Flux-pinning mechanisms in thin films of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathit{x}}$

We consider data from several experiments taken at very small induction in order to discern the nature of the pinning interaction in some thin-film samples of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{\mathit{x}}$ with very large critical current densities. Analysis of typical pinning energies and critical current densities indicate that the pinning is due to a large density of point defects. We propose a simple model of pinning by point defects in the ${\mathrm{CuO}}_2$ planes that predicts a spacing between defects of 53 Å. This large defect density may help to explain other properties of these films.