Order-disorder phase transition in NbSe₂: Absence of amorphous vortex matter

Recent studies have proposed that the peak effect in the critical current (a dynamic property) is a consequence of an order-disorder phase transition in the vortex system. We have made magnetic decorations of vortex structures in samples with both phases. It is found that the structural symmetry of the disordered phase is polycrystalline rather than amorphous and that there is no obvious correlation between the topology of the vortex structure and the enhancement of the critical current in the disordered phase.