title: Microscopic origins of the terahertz carrier relaxation and cooling dynamics in graphene.
abstract: 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 time-resolved 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.
authors.affiliation: Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109, USA.|Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: Momchil T
authors.initials: MT
authors.lastname: Mihnev
authors.affiliation: Institut für Theoretische Physik, Nichtlineare Optik und Quantenelektronik, Technische Universität Berlin, D-10623 Berlin, Germany.
authors.forename: Faris
authors.initials: F
authors.lastname: Kadi
authors.affiliation: Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109, USA.|Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Divin
authors.affiliation: Institut für Theoretische Physik, Nichtlineare Optik und Quantenelektronik, Technische Universität Berlin, D-10623 Berlin, Germany.
authors.forename: Torben
authors.initials: T
authors.lastname: Winzer
authors.affiliation: Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109, USA.|Department of Electronics and Radio Engineering, Kyung Hee University, Gyeonggi 446-701, South Korea.
authors.forename: Seunghyun
authors.initials: S
authors.lastname: Lee
authors.affiliation: Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: Che-Hung
authors.initials: CH
authors.lastname: Liu
authors.affiliation: Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Zhong
authors.affiliation: School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.|Institut Neel, CNRS UJF-INP, Grenoble 38042, Cedex 6, France.
authors.forename: Claire
authors.initials: C
authors.lastname: Berger
authors.affiliation: School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.|King Abdulaziz University, Jeddah 22254, Saudi Arabia.
authors.forename: Walt A
authors.initials: WA
authors.lastname: de Heer
authors.affiliation: Institut für Theoretische Physik, Nichtlineare Optik und Quantenelektronik, Technische Universität Berlin, D-10623 Berlin, Germany.|Department of Applied Physics, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden.
authors.forename: Ermin
authors.initials: E
authors.lastname: Malic
authors.affiliation: Institut für Theoretische Physik, Nichtlineare Optik und Quantenelektronik, Technische Universität Berlin, D-10623 Berlin, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Knorr
authors.affiliation: Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109, USA.|Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: Theodore B
authors.initials: TB
authors.lastname: Norris