Prof. Fulvio Parmigiani: Spin and time resolved photoelectron spectroscopy in the momentum space of archetypal topological insulators
Povzetek:
Spin and time resolved photoelectron spectroscopy in the momentum space of archetypal topological insulators
Prof. Fulvio Parmigiani, Department of Physics - University of Trieste, International Faculty - University of Köln, and FERMI @ Elettra-FEL
The interaction between light and the topologically protected spin polarized Dirac particles at the surface of topological insulators (TIs) constitutes the key issue for the development of a new class of opto-spintronics devices. Hence the prospect of optically inducing and controlling a spin-polarized current has generated a vast interest in the out-of-equilibrium electronic and spin properties of these materials. After several years of intense experimental and theoretical work we demonstrate that only by measuring the spin intensity signal over several orders of magnitude by spin, time and angle resolved photoemission spectroscopy (STAR-PES) is it possible to comprehensively describe the optically excited electronic states in Bi2Se3. The results 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 surface and bulk states display macroscopically different temperatures and, more importantly, different cooling rates over several picoseconds.
