The converse effects of spin photocurrent and current induced spin polarization are experimentally demonstrated in a two-dimensional electron gas system with Rashba spin splitting. Their consistency with the strength of the Rashba coupling as measured for the same system from beating of the Shubnikovde Haas oscillations reveals a unified picture for the spin photocurrent, current-induced spin-polarization, and spin-orbit coupling. In addition, the observed spectral inversion of the spin photocurrent indicates a system with dominating structure inversion asymmetry. DOI: 10.1103/PhysRevLett.96.186605 PACS numbers: 72.25.Fe, 72.25.Pn With the basic idea of the spin field effect transistor, as proposed by Datta and Das [1], the electric field tunable spin-orbit interaction has been an ideal candidate for manipulating the electron spin polarization. The structural inversion asymmetry (SIA) induced spin-orbit coupling (Rashba interaction [2]) in a two-dimensional electron gas (2DEG) system has attracted more and more attention due to its potential applications in spintronics devices. With spin splitting of the energy bands, optical excitation of quantum well (QW) structures by circularly polarized radiation will lead to a current whose direction and magnitude depend on the helicity of the incident light. This is named the circular photogalvanic effect (CPGE) and has been demonstrated using intersubband [3,4] or interband [5] excitations. A related effect, in which the current is driven by the spin-flip process of the nonequilibrium population of electrons in the spin-split bands, is called the spingalvanic effect [6]. The most interesting consequence of the k-dependent spin splitting is the implication that an applied electric field would induce not only a charge current but also a spin polarization [7][8][9][10][11][12][13] along the direction perpendicular to the current.This Letter provides the experimental evidence of circularly polarized optical-excitation-induced spin photocurrent in (001) grown InGaAs=InAlAs 2DEGs under oblique incidence of radiation for interband excitation, which is 2 orders of magnitude stronger than similar observations using far-infrared excitation for intersubband transitions. The current-induced spin polarization in the same samples is measured using the Kerr rotation experiment. These results are consistent with the spin splitting of the energy bands as examined by the beating of the Shubnikovde Haas (SdH) oscillations. The correlation in these experiments with great consistency reveals a unified picture for the spin photocurrent, current-induced spin-polarization and spin-orbit coupling. Furthermore, the theoretically predicted spectral inversion of the CPGE spin photocurrent is experimentally observed.Two samples (named D and E) studied here were In x Ga 1ÿx As=In 0:52 Al 0:48 As 2DEGs grown on a semiinsulating (001) InP substrate with well thickness of 14 nm. The SIA was achieved by doping of only one side of the barrier layer (on top of the well). To enhance the SIA, sample E wa...

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