Breaking Rayleigh's law with spatially correlated disorder to control phonon transport

TL;DR

This paper demonstrates that introducing long-range spatial correlations in defect distributions can significantly reduce phonon lifetimes and thermal conductivity in insulators, challenging Rayleigh's law and enabling better thermal management.

Contribution

It introduces a novel framework for controlling thermal transport via structural spatial correlations and identifies the optimal correlation patterns to minimize thermal conductivity.

Findings

Long-range correlations reduce phonon lifetimes of low-frequency modes.

Thermal conductivity can be decreased by up to an order of magnitude.

A quantitative framework for designing correlated defect structures is established.

Abstract

Controlling thermal transport in insulators and semiconductors is crucial for many technological fields such as thermoelectrics and thermal insulation, for which a low thermal conductivity ($\kappa$) is desirable. A major obstacle for realizing low $\kappa$ materials is Rayleigh's law, which implies that acoustic phonons, which carry most of the heat, are insensitive to scattering by point defects at low energy. We demonstrate, with large scale simulations on tens of millions of atoms, that isotropic long-range spatial correlations in the defect distribution can dramatically reduce phonon lifetimes of important low-frequency heat-carrying modes, leading to a large reduction of $\kappa$ -- potentially an order of magnitude at room temperature. We propose a general and quantitative framework for controlling thermal transport in complex functional materials through structural spatial correlations, and we establish the optimal functional form of spatial correlations that minimize $\kappa$. We end by briefly discussing experimental realizations of various correlated structures.