Critical Temperature and Isotope Exponent in a Two-band Model for Superconducting Fe-pnictides

A minimal two-band model to describe superconducting Fe-pnictide materials is considered. It is assumed that the electronic structure of these materials may be modeled in terms of two tight-binding bands, whereas the pairing mechanism is driven by an attractive interaction with intra-band and inter-band pairing. In the framework of a mean-field BCS-type approach, the two-gap equations at the critical temperature T c are solved, and T c and the chemical potential μ , as functions of the number of carriers n varying the pairing interaction V and cut-off energy ω D , are inferred. Furthermore, using a self-consistent approach, the isotope exponent α , as a function of the number carriers by considering an s -wave pairing symmetry, is calculated. The relevance of the present approach for the description of the recent experimental results of Fe-pnictide materials is finally discussed.