Inverse spin-galvanic effect in topological-insulator graphene heterostructures.*

We study theoretically the inverse spin-galvanic effect in heterostructures formed by a layer of a three dimensional strong topological insulator (TI) and a graphenic layer (single layer graphene, and bilayer graphene). We also consider trilayer structures in which a ferromagnetic thin film is added on top of the graphenic layer. % We consider the cases of coherent, and random tunneling between states in the TI and the graphenic layer. % We obtain the strength of the inverse spin-galvanic effect, taking into account both intraband and interband contributions, as a function of the system's parameters both for the case in which the disorder is short-range and for the case in which the disorder is long-range as when charge impurities are the dominant source of disorder. % We find that for a large range of system's parameters the presence of the graphenic layer enhances the strength of the inverse spin-galvanic effect. Finally, we discuss the relevance of our results for recent experiments.