Supersolidity and phase diagram of softcore bosons in a triangular lattice

Abstract

We study the softcore extended Bose Hubbard model in a two-dimensional triangular lattice by using the quantum Monte Carlo methods. The ground state phase diagram of the system exhibits a very fruitful structure. Except the Mott insulating state, four kinds of solid states with respect to the commensurate filling factors $ρ=1/3,2/3$ and $ρ=1$ are identified. Two of them (CDW II and CDW III) are newly predicted. In incommensurate fillings, superfluid, spuersolid as well as phase separation states are detected . As in the case for the hardcore bosons, a supersolid phase exists in $1/3<ρ<2/3$ while it is unstable towards the phase separation in $ρ<1/3$. However, this instability is refrained in $2/3<ρ<1$ due to the softening of the bosons and then a supersolid phase survives.