Pinning and confinement of vortices: Random disorder and correlated disorder

Abstract

We compare temperature and magnetic field dependence of the critical current density of melt textured YBCO, irradiated with monoenergetic 3.5 and 6.5 MeV protons, and with 235 MeV Au ions, respectively. The Au irradiation affected only a surface layer on the top and on the bottom of our bulk samples,i.e. a volume fraction ranging, in different specimens, from 5% to 13% of the total volume. The point-like defects producedJc enhancements decreasing with the temperature up to a (B, T) point where a crossover to damage occurs. On the contrary, surface columnar defects allow to control the vortex dynamics in the full sample, so that the critical current density enhancement increases as the temperature and the magnetic-field increase. While the addition of point-like defects does not significantly modify the irreversibility line (IL), the ILs of the Au irradiated samples present a shift towards higher temperature as well as smooth matching effects near the dose equivalent field. Magnetic relaxation rates andJc measurements give results in accordance with recent theoretical findings.