Propagative and diffusive regimes of acoustic damping in bulk amorphous material

Abstract

In amorphous solids, a non-negligible part of thermal conductivity results from phonon scattering on the structural disorder. The conversion of acoustic energy into thermal energy is often measured by the Dynamical Structure Factor (DSF) thanks to inelastic neutron or X-Ray scattering. The DSF is used to quantify the dispersion relation of phonons, together with their damping. However, the connection of the dynamical structure factor with dynamical attenuation of wave packets in glasses is still a matter of debate. We focus here on the analysis of wave packets propagation in numerical models of amorphous silicon. We show that the DHO fits (Damped Harmonic Oscillator model) of the dynamical structure factors give a good estimate of the wave packets mean-free path, only below the Ioffe-Regel limit. Above the Ioffe-Regel limit and below the mobility edge, a pure diffusive regime without a definite mean free path is observed. The high-frequency mobility edge is characteristic of a transition to localized vibrations. Below the Ioffe-Regel criterion, a mixed regime is evidenced at intermediate frequencies, with a coexistence of propagative and diffusive wave fronts. The transition between these different regimes is analyzed in details and reveals a complex dynamics for energy transportation, thus raising the question of the correct modeling of thermal transport in amorphous materials.

arXiv comment9 pages, 7 figures

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• Role of a fractal shape of the inclusions on acoustic attenuation in a nanocomposite
• Ioffe-Regel criterion and viscoelastic properties of amorphous solids
• Diffusion of elastic waves in a continuum solid with a random array of pinned dislocations
• Thermomechanical Dissipative behaviour of CuZr metallic glasses
• Phonon transport properties of particulate physical gels
• A continuum model reproducing the multiple frequency crossovers in acoustic attenuation in glasses
• Composition effect in the thermo-mechanical behavior of glasses, and its modelization