Probing the superconducting order parameter of iron-based superconductors through the Josephson effect

We report the results we obtained regarding the use of the Josephson effect to probe the symmetry of the superconducting order parameter of Co-doped Ba(FeAs)2 crystals (Ba122). This measurements were carried out to test the validity of the s+/- model, which predicts the pairing in the multiband Ba122 compounds being mediated by the exchange of spin excitations, with the condition that the electron and hole bands in the superconductor's Fermi surface have opposite signs. Josephson interferometry applied using Pb/Cu/Ba122 SNS structures in corner/edge junction configurations shows two distinct Icphi patterns that support an anisotropic s-wave superconducting gap. The use of IcR N data favors the hypothesis of the gap anisotropy being in direct connection to an electron gap having an opposite sign when compared to the hole gaps in the material. Finally we considered the prediction of proximity-induced changes in the density of states of a thin film of a conventional superconductor due to the presence of a Ba122 crystal. Our results found evidence of both a positive and a negative proximity effect, which in conjunction with other features identified in the density of states spectrum of the thin film of conventional superconductor, points strongly towards the legitimacy of s+/- model.