On the emergence of heat waves in the transient thermal grating geometry

TL;DR

This paper investigates how heat waves emerge in transient thermal grating experiments by analyzing phonon transport, revealing the influence of phonon dispersion, temperature, and scattering regimes on heat wave phenomena.

Contribution

It provides a detailed analysis of heat wave emergence using phonon Boltzmann transport equations, highlighting the effects of phonon dispersion and temperature.

Findings

Heat waves occur when phonon resistive scattering is insufficient.

In frequency-dependent BTE, heat waves can disappear in the ballistic regime.

Heat waves are predicted in low-temperature suspended graphene and silicon.

Abstract

The propagation of heat in the transient thermal grating geometry is studied based on phonon Boltzmann transport equation (BTE) in different phonon transport regimes. Our analytical and numerical results show that the phonon dispersion relation and temperature play a significant role in the emergence of heat wave. For the frequency-independent BTE, the heat wave appears as long as the phonon resistive scattering is not sufficient, while for the frequency-dependent BTE, the heat wave could disappear in the ballistic regime, depending on the grating period and temperature. We predict that the heat wave could appear in the suspended graphene and silicon in extremely low temperature but disappear at room temperature.