Thermally enhanced Majorana-mediated spin transport in the Kitaev model

TL;DR

This paper investigates how thermal fluctuations affect Majorana-mediated spin transport in the Kitaev model, revealing temperature-dependent behaviors and the critical role of flux excitations in spin dynamics.

Contribution

It provides the first detailed analysis of finite-temperature effects on Majorana-mediated spin transport using the time-dependent thermal pure quantum state method.

Findings

Spin transport persists at low temperatures with flux-free states.

Thermal fluctuations at higher temperatures suppress spin propagation.

Oscillations in spin moments increase near the flux transition temperature.

Abstract

We study how stable the Majorana-mediated spin transport in a quantum spin Kitaev model is against thermal fluctuations. Using the time-dependent thermal pure quantum state method, we examine finite-temperature spin dynamics in the Kitaev model. The model exhibits two characteristic temperatures $T_L$ and $T_H$, which correspond to energy scales of the local flux and the itinerant Majorana fermion, respectively. At low temperatures $(T\ll T_L)$, an almost flux-free state is realized and the spin excitation propagates in a similar way to that for the ground state. Namely, after the magnetic pulse is introduced at one of the edges, the itinerant Majorana fermions propagate the spin excitations even through the quantum spin liquid state region, and oscillations in the spin moment appear in the other edge with a tiny magnetic field. When $T\sim T_L$, larger oscillations in the spin moments are induced in the other edge, compared to the results at the ground state. At higher temperatures, excited $Z_2$ fluxes disturb the coherent motion of the itinerant Majorana fermions, which suppresses the spin propagation. Our results demonstrate a crucial role of thermal fluctuations in the Majorana-mediated spin transport.