SUPERCONDUCTIVITY IN HEAVY FERMIONS - EFFECT OF NON-MAGNETIC IMPURITIES ON THE CRITICAL-TEMPERATURE

The s-like and d-like pairing in heavy fermions is studied using a narrow-band model on-site repulsion and short-range attraction. the effect of non-magnetic impurities on the critical temperature is included using a self-consistent T-matrix formalism. Very unusual results are obtained for the s-like superconductivity which can be very strongly destroyed by impurities with a low impurity potential whereas it is nearly unaffected by an impurity potential large compared with the effective Fermi energy, this last case being the one of heavy fermions. The T//c depression of the d-like superconductivity is studied for comparison. These results are applied to recent experiments on (U, Th)Be//1//3 under pressure, and it is proposed that in this material a transition from d- to s-like superconductivity occurs when the concentration of Th increases.