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

We have fabricated step edge superconductor-normal metal-superconductor microbridges using YBa2Cu3O7-x(YBCO) and noble metals with critical current-normal resistance (I(c)R(N)) products as high as 10 mV and normal resistances up to 38 OMEGA. Our fabrication process achieves high values of the I(c)R(N) product by exploiting the anisotropy in the properties of epitaxial YBCO films, allowing contact only between normal metal and superconductor through the crystalline axes which support the largest Josephson coupling. This results in a dramatic increase in the normal resistance of a junction without decreasing its critical current. We discuss the role of the superconductor-normal metal boundary resistance on the junction electrical properties. We have coupled submillimeter wave rf currents quasioptically into junctions integrated at the feeds of noble metal planar log periodic antennas and have induced up to 7 Shapiro steps in the current-voltage characteristics with a 760 GHz beam from a far infrared laser.