Tuning the current-voltage characteristics of Josephson junctions by strong microwave fields

Abstract

We observe some unusual resonance-like structures on the current-voltage characteristics (CVC) of thin film ramp-edge Josephson junctions between YBCO and Nb when applying strong microwave fields (MW). The unusual resonances have their voltage position on the CVC dependent on the MW power rather than the MW frequency, while their amplitude is largely unaffected by an increase in the MW power. Such behaviour indicates an intriguing Josephson dynamics associated with the switching from a parametric excitation regime induced by the magnetic field of the MW via oscillations of the Josephson critical current to an ac-current excitation regime triggered by the electric field of the MW. We propose a model, which describes the experimentally observed features on the CVC in terms of MW-induced multiple switching between running and locked solutions of sine-Gordon equation. Such tuning of the CVC via MW could be used to optimize the output of THz emitters.