Novel microwave-induced steps of intrinsic Josephson junctions in mesa-shaped BSCCO single crystals

We have been investigated the current-voltage characteristics of naturally stacked intrinsic Josephson junctions in mesa-shaped Bi2Sr2CaCu2Oy single crystals, having dimensions in the ab plane larger than the Josephson penetration depth, without and with microwave irradiations. In the absence of microwave irradiation, a gaplike feature and multiple resistive branches that imply SIS series junctions were observed in the current-voltage characteristic. Under appropriate conditions of microwave irradiation, we successfully observed striking microwave-induced subharmonic steps, caused by the phase-locked oscillation of a coupled multifluxon, with nearly equal voltage separations on the I-V characteristics of a mesa in the cavity resonant mode.