High-Resolution Analysis of Currents at Low-Angle Grain Boundaries in YBCO Thin Films Using Magnetooptics and Magnetic X-Ray Microscopy

Current transport in high-temperature superconductors is strongly affected by the presence of grain boundaries (GBs). Thin epitaxial films of high-temperature superconducting YBa₂Cu₃O_7-δ containing low-angle GBs with fixed angles of 5° have been prepared on bicrystalline substrates. The current-carrying capability of these GBs is investigated by quantitative magnetooptical imaging; the results are compared with novel magnetic X-ray microscopy images. We find that not only the misorientation angle of the GB but also the macroscopic geometry of the current path has substantial influence on the critical current. On small length scales, inhomogeneities of the GB behavior are found. A detailed analysis requires investigations with the highest spatial resolution which can be offered by X-ray microscopy.