Disorder, Low-Energy Excitations, and Topology in the Kitaev Spin Liquid

TL;DR

This paper explores how disorder affects the Kitaev spin liquid, revealing power-law behaviors in the density of states and transitions between topological phases, with implications for real materials.

Contribution

It extends the Kitaev model to include disorder effects, analyzing the resulting low-energy excitations and topological phase transitions.

Findings

Power-law divergence in the density of states due to disorder.

Disorder can destroy or induce topological phases in the Kitaev model.

Diluted Kitaev materials may host chiral spin-liquid phases.

Abstract

The Kitaev model is a fascinating example of an exactly solvable model displaying a spin-liquid ground state in two dimensions. However, deviations from the original Kitaev model are expected to appear in real materials. In this Letter, we investigate the fate of Kitaev's spin liquid in the presence of disorder -- bond defects or vacancies -- for an extended version of the model. Considering static flux backgrounds, we observe a power-law divergence in the low-energy limit of the density of states with a nonuniversal exponent. We link this power-law distribution of energy scales to weakly coupled droplets inside the bulk, in an uncanny similarity to the Griffiths phase often present in the vicinity of disordered quantum phase transitions. If time-reversal symmetry is broken, we find that power-law singularities are tied to the destruction of the topological phase of the Kitaev model in the presence of bond disorder alone. However, there is a transition from this topologically trivial phase with power-law singularities to a topologically nontrivial one for weak to moderate site dilution. Therefore, diluted Kitaev materials are potential candidates to host Kitaev's chiral spin-liquid phase.