Direct view on the ultrafast carrier dynamics in graphene

TL;DR

This paper provides a direct, time-resolved ARPES study of ultrafast hot carrier dynamics in graphene, revealing rapid thermalization, carrier decay pathways, and the influence of hot carriers on electronic state lifetimes.

Contribution

It introduces a direct measurement method for hot carrier dynamics in graphene using time-resolved ARPES, offering new insights into ultrafast processes.

Findings

Electron gas thermalizes to over 2000 K instantly.

Carrier decay involves optical and acoustic phonons, including supercollisions.

Hot carrier distribution impacts state lifetimes below Fermi energy.

Abstract

The ultrafast dynamics of excited carriers in graphene is closely linked to the Dirac spectrum and plays a central role for many electronic and optoelectronic applications. Harvesting energy from excited electron-hole pairs, for instance, is only possible if these pairs can be separated before they lose energy to vibrations, merely heating the lattice. While the hot carrier dynamics in graphene could so far only be accessed indirectly, we here present a direct time-resolved view on the Dirac cone by angle-resolved photoemission (ARPES). This allows us to show the quasi-instant thermalisation of the electron gas to a temperature of more than 2000 K; to determine the time-resolved carrier density; to disentangle the subsequent decay into excitations of optical phonons and acoustic phonons (directly and via supercollisions); and to show how the presence of the hot carrier distribution affects the lifetime of the states far below the Fermi energy.