A supersolid phase of hardcore boson in square optical superlattice

We have applied Quantum Monte Carlo technique to study the supersolid phase of hardcore bosons with nearest-neighbor repulsive interactions (NNRI) on square superlattice forming by an external potential. In a same NNRI model investigated by Batrouni et al. [Phys. Rev. Lett. 84, 1599 (2000)], there is no supersolid phase but phase separation. In this study, we have found the supersolid phase in the wide range of particle density with an assistance of the sufficient large external potential. Interestingly, a supersolid phase exists, on both the vacancy and interstitial sides. We have not found supersolid phase simultaneously existing with the crystals at any particle density. In the limit of a weak external potential strength, the system keeps all the features of the square lattice model which is similar to the model without an external potential. Increasing the external potential strength will induce the crystal phases at different filling factors commensurate with the external potential, i.e. ρ = 1 / 3 and 2/3 away from half filling. A strong external potential can even blow out the checkerboard crystal at half filling. The other possible relevance of these results to experiments on other similar systems such as the ultracold atom traping in optical lattice are discussed.