Electron diffusivities in MgB2 from point contact spectroscopy

TL;DR

This paper uses point contact spectroscopy to measure electron diffusivities in MgB2, revealing how magnetic fields influence the two-band superconductor's properties and confirming theoretical predictions.

Contribution

It introduces a method to compare MgB2's properties with dirty two-band superconductor theory using magnetic field-dependent Andreev reflection data.

Findings

Good agreement between experiment and theory for MgB2.

Electron diffusivity ratio between s and p bands inferred.

Field dependence of density of states is isotropic in the p band.

Abstract

We demonstrate that the variation of the Andreev reflection with applied magnetic field provides a direct means of comparing the properties of MgB2 with the theory for a dirty two-band superconductor, and we find good agreement between the two. The ratio of electron diffusivities in the s and p bands can be inferred from this experiment. We find that the field dependence of the density of states at the Fermi level in the p band is independent of the field direction, and that the anisotropic upper critical field is determined by the anisotropic diffusivity in the s band.