ANALYSIS OF JOSEPHSON RADIATION FROM YBA2CU3O7 THIN-FILM JOSEPHSON-JUNCTIONS

We have investigated the Josephson radiation from different types of YBa2Cu3O7 (YBCO) thin-film Josephson junctions: step-edge junctions (SEJs), biepitaxial junctions and SNS junctions with N = Au. The radiation was detected using a non-resonant radiometer system with a receiving frequency of 11-12 GHz. The current-voltage characteristics were measured simultaneously with the radiation spectra in the temperature range 4.2-90 K. All junctions exhibited a large emission peak at a voltage which was related to the frequency through the second Josephson relation. Typically, for high temperatures, and therefore small critical currents, the measured radiation linewidth agreed well with the theoretical predictions. At lower temperatures the experimental linewidths deviated from the theoretical values due to additional noise sources in the junctions. Some of the SEJs showed a non-monotonic dependence of the linewidth on temperature. It is suggested that such SEJ data may be discussed in terms of a model which treats the SEJ as an interferometer consisting of a parallel array of random Josephson junctions.