Gao, Z. X., I. Heyvaert, B. Wuyts, E. Osquiguil, C. V. Haesendonck, and Y. Bruynseraede. "Evidence for a “brick wall” microstructure in epitaxial YBa 2Cu3Ox films." Applied Physics Letters 65, no. 6 (1994): 770–772.
Abstract: We have measured the in-plane (ab plane) critical current density J c in sputtered, c-axis oriented YBa2Cu3O x films as a function of the oxygen content x. The important reduction of Jc with decreasing x can be explained in terms of a “brick wall” microstructure, where the critical current density is dominated by the coupling strength (along the c axis) between the superconducting CuO 2 planes. Scanning tunneling microscopy images of the film surfaces are consistent with the presence of the brick wall structure, which apparently results from the overlap between terraces belonging to adjacent spiral-shaped islands.