Superconductor–normal–superconductor step-edge junctions with Au barriers

YBa2Cu3O7−δ superconductor–normal–superconductor junctions in step-edge geometry are fabricated by an in situ process using off-axis sputter deposition. Gold is used as the normal metal interlayer. A special inhibiting layer is introduced to ensure proper separation of the superconducting electrodes. The temperature dependence of the critical current Ic is nearly linear. The junctions show high normal resistances up to RN=10 Ω and high IcRN products up to 8.8 mV at 4.2 K. I–V characteristics exhibit a large excess current Iex over the whole temperature range, even for electrically narrow junctions. The power dependence of Shapiro step heights shows characteristic deviations from the resistively and capacitively shunted junction model. Calculations using the time-dependent Ginzburg–Landau equations are carried out to model the measured I–V characteristics with and without microwave irradiation. A point-contact-like superconductor–constriction–superconductor model is suggested to explain the excess current and the measured temperature dependence of Ic and Iex. Time-dependent Ginzburg–Landau equations are used to account for the observed dynamic characteristics.