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 Ba1-xKxFe2As2 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 2Delta/kTc ~ 6 - 8. In the electron doped Ba(Fe1-xCox)2As2 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 2Delta/kTc ~ 5 and 6, respectively.

7 pages, 4 figures, to appear in Physica C, special issue on Fe-pnictides

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• Gap-like feature in the normal state of $\mathbf{X}(\mathbf{F}{\mathbf{e}}_{1-\mathbf{x}}\mathbf{C}{\mathbf{o}}_{\mathbf{x}}{)}_2\mathbf{A}{\mathbf{s}}_2$, $\mathbf{X}=\mathbf{Ba},\mathbf{Sr}$ and $\mathbf{F}{\mathbf{e}}_{1+\mathbf{y}}\mathbf{Te}$ revealed by Point Contact Spectroscopy
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