Strong pinning by correlated and point disorder in YBa₂Cu₃O_7-δ thin films

We present a detailed study of the critical current density of YBa₂Cu₃O_7-δ thin films grown by pulsed laser deposition. Among the salient features are the total absence of any traits characteristic for pinning by extended linear defects, and an unexpected increase of the critical current density with film thickness. It turns out that critical current the dependence of critical current density on thickness is correlated with the field dependence of the same quantity; thicknesses of the both are very well described by extending to finite film thickness the Ovchinnikov-Ivlev theory of strong pinning [Phys. Rev. B 43 (1991) 8024].