Strong coupling expansion for bosons on the kagome lattice
  We use series expansion techniques for analyzing properties of the phase transition between the Mott insulating and superfluid phase for bosons on the kagome lattice, and the multicritical point in the ground-state phase diagram for unit-filling is calculated. It is seen that of the clusters that contribute with non-zero weights to the ground state energy, many contain rings. The decay exponents of ground state correlations are also obtained within the Mott phase. For single-particle excited states, quasiparticle dispersion and effective masses for particles and holes are computed along certain symmetry cuts in the first Brillouin zone. Furthermore at eighth order, the coherence-length critical exponent is found to be comparably close to that of the 3D XY model. 
Vipin Kerala Varma and Hartmut Monien
cond-mat.str-el cond-mat.quant-gas cond-mat.stat-mech