Van der Waals Interaction between Flux Lines in High-T_c Superconductors: A Variational Approach

TL;DR

This paper introduces a variational method to analyze the van der Waals attraction between flux lines in high-temperature superconductors, revealing its impact on phase transitions and comparing results with functional RG approaches.

Contribution

A novel variational approach for calculating the flux line lattice free energy in anisotropic superconductors, enabling exploration of the low field phase diagram.

Findings

Van der Waals attraction influences the phase diagram.

First order transition from Meissner to mixed state.

Comparison with functional RG results confirms validity.

Abstract

In pure anisotropic or layered superconductors thermal fluctuations induce a van der Waals attraction between flux lines. This attraction together with the entropic repulsion has interesting consequences for the low field phase diagram; in particular, a first order transition from the Meissner phase to the mixed state is induced. We introduce a new variational approach that allows for the calculation of the effective free energy of the flux line lattice on the scale of the mean flux line distance, which is based on an expansion of the free energy around the regular triangular Abrikosov lattice. Using this technique, the low field phase diagram of these materials may be explored. The results of this technique are compared with a recent functional RG treatment of the same system.