Influence of the Fermi surface geometry on a Josephson effect between an iron-pnictide and conventional superconductors

We study Josephson junctions between a multi-band iron-pnictide Ba1-xNaxFe2As2 and conventional s-wave superconductors Nb and Cu/Nb bilayer. We observe that junctions with a Cu interlayer exhibit much larger IcRn, despite a weaker proximity-induced superconductivity. This counterintuitive result is attributed to the difference in Fermi surface geometries of Nb and Cu, which leads to a selective one-band tunneling from Cu and a non-selective multi-band tunnelng from Nb. The latter leads to a mutual cancellation of supercurrents due to the sign-reversal s+- symmetry of the order parameter in the pnictide. Our results indicate that Fermi surface geometries play a crucial role for pnictide-based junctions. This provides a new tool for phase sensitive studies and paves a way to a conscious engineering of such junctions.