Influence of the Fermi Surface Geometry on the Josephson Effect Between Iron-Pnictide and Conventional Superconductors

We study hybrid Josephson junctions between a multiband Ba1-xNaxFe2As2 iron-pnictide and Nb. We observe that the insertion of a Cu interlayer in such junctions leads to a dramatic enhancement of the IcRn product, despite the weaker proximity-induced superconductivity of Cu. This counterintuitive phenomenon is attributed to the differences in Fermi surface geometries of Nb and Cu, which affect the selectivity of tunneling in sign-reversal s(+/-) bands of pnictide. Our results indicate that the sensitivity to Fermi surface geometries provides a new tool for phase-sensitive studies and paves the way to conscious Fermi surface engineering of pnictide junctions.