Thermal phase transitions of supersolids in the extended Bose-Hubbard model

TL;DR

This study numerically explores the finite-temperature phase diagrams of the extended Bose-Hubbard model, focusing on the melting of supersolid phases with stripe and star orders, revealing the nature of their phase transitions.

Contribution

It provides new insights into the melting processes of supersolid phases and characterizes the order of phase transitions in the extended Bose-Hubbard model.

Findings

Kosterlitz-Thouless transition restores gauge symmetry

Translational symmetry restored via a single second-order transition

Star and stripe order transitions are first order

Abstract

We investigate numerically the finite-temperature phase diagrams of the extended Bose-Hubbard model in a two-dimensional square lattice. In particular, we focus on the melting of supersolid phases of two different crystal orderings, stripe and star orders, arising from the competition of the nearest- and next-nearest -neighbor interactions in the vicinity of quarter filling. The two crystal orders are the result of broken translational symmetry in either one or in both $x$, and $y$ directions. The broken gauge symmetry of the supersolids are found to be restored via a Kosterlitz-Thouless transition while the broken translational symmetries are restored via a single second-order phase transition, instead of two second-order transitions in the Ising universality class. On the other hand, the phase transitions between the star and stripe orders are first order in nature.