Enhancement of high-TC superconducting thin film devices by nanoscale polishing

The effects of mechanical nanoscale polishing on the superconducting parameters of YBa₂Cu₃O_7-δ (YBCO) thin films and bi-crystal grain boundary Josephson junctions have been investigated. We prepared samples with additional gold nanocrystallites in the YBCO film. As they are distributed throughout the whole YBCO film, they provide a low-resistance ohmic contact even if parts of the film are removed. Polishing was performed either before or after the patterning and did not change the properties of the grain boundary. However, nanopolishing reduces the film roughness in a significant way, which makes it an indispensable tool for the preparation of integrated superconducting circuits. We also succeeded in tuning the I_C and R_N of the Josephson junctions of direct current superconducting quantum interference devices (dc-SQUIDs) by systematically reducing the film thickness, which opens up new possibilities in the application of magnetic field sensors.