Deduction of Pure Spin Current from Spin Linear and Circular Photogalvanic Effect in Semiconductor Quantum Wells

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