Quantum spin liquid ground states of the Heisenberg-Kitaev model on the triangular lattice

TL;DR

This paper investigates quantum disordered ground states of the Heisenberg-Kitaev model on a triangular lattice, identifying three distinct gapped Z2 spin liquid phases stabilized by anisotropic interactions, with continuous phase transitions and unique excitation properties.

Contribution

It introduces a Schwinger boson approach to characterize and differentiate three novel gapped Z2 spin liquid phases in the Heisenberg-Kitaev model on a triangular lattice, revealing their stability and transition behavior.

Findings

Identified three symmetric Z2 spin liquid phases separated by continuous quantum phase transitions.

Found that the elementary excitation gap remains finite across phase transitions.

Discovered a spin liquid with unconventional correlations that develops incommensurate Bragg peaks upon spinon condensation.

Abstract

We study quantum disordered ground states of the two dimensional Heisenberg-Kitaev model on the triangular lattice using a Schwinger boson approach. Our aim is to identify and characterize potential gapped quantum spin liquid phases that are stabilized by anisotropic Kitaev interactions. For antiferromagnetic Heisenberg- and Kitaev couplings and sufficiently small spin $S$ we find three different symmetric $Z_2$ spin liquid phases, separated by two continuous quantum phase transitions. Interestingly, the gap of elementary excitations remains finite throughout the transitions. The first spin liquid phase corresponds to the well known zero-flux state in the Heisenberg limit, which is stable with respect to small Kitaev couplings and develops $120^\circ$ order in the semi-classical limit at large $S$. In the opposite Kitaev limit we find a different spin liquid ground-state, which is a quantum disordered version of a magnetically ordered state with antiferromagnetic chains, in accordance with results in the classical limit. Finally, at intermediate couplings we find a spin liquid state with unconventional spin correlations. Upon spinon condensation this state develops Bragg peaks at incommensurate momenta in close analogy to the magnetically ordered Z2 vortex crystal phase, which has been analyzed in recent theoretical works.