EFFECTS OF COLUMNAR DEFECTS ON THE SUPERCONDUCTING PROPERTIES OF Y1BA2CU3O7-DELTA - LIMITS TO THE IRREVERSIBILITY LINE

A series of YBa2Cu3O7-delta(YBCO) epitaxial films and crystals were irradiated with energetic heavy ions (Sn30+ or Ag29+ at energy 0.58 GeV) to produce columnar defects of highly disordered material. The irreversibility lines, B*(T), show enhancement due to the increased pinning. However, while B* does not exceed that observed in the highest-J(c) as-grown epitaxial thin films, the values approach the proposed vortex melting line determined by a number of experiments on nearly defect-free single crystals. These results are interpreted in terms of the predicted upper limit of pinning energies in anisotropic superconductors, and the thermally-induced decoupling of vortex segments.