Comprehensive theory of vortex lattice melting in a clean layered superconductor:

Phys. Rev. B 43, 2835 (1991) [pdf file].

This paper also shows a possibility of a phase transition, within the ordered vortex lattice state. The existence of such a transition, driven by the appearance of pancake vortices as interstitials in the vortex lattice, remains an open question.