The boson-Hubbard model on a kagome lattice with a sextic ring-exchange term*

We present exact quantum Monte Carlo simulations of hard-core bosons in a two-dimensional Kagome lattice with a sextic ring-exchange term. We study how the superfluid density evolves as the ring-exchange interactions are increased. We show that the system becomes unstable in the limit of large interactions at all fillings and undergoes a phase separation, except at $\frac13$ and $\frac23$ fillings for which the superfluid density vanishes and a solid state forms.