STRONG-COUPLING THEORY OF SUPERCONDUCTING FULLERIDES NEAR THE MOTT TRANSITION

We describe superconducting Fullerides by a model of weakly coupled mo lecular levels, in which the bandwidth B and the Debye energy omega(D) have same orders of magnitude. For such a narrow band, electron corre lations are supposed to be important. They are discussed in a Hubbard model, using a Gutzwiller approach, which modifies the electron propag ators. The gap equation for superconductivity is written in the Eliash berg strong coupling theory. Assuming a simple Frohlich electron-elect ron attraction, induced by the electron-phonon coupling, the critical temperature of superconductivity is calculated as a function of B/U, w here U is the Hubbard Coulomb energy. Effects of non adiabaticity asso ciated to large Debye energy is discussed by including corrections to Migdal's theorem. A connection between the critical temperature and th e screening effect is made.