Optical Spin Orientation under Inter- and Intra-Subband Transitions in QWs

We study the optical orientation of electron spins in GaAs/AlGaAs quantum wells for excitation in the growth direction and for in-plane excitation. Time- and polarization-resolved photoluminescence excitation measurements show, for resonant excitation of the heavy-hole conduction band transition, a negligible degree of electron spin polarization for in-plane excitation and nearly 100% for excitation in the growth direction. For resonant excitation of the light-hole conduction...

The pure spin currents, i.e., the counterflow of particles with opposite spin orientations, can be optically injected in semiconductors. Here, we develop a phenomenological theory, which describes the polarization dependencies of spin currents excited by linearly polarized light in bulk semiconductors and quantum well structures of various symmetries. We present microscopic descriptions of the pure spin photocurrents for interband optical transitions in undoped quantum wells ...

We have shown that electron spin density can be generated by a dc current flowing across a $pn$ junction with an embedded asymmetric quantum well. Spin polarization is created in the quantum well by radiative electron-hole recombination when the conduction electron momentum distribution is shifted with respect to the momentum distribution of holes in the spin split valence subbands. Spin current appears when the spin polarization is injected from the quantum well into the $n$...

We report on the study of spin photocurrents in (110)-grown quantum well structures. Investigated effects comprise the circular photogalvanic effect and so far not observed circular photon drag effect. The experimental data can be described by an analytical expression derived from a phenomenological theory. A microscopic model of the circular photon drag effect is developed demonstrating that the generated current has spin dependent origin.

A comparison is made between the degree of spin polarization of electrons excited by one- and two-photon absorption of circularly polarized light in bulk zincblende semiconductors. Time- and polarization-resolved experiments in (001)-oriented GaAs reveal an initial degree of spin polarization of 49% for both one- and two-photon spin injection at wavelengths of 775 and 1550 nm, in agreement with theory. The macroscopic symmetry and microscopic theory for two-photon spin inject...

We present a detailed experimental and theoretical analysis of the optical orientation of electron spins in GaAs/AlAs quantum wells. Using time and polarization resolved photoluminescence excitation spectroscopy, the initial degree of electron spin polarization is measured as a function of excitation energy for a sequence of quantum wells with well widths between 63 Ang and 198 Ang. The experimental results are compared with an accurate theory of excitonic absorption taking f...

A theory of the circular photogalvanic effect caused by spin splitting in quantum wells is developed. Direct interband transitions between the hole and electron size-quantized subbands are considered. The photocurrent excitation spectrum is shown to depend strongly on the form of the spin-orbit interaction. In the case of structure inversion asymmetry induced (Rashba) spin-splitting, the current is a linear function of light frequency near the absorption edge, and for the hig...

We report on the observation of the magneto-photogalvanic effect (MPGE) due to inter-subband transitions in (001)-oriented GaAs quantum wells. This effect is related to the gyrotropic properties of the structures. It is shown that inter-subband absorption of linearly polarized radiation may lead to spin-related as well as spin independent photocurrents if an external magnetic field is applied in the plane of the quantum well. The experimental results are analyzed in terms of ...

We examine electron transport through semiconductor quantum dot subject to a continuous circularly polarized optical irradiation resonant to the electron - heavy hole transition. Electrons having certain spin polarization experience Rabi oscillation and their energy levels are shifted by the Rabi frequency. Correspondingly, the equilibrium chemical potential of the leads and the lead-to-lead bias voltage can be adjusted so only electrons with spin-up polarization or only elec...

It is demonstrated theoretically that the circularly polarized irradiation of two-dimensional electron systems can induce the localized electron states which antiferromagnetically interact with conduction electrons, resulting in the Kondo effect. Conditions of experimental observation of the effect are discussed for semiconductor quantum wells.