Superfluid and supersolid phases of lattice bosons with ring-exchange interaction

TL;DR

This study investigates the phase diagram of lattice bosons with ring-exchange interactions, revealing the destruction of superfluidity by negative K and the emergence of a supersolid phase with coexisting orders, supported by mean-field and Monte Carlo analyses.

Contribution

It introduces a combined mean-field and Monte Carlo analysis of superfluid, supersolid, and phase transition behaviors in a lattice boson model with ring-exchange interactions.

Findings

Negative ring-exchange interactions suppress superfluidity.

A supersolid phase with coexisting orders is predicted.

The Kosterlitz-Thouless transition temperature varies with ring-exchange strength.

Abstract

We examine the superfluid phase of a hard-core boson model with nearest-neighbor exchange J and four-particle ring-exchange K at half-filling on the square lattice. At zero temperature we find that the superfluid in the pure-J model is quickly destroyed by the inclusion of negative-K ring-exchange interactions, favoring a state with a (pi,pi) ordering wavevector. Minimization of the mean-field energy suggests that a supersolid state with coexisting superfluidity, charge-density wave, and valence-bond-like order is formed. We also study the behavior of the finite-T Kosterlitz-Thouless phase transition in the superfluid phase, by forcing the Nelson-Kosterlitz universal jump condition on the finite-T spin wave superfluid density. Away from the pure J point, T_{KT} decreases rapidly for negative K, while for positive K, T_{KT} reaches a maximum at some K \neq 0 in agreement with recent quantum Monte Carlo simulations.