The influence of thermal activation on measured critical currents in HTC and conventional weak links

Abstract

A simple model for thermally activated phase slippage has been used to determine the effect of thermal fluctuations on critical current measurements in HTC, conventional BCS, and HTC/BCS superconducting junctions. The most important manifestation of such effects is a decrease in the measured critical current, below the intrinsic critical current of the junction. This also leads to a depression of the measured critical temperature of the junction, below that of the superconducting materials forming the junction. It is shown that such effects are significant for HTC superconductors with junctions, whether fabricated or naturally occurring between grains, with intrinsic low temperature critical currents <3 mA. This is almost always the case for intergranular ceramic or thin film material. Measurements of the critical temperature as a function of junction strength for both Nb/Nb and YBCO/YBCO junctions are shown to be consistent with the predicted depression due to thermal fluctuations.