Spin dynamics in high-mobility two-dimensional electron systems

Understanding the spin dynamics in semiconductor heterostructures is highly important for future semiconductor spintronic devices. In high-mobility two-dimensional electron systems (2DES), the spin lifetime strongly depends on the initial degree of spin polarization due to the electron-electron interaction. The Hartree-Fock (HF) term of the Coulomb interaction acts like an effective out-of-plane magnetic field and thus reduces the spin-flip rate. By time-resolved Faraday rotation (TRFR) techniques, we demonstrate that the spin lifetime is increased by an order of magnitude as the initial spin polarization degree is raised from the low-polarization limit to several percent. We perform control experiments to decouple the excitation density in the sample from the spin polarization degree and investigate the interplay of the internal HF field and an external perpendicular magnetic field. The lifetime of spins oriented in the plane of a [001]-grown 2DES is strongly anisotropic if the Rashba and Dresselhaus spin-orbit fields are of the same order of magnitude. This anisotropy, which stems from the interference of the Rashba and the Dresselhaus spin-orbit fields, is highly density-dependent: as the electron density is increased, the kubic Dresselhaus term becomes dominant and reduces the anisotropy.Comment: 13 pages, 6 figure

Energy-dependent electron-electron scattering and spin dynamics in a two-dimensional electron gas

The measurement of spin dynamics of electrons in a degenerate two-dimensional electron gas, wherein the Dyakonov–Perel mechanism is dominant, has been used to investigate the electron scattering time (tp*) as a function of energy near the Fermi energy. Close to the Fermi energy, the spin evolution is oscillatory, which indicates a quasicollision-free regime of spin dynamics. As the energy is increased, a transition to an exponential, collision-dominated spin decay occurs. The oscillation frequency and the value of tp* are extracted by using a Monte Carlo simulation method. At the Fermi energy, tp* is very close to the ensemble momentum relaxation time (tp) obtained from the electron mobility. For higher energies, tp* falls quadratically, which is consistent with the theoretical expectations for the onset of the electron-electron scattering, which is inhibited by the Pauli principle at the Fermi energy

All optical measurement of Rashba coefficient in quantum wells

We perform an all-optical spin-dynamic measurement of the Rashba spin-orbit interaction in (110)-oriented GaAs/AlGaAs quantum wells under applied electric field. This crystallographic orientation allows us to isolate the Rashba from other contributions, giving precise values of the Rashba coefficient. At low temperature, we find good agreement between our measurements and the k·p theory. Unexpectedly, we observe a temperature dependence of the Rashba coefficient that may signify the importance of higher-order terms of the Rashba coupling

Spin dynamics of Rashba-Dresselhaus two-dimensional electron systems with electron-electron interactions

Spin dynamics of Rashba-Dresselhaus two-dimensional electron systems is studied by taking account of electron-electron interactions under the D’yakonov-Perel’ mechanism. The diffusion equations for charge and spin densities are obtained through decoupling of the interactions using the auxiliary Bose field. We show that the electron-electron interaction has no effect on the infinite spin lifetime when the Rashba and Dresselhaus coupling constants satisfy the condition α=±β. If the general condition α≠±β is satisfied, the spin lifetime is finite and enhanced by the electron-electron interaction with the increment of the temperature in the ballistic regime. The increasing amplitude of the spin lifetime depends on the ratio of the temperature to the Fermi temperature. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2010