Ultrafast electron dynamics of Rashba-split 2-dimensional electron gas in topological insulators

The study of 2 Dimensional Electron Gasses (2DEGs) at semiconductors interfaces dates back many decades, and today 2DEGs in field effect transistors are at the heart of modern electronics. It was recently discovered that 2DEGs can be induced on the surface of topological insulators (TI), leading to quantum well states with strong and exotic Rashba splitting [1-3]. The coexistence of spin polarized 2DEGs and topological states on the surface of TIs has important repercussions on the transport properties and on the realization of topological devices. Here we report on the ultrafast response of spin-polarized 2DEGs to optical excitation. Samples of bismuth chalcogenide TIs are chemically gated via adsorption of alkali metals on the surface, resulting in the formation of 2DEGs. Time-resolved ARPES is employed to study the ultrafast electron dynamics of the Rashba split 2DEGs as a function of spin-orbit coupling strength, doping level, and chemical composition. Our results give new insights in the physics of Rashba states and on their interplay with the topological state.
[1] P. D. C. King et al., Phys. Rev. Lett. 107, 096802 (2011)
[2] Z.-H. Zhu et al., Phys. Rev. Lett. 107, 186405 (2011)
[3] M. Michiardi et al., Phys. Rev. B 91, 035445 (2015)