Realization and properties of ramp-type YBa2Cu3O7−δ/Au/Nb junctions

All-thin-film ramp type Josephson junctions between YBa2Cu3O7−δ and Nb have been fabricated. This procedure allows connections between high-Tc and low-Tc superconductors at different crystal sides of the high-Tc superconductor on one chip, which is of great interest for novel phase devices. A thin Au layer is incorporated as a chemical barrier to avoid oxygen transfer from the YBa2Cu3O7−δ to the Nb. Critical current densities up to 600 A/cm2 are obtained at T=4.2 K, with typical RnA values of 0.8 μΩ cm2. The variation of the magnetic field dependence of the critical current with the angle between the junction barrier and the YBa2Cu3O7−δ crystal axes is explained by considering a predominant dx2−y2 order parameter symmetry of the YBa2Cu3O7−δ. The successful fabrication of these junctions allows the implementation of novel superconducting electronics, such as complementary Josephson circuitry or proposed qubit concepts, using the unconventional order parameter symmetry of the high-Tc superconductor.