Generalized BCS Equations and the Iron-Pnictide Superconductors

Abstract

A detailed quantitative study of the pnictide composite superconductor (CS) Ba 0.6 K 0.4 Fe 2 As 2 is presented in the frame - work of t he recently derived set of generalized BCS equations . Invoking multiple Debye temperatures to take into account anisotropy of the CS, we address the current experimental data on its T c and the (not so clear-cut) gap-values via different theoretical scenarios that attempt to identify the ion species responsible for pairing in it. This is done with the aid of the Bogoliubov ’ s restriction on the BCS dimensionless electron-phonon coupling constant. Significantly, our study sheds light on the gaps which have recently been observed in different iron-pnictide CSs as nodes or line-nodes on the Fermi surface and have evinced considerable interest.