Striped phase in a quantum XY-model with ring exchange

TL;DR

This paper investigates the phase transitions in a quantum XY-model with ring exchange, revealing a transition from a spin-liquid to a striped phase, and then to a magnetically ordered phase as the ring exchange increases.

Contribution

It provides quantum Monte Carlo evidence for a novel striped phase and characterizes the quantum phase transitions in a ring-exchange XY-model.

Findings

Spin-stiffness vanishes at a critical K/J

A striped bond-plaquette order emerges

System develops staggered magnetization at higher K/J

Abstract

We present quantum Monte Carlo results for a square-lattice S=1/2 XY-model with a standard nearest-neighbor coupling J and a four-spin ring exchange term K. Increasing K/J, we find that the ground state spin-stiffness vanishes at a critical point at which a spin gap opens and a striped bond-plaquette order emerges. At still higher K/J, this phase becomes unstable and the system develops a staggered magnetization. We discuss the quantum phase transitions between these phases.