title: Experimental evidence of the acousticlike character of the high frequency excitations in glasses
abstract: The dynamic structure factor S(Q,E) of glassy glycerol has been measured by inelastic x-ray scattering as a function of momentum transfer Q and at constant energy transfer E. This allows one to establish independently from specific models of S(Q,E) the following: (i) Propagating collective excitations exist in glasses at high Q. (ii) Their dispersion up to E higher than E(BP) (the boson peak energy) confirms that E(BP) is not the onset of modes localization. (iii) The observation of an almost Q independent plateau on the high Q side of the Brillouin peak supports numerical simulations on glasses, describing the vibrational eigenvectors in terms of acousticlike and "random" components.
authors.affiliation: Sincrotrone Trieste, Area Science Park, I-34012, Trieste, Italy.
authors.initials: C
authors.lastname: Masciovecchio
authors.initials: A
authors.lastname: Mermet
authors.initials: G
authors.lastname: Ruocco
authors.initials: F
authors.lastname: Sette