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 $U_c\approx 4.45$ in units of $2t$. This supersolid phase breaks the lattice translation symmetry in a characteristic $\sqrt{3}\times \sqrt{3}$ pattern, and is remarkably stable—indeed, a smooth extrapolation of our results indicates that the supersolid phase persists for arbitrarily large $U/t$.