Phase-transitions in isotropic extreme type-II superconductors

TL;DR

This study uses large-scale Monte Carlo simulations to demonstrate a first-order vortex lattice melting transition in isotropic extreme type-II superconductors, clarifying the nature of vortex liquids and their phase coherence.

Contribution

It provides the first simulation-based evidence of a first-order vortex lattice melting transition in isotropic extreme type-II superconductors, resolving previous finite size effect issues.

Findings

Vortex liquid is always incoherent with no phase coherence.

Vortex-line tension vanishes at the superconducting transition.

Connectivity of the vortex tangle changes abruptly at the transition.

Abstract

Using large scale Monte Carlo simulations on a uniformly frustrated 3DXY model, we report a first order vortex lattice melting transition in clean, isotropic extreme type-II $\kappa \to \infty$ superconductors. This work clarifies an important issue: the unpinned vortex liquid is always incoherent with no phase coherence in any directions for all anisotropies. Previous claims of a disentangled vortex liquid for isotropic superconductors based on simulations, are due to finite size effects. We explicitly show that the effective vortex-line tension vanishes precisely at the superconducting phase transition in zero magnetic field. This loss of line tension is accompanied by an abrupt change in the connectivity of the vortex tangle across the superconductor. We also obtain results indicating that the connectivity of the vortex tangle changes in a similar way even in finite magnetic field, and suggest that this could also be associated with a genuine phase-transition.