Universal Form of the Low-Energy (2 to 10 meV) Vibrational Spectrum of Glasses

By means of inelastic cold neutron scattering the density of vibrational states (DVS) has been determined for a series of vitreous materials: SiO 2 , As 2 S 3 and metallic glass Mg 70 Zn 30 . In the low-energy range of the spectrum ( E ∼ (2 ÷ 10) meV) for these materials DVS reveals a universal, but non-Debye form. The data obtained are compared to different models. A comparison with the Raman scattering data provides the spectral dependence for the coupling of the light to the vibrational excitations.