Electrons and phonons in $\mathrm{Yb}{\mathrm{C}}_{6}$: Density functional calculations and angle-resolved photoemission measurements

Electrons and phonons in $Yb C_{6}$ : Density functional calculations and angle-resolved photoemission measurements

I. I. Mazin and S. L. Molodtsov

Phys. Rev. B 72, 172504 – Published 14 November 2005

Abstract

The electronic structure and selected zone-center phonons in Yb graphite intercalation compound $(Yb C_{6})$ are investigated theoretically using density functional calculations and the local density approximation $(LDA) + U$ approach for Coulomb correlations in the $f$ shell. We find that both in the LDA and $LDA + U$ approach the Yb $f$ states are fully occupied providing no evidence for mixed-valent behavior. The obtained theoretical results are in good agreement with photoemission experiments. The $4 f$ states are considerably hybridized both with the Yb $5 d$ and C $2 p$ states resulting in a non-negligible admixture of Yb $f$ at the Fermi level. Soft Yb phonons, given a noticeable presence of the Yb states at the Fermi level, are probably responsible for the superconductivity recently reported in $Yb C_{6}$ .