Some properties of two-band superconductors: Role of k-dependent hybridization

We discuss the influence of a k-dependent hybridization on a superconductin g material described by a two-band model, within an extended BCS picture. T he effect of hybridization is to create in the normal state new bands with mixed features and the k-dependence arises from its non-local character. We consider a broad s-p conduction band hybridized with a narrow d-band, assu ming that the pairing occurs at the d-band (singlet d-d pairing). We calcul ate self-consistently the SCS type order parameter a and the critical tempe rature T-c. We verify that T-c is stable when hybridization is turned on un til a critical value of V = V-c and both the "phononic" and electronic part s of T-c are renormalized by a parameter alpha, which gives the ratio of th e effective band masses. We calculate the value of 2 Delta (0)/k(B)T(c) and compare with standard BCS results. The isotope effect is almost the same i n the whole range of 0 less than or equal to V < V-c energy.