Observation of integer and fractional giant Shapiro steps in arrays of SNS Josephson junctions

Abstract

We observe giant Shapiro steps in the I-V curves of NxM arrays of SNS Josephson junctions; these steps occur at N times the single junction voltage. Both integer and fractional giant steps are observed as a function of temperature, external magnetic field, and rf current. The fractional steps occur at multiples of 1/q times the giant Shapiro step voltage and are seen at well defined values of the applied field, p/q flux quantum per placquette. We also observe a fractional step at 1/2 integer voltages, even in zero applied field. These fractional steps decrease in size if random site disorder is introduced to the array.