Nuclear field effect on the spin dynamics of electron localized on a donor in a single quantum well
Résumé
We use photoinduced Faraday rotation (PFR) in presence of an applied magnetic field to study the spin dynamics of localized electrons. The sample is a CdTe/CdMgTe quantum well (QW) of width 80 angstrom containing a layer of iodine donors at its center, with, concentration 10(11) cm(-2). The spin polarization of donor bound electrons is built via the optical polarization of donor-bound excitons, their hole spin relaxation, and their recombination. In a transverse (in-plane) magnetic field, PFR shows damped Larmor oscillations from which we deduce a 18 ns electron-spin decoherence time, and a transverse Lande factor of 1.29. In addition, for oblique optical incidence the electron-nuclei hyperfine interaction builds a nuclear spin polarization in presence of polarized electrons. This leads to the construction of an effective magnetic field, the Overhauser field, acting on the electronic spins. The Larmor frequency is then different for sigma+ or sigma- polarizations of the exciting light. The dependence of the phenomenon on the optical incidence allows the determination of the maximal Overhauser field, which is about 10mT, at least two orders of magnitude weaker than for III-V semiconductors. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.