Semiclassical ground-state phase diagram and multi-Q phase of a spin-orbit coupled model on triangular lattice

TL;DR

This paper explores the phase diagram of a spin-orbit coupled model on a triangular lattice, revealing multiple magnetic phases and potential quantum spin liquid states influenced by quantum fluctuations.

Contribution

It provides the first classical and quantum analysis of a spin-orbit coupled model on a triangular lattice, identifying multiple magnetic phases and the conditions for spin liquid emergence.

Findings

Identified classical ground states including 120° Neel and collinear phases.

Discovered intermediate non-collinear multi-Q phases with incommensurate order.

Quantum fluctuations can destabilize magnetic order, leading to spin liquid phases.

Abstract

Motivated by recent experiments on the frustrated quantum magnetic compound YbMgGaO4, we study an effective spin model on triangular lattice taking into account the effects of the spin-orbit coupling. We determine the classical ground-state phase diagram of this model, which includes a 120 degree Neel and two collinear antiferromagnetic phases. In the vicinity of the phase boundary between the Neel and collinear phases, we identify three intermediate non-collinear antiferromagnetic phases. In each of them the magnetic moments are ordered at multiple incommensurate wave vector Q values. We further study the effects of quantum fluctuations in this model via a linear spin-wave theory. We find that the spin excitation gap of the non-collinear multi-Q antiferromagnetic state is finite but can be vanishingly small, and this state is unstable to a spin liquid phase under strong quantum fluctuations in some large J_{z+-} regime.