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.Comment: 14 pages, 4 figure