Investigation of Microwave-Induced Zero-Current-Crossing Steps Observed in BSCCO Intrinsic Josephson Junctions

In order to understand the mechanism producing the microwave-induced zero-current-crossing steps observed in Bi₂Sr₂CaCu₂O_8+x, intrinsic Josephson junctions, the microwave power dependence of the steps was experimentally and theoretically investigated. We fabricated a mesa structure consisting of 10 junctions on a Bi₂Sr₂CaCu₂O_8+x, single crystal and observed the steps in the I - V characteristics of the mesa with 5-GHz microwave irradiation. The step voltage monotonically increased in the low power region and saturated in the higher power region. A numerical simulation using coupled sine-Gordon equations for the intrinsic junctions obtained a power dependence similar to the experimental result. The simulation results show that the step voltage is produced by a Josephson current with high harmonics of the microwave frequency and the inverse ac Josephson effect.