Helicity Modulus and Fluctuating Type II Superconductors: Elastic Approximation and Numerical Simulations

TL;DR

This paper introduces a helicity modulus criterion for superconducting order in fluctuating type II superconductors, linking it to superfluid density via duality, and demonstrates its relevance through numerical simulations and theoretical arguments.

Contribution

It develops a new criterion based on the helicity modulus for identifying superconducting order in the mixed phase of fluctuating type II superconductors, supported by duality relations and simulations.

Findings

Helicity modulus relates to superfluid density through duality.

Vortex line lattice shows perfect Meissner effect for shear perturbations.

Longitudinal superconductivity may persist into the vortex liquid phase for finite systems.

Abstract

We develop the helicity modulus as a criterion for superconducting order in the mixed phase of a fluctuating type II superconductor. We show that there is a duality relation between this helicity modulus and the superfluid density of a system of analog 2D bosons. We show that the vortex line lattice exhibits a perfect Meissner effect with respect to a shearing perturbation of the applied magnetic field, and this becomes our creterion for "longitudinal superconductivity" parallel to the applied field. We present arguments based on the 2D boson analogy, as well as the results of numerical simulations, that suggest that longitudinal superconductivity can persist into the vortex line liquid state for systems of finite thickness, comparable to those commonly found in experiments.