Cacho, C.Crepaldi, A.Battiato, M.Braun, J.Cilento, F.Zacchigna, M.Richter, M. C.Heckmann, O.Springate, E.Liu, Y.Dhesi, S. S.Berger, H.Bugnon, Ph.Held, K.Grioni, M.Ebert, H.Hricovini, K.Minar, J.Parmigiani, F.2015-05-292015-05-292015-05-29201510.1103/PhysRevLett.114.097401https://infoscience.epfl.ch/handle/20.500.14299/114446WOS:000350976700026The prospect of optically inducing and controlling a spin-polarized current in spintronic devices has generated wide interest in the out-of-equilibrium electronic and spin structure of topological insulators. In this Letter we show that only measuring the spin intensity signal over several orders of magnitude by spin-, time-, and angle-resolved photoemission spectroscopy can provide a comprehensive description of the optically excited electronic states in Bi2Se3. Our experiments reveal the existence of a surface resonance state in the second bulk band gap that is benchmarked by fully relativistic ab initio spin- resolved photoemission calculations. We propose that the newly reported state plays a major role in the ultrafast dynamics of the system, acting as a bottleneck for the interaction between the topologically protected surface state and the bulk conduction band. In fact, the spin- polarization dynamics in momentum space show that these states display macroscopically different temperatures and, more importantly, different cooling rates over several picoseconds.text::journal::journal article::research article