Anisotropic Superconducting Gap in Optimally Doped Iron–Based Material

Abstract

We offer a comprehensive optical investigation of the optimally hole-doped Ba0.6K0.4Fe2As2 over a broad spectral range, as a function of temperature and of tunable applied stress, which acts as an external symmetry breaking field. We show that there is a large electronic nematicity at optimal doping which extends right under the superconducting dome and implies an anisotropy of the superconducting energy gaps. © 2019 Springer.