Interlayer Coupling Effect on a Bilayer Kitaev Model

TL;DR

This paper explores how interlayer Heisenberg interactions affect the stability and properties of the Kitaev quantum spin liquid in a bilayer model, revealing a first-order phase transition and persistent thermal features.

Contribution

It provides a detailed analysis of the phase transition and excitations in a bilayer Kitaev model with interlayer coupling, using multiple theoretical methods.

Findings

First-order quantum phase transition between QSL and dimer states.

Localized one-triplet excitations due to conserved quantities.

Double-peak specific heat structure persists above transition.

Abstract

We investigate a bilayer Kitaev model, where two honeycomb layers are coupled by the Heisenberg interactions, to discuss effects of an interlayer coupling against the Kitaev quantum spin liquids (QSLs). In this model, there exists a local conserved quantity, which results in no long-range spin correlations in the system. Using the exact diagonalization, bond operator mean-field theory, and cluster expansion techniques, we study ground state properties in the system. The obtained results suggest the existence of a first-order quantum phase transition between the Kitaev QSL and singlet-dimer states. We find that one-triplet excitation from the singlet-dimer ground state is localized owing to the existence of the local conserved quantity. To examine finite-temperature properties, we make use of the thermal pure quantum state approach. We clarify that double-peak structure in the specific heat inherent in the Kitaev QSL is maintained even above the quantum phase transition. The present results suggest that the Kitaev QSL is stable against the interlayer interference. Magnetic properties of multilayer Kitaev models are also addressed.