Individual Shapiro steps observed in resistively shunted intrinsic Josephson junctions on Bi2Sr2CaCu2O8+x single crystals

With a thin gold layer, we fabricated mesa-like shunted intrinsic Josephson junction stacks on ${\mathrm{Bi}}_{\mathrm{2}}{\mathrm{Sr}}_{\mathrm{2}}{\mathrm{CaCu}}_{\mathrm{2}}{\mathrm{O}}_{\text{8+x}}$ single crystals. Instead of the multibranch structure and large voltage jumps often observed in conventional intrinsic junctions, current–voltage characteristics typical of resistively shunted junctions were obtained. Individual Shapiro steps were clearly visible with irradiation at frequencies from a few to 20 GHz. The experiments demonstrated not only the ac Josephson effects directly but also the possibility of employing intrinsic Josephson junctions in high-frequency applications.