Ultrafast plasmon thermalization in epitaxial graphene probed by time-resolved THz spectroscopy

Abstract

We use optical pump—terahertz (THz) probe spectroscopy to investigate ultrafast sheet conductivity dynamics in various epitaxial graphene layers grown on SiC. Inhomogeneities in graphene layers developed during the growth are at the origin of confinement potentials for the charge carriers. The transient response is governed by the heating and cooling of localized plasmonic excitations induced by the confinement. We show that the spectra are entirely controlled by the temperature (and chemical potential) of carriers undergoing a supercollision cooling process in all studied epigraphene layers representing a large variety of carbon allotropes.