Regensburg 2016 – scientific programme

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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 40.1: Invited Talk

Tuesday, March 8, 2016, 14:45–15:15, H17

Ultrafast carrier dynamics in monolayer graphene — •Daniele Brida — Department of Physics and Center for Applied Photonics, University of Konstanz, Universitätsstr. 10, D-78464 Konstanz, Germany

The impulsive optical excitation of carriers in graphene creates an nonequilibrium distribution, which thermalizes on an ultrafast timescale. The hot Fermi-Dirac distribution subsequently cools via phonon emission within few hundreds of femtoseconds. We investigated the initial stages of the thermalization process that are dominated by electron-electron scattering events. By comparing the two-color pump-probe experimental data with different models, that solve the quantum Boltzmann equation by implementing three different screening methods, we can visualize the importance of Auger recombination processes, such as carrier multiplication, in the ultrafast relaxation of the electronic distribution along the Dirac cone in graphene. Recent theoretical and experimental work also emphasizes the role of the polarization state of the light pulses used for the excitation. When carriers are excited with linearly polarized light, the resulting occupation in momentum space is not isotropic due to the pseudospin selection rules. To observe this anisotropy we compare the transient absorption signal arising for probe pulses with polarizations parallel and perpendicular to the pump pulse. We identify electron-phonon scattering as main driving mechanism of isotropization of the electronic distribution across the Dirac cone since it occurs in approximately 100 fs.