Electronic Thermal Conductivity of Multi-Gap Superconductors with Application to MgB_2

TL;DR

This paper explains the unusual magnetic field dependence of electronic thermal conductivity in MgB_2 as a result of its multi-gap superconductivity, highlighting how quasiparticle delocalization affects thermal transport.

Contribution

It provides a theoretical explanation for the field dependence of thermal conductivity in MgB_2 based on multi-gap superconductivity and quasiparticle delocalization mechanisms.

Findings

Rapid rise in thermal conductivity at low magnetic fields in MgB_2.

Delocalization of quasiparticles occurs across the entire Fermi surface in moderately clean samples.

Contrast with anisotropic or nodal gaps where delocalization is partial.

Abstract

The remarkable field dependence of the electronic thermal conductivity observed in MgB_2 can be explained as a consequence of multi-gap superconductivity. A key point is that for moderately clean samples, the mean free path becomes comparable to coherence length of the smaller gap over its entire Fermi surface. In this case, quasiparticle excitations bound in vortex cores can easily be delocalized causing a rapid rise in the thermal conductivity at low magnetic fields. This feature is in marked contrast to that for anisotropic or nodal gaps, where delocalization occurs only on part of the Fermi surface.