Zero-crossing steps in intrinsic surface junctions of Bi2Sr2CaCu2O8+δ single crystals

Abstract

Irradiating a microwave of several tens GHz on Bi2Sr2CaCu2O8+δ (Bi-2212) single crystals, we observed genuine zero-crossing current steps from intrinsic Josephson junctions forming on the surface of the crystals in contact with normal-metallic (Au) electrodes. The critical current of the surface intrinsic Josephson junction was significantly suppressed due to the proximity contact to the normal-metal electrode, which allowed us to isolate the microwave response of the 'surface junction' from that of rest of the 'inner junctions' in a stack. This indicates that a sufficiently small tunneling critical current density is essential to observing the zero-crossing current steps. An attempt to reduce the interlayer coupling using HgI2-intercalated Bi2Sr2CaCu2O8+δ single crystals, however, gave rise to coherent fluxon motions.