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.
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