Neutron scattering study of the high-energy graphitic phonons in superconductingCaC6

Abstract

We present the results of a neutron scattering study of the high-energy phonons in the superconducting graphite intercalation compound ${\text{CaC}}_{6}$. The study was designed to address hitherto unexplored aspects of the lattice dynamics in ${\text{CaC}}_{6}$, and, in particular, any renormalization of the out-of-plane and in-plane graphitic phonon modes. We present a detailed comparison between the data and the results of density-functional theory (DFT). A description is given of the analysis methods developed to account for the highly textured nature of the samples. The DFT calculations are shown to provide a good description of the general features of the experimental data. This is significant in light of a number of striking disagreements in the literature between other experiments and DFT on ${\text{CaC}}_{6}$. The results presented here demonstrate that the disagreements are not due to any large inaccuracies in the calculated phonon frequencies.