Spin nematics next to spin singlets

TL;DR

This paper proposes a novel mechanism for inducing spin nematic order in a spin-1/2 system near a singlet phase, utilizing inter-dimer ring exchange interactions on a triangular lattice.

Contribution

It introduces a new route to generate spin nematic order without frustration or high magnetic fields, through ring exchange interactions near a singlet phase.

Findings

Ring exchange induces triplet doping and interactions.

Stable nematic order emerges from a first order transition.

Nematic phases can host Bose-Einstein condensates or triplet crystals.

Abstract

We provide a route to generate nematic order in a spin-1/2 system. Unlike the well-known magnon-binding mechanism, our spin nematics requires neigher the frustration effect nor a spin polarization in a high field or in the vicinity of a ferromagnet, but instead appears next to the spin singlet phase. We start from a state consisting of a quantum spin-1/2 singlet dimer placed on each site of a triangular lattice, and show that inter-dimer ring exchange interactions efficiently dope the SU(2) triplets that itinerate and interact, easily driving a stable singlet state to either Bose Einstein condensates or a triplet crystal, some hosting a spin nematic order. A variety of roles the ring exchange serves include the generation of a bilinear-biquadratic interaction between nearby triplets, which is responsible for the emergent nematic order separated from the singlet phase by a first order transition.