Long-Lived Quantum Well State Excitation and Surface Photovoltage Interplay in Topological Insulator*

Topological insulators with Fermi levels doped into the bulk-gap exhibit strong surface band-bending and long-lived surface photovoltage (SPV) effects. Furthermore, in-situ surface doping of the topological insulators Bi2Se3 and Bi2Te3 can lead to strong Rashba-split quantum well states. In this study, we have combined bulk-doping and surface-doping to obtain both a strong surface photovoltage and spin-momentum locked quantum well states. Remarkably, Time- and angle-resolved photoemission spectroscopy reveals an additional pump-induced quantum well state that persists for 100s of picoseconds and coincides with the surface photovoltage, as well as time-dependent modifications to the quantum well states. Our work demonstrates that topological insulators are an exemplary foundation for tunable spin-textures with complex dynamics.