Quantum drift-diffusion modeling of spin transport in nanostructures

We consider a two-dimensional electron gas with a spin-orbit interaction of Bychkov and Rashba type. Starting from a microscopic model, represented by the von Neumann equation endowed with a suitable Bhatnagar–Gross–Krook collision term, we apply the Chapman–Enskog method to derive a quantum diffusive model. Such model is then semiclassically expanded up to second order, leading to nonlinear quantum corrections to the zero-order diffusive models of the literature.