Heat conductivity of amorphous solids: simulation results on model structures

Area of Science:

• Condensed Matter Physics
• Materials Science
• Computational Physics

Background:

• Amorphous solids exhibit unique thermal conductivity (kappa(T)) behaviors, including a characteristic plateau at low temperatures.
• Understanding phonon scattering mechanisms is crucial for modeling heat transport in disordered materials.

Purpose of the Study:

• To calculate the temperature-dependent heat conductivity (kappa(T)) of amorphous solids using numerical simulations.
• To identify key parameters governing thermal conductivity in amorphous materials.
• To validate simulation results against experimental data for various amorphous substances.

Main Methods:

• Numerical simulations were employed to model heat conductivity.
• Phonon scattering by two-level systems was explicitly considered in the models.
• Calculated kappa(T) values were compared with experimental data for polymethylmethacrylate, epoxy, amorphous selenium, and amorphous silicon dioxide.

Main Results:

• The simulations achieved good quantitative agreement with experimental heat conductivity data from 0.1 to 100 K.
• The characteristic low-temperature plateau (5-20 K) in amorphous solid heat conductivity was successfully reproduced.
• Two critical model parameters, related to structural disorder and two-level state absorption, were identified as key to kappa(T) behavior for T >= 5 K.
• A frequency-independent phonon diffusion regime, consistent with the minimum phonon mean-free-path hypothesis, was indicated by the simulations.

Conclusions:

• Numerical simulations provide a reliable method for predicting the thermal conductivity of amorphous solids.
• The study elucidates the role of structural disorder and two-level systems in dictating heat transport properties.
• The findings support the existence of a phonon diffusion regime and its contribution to high-temperature thermal conductivity in amorphous materials.