Josephson current in Fe-based superconducting junctions: Theory and experiment

We present a theory of the dc Josephson effect in contacts between Fe-based and spin-singlet sub( delta )-wave superconductors. The method is based on the calculation of temperature Green's function in the junction within the tight-binding model. We calculate the phase dependencies of the Josephson current for different orientations of the junction relative to the crystallographic axes of Fe-based superconductor. Further, we consider the dependence of the Josephson current on the thickness of an insulating layer and on temperature. Experimental data for PbIn/Ba sub(1-x)K sub(x)(FeAs) sub(2) point-contact Josephson junctions are consistent with theoretical predictions for delta + or - symmetry of an order parameter in this material. The proposed method can be further applied to calculations of the dc Josephson current in contacts with other new unconventional multi orbital superconductors, such as Sr sub(2) RuO sub(4) and the superconducting topological insulator Cu sub(x)Bi sub(2) Se sub(3)