Coherent motion of vortices driven by both dc and ac current in a Josephson junction ratchet array

► Correlation functions are used to analyze vortex dynamics in Josephson junction ratchet array. ►I-V charcteristics show asymmetric Shapiro steps and rectification effect. ► Vortices on a Shapiro n/5-step move coherently by n plaquettes during an ac cycle. ► Asymmetric features of the ratchet array gradually disappear as temperature increases.