Regensburg 2016 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 7: Graphene I: Structure and Dynamics
O 7.5: Hauptvortrag
Montag, 7. März 2016, 11:30–12:00, H24
Direct view on non-equilibrium carriers in graphene with time-resolved ARPES — •Isabella Gierz — Max Planck Institute for the Structure and Dynamics of Matter, Hamburg, Germany
The linear band structure of graphene bares great potential for optoelectronic applications ranging from Terahertz lasing to efficient light harvesting. We explore the response of the Dirac carriers in lightly hole-doped epitaxial graphene samples to three different excitation schemes: interband transitions for ℏωpump>2µe, free carrier absorption for ℏωpump<2µe, and resonant phonon excitation for ℏωpump=200 meV. Time- and angle-resolved photoemission spectroscopy (tr-ARPES) allows us to map the transient population of the Dirac cone in momentum space over a large energy window of several electron Volts down to arbitrarily small excitation energies.
We find a short-lived population-inverted state for interband excitation [1], a simple metallic relaxation behaviour for free carrier absorption [1], and indications for a transient enhancement of the electron-phonon coupling constant when resonantly driving the in-plane phonon in bilayer graphene [2]. Furthermore, by improving the temporal resolution to ∼10 fs, we were able to identify impact ionization as the primary thermalization channel within the first ∼25 fs [3].
[1] Gierz et al., Nature Materials 12, 1119 (2013)
[2] Gierz et al., PRL 114, 125503 (2015)
[3] Gierz et al., PRL 115, 086803 (2015)