Vortex-line liquid phases: Longitudinal superconductivity in the lattice London model

TL;DR

This paper uses Monte Carlo simulations to analyze vortex-line phases in a type-II superconductor, revealing conditions under which longitudinal superconductivity persists or diminishes due to anisotropy and vortex loops.

Contribution

It provides a direct comparison of methods to measure longitudinal coherence and clarifies the existence of a long-range vortex-liquid regime in isotropic superconductors.

Findings

Long-range longitudinal coherence exists in isotropic cases.

Anisotropy suppresses the vortex-liquid regime near melting.

Vortex loops between layers influence coherence in anisotropic superconductors.

Abstract

We study the vortex-line lattice and liquid phases of a clean type-II superconductor by means of Monte Carlo simulations of the lattice London model. Motivated by a recent controversy regarding the presence, within this model, of a vortex-liquid regime with longitudinal superconducting coherence over long length scales, we directly compare two different ways to calculate the longitudinal coherence. For an isotropic superconductor, we interpret our results in terms of a temperature regime within the liquid phase in which longitudinal superconducting coherence extends over length scales larger than the system thickness studied. We note that this regime disappears in the moderately anisotropic case due to a proliferation, close to the flux-line lattice melting temperature, of vortex loops between the layers.