Sublimated Decoupling of the Vortex Lattice in Extremely Type-II Layered Superconductors

The question of whether layer decoupling and vortex-lattice melting occur seperately or not in the mixed phase of pristine layered superconductors in the extreme type-II limit is studied through a partial duality analysis of the layered XY model with uniform frustration. We find that both transitions occur simultaneously if the normal/superconducting transition of the vortex lattice in an isolated layer is first-order and if a sufficient degree of layer anisotropy exists. We also find that a cross-over to a highly entangled vortex lattice phase with relatively low phase rigidity across layers does not occur in practice under any circumstances at temperatures below the two-dimensional vortex-lattice melting transition.