Josephson effects in Nb3Sn microbridges

We have studied Josephson effects in long narrow Nb
3
Sn microbridges at temperatures up to 17 K. 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 micro wave steps in their I-V characteristics whose amplitudes are in excellent agreement with the Resistively Shunted Junction (RSJ) model. I-V characteristics (with and without microwaves) can be fit assuming an effective temperature approximately 15 K above the bath temperature. We have also investigated in detail structures in the I-V characteristics in the absence of microwaves. We show experimentally 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
)
^1/2
instead of the usual mean field result (1-T/T
c
)
^3/2
.