Spin accumulation in a 2D electron gas with Rashba spin-orbit interaction  subject to an electric field can take place without bulk spin currents (edge spin Hall effect).  This is demonstrated for the collisional regime using the non-equilibrium distribution function determined from the standard Boltzmann equation. Spin accumulation originates from interference of incident and reflected electron waves  at the sample boundary.

The experimental evidences of the spin Hall effect reported in the literature, were based on measurement of the spin accumulated on the sample edges. Meanwhile, the present analysis demonstrates that spin accumulation is not really a probe of the bulk spin current: the former can be absent in the presence of the bulk current and can appear in the absence of the latter. This should be taken into account interpreting experiments on the spin Hall effect.