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'', respective ly). Since a flat surface is topologically similar to the artificial c olumnar defects, their comparison is useful. The vortex creep over the surface is equivalent to that over the cylinder defect of radius r > lambda whereas the radii of real defects obtained so far are of order xi much-less-than lambda. We discuss the effect of the smallness of de fect radius on the creep process, which results in very small activati on energies U at large critical current J(c). The importance of the in crease of the defect radius is predicted.