Anomalous Metal Interface Effect of Iron-based Superconductors

We report the results of the Andreev spectroscopy of the (Co-doped Ba-122 single crystals)/metal/Pb junctions with a metal layer of Al, Pb, Ag, and Sn. We observed Andreev-like spectra for each metal layer and the junctions were identified to be (superconductor)/(normal metal) type. The spectra showed different behaviors for each metal layer. Especially in the case of Sn, the junction showed complex structure where different S/N type features were folded. We consider this behavior is due to a chemical reaction, in the interface between an iron-based superconductor and a layering metal.