Density of states of interacting quasilocal harmonic modes in glasses

Abstract We have established for the first time that as a result of a bilinear coupling between quasilocal harmonic modes and phonons in glasses there should be always a correlation between the position of the boson peak and the Ioffe–Regel crossover frequency for phonons. Above this frequency, phonons (i.e. usual plane waves) cease to exist. At the same frequency the density of states of the quasilocal harmonic modes, as a result of their interaction (and strong level repulsion), transforms into a universal linear function of the frequency. As a result the new harmonic modes become completely delocalized and have a diffusive nature. We show that existing experimental data are in excellent agreement with these predictions.