Vortex ratchets based on asymmetric arrays of Josephson junctions

Magnetic vortex-ratchet effects in various designs of asymmetric arrays of Josephson junctions (JJs) ratchets have been simulated numerically and measured experimentally. Asymmetry in the designs is achieved by spatial asymmetric variations of either the critical current (j(c)) of the JJ or the area (A) of the superconducting loops in between the JJ or both. It was found that larger arrays result in larger ratchet efficiency and are less susceptible to noise fluctuations. The simulation results were compared with measurements of various designs of JJ arrays ratchets made of YBa2Cu3O7-delta thin film superconductor and having either asymmetric or symmetric loop areas. We demonstrate that the ratchet efficiency can be very efficiently tuned by an applied magnetic field. Such vortex ratchets could be used as vortex diodes to pump out Josephson vortices from sensitive superconducting electronic or as sensitive magnetic sensors.