Pair Superfluid and Supersolid of Correlated Hard-Core Bosons on a   Triangular Lattice
  We have systematically studied the hard-core Bose-Hubbard model with correlated hopping on a triangular lattice using density-matrix renormalization group method. A rich ground state phase diagram is determined. In this phase diagram there is a supersolid phase and a pair superfluid phase due to the interplay between the ordinary frustrated boson hopping and an unusual correlated hopping. In particular, we find that the quantum phase transition between the supersolid phase and the pair superfluid phase is continuous. 
Hong-Chen Jiang, Liang Fu, and Cenke Xu
cond-mat.str-el