Thermal engineering in low-dimensional quantum devices: a tutorial review of nonequilibrium Green's function methods

TL;DR

This tutorial review discusses the application of nonequilibrium Green's function methods to thermal engineering in low-dimensional quantum devices, focusing on phonon transport and caloritronic effects at the nanoscale.

Contribution

It provides a comprehensive overview of NEGF techniques for phonon transport and caloritronic effects, including recent advances in phonon topologies and generalized methods.

Findings

NEGF effectively models nanoscale phonon transport.

Caloritronic effects enable manipulation of charge, spin, and valley via temperature gradients.

Survey of models and materials enhances understanding of quantum thermal engineering.

Abstract

Thermal engineering of quantum devices has attracted much attention since the discovery of quantized thermal conductance of phonons. Although easily submerged in numerous excitations in macro-systems, quantum behaviors of phonons manifest in nanoscale low-dimensional systems even at room temperature. Especially in nano transport devices, phonons move quasi-ballistically when the transport length is smaller than their bulk mean free paths. It has been shown that phonon nonequilibrium Green's function method (NEGF) is effective for the investigation of nanoscale quantum transport of phonons. In this tutorial review two aspects of thermal engineering of quantum devices are discussed using NEGF methods. One covers transport properties of pure phonons; the other concerns the caloritronic effects, which manipulate other degrees of freedom, such as charge, spin, and valley, via the temperature gradient. For each part, we outline basic theoretical formalisms first, then provide a survey on related investigations on models or realistic materials. Particular attention is given to phonon topologies and a generalized phonon NEGF method. Finally, we conclude our review and summarize with an outlook.