Ultrafast dynamics of Bi2Te3 topological insulator: don't get excitoned

The formation of excitons in topological insulators, possibly characterized by a complex interplay between bulk and surface contributions, represents an extremely interesting case-of-study because of the possibility to get long standing and robust topological excitons. We present time- and angle- resolved photoemission (TR-ARPES) experiments [RMP 96, 015003 (2024)], performed at the Advanced Laser Light Source facility (ALLS) [Optics Express 32, 29549 (2024)], on a p-doped topological insulator. This is the first investigation of the ultrafast dynamics of electronic states with high energy and momentum resolution, performed using TR-ARPES with a mid-IR pump pulse (300 meV). The integration of deflectors into the photoemission system, in conjunction with sample bias facilitates an in-depth investigation into the existence of a distinctive, long-lasting (~20 ps) intensity build-up above the Fermi level, recently attributed to the first observation of spatially indirect excitons [R. Mori, Nature 614, 255 (2023)]. In order to address the controversial nature of the observed long-lasting intensity build-up, we present experiments performed as a function of the probe polarization, the pump fluence, and the temperature.