Abstract:
We study the origin of the boson peak and an associated mechanism for
acoustic-phonon broadening (below the peak) in glasses exhibiting
a high-frequency sound above the peak. The origin is related to the Ioffe–Regel crossover for inelastic (resonant) scattering of
acoustic phonons from harmonic soft-mode vibrations. The broadening mechanism
is due to the resonant interaction of a harmonic soft-mode vibration with
acoustic phonons, which results in the resonant scattering. We find that
the associated width of the phonon is independent of temperature and is
characterized by a power-law frequency dependence with the exponent varying
from $\varkappa=2$ just below the boson peak to $\varkappa=4$ at lower frequencies. The dependences seem to partly agree with some recent experimental data for the glasses under consideration.
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