Intrinsic Josephson effect in La2−xSrxCuO4 mesa junctions with niobium counter electrode

Abstract

We reveal the intrinsic Josephson effect in a La2−xSrxCuO4 (LSCO) high-Tc superconductor. Nb counterelectrodes are deposited on top of mesas, which are formed on surfaces either parallel or perpendicular to the ab plane of LSCO single crystals. Nb/LSCO interfaces behave as SNS Josephson junctions. For the junctions parallel to the ab plane, we observe many branches in the current–voltage characteristics due to intrinsic Josephson effects. The voltage gaps between the branches are typically 0.1 mV, which is much smaller than the superconducting energy gap 2Δ≅11 mV expected for LSCO from Bardeen–Cooper–Schrieffer theory.