Electronic, dynamical and superconducting properties of CaBeSi

TL;DR

This study uses first-principles calculations to investigate the electronic, vibrational, and superconducting properties of CaBeSi, revealing a complex multi-gap structure and a very low critical temperature despite similarities to MgB2.

Contribution

It provides the first detailed theoretical analysis of CaBeSi's superconducting properties, highlighting the impact of Coulomb anisotropy on its multi-gap structure.

Findings

CaBeSi has a very low Tc (~0.4 K) despite similarities to MgB2.

CaBeSi exhibits a three-gap structure at the Fermi level.

The anisotropy of Coulomb repulsion influences the gap structure.

Abstract

We report first-principles calculations on the normal and superconducting state of CaBe(x)Si(2-x) (x=1), in the framework of density functional theory for superconductors (SCDFT). CaBeSi is isostructural and isoelectronic to MgB2 and this makes possible a direct comparison of the electronic and vibrational properties and the electron-phonon interaction of the two materials. Despite the many similarities with MgB2 (e.g. sigma bands at the Fermi level and a larger Fermi surface nesting), according to our calculations CaBeSi has a very low critical temperature (Tc ~ 0.4 K, consistent with the experiment). CaBeSi exhibits a complex gap structure, with three gaps at Fermi level: besides the two sigma and pi gaps, present also in MgB2, the appearance of a third gap is related to the anisotropy of the Coulomb repulsion, acting in different way on the bonding and antibonding electronic pi states.