JOSEPHSON EFFECTS IN Nb/YBa₂Cu₃0_7-δ POINT CONTACTS AND YBa₂Cu₃0_7-δ BREAK JUNCTIONS

Josephson effects have been observed in Nb/YBa₂Cu₃0_7-δ point
contacts and YBa₂Cu₃0_7-δ break junctions. When the junctions are exposed to a microwave field, the I -V characteristics show constant voltage steps, the heights of which follow the Bessel function behavior. Obvious asymmetry about zero bias has been observed in YBCO break junctions which, we suggest, may possibly result from flux trapping in the complicated weak link structure of the system. Micrmave-induced sub-steps have also been found in YBCO break junctions. All experiments were conducted at liquid helium temperature.