Intrinsic Josephson junctions in c-axis-oriented La1.85Sr0.15CuO4 thin films

Abstract

We investigated current–voltage characteristics (IVCs) of intrinsic Josephson junctions (IJJs) for c-axis oriented La1.85Sr0.15CuO4 thin films. We fabricated IJJs with two kinds of structures. One was a mesa structure with a junction area of 22–194 μm2 fabricated by using conventional photolithography and Ar-ion milling, and the other was a microbridge structure with a junction area of 1.1–3.6 μm2 fabricated by using a focused-ion-beam technique. The mesa-type IJJs exhibited resistively-shunted-junction-like IVCs with no hysteresis. The temperature dependence of their critical current followed the Ambegaokar–Baratoff relation. IVCs of the microbridge-type IJJs, on the other hand, exhibited voltage jump and clear hysteresis. The different behaviors between the mesa-type and the microbridge-type IJJs were explained by the different numbers of grain boundaries involved in the IJJs.