Soft-mode-dynamics model of acoustic-like high-frequency excitations in boson-peak spectra of glasses

A theoretical model of vibrational dynamics is proposed for a glass, which comprises acoustic and soft-mode vibrational excitations interacting with each other and gives rise to a vibrational spectrum "broken" into two branches separated by a pseudogap. The latter appears to be associated with a Ioffe-Regel cross-over to strong inelastic scattering of the excitations. The upper branch contains acoustic-like high-frequency excitations, which are similar to those recently observed in inelastic X-ray scattering spectra of a series of glasses. The present model may resolve the recent controversy concerning the interpretation of the scattering spectra. (C) 2001 Published by Elsevier Science B.V.