Probing spin chirality of photoexcited topological insulators with circular dichroism: multi-dimensional time-resolved ARPES on Bi₂Te₂Se and Bi₂Se₃

Using time-resolved multi-dimensional angle-resolved photoelectron spectroscopy (ARPES) we explore the angular momentum transfer of low energy polarized photons to two prototype topological insulators, Bi₂Te₂Se and Bi₂Se₃. Our comparative study is based on the analysis of circular dichroism in the photoemission yield of photoexcited Dirac states, and reveals that the spin vector of in-gap Dirac electrons in Bi₂Te₂Se presents a more pronounced out-of-plane component compared to that of Bi₂Se₃. We show that the multi-dimensional ARPES approach can be effectively used to observe the spin texture of photoexcited topological insulators, and to unambiguously disentangle experimental geometry and matrix element effects.