Critical Josephson current in the dynamical Coulomb blockade regime

Abstract

The current-voltage characteristics of a voltage-biased Josephson junction in the low conductance regime of an ultra-low temperature scanning tunneling microscope (STM) is dominated by sequential charge tunneling. Using $P(E)$ theory we show that the Josephson coupling energy, experimentally determined in this regime, is in good agreement with the critical current ${I}_{0}$ calculated from the Ambegaokar-Baratoff formula. In this way, we can determine the critical current values of a Josephson junction in an STM. Furthermore, we experimentally determine a range of validity for $P(E)$ theory, which is in accordance with theoretical predictions. In this way, we establish an optimal parameter range, in which Josephson STM can be performed.