JOSEPHSON EFFECTS IN Nb₃Sn MICROBRIDGES.

Josephson effects in long narrow Nb//3Sn microbridges at temperatures up to 17 K were studied. These microbridges are formed by photolithographic techniques and subsequently subjected to controlled electrical discharges to modifY the intrinsic T//c of the bridge region. The bridges exhibit 10 GHz microwave steps in their I-V characteristics whose amplitudes are in agreement with the Resistively Shunted Junction (RSJ) model. I-V characteristics can be fit assuming an effective temperature approximately 15 K above the bath temperature. Structures in the I-V characteristics in the absence of microwaves were also investigated. It was demonstrated that phase-slip centers are induced at weak superconducting positions along the bridge when the S-N boundarY of an expanding hot spot reaches within a thermal healing distance. The critical current of the phase-slip center thus formed exhibits a temperature dependence (1-T/T//c) one-half insteady of the usual mean field result (1-T/T//c)**3**/**2.