Phonon Hydrodynamic Heat Conduction and Knudsen Minimum in Graphite

TL;DR

This paper predicts that graphite exhibits phonon hydrodynamics at temperatures around 100 K, with observable phenomena like Poiseuille flow and Knudsen minimum, due to its unique microscopic phonon interactions.

Contribution

It identifies graphite as a three-dimensional material supporting high-temperature phonon hydrodynamics through first-principles calculations and Boltzmann equation solutions.

Findings

Prediction of phonon Poiseuille flow in graphite above 100 K

Observation of Knudsen minimum in graphite at elevated temperatures

Microscopic explanation of hydrodynamic phenomena based on phonon scattering processes

Abstract

In the hydrodynamic regime, phonons drift with a nonzero collective velocity under a temperature gradient, reminiscent of viscous gas and fluid flow. The study of hydrodynamic phonon transport has spanned over half a century but has been mostly limited to cryogenic temperatures (~1 K) and more recently to low-dimensional materials. Here, we identify graphite as a three-dimensional material that supports phonon hydrodynamics at significantly higher temperatures (~100 K) based on first-principles calculations. In particular, by solving the Boltzmann equation for phonon transport in graphite ribbons, we predict that phonon Poiseuille flow and Knudsen minimum can be experimentally observed above liquid nitrogen temperature. Further, we reveal the microscopic origin of these intriguing phenomena in terms of the dependence of the effective boundary scattering rate on momentum-conserving phonon-phonon scattering processes and the collective motion of phonons. The significant hydrodynamic nature of phonon transport in graphite is attributed to its strong intralayer sp2 hybrid bonding and weak van der Waals interlayer interactions. As a boundary-sensitive transport regime, phonon hydrodynamics opens up new possibilities for thermal management and energy conversion.