QUANTUM PHASE-TRANSITIONS OF INTERACTING BOSONS AND THE SUPERSOLID PHASE

We investigate the properties of strongly interacting bosons in two di mensions at zero temperature using mean-field theory, a variational an satz for the ground-state wave function, and Monte Carlo methods. With on-site and short-range interactions a rich phase diagram is obtained . Apart from the homogeneous superfluid and Mott-insulating phases, in homogeneous charge-density wave phases appear, that are stabilized by the finite-range interaction. Furthermore, our analysis demonstrates t he existence of a supersolid phase, in which both long-range order (re lated to the charge-density wave) and off-diagonal long-range order co exist. We also obtain the critical exponents for the various phase tra nsitions.