Phonons scattering universality

In this section we continue to explore the consequences of the existence of the low temperature excitations in amorphous substances, which, as argued in Section III, are really resonances that arise from residual molecular motions otherwise representative of the molecular rearrangements in the material at the temperature of vitrification. We were able to see why these degrees of freedom should exist in glasses and explain their number density and the nearly flat energy spectrum, as well as the universal nature of phonon scattering off these excitations at low T < 1 K). 

Stability requirements for the existence of these alternative conformational states at Tg allowed us also to estimate the strength of their coupling to the regular lattice vibrations, which is determined by Tg, the material mass density, and the speed of sound. This enabled us to understand the universality of the phonon scattering at the low temperatures. 

Rosenberg, H.M. (1988) The Solid State, 3rd. edition, Oxford University Press, Oxford, p. 96. Has a clear discussion of phonon scattering mechanisms. 

Auerbach DH (1992p) Multiple-phonon inelastic scattering. In Scoles G (ed.) Atomic and Molecular Beam Methods, vol. 2, pp. 444-462 Oxford University Press. 

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