Direct Observation of a Temperature Dependent 0-pi Junction Transition in a Mesoscopic High Critical Temperature Grain Boundary Junction

摘要

We have observed, for the first time, a temperature dependent 0-pi junctioncrossover in a 45 symmetric [001] tilt grain boundary junction. Experimentaldata, obtained by a double phase-sensitive test based on a low inductance dcSQUID, show an anomalous nonmonotonic temperature dependence of the Josephsoncurrent, clear evidence of a critical current sign change at a temperature T*.At the same temperature, the SQUID undergoes a transition from a 0-SQUID to api-SQUID. Results are in good agreement with theoretical models taking intoaccount mid-gap states in low transparency junctions.