Model of defect diffusion and development of the boson peak in an amorphous solid

A schematic model is proposed for understanding the boson peak as a consequ ence of the coupling between slowly decaying density fluctuations and the t ransverse sound modes th;lt develop in the amorphous solid. The present ana lysis demonstrates that the nature of the dynamics of defect densities in t he disordered system plays a crucial role for the appearance of the peak. W e compare the results for the dynamic structure factor with the scattering data of Sokolov et al.. [J. Non-Cryst. Solids 172-174. 138 (1994)]. With th e relaxation time for the defects becoming longer which is the case more ap propriate for the strong glasses as compared to the fragile glasses where s tructural degradation occurs more easily, the boson peak become more pronou nced.