Disorder in a quantum spin liquid: flux binding and local moment formation

TL;DR

This paper investigates how disorder affects the Kitaev honeycomb model, revealing flux binding to vacancies, local moment formation, and disorder-dependent thermodynamic responses, with implications for quantum spin liquids.

Contribution

It demonstrates that vacancies bind fluxes and induce local moments, and analyzes how disorder influences susceptibility and heat capacity in the model.

Findings

Vacancies bind fluxes and create local moments.

Local susceptibility diverges logarithmically with field in the gapless phase.

Weak exchange randomness alters heat capacity, making it power-law dependent on temperature.

Abstract

We study the consequences of disorder in the Kitaev honeycomb model, considering both site dilution and exchange randomness. We show that a single vacancy binds a flux and induces a local moment. This moment is polarised by an applied field $h$: in the gapless phase, for small $h$ the local susceptibility diverges as $\chi(h)\sim\ln(1/h)$; for a pair of nearby vacancies on the same sublattice, this even increases to $\chi(h)\sim1/(h[\ln(1/h)]^{3/2})$. By contrast, weak exchange randomness does not qualitatively alter the susceptibility but has its signature in the heat capacity, which in the gapless phase is power law in temperature with an exponent dependent on disorder strength.