Pal, A.

Anisotropic Superconducting Gap in Optimally Doped Iron–Based Material

In this work we offer a comprehensive optical investigation of the optimally hole-doped Ba 0.6 K 0.4 Fe 2 As 2 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.