Ginzburg-Landau theory of vortices in a multi-gap superconductor

TL;DR

This paper derives a Ginzburg-Landau theory for two-gap superconductors from the BCS model and applies it to MgB2, revealing unique magnetic properties and vortex lattice behaviors due to multi-gap effects.

Contribution

It introduces a two-gap Ginzburg-Landau functional derived from the BCS model and applies it to analyze vortex structures and magnetic properties in MgB2.

Findings

Observed upturn in transverse upper critical field with temperature.

Identified a 30-degree vortex lattice rotation with increasing field.

Explained vortex lattice rotation as a consequence of multi-gap superconductivity.

Abstract

The Ginzburg-Landau functional for a two-gap superconductor is derived within the weak-coupling BCS model. The two-gap Ginzburg-Landau theory is, then, applied to investigate various magnetic properties of MgB2 including an upturn temperature dependence of the transverse upper critical field and a core structure of an isolated vortex. Orientation of vortex lattice relative to crystallographic axes is studied for magnetic fields parallel to the c-axis. A peculiar 30-degree rotation of the vortex lattice with increasing strength of an applied field observed by neutron scattering is attributed to the multi-gap nature of superconductivity in MgB2.