Ratchet effect in an ac-current driven Josephson junction array

The current–voltage characteristics have been studied in an underdamped Josephson junction ratchet array driven by dc and ac current. A higher coupling strength along the direction of the vortex flow is used to guide vortices. As the ac current increases, the critical currents become dependent on the bias direction and the current–voltage curves become asymmetric. In some higher ac currents, nonzero voltage is shown even at zero-dc current. This off-center behavior is a rectifying effect of an applied ac current and a clear evidence of the directional motion of vortices.