English: Topological insulator bands (a) in equilibrium and (b) in a non equilibrium situation when a spin-charge interconversion meccanism occurs. The non-equilibrium case can be produced by two possible effects: the injection of a charge current (i.e., a momentum unbalance) which produces a spin accumulation (Edelstein effect) or the injection of a spin current resulting in a charge current (inverse Edelstein effect).