Even-odd effect in multilayer Kitaev honeycomb magnets

TL;DR

This paper investigates multilayer Kitaev honeycomb models, revealing an even-odd layer effect on quantum spin liquids, with even layers hosting gapped and odd layers hosting gapless QSLs, relevant to real materials like alpha-RuCl3.

Contribution

It introduces a multilayer Kitaev model analysis showing layer parity affects QSL type and uncovers a layer-to-layer inversion symmetry, extending understanding of Kitaev materials.

Findings

Even layers host gapped quantum spin liquids.

Odd layers host gapless quantum spin liquids.

External magnetic fields stabilize chiral QSLs with interlayer coupling.

Abstract

Motivated by the three-dimensional structure of Kitaev materials we explore multilayer Kitaev models. The magnetic properties of a multilayer of an arbitrary number of Kitaev honeycomb layers stacked on top of each other coupled through a Heisenberg interaction, J, is analyzed through Abrikosov fermion mean-field theory. The system sustains quantum spin liquid (QSL) solutions which have different character depending on parity of the number of layers. While in even layered Kitaev models a gapped QSL emerges, odd-layered models host gapless QSLs. The projective symmetry group analysis of these solutions unravel a layer-to-layer inversion symmetry rather than an expected reflection. Although these QSLs retain features of the single layer Kitaev spin liquid (KSL), they should be regarded hybrid QSLs consisting on several KSLs. The good agreement at large-J between the energy of the Gutzwiller projected mean-field QSL and the exact energy indicates that such QSL Ansatz is adiabatically connected to the exact ground state. We also find that the Kitaev gapped chiral quantum spin liquid induced by external magnetic fields is stabilized by an antiferromagnetic interlayer coupling. Our results are relevant to the physics of alpha-RuCl3 and H3LiIr2O6 which are examples of magnetically coupled multilayer Kitaev models.