Voltage rectification in two-dimensional Josephson junction arrays

We study numerically the directed motion of vortices (antivortices) under an applied ac bias in two-dimensional Josephson junction arrays (JJA) with an asymmetrically modulated periodic vortex pinning potential. We find that the ratchet effect in large 2D JJA can be obtained using the RSJ model for the overdamped vortex dynamics. The rectification effect shows a strong dependence on vortex density as well as an inversion of the vortex flow direction with the ac amplitude, for a wide range of magnetic field around f = 1/2 (f being the vortex density). Our results are in good agreement with very recent experiments by D.E. Shalóm and H. Pastoriza [D.E. Shalóm, H. Pastoriza, Phys. Rev. Lett. 94 (2005) 177001].