Origin of boson peak in glasses: Role of Ioffe-Regel crossover and atomic soft modes

A theoretical 'complete soft-mode-dynamics' model of the origin and properties of the boson peak accompanied by a high-frequency sound, observed in glasses of a certain type, is described. The origin is determined by interaction of non-acoustic vibrations with acoustic phonons and a Ioffe-Regel crossover for their inelastic scattering. The non-acoustic excitations are associated with vibrations of atomic soft-mode 'defects'. Two types of boson peak can be predicted in agreement with experiments.