Microwave oscillations in parallel Josephson junctions

It was found that when two Josephson junctions were connected in parallel, constant voltage-current steps appeared in the V-I characteristics for currents above the sum of the zero-field critical currents of the two junctions. These steps only occurred when the critical currents of the two junctions were different. The current steps were separated by voltages which corresponded fairly closely with the fundamental and 2nd and 6th harmonics of fundamental frequency determined by the length of the superconducting strips which connected the two junctions. When junctions which had the same critical currents were connected in parallel no such steps were observed. An analysis, based on the equations derived by Ivanchenko and Stewart is also presented.