# Thermal Transport in the Kitaev Model

## TL;DR

This paper explores how exotic fractional excitations in the Kitaev quantum spin liquid influence thermal transport, revealing distinctive temperature-dependent behaviors in longitudinal and transverse thermal conductivities.

## Contribution

It provides a detailed analysis of thermal transport signatures of fractionalized Majorana fermions and $Z_2$ fluxes in the Kitaev model, linking theory to experimental observables.

## Key findings

- Longitudinal thermal conductivity peaks at different temperatures for zero and nonzero frequencies.
- Transverse thermal conductivity shows nonmonotonic temperature dependence due to $Z_2$ fluxes.
- Low-temperature linear thermal conductance approaches a quantized value, indicating topological Majorana fermions.

## Abstract

In conventional insulating magnets, heat is carried by magnons and phonons. In contrast, when the magnets harbor a quantum spin liquid state, emergent quasiparticles from the fractionalization of quantum spins can carry heat. Here, we investigate unconventional thermal transport yielded by such exotic carriers, in both longitudinal and transverse components, for the Kitaev model, whose ground state is exactly shown to be a quantum spin liquid with fractional excitations described as itinerant Majorana fermions and localized $Z_2$ fluxes. We find that the longitudinal thermal conductivity exhibits a broad peak at very different temperatures between the zero and nonzero frequency components, reflecting the spin fractionalization. On the other hand, the transverse thermal conductivity induced by the magnetic field shows nonmonotonic temperature dependence, due to thermal excitations of the localized $Z_2$ fluxes. In the low-temperature limit, the temperature-linear coefficient rapidly approaches a quantized value, as expected from the topologically nontrivial nature of itinerant Majorana fermions. The characteristic behaviors provide experimentally-accessible evidences of fractional excitations in the proximity to Kitaev quantum spin liquid.