Role of Majorana fermions in spin transport of anisotropic Kitaev model

TL;DR

This paper investigates how anisotropy in the Kitaev model affects spin and Majorana fermion dynamics, revealing that small anisotropy allows gapless Majorana modes to facilitate spin transport, while large anisotropy suppresses it.

Contribution

It provides a detailed analysis of spin transport in anisotropic Kitaev models using real-space time-dependent Majorana mean-field theory, highlighting the impact of anisotropy on Majorana fermions and spin propagation.

Findings

Gapless Majorana fermions enable spin propagation at small anisotropy.

Large anisotropy induces a gap, suppressing spin transport.

Spin dynamics depend on pulse shape and anisotropy in junction systems.

Abstract

We study a quantum spin Kitaev model with zigzag edges to clarify the effects of anisotropy in the exchange couplings on the spin propagation. We simulate the spin and Majorana dynamics triggered by a magnetic pulse, using the real-space time-dependent Majorana mean-field theory. When the anisotropy is small, the dispersion of the itinerant Majorana fermions remains gapless, where the velocity of the spin propagation matches the group velocity of the itinerant Majorana fermions at the nodal points. On the other hand, in the gapped system with a large anisotropy, the spin propagation is strongly suppressed although its nature depends on the shape of the pulse. The spin transport in the junction system described by the Kitaev models with distinct anisotropies is also dressed.