Energy flows in graphene: hot carrier dynamics and cooling
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.
© 2015 IOP Publishing Ltd. Received 24 July 2014, revised 2 October 2014; Accepted for publication 15 October 2014; Published 2 April 2015. We are grateful to FHL Koppens, MY Reizer and KJ Tielrooij for collaboration on some of the topics discussed above and many useful discussions. We also thank A J Frenzel for useful discussions. This work was supported as part of the Center for Excitonics, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences under Award No. DE-SC0001088 (photoexcitation cascade) and by the Office of Naval Research Grant No. N00014-09-1-0724 (cooling mechanisms). JS acknowledges financial support from the NSS program (Singapore).
Submitted - 1410.5426v1.pdf