Fluctuation dominated Josephson tunneling with a scanning tunneling microscope - art. no. 097004

We demonstrate Josephson tunneling in vacuum tunnel junctions formed betwee n a superconducting scanning tunneling microscope tip and a Pb film, for ju nction resistances in the range 50-300 k Omega. We show that the supercondu cting phase dynamics is dominated by thermal fluctuations, and that the Jos ephson current appears as a peak centered at small finite voltage. In the p resence of microwave fields (f = 15.0 GHz) the peak decreases in magnitude and shifts to higher voltages with increasing rf power, in agreement with t heory.