Relation of vibrational excitations and thermal conductivity to elastic heterogeneities in disordered solids

TL;DR

This study investigates how elastic heterogeneities in disordered solids influence vibrational excitations and thermal conductivity, revealing their critical role in explaining anomalous thermal and vibrational behaviors.

Contribution

The paper demonstrates the direct correlation between elastic heterogeneity and vibrational/thermal properties in disordered solids using molecular dynamics simulations.

Findings

Elastic heterogeneity correlates with vibrational localization.

Heterogeneous elastic moduli influence thermal conductivity.

Disorder increases elastic heterogeneity and affects vibrational states.

Abstract

In crystals, molecules thermally vibrate around the periodic lattice sites. Vibrational motions are well understood in terms of phonons, which carry heat and control heat transport. The situation is notably different in disordered solids, where vibrational excitations are not phonons and can be even localized. Recent numerical work has established the concept of elastic heterogeneity: disordered solids show inhomogeneous local mechanical response. Clearly, the heterogeneous nature of elastic properties strongly influences vibrational and thermal properties, and it is expected to be the origin of anomalous features, including boson peak, vibrational localization, and temperature dependence of thermal conductivity. These are all crucial long-standing problems in materials physics, which we address in the present work. We have considered a toy model able to stabilize different states of matter, by introducing an increasing amount of size disorder. The phase diagram generated by molecular dynamics simulations encompasses the perfect crystalline state with a spatially homogeneous elastic moduli distribution, multiple defective phases with increasing moduli heterogeneities, and eventually a series of amorphous states. We have established clear correlations among the heterogeneous local mechanical response, vibrational states, and thermal conductivity. We provide evidence that elastic heterogeneity controls both vibrational and thermal properties, and is a key concept to understand the anomalous puzzling features of disordered solids.