Dr. Rousseau's research on the Bose-Hubbard model on a triangular lattice with diamond ring-exchange was recently published in Physical Review B.
Ring-exchange interactions have been proposed as a possible mechanism for a Bose-liquid phase at zero temperature, a phase that is compressible with no super fluidity. Dr. Rousseau, along with his collaborators from Louisiana State University, performed the first exact simulations of a model with ring-exchange by using a method that he developed called the Stochastic Green Function (SGF) algorithm. This model was proposed by several research groups as a candidate for the exhibition of the sought Bose-liquid phase. However, Dr. Rousseau's results show that the super solid phase that is known to exist in the absence of ring-exchange is rapidly destroyed as ring-exchange interactions are turned on, yielding a super fluid phase instead of the Bose-liquid phase.
In their paper, Dr. Rousseau and his collaborators determine the exact phase diagram of the proposed model.
The abstract of the paper is available here