The microwave responses of stacked Bi2Sr2CaCu2O8 (BSCCO) intrinsic junctions at frequencies around 7 GHz are presented. Remarkable current steps on its current-voltage (I-V) curves were observed by measuring the c-axis transport of the BSCCO with a-b plane sizes of 10 μm×10 μm. The stack is regularly spaced with 4 mV intervals with increasing microwave power, although more steps are visible and their heights are modulated. Both temperature dependence and frequency dependence of the step structures are also observed. Possible explanations for the step structures, based on resonances excited by microwave or geometric resonances in the junction cavity, are discussed.
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