VORTEX PINNING AND CRITICAL CURRENTS IN JOSEPHSON-JUNCTION ARRAYS WITH DEFECTS

We develop an algorithm based on the Fast Cosine Transform to study tw o-dimensional arrays of Josephson junctions containing defects. We app ly it to arrays as large as 128 x 256 and study vortex pinning, the tr ansition from she superconducting to the resistive state, and various finite size effects. We find that the pinning potential for vortices i s highly anisotropic in rectangular arrays due to boundaries and finit e size effects. As a result we observe pinned vortices in arrays much smaller than expected so far. The energy of an array changes discontin uously at transitions from one vortex sector to another in the steady- state regime.