Regensburg 2016 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 40: Graphene: Optics
(Joint session of DS, DY, HL, MA, O and TT organized by HL)
TT 40.2: Vortrag
Dienstag, 8. März 2016, 15:15–15:30, H17
Noncollinear Coulomb scattering in graphene — •Jacob C. König-Otto1,2, Martin Mittendorff3, Torben Winzer4, Ermin Malic5, Andreas Knorr4, Alexej Pashkin1, Harald Schneider1, Manfred Helm1,2, and Stephan Winnerl1 — 1Helmholtz-Zentrum Dresden-Rossendorf, Germany — 2Technische Universität Dresden, Germany — 3University of Maryland, USA — 4Technische Universität Berlin, Germany — 5Chalmers University of Technology, Sweden
Utilizing the anisotropy of the optical excitation in graphene, we reveal the twofold nature of Coulomb scattering in graphene. The initial non-equilibrium charge carrier distribution in graphene created by linearly polarized light possesses a pronounced anisotropy, which has been observed in our recent experiment [1]. In the present study we perform polarization-dependent pump-probe measurements using a photon energy of 88 meV to suppress efficiently the optical phonon scattering. In this case the relaxation dynamics leading to an isotropic distribution is dominated by noncollinear Coulomb scattering. By varying the pump fluence over a range of several orders of magnitudes we are able to successfully control the efficiency of this process. This reveals a surprising twofold nature of Coulomb scattering in graphene: Whereas collinear Coulomb scattering is known to be a very fast process on the fs timescale, noncollinear scattering is remarkably slow, resulting in a thermalization time of several ps in our experiment. Our experimental findings are complemented by the results of microscopic modelling.
M. Mittendorff et al., Nano Lett. 14, 1504 (2014).