The effect of bond disorder on the radio-frequency response of planar arrays of proximity-coupled Josephson junctions

The effect of disorder on planar arrays of proximity-coupled (Nb-Au-Nb) Josephson junctions has been studied as a function of the radio-frequency (rf) current and the temperature. In these arrays, giant Shapiro steps occur at the time averaged voltage < V > = n/m(Nh nu(rf)/2e), where n and m are integers and N is the number of junctions between the voltage leads. Disorder is inherent in the arrays due to the junction fabrication processes. This disorder manifests itself as a distribution of normal metal junction lengths. A consequence of this disorder is that the global phase coherence of the array is disturbed. This results in finite giant Shapiro-step slopes and rounded step edges. This places limitations on the experimental observation of higher-order steps. Our experimental results are compared with those of numerical calculations.