Phonon dispersion and low energy anomaly in CaC${}_6$

Abstract

We report measurements of phonon dispersion in CaC${}_6$ using inelastic X-ray and neutron scattering. We find good overall agreement, particularly in the 50 meV energy region, between experimental data and first-principles density-functional-theory calculations. However, on the longitudinal dispersion along the $(111)$ axis of the rhombohedral representation, we find an unexpected anti-crossing with an additional longitudinal mode, at about 11 meV. At a comparable energy, we observe also unexpected intensity on the in-plane direction. These results resolve the previous incorrect assignment of a longitudinal phonon mode to a transverse mode in the same energy range. By calculating the electron susceptibility from first principles we show that this longitudinal excitation is unlikely to be due to a plasmon and consequently can probably be due to defects or vacancies present in the sample.

Accepted for publication in Physical Review B

References in corpus (3)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Possibility of superconductivity in graphite intercalated with alkaline earths investigated with density functional theory
• Anharmonic effects in MgB2? A comparative inelastic X-ray scattering and Raman study

Cited by in corpus (5)

• Comparative study of the phonons in non-superconducting BaC6 and superconducting CaC6 using inelastic x-ray scattering
• Introduction to High-Resolution Inelastic X-Ray Scattering
• Phonons and superconductivity in YbC${}_6$ and related compounds
• Neutron scattering study of the high energy graphitic phonons in superconducting CaC${}_6$
• Theory of Superconductivity in Graphite Intercalation Compounds