Coherent ultrafast spin-dynamics probed in three dimensional topological insulators

Topological insulators are candidates to open up a novel route in spin based electronics. Different to traditional ferromagnetic materials, where the carrier spin-polarization and magnetization are based on the exchange interaction, the spin properties in topological insulators are based on the coupling of spin- and orbit interaction connected to its momentum. Specific ways to control the spin-polarization with light have been demonstrated: the energy momentum landscape of the Dirac cone provides spin-momentum locking of the charge current and its spin. The directionality of spin and momentum, as well as control with light has been demonstrated. Here we demonstrate a coherent femtosecond control of spin-polarization for states in the valence band at around the Dirac cone.