Topological materials represent a new quantum state of matter that is currently attracting great interest thanks to unique electrical transport properties. In particular, Topological Insulators (TIs) have been the subject of several studies due to their peculiar spin texture and because they are ideal candidates for future spintronics devices [1,2,3]. Moreover, the possibility to inject spin currents by ultrashort optical pulses has stimulated intense studies of their out-of-equilibrium electronic properties. However, a comprehensive description of the electronic relaxation dynamics has been elusive, so far. In order to reveal the role of the bulk and surface states in determining the microscopic scattering mechanisms, we investigated by means of time- and angle-resolved photoemission spectroscopy (TR-ARPES) a wide set of TIs. We studied n-doped (GeBi2Te4, GeBi4Te7), intrinsic (Bi2Te3, GeBi2Te4) and p-doped (Sb2Te3, Sb6Te3) compounds. Our data clearly show markedly different relaxation dynamics, mainly influenced by the doping of the compound, indicating that surface and bulk states play a crucial role in determining the electron relaxation processes. We also report on the study of the electron relaxation dynamics exhibited by the Kondo Insulator (KI) SmB6. Albeit its topological character is still under debate, this material attracted the scientific interest since it was proposed as the first Topological Kondo Insulator (TKI) [4–6]. Following the idea to address the scattering mechanisms at play in SmB6, we develop an effective temperature model for this material and provide the first experimental estimation of the electron-phonon coupling constant, being the thermalization in this material mainly governed by electron-phonon scattering events.
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