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 hoppi ng of electrons in a lattice of Berry phase molecules is presented. El ectrons hop in the presence of an extra orbital degree of freedom at e ach site. This is mimicked as a spin-1 variable whose allowed states d epend on the electron occupancy so as to take into account the orbital degeneracies of different molecular occupancies. In the ID case we fi nd that at low electron densities n much less than 1 there is a region with dominant superconducting correlations surviving an additional re pulsive on-site interaction U as strong as the bandwidth, W=4t. The cr itical value U-c of U below which superconductivity is found to be dom inant decreases with increasing density n. For n=1/2 we find U-c/t app roximate to 1, whereas at n=1 (half-filling) our (less accurate) resul ts are compatible with U-c/t approximate to 0. For U>U-c(n) and away f rom half-filling (n not equal 1) the system is metallic with dominant 2k(F) charge density wave correlations. At half-filling a charge gap o pens for U>U-c and the system becomes an insulator. A spin gap charact erizes the phase diagram for all densities and for all values of U, ev en in the metallic regime U>U-c.