Fluctuation Dominated Josephson Tunneling with a Scanning Tunneling Microscope

Abstract

We demonstrate Josephson tunneling in vacuum tunnel junctions formed between a superconducting scanning tunneling microscope tip and a Pb film, for junction resistances in the range $50–300\mathrm{k}\Omega$. We show that the superconducting phase dynamics is dominated by thermal fluctuations, and that the Josephson current appears as a peak centered at small finite voltage. In the presence of microwave fields ( $f=15.0\mathrm{}\mathrm{GHz}$) the peak decreases in magnitude and shifts to higher voltages with increasing rf power, in agreement with theory.