Superconducting proximity effect in epitaxial Nb(110)/Au(111)/Nb(110) trilayers

Single-domain, epitaxially-grown Nb(110)/Au(111)/Nb(110) trilayers are studied in order to elucidate the superconducting proximity effect in the Au(111) layer. The critical current density, superconducting coherence length, and superconducting transition temperature, all show a non-monotonic dependence on the thickness of the Au layer. The analysis of the experimental data reasonably argues that a form of order-parameter oscillation is intrinsic to the proximity-induced Cooper pairs in the Au layer. We find that relative phase of the superconducting order parameter in the two Nb(110) layers changes sign as a function of Au(111) layer thickness tAu, offering a route to achieving a {\pi} junction for 0.94 nm<tAu<1.88 nm.