Time-resolved spectroscopy on epitaxial graphene in the infrared spectral range: relaxation dynamics and saturation behavior

Stephan Winnerl (1) , F. Göttfert (1) , Martin Mittendorff (1) , Henri Schneider (1) , Manfred Helm (1) , Torben Winzer (2) , Ermin Malic (2) , Andreas Knorr (2) , Milan Orlita (3) , Marek Potemski (3) , Mike Sprinkle (4) , Claire Berger (5) , Walt A. de Heer (4)

1 HZDR - Helmholtz-Zentrum Dresden-Rossendorf
2 TU - Technical University of Berlin / Technische Universität Berlin
3 LNCMI-G - Laboratoire national des champs magnétiques intenses - Grenoble
4 School of Physics
5 NEEL - QuantECA - Circuits électroniques quantiques Alpes

We present the results of pump-probe experiments on multilayer graphene samples performed in a wide spectral range, namely from the near-infrared (photon energy 1.5 eV) to the terahertz (photon energy 8 meV) spectral range. In the near infrared, exciting carriers and probing at higher photon energies provides direct evidence for a hot carrier distribution. Furthermore spectroscopic signatures of the highly doped graphene layers at the interface to SiC are observed in the near-infrared range. In the mid-infrared range, the various relaxation mechanisms, in particular scattering via optical phonons and Auger-type processes, are identified by comparing the experimental results to microscopic modelling. Changes from induced transmission to induced absorption are attributed to probing above or below the Fermi edge of the graphene layers. This effect occurs for certain photon energies in the near infrared range, where it is related to highly doped graphene layers at the interface to SiC, and in the far infrared range for the quasi-intrinsic graphene layers.In addition to the relaxation dynamics, the saturation of pump-induced bleaching of graphene is studied. Here a quadratic dependence of the saturation fluence photon energy in the infrared spectral range is revealed.

Domaines: Systèmes mésoscopiques et effet Hall quantique [cond-mat.mes-hall]

Stephan Winnerl, F. Göttfert, Martin Mittendorff, Henri Schneider, Manfred Helm, et al.. Time-resolved spectroscopy on epitaxial graphene in the infrared spectral range: relaxation dynamics and saturation behavior. Journal of Physics: Condensed Matter, 2013, 25 (5), pp.054202. ⟨10.1088/0953-8984/25/5/054202⟩. ⟨hal-01003137⟩