Point-contact spectroscopy of Al- and C-doped MgB2. Superconducting energy gaps and scattering studies

TL;DR

This study uses point-contact spectroscopy to investigate how aluminium and carbon doping affect the superconducting energy gaps and scattering mechanisms in MgB2, revealing doping-specific changes in interband and intraband scattering.

Contribution

It provides detailed insights into the effects of Al and C doping on two-gap superconductivity and scattering processes in MgB2, highlighting the role of band-filling and scattering.

Findings

Two gaps persist down to 22 K in all samples.

Al-doping enhances interband scattering as T_c decreases.

C-doping increases intraband scattering in the π-band more rapidly.

Abstract

The two-band/two-gap superconductivity in aluminium and carbon doped MgB$_2$ has been addressed by the point-contact spectroscopy. Two gaps are preserved in all samples with $T_c's$ down to 22 K. The evolution of two gaps as a function of the critical temperature in the doped systems suggest the dominance of the band-filling effects but for the increased Al-doping the enhanced interband scattering approaching two gaps must be considered. The magnetic field dependences of the Andreev reflection excess currents as well as zero-energy density of states determined from the experimental data are used to analyze the intraband scattering. It is shown, that while the C-doping increases the intraband scattering in the $\pi$-band more rapidly then in the $\sigma$ band, the Al-doping does not change their relative weight.