On some manifestations of soft atomic motion modes in glass dynamics

Recent advances in investigations of low-energy atomic dynamics of glasses have led to new essential experimental data and theoretical models for a qualitative description of the universal dynamic and thermal properties at low temperatures and frequencies, which are “anomalous” in the sense that they significantly differ from the properties of crystalline materials interpreted in the Debye model of low-energy phonons. One of the models is the soft-mode model in which the anomalous properties are determined by contributions of nonacoustic soft atomic motion modes for a minority of atoms, characterized by spring constants much smaller than those related to standard Debye acoustic modes for the vast majority of atoms. The present Letter interprets a recently observed effect in the attenuation of Debye acoustic phonons in glasses like SiO 2 and predicts a strong suppression of the universal dynamic properties of glasses under moderately high pressure as manifestations of “soft” atomic motion modes.