Resonance effects in Josephson tunnel junctions with integrated tuning structures
Thomas Lehnert, Frank Schafer, K. H. Gundlach
Large-current steps have been found in the I/V characteristics of superconducting tunnel elements that are integrated within fixed tuning structures. The Josephson frequency at the steps corresponds to the operation frequencies of the different tuning structures at 345, 460, or 600 GHz. Therefore, these current steps are interpreted as resonance effects generated by an internal interaction of the Josephson oscillation with the tuning structure. The result of a spectrometer measurement around 350 GHz is in very good agreement with the resonance frequency obtained from the I/V characteristic. This confirms the interpretation of the current steps. A simple dc measurement is therefore sufficient to determine the actual resonance frequency of the tuning structure. It may be shifted with respect to the expected frequency, due to deviations of the junction size or other parameters from their required values. The exact knowledge of the resonance frequency is important for the application of these integrated tunnel elements as mixers in radioastronomical receivers. In single junctions a splitting of the resonance step into several branches was observed, whereas in two-junction arrays a splitting into two distinct states was found. Irregular switching appeared between these two states. The temperature and magnetic-field dependence of the current steps was investigated.
Journal of Applied Physics•Jul 15, 1993•5 citations