Low-energy Spin Dynamics of the Honeycomb Spin Liquid Beyond the Kitaev Limit

TL;DR

This paper explores the low-energy spin dynamics of the Kitaev honeycomb quantum spin liquid when perturbed by generic interactions, revealing persistent spin gaps only under specific conditions and identifying characteristic power-law behaviors near Dirac points.

Contribution

It formulates a generic expansion of the spin operator in terms of Majorana fermions considering symmetry, extending understanding beyond the exactly solvable Kitaev limit.

Findings

Spin gap persists in the Kitaev-Heisenberg model.

Spin gap generally vanishes with generic interactions.

Dynamical structure factor shows power-law scaling near Dirac cones.

Abstract

We investigate the generic features of the low energy dynamical spin structure factor of the Kitaev honeycomb quantum spin liquid perturbed away from its exact soluble limit by generic symmetry-allowed exchange couplings. We find that the spin gap persists in the Kitaev-Heisenberg model, but generally vanishes provided more generic symmetry-allowed interactions exist. We formulate the generic expansion of the spin operator in terms of fractionalized Majorana fermion operators according to the symmetry enriched topological order of the Kitaev spin liquid, described by its projective symmetry group. The dynamical spin structure factor displays power-law scaling bounded by Dirac cones in the vicinity of the $\Gamma$, $K$ and $K'$ points of the Brillouin zone, rather than the spin gap found for the exactly soluble point.