FINITE BANDWIDTH EFFECTS ON THE TRANSITION-TEMPERATURE AND NMR RELAXATION RATE OF IMPURE SUPERCONDUCTORS

We study the thermodynamic properties of impure superconductors by exp licitly taking into consideration the finiteness of electronic bandwid ths within the phonon-mediated Eliashberg formalism. For a finite elec tronic bandwidth, the superconducting transition temperature, T-c, is suppressed by nonmagnetic impurity scatterings. This is a consequence of a reduction in the effective electron-phonon coupling, lambda(eff). The reduced lambda(eff) is reflected in the observation that the cohe rence peak in 1/(T1T), where T-1 is the nuclear spin-lattice relaxatio n time and T is the temperature, is enhanced by impurity scatterings f or a finite bandwidth. Calculations are presented for T-c and 1/(T1T) as bandwidths and impurity scattering rates are varied. Implications f or doped C-60 superconductors are discussed in connection with T-c and 1/T-1 measurements.