Anomalous Angular Dependence of the Dynamic Structure Factor near Bragg Reflections: Graphite

R. Hambach (1, 2) , C. Giorgetti (1, 2) , N. Hiraoka (3) , Y.Q. Cai (3) , F. Sottile (1, 2) , A.G. Marinopoulos (4) , F. Bechstedt (5) , Lucia Reining (1, 2)

1 LSI - Laboratoire des Solides Irradiés
2 ETSF - European Theoretical Spectroscopy Facility
3 National Synchrotron Radiation Research Center
4 CEMDRX - Centro de Estudos de Materiais por Difracção de Raios-X
5 IFTO - Institut für Festkörpertheorie und -optik

The electron energy-loss function of graphite is studied for momentum transfers q beyond the first Brillouin zone. We find that near Bragg reflections the spectra can change drastically for very small variations in q. The effect is investigated by means of first principle calculations in the random phase approximation and confirmed by inelastic x-ray scattering measurements of the dynamic structure factor S(q,ω). We demonstrate that this effect is governed by crystal local field effects and the stacking of graphite. It is traced back to a strong coupling between excitations at small and large momentum transfers.

Keywords: dynamic structure factor; IXS; EELS; Graphite; Bragg; anisotropy

Domains: Physics [physics]; Condensed Matter [cond-mat]; Materials Science [cond-mat.mtrl-sci]

R. Hambach, C. Giorgetti, N. Hiraoka, Y.Q. Cai, F. Sottile, et al.. Anomalous Angular Dependence of the Dynamic Structure Factor near Bragg Reflections: Graphite. Physical Review Letters, 2008, 101 (26), http://prl.aps.org/abstract/PRL/v101/i26/e266406. ⟨10.1103/PhysRevLett.101.266406⟩. ⟨hal-00476164⟩