Edge absorption and pure spin current in 2D topological insulator in the Volkov-Pankratov model

The light absorption due to the transitions between the edge and two-dimensional (2D) states of a 2D topological insulator (TI) is considered in the Volkov-Pankratov model. It is shown that the transitions are allowed only for the in-plane electric field orthogonal to the edge of the TI. It is found that the absorption is accompanied by the pure spin photocurrent along the TI edge. The possibility of the spin current measurement using polarized luminescence from 2D TI quantum dots is discussed.