Directional point-contact spectroscopy of MgB2 single crystals in magnetic fields: two-band superconductivity and critical fields

TL;DR

This study uses directional point-contact spectroscopy to investigate two-band superconductivity in MgB2 single crystals under magnetic fields, accurately determining gap behaviors and critical fields aligned with theoretical models.

Contribution

It provides the first detailed measurements of the temperature dependence of anisotropic and isotropic upper critical fields in MgB2 using point-contact spectroscopy.

Findings

Separated sigma and pi band contributions to conductance

Determined temperature dependence of superconducting gaps

Measured anisotropic upper critical field of sigma band

Abstract

The results of the first directional point-contact measurements in MgB2 single crystals, in the presence of magnetic fields up to 9 T either parallel or perpendicular to the ab planes, are presented. By applying suitable magnetic fields, we separated the partial contributions of the sigma and pi bands to the total Andreev-reflection conductance. Their fit with the BTK model allowed a very accurate determination of the temperature dependency of the gaps (Delta_sigma and Delta_pi), that resulted in close agreement with the predictions of the two-band models for MgB2. We also obtained, for the first time with point-contact spectroscopy, the temperature dependence of the (anisotropic) upper critical field of the sigma band and of the (isotropic) upper critical field of the pi band.