Disordering Transitions in Vortex Matter: Peak Effect and Phase Diagram

Using numerical simulations of magnetically interacting vortices in disordered layered superconductors we obtain the static vortex phase diagram as a function of magnetic field and temperature. For increasing field or temperature, we find a transition from ordered straight vortices to disordered decoupled vortices. This transition is associated with a peak effect in the critical current. For samples with increasing disorder strength the field at which the decoupling occurs decreases. Long range, nonlinear interactions in the c-axis are required to observe the effect.