Conversion between spin and charge currents with topological insulators

Injection of a spin current into the surface or interface states of a topological insulator (TI) induces a charge current (inverse Edelstein effect or IEE) and, inversely, a charge current flowing at the surface or interface states of a TI generates a nonzero spin density (Edelstein Effect or EE) from which a spin current can be ejected into an adjacent layer. The parameters characterizing the efficiency of these conversions between spin and charge currents have been derived in recent experiments. By using a spinor distribution function for a momentum-spin locked TI, we determine a number of spin transport properties of TI-based heterostructure and find that the spin to charge conversion in IEE is controlled by the relaxation of an out-of equilibrium distribution in the TI states while the charge to spin conversion in EE depends on the electron transmission rate at the interface of the TI.