Transition from elastic to plastic vortex dynamics in YBa2Cu3O7-delta single crystals: the effect of columnar defects

We have performed partial magnetization loops in pure YBa2Cu3O7-delta Singl e crystals with point and columnar defects. These results have demonstrated that the critical current density in detwinned samples depends strongly on the magnetic history of the superconductor. As shown recently in Ref. [1], this effect is due to metastable topological disorder present in the vorte x lattice and is a precursor to the transition from a dislocation-free Brag g glass to a disordered vortex phase. However, even low densities of column ar defects have been found to suppress this transition and eliminate the me mory effects.