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We address the temperature influence on the precessional motion of electron spins under a transverse magnetic field, studied in GaAs/AlGaAs triple quantum wells, using pump-probe Kerr rotation. In the presence of an applied in-plane magnetic field, the TRKR measurements show the robustness of carrier's spin polarization against temperature, which can be easily traced in an extended range up to 250 K. By tuning the pump-probe wavelength to the exciton bound to a neutral donor transition, we observed a remarkably long-lasting spin coherence (with dephasing time T 2 * > 14 ns) limited by the spin hopping process and exchange interaction between the donor sites, as well as the ensemble spread of the g-factor. The temperature dependent spin dephasing time revealed a double linear dependence due to the different relaxation mechanisms active in respective temperature ranges. We observed that the increase in sample temperature from 5 K to 250 K leads to a strong T 2 * reduction by almost 98%/97% for the excitation wavelengths of 823/821 nm. Furthermore, we noticed that the temperature increase not only causes the reduction of spin lifetime, but can also lead to the variation of the electron g-factor. Additionally, the spin dynamics were studied through the dependencies on the applied magnetic field and optical pump power. [ABSTRACT FROM AUTHOR]

Spin transport was studied in a two-dimensional electron gas hosted in a wide GaAs quantum well occupying two subbands. Using space and time Kerr rotation microscopy to image drifting spin packets under an in-plane accelerating electric field, optical injection and detection of spin polarization were achieved in a pump–probe configuration. The experimental data exhibited high spin mobility and long spin lifetimes allowing us to obtain the spin–orbit fields as a function of the spin velocities. Surprisingly, above moderate electric fields of 0.4 V/cm with velocities higher than 2 µm/ns, we observed a dependence of both bulk and structure-related spin–orbit interactions on the velocity magnitude. A remarkable feature is the increase in the cubic Dresselhaus term to approximately half of the linear coupling when the velocity is raised to 10 µm/ns. In contrast, the Rashba coupling for both subbands decreases to about half of its value in the same range. These results yield new information on the application of drift models in spin–orbit fields and about limitations for the operation of spin transistors. [ABSTRACT FROM AUTHOR]

The recent discovery of a polaron-associated zero phonon line in the band-edge photoluminescence of high optical quality EuTe crystals opens up the prospect of answering long-standing questions about the polaron internal structure, thermal stability, and generation efficiency. Here, a Schrödinger equation for the polaron was formulated and resolved by using both variational and self-consistent methods. The theory is in good agreement with measurements of the zero phonon line as a function of magnetic field and temperature, and it could be applied to other polaronic systems. It is deduced that, in EuTe, at 0 K, a polaron carries a magnetic moment of 610μB, and its binding energy is 27 meV. However, this binding energy does not carry the usual meaning of thermal stability, because it decreases drastically when the sample is warmed up. For instance, at T = 100 K, the binding energy is already reduced to only 6 meV. The thermal destruction of a polaron is brought about by thermal fluctuations of the spin lattice that suppress the electron's self-energy. Photoluminescence excitation spectra of EuTe demonstrate that the photogeneration of polarons becomes increasingly inefficient when the energy of the pumping photon is increased above the band gap. [ABSTRACT FROM AUTHOR]

Spin drag measurements were performed in a two-dimensional electron system set close to the crossed spin helix regime and coupled by strong intersubband scattering. In a sample with an uncommon combination of long spin lifetime and high charge mobility, the drift transport allows us to determine the spin-orbit field and the spin mobility anisotropies. We used a random walk model to describe the system dynamics and found excellent agreement for the Rashba and Dresselhaus couplings. The proposed two-subband system displays a large tuning lever arm for the Rashba constant with gate voltage, which provides a new path towards a spin transistor. Furthermore, the data show large spin mobility controlled by the spin-orbit constants setting the field along the direction perpendicular to the drift velocity. This work directly reveals the resistance experienced in the transport of a spin-polarized packet as a function of the strength of anisotropic spin-orbit fields. [ABSTRACT FROM AUTHOR]