Hot Dirac Fermions in Epitaxial Graphene

TL;DR

This study explores the ultrafast relaxation of hot Dirac fermions in multilayer epitaxial graphene, revealing electron cooling times and structural insights through optical spectroscopy.

Contribution

It provides new measurements of electron cooling times and confirms multilayer structure and doping profiles using ultrafast optical spectroscopy.

Findings

Electron cooling occurs in 1 ps for doped layers and 4-11 ps for undoped layers.

Spectra indicate interband transitions without electron-hole interactions.

Strong evidence for multilayer structure and doping profile of epitaxial graphene.

Abstract

We investigate the ultrafast relaxation dynamics of hot Dirac fermionic quasiparticles in multilayer epitaxial graphene using ultrafast optical differential transmission spectroscopy. We observe DT spectra which are well described by interband transitions with no electron-hole interaction. Following the initial thermalization and emission of high-energy phonons, the electron cooling is determined by electron-acoustic phonon scattering, found to occur on the time scale of 1 ps for highly doped layers, and 4-11 ps in undoped layers. The spectra also provide strong evidence for the multilayer stucture and doping profile of thermally grown epitaxial graphene on SiC.