Softening and melting of a vortex lattice in presence of point disorder

Abstract

A phenomenological model is proposed for melting of a vortex lattice, based on screening of the elastic shear modulus by mobile or partially pinned dislocations. A first-order softening line is found and ends at a critical point beyond which the lattice crosses over to an hexatic vortex solid. The consequences of softening on vortex dynamics are explored, as fingerprints of plastic dynamics: a reentrance of single vortex behaviour, for both depinning and collective creep, occurs as the field increases, with non-monotonous creep exponents. This general scenario is supported by recent experiments in high-$T_c$ materials and suggests that for a 3D vortex lattice at low temperature the field induces a continuous order-disorder transition towards a glassy phase.