Specific heat jump in two-band superconductors

We discuss the effect of k-dependent hybridization in the specific heat jum p AC at the superconducting critical temperature T-c, considering an exact analytical expression obtained from the extended BCS gap equation. Our mode l intends to discuss a superconducting material described by a two-band mod el, within an extended BCS picture. We consider a broad s-p conducting band . hybridized with a narrow d-band. assuming that: (i) electron-electron rep ulsion U-r, formulated via the Hubbard model and (ii) electron-electron att raction 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 va lue V-c for the hybridization (depending on the ratio a of the effective ma sses of the narrow and broad bands), above which there is no AC jump. Moreo ver, 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) th e Hubbard like repulsive interaction is very small and therefore plays no s ignificant role in the range of temperatures where superconductivity occurs . (C) 2001 Elsevier Science B.V. All rights reserved.