Elastic-to-plastic crossover below the peak effect in the vortex solid   of YBa2Cu3O7 single crystals
  We report on transport and ac susceptibility studies below the peak effect in twinned YBa2Cu3O7 single crystals. We find that disorder generated at the peak effect can be partially inhibited by forcing vortices to move with an ac driving current. The vortex system can be additionally ordered below a well-defined temperature where elastic interactions between vortices overcome pinning-generated stress and a plastic to elastic crossover seems to occur. The combined effect of these two processes results in vortex structures with different mobilities that give place to history effects. 
Sergio O. Valenzuela, Boris Maiorov, Eduardo Osquiguil and Victoria   Bekeris