Two Step Restoration of SU(2) Symmetry in a Frustrated Ring-Exchange Magnet

TL;DR

This paper uncovers a novel spin-nematic phase in a frustrated quantum ring exchange model, showing how frustration and quantum fluctuations can restore SU(2) symmetry and lead to exotic magnetic states.

Contribution

It introduces a new quantum spin-nematic phase arising from frustration and quantum fluctuations in a four-spin ring exchange model on a square lattice.

Findings

Identification of a spin-nematic, moment-free phase

Observation of partial SU(2) symmetry restoration

Transition to a gapped SU(2) symmetric valence bond crystal

Abstract

We demonstrate the existence of a spin-nematic, moment-free phase in a quantum four-spin ring exchange model on the square lattice. This unusual quantum state is created by the interplay of frustration and quantum fluctuations which lead to a partial restoration of SU(2) symmetry when going from a four-sublattice orthogonal biaxial Neel order to this exotic uniaxial magnet. A further increase of frustration drives a transition to a fully gapped SU(2) symmetric valence bond crystal.