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Berlin 2015 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 7: Graphene: THz, NIR and Transport Properties (HL with O/TT)

O 7.3: Vortrag

Montag, 16. März 2015, 10:00–10:15, ER 270

Investigations on the polarization dependent carrier excitation in graphene with low energetic photons — •Jacob Otto1,2, Martin Mittendorff1,2, Torben Winzer3, Ermin Malic3, Andreas Knorr3, Harald Schneider1, Manfred Helm1,2, and Stephan Winnerl11Helmholtz-Zentrum Dresden-Rossendorf, 01314 Dresden, Germany — 2Technische Universität Dresden, 01062 Dresden, Germany — 3Technische Universität Berlin, 10623 Berlin, Germany

We demonstrate that in graphene a nonequelibrium charge carrier distribution retains its anisotropic nature on a 10 ps timescale if the photon energy is below the optical phonon energy. Recently evidence for an anisotropic carrier distribution has been found in near-infrared pump-probe experiments with varied angle between the orientation of pump and probe polarization [1]. This anisotropy vanishes after 150 fs due to electron optical-phonon scattering. Extending this study to the mid-infrared range (EPhoton=74 meV), i.e. to energies below the optical phonon energy, allows to strongly suppress this scattering mechanism. In accord with microscopic theory, traces of an anisotropic distribution on a 10 ps timescale are found. Note that carrier-carrier scattering, acting on a 10 fs timescale, is mainly colinear and therefor preserves the anisotropic distribution on rather long timsecales.
M. Mittendorff, T. Winzer, E. Malic, A. Knorr, C. Berger, W. A. de Heer, H. Schneider, M. Helm and S. Winnerl Nano Lett. 2014, 14, 1504-1507

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