Spontaneous chirality selection and nonreciprocal spin wave in breathing-kagome antiferromagnets at zero field

TL;DR

This paper theoretically shows that breathing-kagome antiferromagnets can exhibit nonreciprocal spin waves and spontaneous chirality selection without external magnetic fields or Dzyaloshinskii-Moriya interactions, due to geometric phase effects.

Contribution

It introduces a mechanism for nonreciprocal spin waves in breathing kagome antiferromagnets arising from geometric phases, independent of DM interaction and magnetic field.

Findings

Nonreciprocal spin wave dispersion in zero field.

Spontaneous selection of chiral states at low temperature.

Distinct spin-wave behaviors for different chiral states.

Abstract

It has been known that the spin-wave dispersion, which is usually symmetric in the momentum space with respect to ${\bf q}=0$, can be asymmetric in the presence of the Dzyaloshinskii-Moriya (DM) interaction and an applied magnetic field. Here, we theoretically demonstrate that in $J_3$-dominant classical Heisenberg antiferromagnets on the breathing kagome lattice, the asymmetric spin-wave dispersion appears in a chiral phase due to non-uniform geometric phases acquired in the spin-wave propagation processes. This points to the emergence of a nonreciprocal spin wave in the absence of both the DM interaction and the magnetic field. Reflecting the asymmetry, positive-spin-chirality and negative-spin-chirality states, either one of which is selected in the low-temperature phase by the symmetry breaking, show different spin-wave dispersions, suggesting that the two energetically-degenerate chiral states can be distinguished by the spin-wave propagation.