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

The two-band and/or two-gap superconductivity in aluminum- and carbon-doped MgB₂ 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 suggests the dominance of the band-filling effects, but for the increased Al doping, the enhanced interband scattering must also be considered. The extraction of the zero-energy density of states for the π and σ bands using a simple physical model demonstrates that significant changes in the relative weighting of the intraband scattering are created in the case of the C doping with the scattering in the π band enhanced faster than in the σ one. The Al doping does not change the relative weight of the scatterings within the bands.