Shapiro steps observed in annular intrinsic Josephson junctions at low microwave frequencies

Abstract

With annular intrinsic Josephson junctions structured from a slice of Bi2Sr2CaCu2O8+δ single crystal 200nm thick, we have devised a way to inject fluxons into the junctions only by sweeping the bias current. The stacks have shown typical properties concerning Josephson fluxon conservation. These annular junctions are sensitive to microwave irradiation, and quite sharp Shapiro steps have been observed at ∼20GHz which is much lower than the plasma frequency of the junctions, indicating many applications can be possible with practically accessible microwave sources.