RF-induced steps in intrinsic Josephson junctions in Bi2Sr2CaCu2Oy

We have investigated the RF-induced steps in intrinsic Josephson junctions in mesa-shaped Bi₂Sr₂CaCu₂O_y single crystals. By applying RF signal in the frequency range 2-20 GHz to the mesa, two types of responses were observed depending on the frequency of the applied microwave. One is the Shapiro step response observed at the frequencies above the Josephson plasma frequency for surface junction. Another is the microwave-induced vortex flow response for surface and inner junctions. We found that the junction size is also the key condition for the observation of Shapiro steps together with the frequency of applied microwave.