Theory of resonant absorption of THz frequency waves by boson peak excitations in glasses

Abstract A resonant mechanism is predicted for the absorption of ultrasonic and electromagnetic waves of THz frequencies in glasses exhibiting both a boson peak and ‘high frequency sound’. The absorption is due to resonant transitions for harmonic excitations related to soft modes, determining the THz frequency dynamics of such glasses. The frequency dependence of the absorption coefficient exhibits a broad peak similar to the boson peak, related to a Ioffe–Regel crossover. For sufficiently low temperatures (still above a few K), the predicted qualitative behavior of the absorption coefficient can be observed in experiment. Furthermore, the as yet unknown frequency dependence of the large width of ill-defined excitations, in the Ioffe–Regel crossover, could be found by comparing the theoretical expression for the predicted absorption coefficient with experimental results.