Supersolids versus phase separation in two-dimensional lattice bosons

TL;DR

This paper investigates the ground states of a two-dimensional extended boson Hubbard model, revealing conditions under which a stable supersolid phase exists and mapping the complex phase diagram using quantum Monte Carlo simulations.

Contribution

It demonstrates that a stable supersolid phase appears in the model with specific interactions, and details the phase diagram including the instability of the checker-board crystal.

Findings

Supersolid phase exists above half-filling with strong on-site and nearest-neighbor interactions.

Checker-board crystal is unstable below half-filling and for smaller V.

Quantum Monte Carlo effectively maps the phase diagram.

Abstract

We study the nature of the ground state of the strongly-coupled two dimensional extended boson Hubbard model on a square lattice. We demonstrate that strong but finite on-site interaction U along with a comparable nearest-neighbor repulsion V result in a thermodynamically stable supersolid ground state just above half-filling, and that the checker-board crystal is unstable for smaller V, and for any V just below half-filling. The interplay between these two interaction energies results in a rich phase diagram which is studied in detail using quantum Monte Carlo methods.