EVIDENCE FOR A BRICK WALL MICROSTRUCTURE IN EPITAXIAL YBA2CU3OX FILMS

We have measured the in-plane (ab plane) critical current density J(c) in sputtered, c-axis oriented YBa2Cu3Ox films as a function of the ox ygen content x. The important reduction of J(c) with decreasing x can be explained in terms of a ''brick wall'' microstructure, where the cr itical current density is dominated by the coupling strength (along th e c axis) between the superconducting CuO2 planes. Scanning tunneling microscopy images of the film surfaces are consistent with the presenc e of the brick wall structure, which apparently results from the overl ap between terraces belonging to adjacent spiral-shaped islands.