On the shape of the dynamic structure factor in glasses

The peculiar shape of the dynamie structure factor of glasses has been investigated thoroughly by light scattering and computer simulation techniques. The experimental spectra show a pronounced asymmetry with respect to their peak frequencies. Similar asymmetries have already been observed by simulation on argon glass in a range of exchanged momentum about ten times higher than that probed by light scattering. New simulation on a large sample of silica glass also shows similar features. Moreover the calculated dynamie structure factors appear as the straight continuation at higher momentum values of the experimental light scattering data. The qualitative independence of this phenomenon from the glass type together with the analysis of the eigenvector pattems in argon glass suggest that this asymmetric shape is a mark of the topological disorder.