Nonideal integer giant shapiro steps observed in Josephson-junction arrays: A disorder effect?

Abstract

We have studied the dynamic properties of Pb/Cu proximity-coupled Josephson-junction square arrays. With the application of an external dc + ac current, clear integer giant Shapiro steps were observed in the de current-voltage (IV) curves. Contrary to the case of ideal systems, however, the de IV and the dynamic resistance curves of the arrays in zero field deviated widely from those of a single Josephson junction, which can be explained by the effect of disorder in the junction critical currents. Although the ac current dependence of the integer step widths showed Besser-function-like oscillatory behavior as in a single Josephson junction, the minimum integer step widths did not vanish completely, which cannot be explained in terms of a single junction or a simple one-dimensional chain with disorder in the junction critical currents, but may be explained by a two-dimensional nature of the system such as a self-induced magnetic field due to an external bias current.