Chiral phase transition and thermal Hall effect in an anisotropic spin model on the kagome lattice

Abstract

We present a study of the thermal Hall effect in the extended Heisenberg model with XXZ anisotropy in the kagome lattice. This model has the particularity that, in the classical case, and for a broad region in parameter space, an external magnetic field induces a chiral symmetry breaking: the ground state is a doubly degenerate q=0 order with either positive or negative net chirality. Here, we focus on the effect of this chiral phase transition in the thermal Hall conductivity using linear-spin-waves theory. We explore the topology and calculate the Chern numbers of the magnonic bands, obtaining a variety of topological phase transitions. We also compute the magnonic effect to the critical temperature associated with the chiral phase transition (TcSW). Our main result is that, the thermal Hall conductivity, which is null for T>TcSW, becomes nonzero as a consequence of the spontaneous chiral symmetry breaking at low temperatures. Therefore, we present a simple model where it is possible to "switch"on/off the thermal transport properties introducing a magnetic field and heating or cooling the system.