Microwave-induced current steps in intrinsic Josephson junctions patterned on Bi2Sr2CaCu2O8 single crystal

With a $\mathrm{10 \mu m\times 10 \mu m}$ mesa patterned on ${\mathrm{Bi}}_{\mathrm{2}}{\mathrm{Sr}}_{\mathrm{2}}{\mathrm{CaCu}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{8}}$ single crystals, we measure the current–voltage $\mathrm{(I–V)}$ curves of a stack of intrinsic Josephson junctions. Current steps are observed at an equal voltage spacing of 4 mV when the sample is subjected to microwave radiation at around 7 GHz. With increase of the microwave power, more steps occur while the spacing between neighboring steps does not seem to change. The magnitude of each step depends on the microwave power in an oscillating way. Tuning the microwave frequency causes such steps to occur over separate frequency ranges, and each range is quite narrow. A temperature rise from 4.2 to 14.3 K completely quenches the step structures. Possible explanations for the step structures, based on resonances excited by microwave or geometric resonances in the junction cavity, are discussed.