Phase diagram of a model of correlated hopping of electrons in a lattice of Berry molecules

The one-dimensional (ID) phase diagram of a model for correlated hopping of electrons in a lattice of Berry phase molecules is presented. Electrons hop in the presence of an extra orbital degree of freedom at each site. This is mimicked as a spin-1 variable whose allowed states depend on the electron occupancy so as to take into account the orbital degeneracies of different molecular occupancies. In the ID case we find that at low electron densities n much less than 1 there is a region with dominant superconducting correlations surviving an additional repulsive on-site interaction U as strong as the bandwidth, W=4t. The critical value U-c of U below which superconductivity is found to be dominant decreases with increasing density n. For n=1/2 we find U-c/t approximate to 1, whereas at n=1 (half-filling) our (less accurate) results are compatible with U-c/t approximate to 0. For U>U-c(n) and away from half-filling (n not equal 1) the system is metallic with dominant 2k(F) charge density wave correlations. At half-filling a charge gap opens for U>U-c and the system becomes an insulator. A spin gap characterizes the phase diagram for all densities and for all values of U, even in the metallic regime U>U-c.