Electronic Cooling via Interlayer Coulomb Coupling in Multilayer Epitaxial Graphene

TL;DR

This paper reveals that Coulomb interactions between electrons in different layers of multilayer epitaxial graphene enable significant interlayer thermal transport, demonstrated through ultrafast spectroscopy and supported by a parameter-free theoretical model.

Contribution

It introduces a new understanding of interlayer thermal coupling in multilayer 2D materials via Coulomb interactions, contrasting with traditional phonon-mediated mechanisms.

Findings

Coulomb interactions facilitate interlayer thermal transport in multilayer graphene.

Hot-carrier relaxation dynamics depend on temperature and layer number.

A parameter-free theory explains experimental observations.

Abstract

In van der Waals bonded or rotationally disordered multilayer stacks of two-dimensional (2D) materials, the electronic states remain tightly confined within individual 2D layers. As a result, electron-phonon interactions occur primarily within layers and interlayer electrical conductivities are low. In addition, strong covalent in-plane intralayer bonding combined with weak van der Waals interlayer bonding results in weak phonon-mediated thermal coupling between the layers. We demonstrate here, however, that Coulomb interactions between electrons in different layers of multilayer epitaxial graphene provide an important mechanism for interlayer thermal transport even though all electronic states are strongly confined within individual 2D layers. This effect is manifested in the relaxation dynamics of hot carriers in ultrafast time-resolved terahertz spectroscopy. We develop a theory of interlayer Coulomb coupling containing no free parameters that accounts for the experimentally observed trends in hot-carrier dynamics as temperature and the number of layers is varied.