Ultrafast carrier dynamics in topological insulators

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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.