Berlin 2015 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 22: Ultrafast Surface Dynamics

O 22.4: Vortrag

Dienstag, 17. März 2015, 11:30–11:45, MA 042

Thermalization dynamics in graphite - Phonon-phonon interaction vs. supercollision — •Ankatrin Stange, Christian Sohrt, Lexian Yang, Gerald Rohde, Petra Hein, Lars Oloff, Kerstin Hanff, Kai Rossnagel, and Michael Bauer — Institute of Experimental and Applied Physics, University of Kiel, Germany

Recent studies reported on a defect-assisted (supercollision) process yielding an enhanced coupling between optically excited electrons and acoustic phonons in graphene [1,2] and accelerating electron-lattice thermalization down to timescales in the few picosecond regime. In this work we address the question to what extent also the relaxation dynamics in the parent compound graphite is governed by supercollision. Time- and angleresolved photoelectron spectroscopy is used to monitor the transient carrier population in the π-bands at the H point at absorption of intense near-infrared laser pulses. In correspondence to other works the relaxation due to interaction with the lattice proceeds on two characteristic timescales: A fast (≈250 fs) cool down of the electron gas arising from the interaction of the electronic system with strongly coupled optical phonons (SCOPs) [3] is followed by a picosecond dynamics that can consistently be reproduced within a three-temperature model only if the coupling between SCOPs and acoustic phonons is taken into account [3]. In contrast, the supercollision model clearly fails in describing the recorded electron temperature transients.
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