[Seminar] Professor Kazushi Aoyama "Chiral symmetry breaking and spin dynamics in zero-field breathing-Kagome antiferromagnets"

Speaker

Prof. Kazushi Aoyama / Department of Earth and Space Science, Osaka University

Title

Chiral symmetry breaking and spin dynamics in zero-field breathing-Kagome antiferromagnets

Abstract

In magnetic materials, the scalar spin chirality χ_ijk = S_i・(S_j × S_k) open plays an important role. When the total chirality summed over the whole system χ^T is nonzero, the associated noncoplanar spin state can be characterized by the sign of χ^T. For example, skyrmion crystal (SkX) and anti-skyrmion crystal (anti-SkX) states [1] correspond to negative- and positive-chirality states, respectively. Although the SkX is usually realized in a magnetic field, such a chiral order can appear even at zero field, one example of which is realized in J₁-J₃ Heisenberg antiferromagnets on the breathing kagome lattice [2] where the spin structure in the chiral phase can be viewed as a miniature version of the SkX. In this system, χ^T<0 and χ^T>0 states (miniature SkX and anti-SkX structures) are energetically degenerate, and either one of the two is realized in the low-temperature ordered phase. In this work, we theoretically investigate how such a chirality selection affects the spin dynamics of the system.

By performing the hybrid Monte-Carlo and spin-dynamics simulations, we find that the dynamical spin structure exhibits different features depending on the sign of the chirality and that in each chiral state, the spin-wave dispersion becomes asymmetric with respect to the Γ point, suggestive of nonreciprocal spin-wave propagations. In the presentation, we will also discuss the real-space spin and chirality dynamics.

[1] N. Nagaosa and Y. Tokura, Nat. Nanotech. 8, 899 (2013).
[2] K. Aoyama and H. Kawamura, Phys. Rev. B 105, L100407 (2022); J. Phys. Soc. Jpn. 92 033701 (2023).

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