ABSTRACT
The spin degree of freedom of charge carriers and its manipulation has become a hot topic in material science under the perspective of spin-based electronic devices (for a review see [1]). Here we report on a new property of the electron spin in a spin-polarized electron gas: its ability to drive an electric current. Recently it has been demonstrated that optical excitation of quantum well structures with circularly polarized radiation leads to a current whose direction and magnitude depends on the degree of circular polarization of the incident light [2]. This effect belongs to the class of photogalvanic effects [3] and represents a circular photogalvanic effect (CPGE). It was shown in [4] that in zinc-blende-based structures the CPGE is caused by spin orientation of carriers in systems with band splitting in k-space due to k-linear terms in the Hamiltonian [5,6]. In this case irradiation of QWs with circularly polarized light results in a non-uniform distribution of photoexcited carriers in k-space due to optical selection rules and energy and momentum conservation [7]. Furthermore, most recently we have shown that a spin-polarized electron gas obtained by any means, optical as well as electrical, can drive an electrical current, even at room temperature, if some general symmetry requirements are met [8 ]. While electrical currents are usually generated by electric or magnetic fields or gradients, we demonstrated that a uniform non-equilibrium population of electron spins gives rise to an electric current. The microscopic origin of this spin-galvanic effect is an inherent asymmetry of the spin-flip scattering of electrons in systems with removed k-space spin degeneracy of the band structure.
