Point-contact spectroscopy in MgB2 single crystals in magnetic field

TL;DR

This study uses point-contact spectroscopy on MgB2 single crystals to analyze the effects of magnetic fields on its two-band superconductivity, providing detailed insights into the upper critical fields and band contributions.

Contribution

It presents the first thorough analysis of the upper critical field of the pi band and separates the contributions of sigma and pi bands using magnetic field effects.

Findings

Complete thermal evolution of the pi band upper critical field is determined.

Quantitative measurements of the sigma band upper critical field and its anisotropy are obtained.

Partial contributions of sigma and pi bands to conductance are separated and analyzed.

Abstract

We present the results of a spectroscopic study of state-of-the-art MgB2 single crystals, carried out by using a modified point-contact technique. The use of single crystals allowed us to obtain point contacts with current injection either parallel or perpendicular to the ab planes. The effect of magnetic fields up to 9 T on the conductance spectra of these contacts is here thoroughly studied, for both B parallel and perpendicular to the ab planes. The complete thermal evolution of the upper critical field of the "pi" band is determined for the first time, and quantitative information about the upper critical field of the "sigma" band and its anisotropy is obtained. Finally, by exploiting the different effect of a magnetic field applied parallel to the ab planes on the two band systems, the partial contributions of the "sigma" and "pi" bands to the total conductance are obtained separately. Fitting each of them with the standard BTK model yields a great reduction of the uncertainty on Delta_sigma and Delta_pi, whose complete temperature dependence is obtained with the greatest accuracy.