasi, M.*; Kikkawa, Takashi*; Saito, Eiji; Bauer, G. E. W.*; Kurebayashi, Hidekazu*

Physical Review Letters, 130(4), p.046703_1 - 046703_6, 2023/01

https://doi.org/10.1103/PhysRevLett.130.046703

Skyrmion creation and annihilation by electric current vorticity

Fujimoto, Junji*; Funaki, Hiroshi*; Koshibae, Wataru*; Matsuo, Mamoru; Maekawa, Sadamichi*

IEEE Transactions on Magnetics, 58(8), p.1500407_1 - 1500407_7, 2022/08

https://doi.org/10.1109/TMAG.2021.3139638