Microscopic origins of the terahertz carrier relaxation and cooling dynamics in graphene
Résumé
The ultrafast dynamics of hot carriers in graphene are key to both understanding of fundamental
carrier–carrier interactions and carrier–phonon relaxation processes in two-dimensional
materials, and understanding of the physics underlying novel high-speed electronic and
optoelectronic devices. Many recent experiments on hot carriers using terahertz spectroscopy
and related techniques have interpreted the variety of observed signals within
phenomenological frameworks, and sometimes invoke extrinsic effects such as disorder.
Here, we present an integrated experimental and theoretical programme, using ultrafast timeresolved
terahertz spectroscopy combined with microscopic modelling, to systematically
investigate the hot-carrier dynamics in a wide array of graphene samples having varying
amounts of disorder and with either high or low doping levels. The theory reproduces the
observed dynamics quantitatively without the need to invoke any fitting parameters,
phenomenological models or extrinsic effects such as disorder. We demonstrate that the
dynamics are dominated by the combined effect of efficient carrier–carrier scattering, which
maintains a thermalized carrier distribution, and carrier–optical–phonon scattering, which
removes energy from the carrier liquid.