Dresden 2017 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 94: Graphene: Electronic Properties, Structure and Substrate Interaction II
O 94.7: Vortrag
Donnerstag, 23. März 2017, 16:30–16:45, TRE Ma
Imaging Anisotropic Carrier Dynamics in Graphene — •Sven Aeschlimann1, Mariana Chavez-Cervantes1, Hubertus Bromberger1, Razvan Krause1, Ameer Al-Temimy2, Camilla Coletti2, Andrea Cavalleri1,3, and Isabella Gierz1 — 1Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, Hamburg, Germany — 2Center for Nanotechnology @ NEST, Istituto Italiano di Tecnologia, Pisa, Italy — 3Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, United Kingdom
Photo-excitation of graphene transfers electrons from the valence band to the conduction band in a direct interband transition. The initial distribution of holes and electrons is known to be anisotropic with nodes along the direction of the light polarization. We use time- and angle-resolved photoemission spectroscopy to image the initially anisotropic carrier distribution on constant energy cuts through the Dirac cone and follow its relaxation as a function of pump-probe time delay. We find that ultrafast collinear electron-electron scattering rapidly redistributes the energy among the carriers and establishes a momentum-dependent electronic temperature on time scales short compared to our experimental resolution. Momentum relaxation occurs mainly through optical phonon emission within approximately 100 femtoseconds determined from the time it takes for the electron distribution to become isotropic. Our measurements provide a complete picture of the ultrafast thermalization dynamics in photo-excited graphene.