Microwave response of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$-Ag-Al-Pb superconducting proximity junctions

Thin-film ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$-Ag-Al-Pb proximity structures have been fabricated. The current-voltage characteristics are typically those of a superconductor-normal metal-superconductor (S-N-S) junction. Sharp Shapiro steps appear in a microwave field. The dependence of step height on microwave power can be interpreted in terms of the resistively shunted junction (RSJ) model, with a critical current ${\mathit{I}}_{\mathit{c}}$∝sinφ, where φ is the phase difference of the superconducting order parameter across the junction. It is the first time that this behavior is demonstrated for a S-N-S junction composed of both a classical and an oxide superconducting electrode.