Thermal conductivity minimum of graded superlattices due to phonon localization

TL;DR

This paper demonstrates a new type of phonon localization in graded superlattices with moderate disorder, leading to a thermal conductivity minimum due to partial phonon localization, supported by quantum transport simulations.

Contribution

It introduces a novel phonon localization mechanism in graded superlattices with short-range order and long-range disorder, showing a thermal conductivity minimum.

Findings

Thermal conductivity exhibits a minimum with system length.

Exponential decay of transmission to a non-zero constant indicates partial localization.

Localization evidenced by participation ratio, transmission, and phonon density analysis.

Abstract

The Anderson localization of thermal phonons has been shown only in few nano-structures with strong random disorder by the exponential decay of transmission to zero and a thermal conductivity maximum when increasing system length. In this work, we present a path to demonstrate the phonon localization with distinctive features in graded superlattices with short-range order and long-range disorder. A thermal conductivity minimum with system length appears due to the exponential decay of transmission to a non-zero constant, which is a feature of partial phonon localization caused by the moderate disorder. We provide clear evidence of localization through the combined analysis of the participation ratio, transmission, and real-space phonon number density distribution based on our quantum transport simulation. The present work would promote heat conduction engineering by localization via the wave nature of phonons.