Ring Exchange and Phase Separation in the Two-dimensional Boson Hubbard model

TL;DR

This study uses Quantum Monte Carlo simulations to explore how ring exchange interactions influence phase separation in the two-dimensional bosonic Hubbard model, revealing non-monotonic density behavior and tendencies toward phase separation.

Contribution

It demonstrates the impact of ring exchange term K on phase separation and shows that near-neighbor repulsion cannot stabilize a normal Bose liquid in this context.

Findings

Non-monotonic density as a function of chemical potential for high K

Evidence of phase separation from structure factor and real space images

Near-neighbor repulsion does not stabilize a normal Bose liquid

Abstract

We present Quantum Monte Carlo simulations of the soft-core bosonic Hubbard model with a ring exchange term K. For values of K which exceed roughly half the on-site repulsion U, the density is a non-monotonic function of the chemical potential, indicating that the system has a tendency to phase separate. This behavior is confirmed by an examination of the density-density structure factor and real space images of the boson configurations. Adding a near-neighbor repulsion can compete with phase separation, but still does not give rise to a stable normal Bose liquid.