HIGH-TEMPERATURE SUPERCONDUCTOR-NORMAL METAL-SUPERCONDUCTOR JOSEPHSON-JUNCTIONS WITH HIGH CHARACTERISTIC VOLTAGES

We have fabricated step edge superconductor-normal metal-superconducto r microbridges using YBa2Cu3O7-x(YBCO) and noble metals with critical current-normal resistance (I(c)R(N)) products as high as 10 mV and nor mal resistances up to 38 OMEGA. Our fabrication process achieves high values of the I(c)R(N) product by exploiting the anisotropy in the pro perties of epitaxial YBCO films, allowing contact only between normal metal and superconductor through the crystalline axes which support th e largest Josephson coupling. This results in a dramatic increase in t he normal resistance of a junction without decreasing its critical cur rent. We discuss the role of the superconductor-normal metal boundary resistance on the junction electrical properties. We have coupled subm illimeter wave rf currents quasioptically into junctions integrated at the feeds of noble metal planar log periodic antennas and have induce d up to 7 Shapiro steps in the current-voltage characteristics with a 760 GHz beam from a far infrared laser.