Mixing characteristics of a microwave detector using a granular YBCO superconductor

Microbridge-type Josephson junctions made of granular bulk YBCO superconductors were experimentally studied at microwave frequencies. Although the bridge included many grain boundaries, clear Shapiro steps were induced at every hf/2e voltage for microwave frequencies, and step height dependence for microwave power similar to that of a single weak link bridge was observed. A heterodyne mixing experiment of microwaves at about 20 GHz was also performed using the detector. The IF signal showed peak amplitudes corresponding to the peak dynamic resistance due to nonlinearity resulting from the Josephson effect. It was confirmed that the detector operates stably for the Josephson-effect heterodyne mixer at 60 K or below. The detector has potential for high sensitivity and good impedance matching due to its large dynamic resistance and high normal state resistance, respectively.