THE ORIGIN OF THE BOSON PEAK IN NETWORK-FORMING GLASSES

An analysis using a simple model is presented with the aim of providin g an explanation for the characteristics of low-energy excitations in glasses with directional bonds. The model predicts the appearance of t hree types of acoustic excitation: weakly, strongly, and mesoscopicall y localized modes, and, in addition, recovers the excess density of st ates at low energies. We claim that the latter two excitations constit ute the two broad bands observed in Raman spectra, i.e. the lower band (the boson peak) consists of strongly localized modes, and mesoscopic ally localized modes contribute to the second higher band at around th e Debye cut-off frequency omega(D).