Energy Flows in Graphene: Hot Carrier Dynamics and Cooling

TL;DR

This paper explores the energy flow mechanisms in graphene, focusing on hot carrier generation via Auger processes and electron-lattice cooling pathways, including supercollisions that can overcome cooling bottlenecks.

Contribution

It provides a detailed microscopic analysis of hot carrier dynamics and cooling processes in graphene, highlighting the role of supercollisions in energy dissipation.

Findings

Hot carriers multiply through Auger-like scattering.

Elevated electronic temperatures can be measured via optical conductivity.

Supercollisions help overcome electron-phonon cooling bottlenecks.

Abstract

Long lifetimes of hot carriers can lead to qualitatively new types of responses in materials. The magnitude and time scales for these responses reflect the mechanisms governing energy flows. We examine the microscopics of two processes which are key for energy transport, focusing on the unusual behavior arising due to graphene's unique combination of material properties. One is hot carrier generation in its photoexcitation dynamics, where hot carriers multiply through an Auger type carrier-carrier scattering cascade. The hot-carrier generation manifests itself through elevated electronic temperatures which can be accessed in a variety of ways, in particular optical conductivity measurements. Another process of high interest is electron-lattice cooling. We survey different cooling pathways and discuss the cooling bottleneck arising for the momentum-conserving electron-phonon scattering pathway. We show how this bottleneck can be relieved by higher-order collisions - supercollisions - and examine the variety of supercollision processes that can occur in graphene.