Peak effect and vortex phase diagram in twin-free YBa 2Cu 3O 7− δ single crystals

Abstract

The peak effect of the current density j vs. magnetic field B and its relation to the vortex phase diagram is investigated in a twin-free YBa 2Cu 3O 7− δ single crystal. The fully oxidized crystal without any j( B) peak and with a first-order melting transition of the vortex lattice was subsequently oxygen-reduced. The solid/liquid transition, the upper critical point, the evolution of the peak, and the transition from the lattice below the peak into the amorphous state above are investigated as a function of random disorder from oxygen reduction. The influence from disorder and thermal fluctuation on the lattice/glass transition in the solid vortex state is compared with the model of field-driven introduced dislocation into the vortex solid.