Flux creep through the surface barrier and columnar defects in HTSC

The rate of flux creep over the surface barrier in clean HTSC samples is found. This rate proves to be significantly different for the cases of vortex entry and escape (relaxation "in" and "out", respectively). Since a flat surface is topologically similar to the artificial columnar defects, their comparison is useful. The vortex creep over the surface is equivalent to that over the cylinder defect of radius r > λ, whereas the radii of real defects obtained so far are of order ξ{A figure is presented} λ. We discuss the effect of the smallness of defect radius on the creep process, which results in very small activation energies U at large critical current J_c. The importance of the increase of the defect radius is predicted.