Chiral fluctuations in triangular antiferromagnets at $T\ll T_N$

Abstract

Chiral fluctuations in triangular antiferromagnets (TAFs) at $T\ll T_N$ are studied theoretically. The case of a ferromagnetic interaction along c axis (which is directed perpendicular to the plane of the lattice), Dzyaloshinskii-Moriya interaction $\mathbf{D}\Vert c$ and a weak magnetic field $\mathbf{H}\Vert c$ is considered in detail. Previously, this model has been proposed to describe quantum TAF CsCuCl${}_3$. Expressions for dynamical chirality (DC) are derived within the linear spin-wave approximation. In contrast to non-frustrated antiferromagnets, DC is found to be nonzero even at $D,H=0$ in a one-domain sample. We argue that this unusual behavior stems from the fact that a ground state of XY and Heisenberg TAFs is characterized by an axial vector along which DC is directed.