VORTEX-LINE LIQUID-PHASES - LONGITUDINAL SUPERCONDUCTIVITY IN THE LATTICE LONDON MODEL

We study the vortex-line lattice and liquid phases of a clean type-II superconductor by means of Monte Carlo simulations of the lattice Lond on model. Motivated by a recent controversy regarding the presence, wi thin this model, of a vortex-liquid regime with longitudinal supercond ucting coherence over long length scales, we directly compare two diff erent ways to calculate the longitudinal coherence. For an isotropic s uperconductor, we interpret our results in terms of a temperature regi me within the liquid phase in which longitudinal superconducting coher ence extends over length scales larger than the system thickness studi ed. We note that this regime disappears in the moderately anisotropic case due to a proliferation, close to the flux-line lattice melting te mperature, of vortex loops between the layers.