Fractional Shapiro steps in resistively shunted Josephson junctions as a fingerprint of a skewed current-phase relationship

Abstract

We study numerically the fractional Shapiro step response in low-frequency driven Josephson junctions which have a nonsinusoidal current-phase relation. We perform this study within the resistively shunted Josephson junction model. We demonstrate that fractional steps, as a fingerprint of a skewed current phase relation, will manifest themselves only for higher values of the reduced frequency. We compare the theoretical observations with experimental measurements in an anisotropic Josephson junction array containing over 500 superconductor-normal-superconductor junctions having a skewed current phase relation. We demonstrate that changing the critical current by applying a magnetic field is a robust method to modify the reduced frequency over a broad range of values. The presence of fractional Shapiro steps at high values of the reduced frequency directly confirm the theoretical results.