Carrier dynamics in epitaxial graphene close to the Dirac point

TL;DR

This study investigates how carrier relaxation in epitaxial graphene varies with photon energy, revealing slowed relaxation at low energies and a transition from transmission to absorption linked to interband and intraband processes.

Contribution

It provides new insights into carrier dynamics near the Dirac point, combining experimental data with microscopic modeling to understand relaxation mechanisms.

Findings

Carrier relaxation slows down below optical phonon frequency.

Optical phonon emission remains dominant due to hot carriers.

Transition from transmission to absorption occurs at specific photon energies.

Abstract

We study the carrier dynamics in epitaxially grown graphene in the range of photon energies from 10 - 250 meV. The experiments complemented by microscopic modeling reveal that the carrier relaxation is significantly slowed down as the photon energy is tuned to values below the optical phonon frequency, however, owing to the presence of hot carriers, optical phonon emission is still the predominant relaxation process. For photon energies about twice the value of the Fermi energy, a transition from pump-induced transmission to pump-induced absorption occurs due to the interplay of interband and intraband processes.