Stability Dependence of the Vibrational Properties of Glasses

To understand the origin of universal low-temperature properties of
glasses, which differ dramatically from those of their crystalline counterparts, it is
paramount to understand what controls the low frequency vibrational modes of glasses.
Numerical methods generally create glasses by quenching mildly
supercooled liquids, which limits the variation of glasses' vibrational spectra and the
ability to examine correlations between the properties and the vibrational
spectra. Due to a combination of advances in simulation techniques
and the formulation of new glass forming models, we are now able to study glasses with a wide range of
stabilities. Here we study vibrational modes, sound attenuation, and energy
transport in simulated glasses with stabilities that range from very poorly annealed to
very stable. Our most stable glass is comparable to exceptionally-stable,
vapor-deposited laboratory glasses. We find that the density of the
localized, low-frequency modes decreases quickly with increasing stability. This
decrease is accompanied by a a large decrease in sound attenuation. We find that
at low-frequencies, in the harmonic approximation, sound attenuation follows
Rayleigh scattering scaling with wave-vector. We examined energy
transport by exciting a wave packet and determined the energy diffusivity. For a low
frequency excitation, the decrease in sound attenuation is mirrored by an increase in
the energy diffusivity. However, for a high frequency excitation, the diffusivity is nearly
constant and independent of stability.