Superconductivity in the Hubbard model with correlated hopping: Slave-boson study

Slave boson mean-field studies of the ground state of the Hubbard model with correlated hopping were performed. The approach qualitatively recovers the exact results for the case when the hopping integral t equals the correlated hopping integral X. The phase diagram for the strongly correlated state with only singly occupied sites, the weakly correlated state, where single and double occupation is allowed, and for the superconducting state, was determined for any value of X and any electron concentration n. At the half-filled band (n=1) a direct transition from the superconductor to the Mob insulator was found. In the region of strong correlations the superconducting solution is stable for n close to 1, in contrast to the case of weak correlations, in which superconductivity occurs at n approximate to 0 and n approximate to 2. We have also found that strong correlations change the characteristics of the superconducting phase, e.g., the gap in the excitation spectrum exhibits a nonexponential dependence on the on-site Coulomb integral U close to the phase-transition point. [S0163-1829(98)05117-0].