SUPERFLUIDITY OF THE BOSE-HUBBARD MODEL - SU-(1,1) LINEARIZATION SCHEME

Statistical mechanics of the bosonic Hubbard model is studied in the f rame of an improved linearization scheme, applied in such a way so as to approximate in thermodynamically self-consistent way the local inte raction and keeping all long-range correlations exact in the linearize d form. The hamiltonian spectrum can be obtained due to the resulting dynamical symmetry, and the self-consistent free energy allows us to o btain the temperature dependence of the diagonal and off-diagonal orde r parameters. The phase diagram exhibits a superfluid condensate phase possibly co-existing, for appropriate values of (U/t)v, with a fluctu ation-mediated off-diagonal long-range-ordered phase. The correspondin g transition can be thought of as a conductor-insulator transition.