Theoretical study of magnetic hedgehog lattices in itinerant magnets

Seminar über Theoretische Festkörperphysik

Vortragender:

Shun Okumura

Datum:

30.09.2024 14:00

Ort:

10.01, Geb. 30.23, CS

Zugehörigkeit:

University of Tokyo

Gastgeber:

Markus Garst

Abstract

In the past decade, magnetic structures protected by topology have attracted much attention in condensed matter physics, stimulating both experimental and theoretical research. The main research subjects are a one-dimensional chiral solition and a two-dimensional magnetic skyrmion, which are swirling solitonic textures. In recent years, through the developement of stereoscopic real-space imaging techniques, three-dimensional topological magnetic structures have attracted attention, exemplified by magnetic skyrmion strings, hedgehogs, and hopfions. However, while abundant theoretical studies have been conducted on two-dimensional skyrmions, there have been surprisingly few theoretical proposals on the stability and response of these three-dimensional topological magnetic strucures.

Against this background, we focus on the magnetic hedgehog lattice, which is a spin crystal of three-dimensional topological defects named magnetic hedgehogs and antihedgehogs. We investigate the stabilization mechanism and transport phenomena of the mgnetic hedgehog lattices in itinerant magnets since the experimentally reported materials show metallic natures and quantum transport phenomena such as topological Hall effect, whose characteristics are substantially different from those of the magnetic skyrmion lattice [1]. We theoretically found that the magnetic hedgehog lattices are stabilized at zero magnetic field and in the ground state by the long-range RKKY interaction originating from the instability of the Fermi surface. Not only in chiral magnets breaking the spatial inversion symmetry [2], but we also clarified that the magnetic hedgehog lattices stabilize similarly in centrosymmetric systems with spatial inversion symmetry [3], and that the topological Hall effect appears in the magnetic field by incorporating anisotropic interaction derived from spin-orbit coupling [2,4]. We have developed these research results and pioneered a new field called "spin moiré engineering" to comprehensively understand topological magnetic structures over the magnetic skyrmion and hedgehog lattices [5].

[1] For review, Y. Fujishiro, N. Kanazawa, and Y. Tokura, Appl. Phys. Lett. 116, 090501 (2020).
[2] S. Okumura, S. Hayami, Y. Kato, and Y. Motome, Phys. Rev. B 101, 144416 (2020).
[3] S. Okumura, S. Hayami, Y. Kato, and Y. Motome, J. Phys. Soc. Jpn 91, 093702 (2020).
[4] S. Okumura, S. Hayami, Y. Kato, and Y. Motome, in preparation.
[5] K. Shimizu, S. Okumura, Y. Kato, and Y. Motome, Phys. Rev. B 103, 054427 (2021); ibid, Phys. Rev. B 103, 184421 (2021); ibid, Phys. Rev. B 105, 224405 (2022).