Universal time-temperature scaling of conductivities in random site energy and associated random barrier model

TL;DR

This paper demonstrates that the random barrier model explains universal conductivity scaling in disordered solids, accounting for site energy disorder and aligning with experimental observations, especially at low temperatures.

Contribution

It establishes a mapping between site energy and barrier models, showing the barrier model's validity at low temperatures and explaining the absence of superposition in mixed glasses.

Findings

Barrier model accurately describes low-temperature scaling.

Site energy model shows good scaling at higher temperatures.

Mapping explains absence of superposition in mixed alkali glasses.

Abstract

Universal time-temperature scaling of conductivity spectra in disordered solids has been explained by thermally activated hopping of noninteracting particles over random energy barriers. An open problem is whether the random barrier model accounts for site energy disorder in real materials. Through mapping many-particle hopping in a disordered site energy landscape to that of independent particles in a barrier landscape, we show that time-temperature scaling is correctly described by the associated barrier model in the low temperature limit. However, the site energy model displays good scaling behavior at substantially higher temperatures than the barrier model, in agreement with experimental observations. Extending the mapping to different types of mobile charge carriers allows us to understand why time-temperature superposition can be absent in mixed alkali glasses.