Structure and Anisotropy of the Superconducting Order Parameter in Ba0.65K0.35Fe2As2 Probed by Andreev Spectroscopy

Abstract

The superconducting order parameters in optimally doped Ba0.65K0.35Fe2As2 single crystals have been directly measured using multiple Andreev reflection effect spectroscopy of superconductor–normal metal–superconductor break-junctions. We determine two superconducting gaps, which are nodeless in the k x k y -plane of the momentum space, and resolve a substantial in-plane anisotropy of the large gap. The temperature dependences of the gaps indicate a strong coupling within the bands where ΔL develops, a weak coupling in the condensate with the small gap ΔS, and a moderate interband interaction between the two condensates. The own critical temperatures of both condensates have been estimated (under the hypotherical assumption of zero interband interaction).