Anomalous Differential Resistances in Point Contact Josephson Junctions

Abstract

New structures of voltage-current characteristics in Nb-Nb point contact Josephson junctions were found by using a differentiation technique. The first and the second derivatives of junction voltage with respect to the current as a function of bias reveal finer structures than V–I characteristics of junction. These new structures can be regarded as the result of thermal runaway of multiple point contacts in the Josephson junctions due to Joule heating. When one of the multiple point contacts suffers thermal runaway, the resistance of the junction changes suddenly and the peaks appear in V–dV⁄dI and V–d²V⁄dI² characteristics.