Microwave response of long intrinsic Josephson junctions fabricated on Bi-2212 single crystals

The microwave response properties of Bi(2)Sr(2)CaCu(2)O(8+x) long intrinsic Josephson junctions have been experimentally and theoretically investigated. We fabricated a mesa structure consisting of 14 junctions, 50 mu m long and 4 mu m wide, and observed the microwave-induced steps in the I-V characteristics under irradiation with microwaves in the range 5-8 GHz. The step voltages were proportional to the square root of the microwave power, implying that the steps were produced by the motion of fluxons created by the microwaves. The Josephson frequency corresponding to the maximum step voltage was estimated to be 570 GHz. The step voltage decreased with increasing temperature, which can be explained by the decrease of the Swihart velocity. We performed a numerical simulation using coupled sine-Gordon equations and obtained a power dependence of the step voltage similar to the experimental result, and demonstrated standing waves of electric fields with in-phase plasma oscillation in all the junctions. These facts suggest that the steps observed in the experiment were produced by plasma resonance excited by the external microwaves.