Berlin 2018 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 69: Poster: Quantum Systems

DY 69.1: Poster

Donnerstag, 15. März 2018, 15:30–18:00, Poster A

Nonequilibrium dynamics of laser-excited graphene: ab-initio MD simulations including electron-phonon coupling — •Sergej Krylow and Martin E. Garcia — Universität Kassel, Theoretische Physik II

Graphene attracted a lot of interest in the last decade due to its unique physical properties. Despite intensive research, there are still open questions regarding the response of Graphene to ultrashort laser pulses. In ultrafast electron diffraction experiments, a decay of Bragg peak intensities with two different decay times can be observed. The generation of a few optical phonons, so called SCOPs, which are strongly coupled to the electronic subsystem is believed to play a major role for this effect. However, the origin of the two timescales and the involved dynamics are not fully understood yet. To address this problem, we performed ab-initio molecular dynamic simulations of monolayer graphene immediately after laser excitation. Our results show that the short decay time can be accounted by the generation of the SCOPs and the long decay time to the equilibration of the phonon system. Furthermore, we see two stages in the dynamics of the lattice towards thermal equilibrium. Within the first picosecond after laser excitation mainly high- and mid-frequency phonons are created. Then, on a much longer timescale, the equilibration with low-frequency phonons occurs. Our result clearly suggest that the bottleneck for thermal equilibration in monolayer graphene are the low-frequency phonons.