Carrier dynamics in graphene close to the Dirac point as well as under Landau quantization

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The key for designing and engineering novel graphene-based optoelectronic devices is a thorough microscopic understanding of the fundamental ultrafast carrier relaxation channels in graphene. The main goal of our project is to shed light on the ultrafast carrier and phonon dynamics close to the Dirac point including the elementary scattering channels in Landau-quantized graphene. To this end, we will continue the successful close experiment-theory collaboration of the previous project phase. The terahertz region around the Dirac point is interesting for both fundamental research and technological application. It has not been intensively studied so far, since it is very challenging to access this spectral region in experiment and theory. Based on the density matrix formalism, we will investigate the impact of (I) phonon- and Coulomb-assisted intraband absorption, (II) substrate-induced doping, (III) impurity-assisted carrier-phonon scattering and (IV) quantum-kinetic memory contributi ons to the carrier relaxation dynamics. Experimentally, graphene samples of systematically varied structural quality and carrier concentration will be analyzed in time-resolved spectroscopic studies performed in the terahertz frequency range. Both the theoretical and experimental studies will also address the relaxation dynamics in Landau-quantized graphene, which is to a large extent completely unexplored, so far. The new insights will be exploited to study the intriguing possibility of tunable gain in a three-level Landau system as well as the possibility of ultra-broadband fast graphene detectors.