Flux Creep and High-Field Critical Currents in Epitaxial Thin Films of YBa2Cu3O7.

The critical current density ${J}_{c}$(B,T) is measured to 15 T for c-axis-perpendicular expitaxial thin films of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ with ${J}_{c}$(0,77 K) of order ${10}^{6}$ A/${\mathrm{cm}}^{2}$. Even in the least-favorable perpendicular orientation, critical currents can exceed 5\ifmmode\times\else\texttimes\fi{}${10}^{5}$ A/${\mathrm{cm}}^{2}$ at 20 K in 15-T fields. Thermally activated flux motion (flux creep) is prominently observed, and can in large part explain the magnitude, temperature, and field dependence of the high-field critical currents.