Persistent supersolid phase of hard-core bosons on the triangular lattice

We study hard-core bosons with unfrustrated hopping (t) and nearest neighbor repulsion (U) (spin S = 1/2 XXZ model) on the triangular lattice. At half filling, the system undergoes a zero temperature (T) quantum phase transition from a superfluid phase at small U to a supersolid at U-c approximate to 4: 45 in units of 2t. This supersolid phase breaks the lattice translation symmetry in a characteristic root 3 x root 3 pattern, and is remarkably stable-indeed, a smooth extrapolation of our results indicates that the supersolid phase persists for arbitrarily large U/t.