Comment on "First-principles calculation of the superconducting transition in MgB2 within the anisotropic Eliashberg formalism"

TL;DR

This paper comments on previous first-principles calculations of MgB2 superconductivity, highlighting that gap variation within bands is unobservable and that Coulomb anisotropy affects the small gap size.

Contribution

It provides critical insights into the limitations of observing gap variations and the impact of Coulomb anisotropy on the superconducting gap in MgB2.

Findings

Superconducting gap variation inside bands is hardly observable.

Coulomb anisotropy influences the small gap Delta_pi.

Observations align with experimental limitations.

Abstract

Choi et al. [Phys. Rev. B 66, 020513 (2002)] recently presented first principles calculations of the electron-phonon coupling and superconductivity in MgB2, emphasizing the importance of anisotropy and anharmonicity. We point out that (1) variation of the superconducting gap inside the sigma- or the pi-bands can hardly be observed in real samples, and (2) taking the anisotropy of the Coulomb repulsion into account influences the size of the small gap, Delta_pi.