Electron-phonon coupling and two-band superconductivity of Al- and C-doped MgB2

TL;DR

This study uses density functional theory to analyze how Al and C doping affect electron-phonon interactions and two-band superconductivity in MgB2, accurately matching experimental data without considering interband scattering.

Contribution

It provides a detailed theoretical analysis of doping effects on MgB2's superconductivity using a two-band Eliashberg approach without interband scattering.

Findings

Doping influences on superconducting gaps and T_c are accurately modeled.

Doping site significantly affects superconductivity, explained without interband scattering.

Theoretical results match experimental doping dependence of superconducting properties.

Abstract

We have studied the electron-phonon and superconducting properties of the Mg{1-x}AlxB2 and MgB{2(1-y)}C{2y} alloys within the framework of density functional theory using the self-consistent virtual-crystal approximation. For both alloys, the Eliashberg spectral functions and the electron-phonon coupling constants have been calculated in the two-band model for several concentrations up to x(Al)=0.55 and y(C)=0.175. We solved numerically the two-band Eliashberg gap equations without considering interband scattering. Using a single parameter for the Coulomb pseudopotential, which was determined for the undoped compound, we were able to reproduce the experimental doping dependence of Delta_sigma, Delta_pi, and T_c for both alloys on a quantitative level. In particular, the observed differences in the doping range of superconductivity between Al and C doping indicate a pronounced influence of the doping site, which can be explained naturally in the present approach without the need to invoke interband scattering, suggesting that this factor plays only a minor role.