Optoelectronics of Graphene-based Van der Waals Heterostructures
Speaker: Qiong Ma (MIT)
Time: May 13, 2016 10:00
报告摘要：The photoresponse of materials is governed by energy relaxation pathways of photo-excited electron-hole pairs. In graphene, due to frequent electron-electron collision and weak electron-lattice coupling, a novel transport regime is reached in which the photo-generated carrier population can remain hot while the lattice stays cool. In this talk, I will show that light is converted to electrical currents through a hot-carrier assisted thermoelectric effect in intrinsic graphene. The thermal energy slowly leaks to the lattice via two distinct processes of electron-phonon coupling that can be tuned by temperature and charge density. We also implemented a scheme to control the initial stage of photo-excited carriers before they collide with ambient carriers (less than ten femtoseconds) to form a hot Fermi-Dirac distribution, which is realized in a graphene-boron nitride-graphene heterostructure.
The weak electron-phonon coupling and frequent electron-electron scattering revealed above strongly alter the nature of particle and energy transport, leading to a collision dominant fluid behavior for electrons. In the last part of the talk, I will discuss our observation of highly-ordered photocurrent patterns at the charge neutral point of graphene, which is likely related to the ballistic thermal transport of hot electron-hole plasma in the hydrodynamic regime.
 N. Gabor, J. Song, Q. Ma, N. Nair, T. Taychatanapat, K. Watanabe, T. Taniguchi, L. Levitov and P. Jarillo-Herrero, Science 334, 648 (2011).
 Q. Ma, N. Gabor, T. Andersen, N. Nair, K. Watanabe, T. Taniguchi and P. Jarillo-Herrero, Phys. Rev. Lett. 112, 247401 (2014).
 Q. Ma, T. Andersen, N. Nair, N. Gabor, M. Massicotte, C. Lui, A. Young, W. Fang, J. Kong, K. Watanabe, T. Taniguchi, N. Gedik, F. Koppens and P. Jarillo-Herrero, Nature Physics (2016) doi:10.1038/nphys3620.
 Q. Ma, et al., “Geometric Edge Photocurrent Generation and Hydrodynamics in Graphene.” In preparation (2016)