Specific heat jump in two-band superconductors

We discuss the effect of k-dependent hybridization in the specific heat jump AC at the superconducting critical temperature T-c, considering an exact analytical expression obtained from the extended BCS gap equation. Our model intends to discuss a superconducting material described by a two-band model, within an extended BCS picture. We consider a broad s-p conducting band. hybridized with a narrow d-band. assuming that: (i) electron-electron repulsion U-r, formulated via the Hubbard model and (ii) electron-electron attraction due to electron-fonon interaction U-a, treated in a BCS framework, both occur at the narrow d-band. One observes that there is a critical value V-c for the hybridization (depending on the ratio a of the effective masses of the narrow and broad bands), above which there is no AC jump. Moreover, one observes that: (i) the ratio alpha of the effective band masses in a homothetic band picture plays an important role in the jump, and (ii) the Hubbard like repulsive interaction is very small and therefore plays no significant role in the range of temperatures where superconductivity occurs. (C) 2001 Elsevier Science B.V. All rights reserved.