Absence of weak-link behaviour in YBa₂Cu₃0₇ grains connected by 90^° [010] twist boundaries

Abstract

ONE of the obstacles to developing applications of the high-T_c copper oxide superconductors is the low critical current density (J_c) of the bulk polycrystalline materials, due to the presence of grain boundaries. On the other hand, these same grain boundaries can be put to good use in device applications, where their low J_c allows them to be used as "weak links9 in Josephson junctions^1,2. Dimos et al.^3,4 have shown that the transport properties of certain twist and tilt boundaries degrade as the misorientation angle increases, suggesting that high-angle grain boundaries are generally deleterious to the overall J^c. More recently, however, Babcock et al.⁵ reported weak-link-free behaviour at high magnetic field in an YBa₂Cu₃O_7-δ (YBCO) bicrystal containing two kinds of 90^°. boundary; they were not able to distinguish between the characteristics of the two types, which were electrically in parallel. Here we report the observation of 90^° [010] twist boundaries in {103}-oriented YBCO thin films. (Because of the twin microstruc-ture, we do not distinguish between the a and b axes.) Across these boundaries the J_c and normal-state conductivity are as high as those of high-quality c-axis-oriented films with no high-angle grain boundaries.