Abstract
We investigate two-species bosons in a two-dimensional square lattice by the quantum Monte Carlo method. We show that the interspecies attraction and nearest-neighbor intraspecies repulsion result in the pair-supersolid phase, where a diagonal solid order coexists with an off-diagonal pair-superfluid order. The quantum and thermal transitions out of the pair-supersolid phase are characterized. It is found that there is a direct first-order transition from the pair-supersolid phase to the double-superfluid phase without an intermediate region. Furthermore, the melting of the pair supersolid occurs in two steps. Upon heating, first the pair superfluid is destroyed via a Kosterlitz-Thouless transition, then the solid order melts via an Ising transition. © 2012 American Physical Society.