Ultrafast carrier dynamics in topological insulators

该项目的主题是利用时间分辨和角度分辨的双光子光电发射(2PPE)研究三维拓扑绝缘体表面的超快动力学光激发电子。主要目的是识别和量化在拓扑表面态中激发电子的不同衰减通道，以便对这些新材料表面的载流子动力学和载流子输运机制有一个详细的了解。为此，2PPE将被用来确定激发电子沿表面带非弹性衰变的寿命。研究声子和缺陷的准弹性散射过程将通过使用2PPE来监测表面电流的衰减，该表面电流将由最近发展的利用中红外飞秒激光脉冲的光学激发方案产生。这一激发方案将成为在拓扑表面态中相干控制自旋偏振光电流的基础。这些研究将主要集中在P掺杂单晶拓扑绝缘体上。为了阐明掺杂对不同衰变通道的影响，我们将研究不同化学计量比的单晶和在生长过程中掺杂可以控制的外延生长的薄膜。

The topic of the project is the investigation of the ultrafast dynamics optically excited electrons at the surface of three dimensional topological insulators using time- and angle-resolved two-photon photoemission (2PPE). The primary goal is the identification and quantification of different decay channels of excited electrons in the topological surface state in order to develop a detailed under¬standing of the mechanism of charge carrier dynamics and charge carrier transport at the surface of these new materials. For this purpose, 2PPE will be employed to determine the lifetime of excited electrons for inelastic decay along the surface band. The investigation of quasi-elastic scattering processes at phonons and defects will be realized by using 2PPE to monitor the decay of surface currents that will be generated by a recently developed optical excitation scheme using femtosecond laser pulses in the mid infrared. This excitation scheme will be the basis for a coherent control of spin-polarized photocurrents in topological surface states. The studies will mainly focus on p-doped single crystalline topological insulators. In order to clarify the influence of doping on the different decay channels we will investigate single crystals of different stoichiometry and epitaxially grown thin films where the doping can be controlled during the growth.