Direct evidence for a Transition from Elastic to Plastic Dynamics in the Vortex System of YBa2Cu3O7−δ

Partial magnetization loops have been performed in order to study history effects in high quality detwinned YBa2Cu3O7−δsingle crystals. The obtained results have disclosed a transition within the vortex system from a dislocation-free Bragg glass to a disordered vortex phase. This boundary has been mapped in the field – temperature phase diagram and found to lie in the vicinity of the onset of the second magnetization peak. The effect of decreasing oxygen deficiency is shown to be the shift of this line to higher fields. For fields above the transition, metastable topological disorder invades the lattice leading to a prominent dependence of the critical current density on the history of the superconductor.