FINE-STRUCTURES ON ZERO-FIELD STEPS IN LOW-LOSS JOSEPHSON TUNNEL-JUNCTIONS

The first zero-field step in the current-voltage characteristic of int ermediate-length, high-quality, low-loss Nb/Al-AlOx/Nb Josephson tunne l junctions has been carefully investigated as a function of temperatu re. When decreasing the temperature, a number of structures develop in the form of regular and slightly hysteretic steps whose voltage posit ion depends on the junction temperature and length. This phenomenon is interesting for the study of nonlinear dynamics and for application o f long Josephson tunnel junctions as microwave and millimeter-waveleng th oscillators.