Flux creep and high-field critical currents in epitaxial thin films of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$

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×${10}^5$ 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.