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

设计和工程新型石墨烯光电器件的关键是对石墨烯中基本的超快载流子弛豫通道进行彻底的微观理解。我们项目的主要目标是阐明狄拉克点附近的超快载流子和声子动力学，包括朗道量子化石墨烯中的基本散射通道。为此，我们将继续上一个项目阶段成功的紧密实验-理论合作。狄拉克点周围的太赫兹区域对于基础研究和技术应用都很有趣。到目前为止，由于在实验和理论上都很难进入这个光谱区域，因此对它的研究还不是很深入。基于密度矩阵的形式，我们将研究(I)声子和库仑辅助带内吸收，（II）衬底诱导掺杂，（III）杂质辅助载流子-声子散射和（IV）量子动力学记忆对载流子弛豫动力学的影响。实验中，系统地改变结构质量和载流子浓度的石墨烯样品将在太赫兹频率范围内进行时间分辨光谱研究。理论和实验研究也将解决朗道量子化石墨烯的弛豫动力学，这在很大程度上是迄今为止尚未探索的。新的见解将被用于研究三能级朗道系统中可调增益的可能性，以及超宽带快速石墨烯探测器的可能性。

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.