Berlin 2015 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 12: Graphene: THz, NIR, and Transport Properties (jointly with HL, O)

TT 12.3: Talk

Monday, March 16, 2015, 10:00–10:15, ER 270

Investigations on the polarization dependent carrier excitation in graphene with low energetic photons — •Jacob Otto^1,2, Martin Mittendorff^1,2, Torben Winzer³, Ermin Malic³, Andreas Knorr³, Harald Schneider¹, Manfred Helm^1,2, and Stephan Winnerl¹ — ¹Helmholtz-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 (E_Photon=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