Deduction of pure spin current from the linear and circular spin photogalvanic effect in semiconductor quantum wells

We study the spin photogalvanic effect in a two-dimensional electron system with structure-inversion asymmetry by means of solution of the semiconductor optical Bloch equations. It is shown that linearly polarized light may inject a pure spin current into spin-splitting conduction bands due to Rashba spin-orbit coupling, while circularly polarized light may inject a spin-dependent photocurrent. We establish an explicit relation between the photocurrent caused by oblique incidence of circularly polarized light and the pure spin current caused by normal incidence of linearly polarized light such that we can deduce the amplitude of the spin current from the experimentally measured spin photocurrent. This method may provide a source of spin current to study spin transport in semiconductors quantitatively.