Half-harmonic parametric oscillations in Josephson junctions

Half-harmonic generation in Josephson tunnel junctions and microbridges is investigated theoretically, numerically, and experimentally. It is found that such generation may take place both a zero voltage and on rf-induced steps in tunnel junctions, but not in microbridges. A simplified theory, which leads to the definition of a plasma resonance on rf-induced steps, is presented. The experiments are made on junctions with different current densities and with pump frequencies at 18 and 70 GHz.