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Phonon dispersion and low-energy anomaly in CaC6 from inelastic neutron and x-ray scattering experiments

DOI: 10.1103/PhysRevB.81.104519 DOI Help

Authors: Moritz Hoesch (Diamond Light Source) , Matteo D’astuto (Université Pierre et Marie Curie-Paris) , Matteo Calandra (Université Pierre et Marie Curie-Paris) , Geneviève Loupias (Pierre et Marie Curie-Paris) , Francesco Mauri (Université Pierre et Marie Curie-Paris) , Shuyun Zhou (Lawrence Berkeley National Laboratory; University of California, Berkeley) , Jeff Graf (Lawrence Berkeley National Laboratory) , Alessandra Lanzara (University of California, Berkeley) , Nicolas Emery (Institut Jean Lamour - UMR 7198 CNRS) , Claire Hérold (Institut Jean Lamour - UMR 7198 CNRS) , P. Lagrange (Institut Jean Lamour - UMR 7198 CNRS) , Daniel Petitgrand (CEA–CNRS)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Physical Review B , VOL 81 (10) , PAGES 104519

State: Published (Approved)
Published: March 2010

Abstract: We report measurements of phonon dispersion in CaC6 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 anticrossing 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.

Subject Areas: Physics

Facility: esrf