Anharmonic phonon-phonon scattering at interface by non-equilibrium Green's function formalism

TL;DR

This paper introduces a quantum NEGF-based method to analyze anharmonic phonon scattering at interfaces, revealing the roles of local and non-local interactions and their impact on thermal boundary conductance.

Contribution

It develops a comprehensive quantum NEGF framework to quantify anharmonic phonon scattering effects at interfaces, including spectral decomposition and decay mechanisms.

Findings

Local anharmonic interactions dominate high-frequency phonons

Both local and non-local interactions are important for low-frequency phonons

Anharmonic decay significantly influences interfacial phonon transport

Abstract

The understanding and modeling of inelastic scattering of thermal phonons at a solid/solid interface remain an open question. We present a fully quantum theoretical scheme to quantify the effect of anharmonic phonon-phonon scattering at an interface via non-equilibrium Green's function (NEGF) formalism. Based on the real-space scattering rate matrix, a decomposition of the interfacial spectral energy exchange is made into contributions from local and non-local anharmonic interactions, of which the former is shown to be predominant for high-frequency phonons whereas both are important for low-frequency phonons. The anharmonic decay of interfacial phonon modes is revealed to play a crucial role in bridging the bulk modes across the interface. The overall quantitative contribution of anharmonicity to thermal boundary conductance is found to be moderate. The present work promotes a deeper understanding of heat transport at the interface and an intuitive interpretation of anharmonic phonon NEGF formalism.