Imaging high-temperature superconducting films

A magneto-optically active glass, Ce(PO₃)₃, was used to image field penetration into three superconducting films of YBa₂Cu₃O₇ that were laser ablated on (100)-oriented SrTiO₃ substrates. The magnetic-field profile in these films was mapped using the Faraday effect in an external field of 92 mT for two of the films and 181 mT for the third film. These contours show regions where flux had easily penetrated, indicating weak pinning, and other regions that were strongly pinning. From the measured field gradients, it was determined that J_c varies by at least an order of magnitude across the surface of the films.