Transport characteristics in YBCO thin film superconductors

We studied influences of growth temperature on superconducting characteristics in YBa2Cu3O7-x (YBCO) thin films prepared by pulsed laser deposition (PLD). The films deposited at low growth temperature (below 730 degrees C) have a high c-axis orientation, good in-plane alignment and large amount of a-axis grains. With increasing growth temperature, the number of a-axis grains in the films were decreased, whereas superconducting properties were degraded due to the formation of misoriented grain boundaries. The crystal defects acting as barriers to supercurrent flow were observed by magneto-optical imaging (MOI) technique. Using this technique, we confirmed that the critical current densities of the films were limited by these defects. Dynamic magnetic flux behaviors in flux flow state were also observed by MOI system.