Dynamics of visons and thermal Hall effect in perturbed Kitaev models

TL;DR

This paper investigates how visons, excitations in Kitaev spin liquids, become mobile under perturbations and how this affects thermal Hall effects, revealing differences between ferromagnetic and antiferromagnetic cases.

Contribution

It provides a detailed analysis of vison dynamics and their impact on thermal Hall effects in perturbed Kitaev models, highlighting the role of different perturbations and magnetic interactions.

Findings

Visons acquire dispersion and mobility in perturbed ferromagnetic Kitaev models.

In antiferromagnetic models, interference suppresses vison coherence, leading to incoherent hopping.

Topological vison bands may produce observable thermal Hall signatures.

Abstract

A vison is an excitation of the Kitaev spin liquid which carries a $\mathbb Z_2$ gauge flux. While immobile in the pure Kitaev model, it becomes a dynamical degree of freedom in the presence of perturbations. We study an isolated vison in the isotropic Kitaev model perturbed by a small external magnetic field $h$, an offdiagonal exchange interactions $\Gamma$ and a Heisenberg coupling $J$. In the ferromagnetic Kitaev model, the dressed vison obtains a dispersion linear in $\Gamma$ and $h$ and a fully universal low-$T$ mobility, $\mu=6 v_m^2/T^{2}$, where $v_m$ is the velocity of Majorana fermions. In contrast, in the antiferromagnetic Kitaev model interference effects suppress the coherent propagation and an incoherent Majorana-assisted hopping leads to a $T$-independent mobility. The motion of a single vison due to Heisenberg interactions is strongly suppressed for both signs of the Kitaev coupling. Vison bands in the antiferromagnetic Kitaev models can be topological and may lead to a characteristic features in thermal Hall effects in Kitaev materials.