Type-1.5 superconductivity in two-band systems

TL;DR

This paper reviews the concept of type-1.5 superconductivity in two-band systems, highlighting the existence of a distinct vortex phase with mixed attractive and repulsive interactions due to multiple length scales.

Contribution

It discusses the role of interband Josephson coupling and the case where only one band is intrinsically superconducting, expanding understanding of vortex interactions in multi-band superconductors.

Findings

Existence of a phase with vortex attraction at large scales and repulsion at short scales.

Influence of interband Josephson coupling on vortex interactions.

Behavior when only one band is superconducting.

Abstract

In the usual Ginzburg-Landau theory the critical value of the ratio of two fundamental length scales in the thery $\kappa_c=1/\sqrt{2}$ separates regimes of type-I and type-II superconductivity. The latter regime possess thermodynamically stable vortex excitations which interact with each other repulsively and tend to form vortex lattices. It was shown in [5] that this dichotomy in broken in U(1)xU(1) Ginzburg-Landau models which possess three fundamental length scales which results in the existence of a distinct phase with vortex excitations which interact attractively at large length scales and repulsively at shorter distances. Here we briefly review these results in particular discussing the role of interband Josephson coupling and the case where only one band is superconducting while superconductivity in another band is induced by interband proximity effect. The report is partially based on E. Babaev, J. Carlstrom, J. M. Speight arXiv:0910.1607.