Point contact Andreev reflection spectroscopy of superconducting energy gaps in 122-type family of iron pnictides

Abstract

A brief overview of the superconducting energy gap studies on 122-type family of iron pnictides is given. It seems that the situation in the hole doped Ba 1− x K x Fe 2As 2 is well resolved. Most of the measurements including the presented here point contact Andreev reflection spectra agree on existence of multiple nodeless gaps in the excitation spectrum of this multiband system. The gaps have basically two sizes – the small one with a strength up to the BCS weak coupling limit and the large one with a very strong coupling with 2 Δ L / kT c > 6–8. In the electron doped Ba(Fe 1− x Co x ) 2As 2 the most of the experiments including our point contact measurements reveal in quite broadened spectra only a single gap with a strong coupling strength. The high precision ARPES measurements on this system identified two gaps but very close to each other, both showing a strong coupling with 2 Δ/ kT c ∼ 5 and 6, respectively.