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Electron spin dynamics of dilute nitride GaNAs quantum well (QW)-InAs quantum dots (QDs) tunnel-coupled structures having different QW thicknesses were studied via circularly polarized time-resolved photoluminescence. The rate equation fitting considering a capture of QD electron spins by the GaNAs localized states via tunnel transfer revealed that the spin amplification dynamics of the QDs depended on the QW thickness. For the QW thickness of 5 nm, although the temporal amplification of QD electron spin polarization was slow owing to the weak wavefunction coupling between the QW and QD, the long duration of high electron spin polarization was observed because of the suppressed capture of QD majority spins relative to the efficient removal of QD minority spins. When the QW thickness increased from 5 to 20 nm, the strong spin filtering in GaNAs and strong wavefunction coupling led to the fast amplification of QD electron spin polarization with high initial spin polarization. However, the spin polarization rapidly decays after the amplification owing to the removal of both QD majority and minority spins, originating from many effective localized states. These results indicate that the time-dependent QD electron spin polarization and the resultant spin amplification can be widely tuned by changing the thickness of the tunnel-coupled GaNAs QW. [ABSTRACT FROM AUTHOR]

The effective mass at the Fermi level is measured in the strongly interacting two-dimensional (2D) electron system in ultra-clean SiGe/Si/SiGe quantum wells in the low-temperature limit in tilted magnetic fields. At low electron densities, the effective mass is found to be strongly enhanced and independent of the degree of spin polarization, which indicates that the mass enhancement is not related to the electrons' spins. The observed effect turns out to be universal for silicon-based 2D electron systems, regardless of random potential, and cannot be explained by existing theories. [ABSTRACT FROM AUTHOR]

The impact of inter-valley scattering in modifying the density of optically injected spin polarized electrons in AlxGa1−xAs/GaAs heterostructure is investigated. Polarization resolved photoluminescence excitation measurements are performed for studying the spectral dependence of degree of circular polarization (DCP) of photoluminescence signal emanating from an adjacent quantum well layer. The experimental DCP spectra is found to deviate from the theoretically calculated curve at high excitation energy and the deviation is seen to widen with the Al-content of AlxGa1−xAs barrier layer. In the past, researchers had attributed similar deviations to the Dyakonov–Perel (DP) spin relaxation mechanism which dominates the electrons spin dynamics at high excitation energy. However, we find that the inter-valley scattering along with the DP mechanism decide the shape of optical spin orientation spectra at higher energy. In fact, at higher Al-content, the inter-valley scattering in AlxGa1–xAs layer becomes the most dominant mechanism to govern the steady state electron spin polarization at the band edge. A numerical model is also proposed for estimating the steady state electron spin polarization at zone centre by including the inter-valley scattering, energy relaxation and DP spin relaxation mechanisms. [ABSTRACT FROM AUTHOR]

A transmission-grating-sampled circular dichroism absorption spectroscopy (TGS-CDAS) and its theoretical model are developed sensitively to measure decay dynamics of a transient spin grating (TSG). A binary transmission grating with the same period as TSG is set behind TSG. It allows only a same small part of each period in TSG measured by circular dichroism absorption effect of a probe. In this way, the zero average of spin-dependent effects measured over a whole period in TSG is avoided so that TGS-CDAS has a high sensitivity to spin evolution in TSG. Spin transport experiments are performed on GaAs/AlGaAs quantum wells. Experimental results prove the feasibility and reliability of TGS-CDAS. [ABSTRACT FROM AUTHOR]

Mechanisms of the suppression of the electron-hole exchange interaction in nonradiative excitons with a large in-plane wave vector in high-quality heterostructures with quantum wells are analyzed theoretically. It is shown that the dominant suppression mechanism is exciton-exciton scattering accompanied by the mutual spin flips of like carriers (either two electrons or two holes), comprising the excitons. As a result, the electron spin polarization in nonradiative excitons may be retained for a long time. The analysis of experimental data shows that this relaxation time can exceed one nanosecond. This long-term and optically controllable spin memory in an exciton reservoir may be of interest for future information technologies. [ABSTRACT FROM AUTHOR]

Carrier recombination and electron spin relaxation dynamics in asymmetric n-doped (110) GaAs/AlGaAs quantum wells are investigated with time-resolved pump-probe spectroscopy. The experiment results reveal that the measured carrier recombination time depends strongly on the polarization of pump pulse. With the same pump photon flux densities, the recombination time of spin-polarized carriers is always longer than that of the spin-balanced carriers except at low pump photon flux densities, this anomaly originates from the polarization-sensitive nonlinear absorption effect. Differing from the traditional views, in the low carrier density regime, the D'yakonov–Perel' (DP) mechanism can be more important than the Bir–Aronov–Pikus (BAP) mechanism, since the DP mechanism takes effect, the spin relaxation time in (110) GaAs QWs is shortened obviously via asymmetric doping. [ABSTRACT FROM AUTHOR]

We review experimental and theoretical study of dynamic electron spin injection in semiconductor nanostructures. The review is focused on spin-dependent recombination and spin-dependent tunneling phenomena leading to a photoluminescence polarization. These phenomena lead to fundamentally different dynamic spin polarization of the electrons in contrast to the polarization in a steady state under, stationary spin injection or in the case of s(p)–d exchange interaction in typical metal/ferromagnetic or semiconductor/ferromagnetic hybrid structures. Growing attention to the mechanisms leading to dynamic spin polarization is the result of (i) the possibility to precisely control the process by means of external gating and (ii) rich and still not well understood physics of the time dependent processes in semiconductor nanostructures. Moreover, non stationary processes allow to highlight the role of Coulomb correlations in the formation of carriers spin polarization. The described physics of dynamic polarization is expected in a variety of systems including semiconductor-QW based heterostructures, nanoplatelets and novel 2D materials. In the first part of the review the spin-dependent recombination via deep paramagnetic centers is discussed, which allows to obtain an unusually high spin polarization for carriers in nonmagnetic semiconductor alloys. The second part deals with the dynamic spin polarization in hybrid heterostructures semiconductor quantum well — magnetic dopant layer. Finally, possible implementation of the dynamic spin polarization in spin lasers is addressed. We also shortly discuss such perspective area as spin injection in microwave and terahertz frequency. We conclude with some open questions and other promising implementation of discussed effect which we consider very important for further development of spintronics. • The review is focused on spin-dependent recombination and spin-dependent tunneling. • A study of dynamic electron spin injection in nanostructures is discussed. • The described physics of dynamic polarization is expected in a variety of systems. • The considered phenomena are sensitive to electron correlations. • The obtained results open the possibility to effective and fast control of PL polarization. [ABSTRACT FROM AUTHOR]

A quantum kinetic theory of the spin transfer between carriers and Mn atoms in a Mn-doped diluted magnetic semiconductor is presented. It turns out that the typical memory time associated with these processes is orders of magnitude shorter than the time scale of the spin transfer. Nevertheless, Markovian rate equations, which are obtained by neglecting the memory, work well only for bulk systems. For quantum wells and wires the quantum kinetic results qualitatively deviate from the Markovian limit under certain conditions. Instead of a monotonic decay of an initially prepared excess electron spin, an overshoot or even coherent oscillations are found. It is demonstrated that these features are caused by energetic redistributions of the carriers due to the energy-time uncertainty. [ABSTRACT FROM AUTHOR]

• Semiconductor superlattice can generate larger spin splitting than single asymmetric quantum well, resulting in desirable spin polarization. • Spin orientations of electrons of semiconductor superlattice may not change during transport processes, resulting in long spin relaxation time. • One superlattice structure can realize two functions, acting as a spin field effect transistor and a spin filter. • Spin splitting of some sublevels does not vary with structure parameters, reducing the demand for accuracy in quantum wells size. • Using semiconductor superlattice will contribute to the detection of spin related phenomenon and promote the progress of spintronic devices. The purpose of this paper is to theoretically investigate the spin-orbit interactions of common semiconductor superlattices. Spin splitting and spin-orbit interaction coefficients are calculated based on interactions between the interface-related-Rashba effect and Dresselhaus effect. Semiconductor superlattice shows a series of specific characteristics in spin splitting as follows. The spin splitting of the superlattice structure is greater than that of a single quantum well, contributing to significant spin polarization, spin filtering, and convenient manipulation of spintronic devices. The spin splitting of some superlattice structures does not change with variation of the size of some constituent quantum wells, reducing the requirements for accuracy in the size of quantum wells. The total spin splitting of lower sub-levels of some superlattice can be designed to be zero, realizing a persistent spin helix effect and long spin relaxation time, however, the total spin splitting of higher sub-levels is still appreciable, contributing to desirable spin polarization. These results demonstrate that one superlattice structure can realize two functions, acting as a spin field effect transistor and a spin filter. [ABSTRACT FROM AUTHOR]