Electric field dependence of the spin relaxation anisotropy in (111) GaAs/AlGaAs quantum wells

Abstract

Time-resolved optical spectroscopy experiments in (111)-oriented GaAs/AlGaAs quantum wells (QWs) show a strong electric field dependence of the conduction electron spin relaxation anisotropy. This results from the interplay between the Dresselhaus and Rashba spin splitting in this system with C _3v symmetry. By varying the electric field applied perpendicular to the QW plane from 20 to 50 kV cm ^−1 the anisotropy of the spin relaxation time parallel ( τ ^s _∥ ) and perpendicular ( τ ^s _⊥ ) to the growth axis can be first canceled and eventually inversed with respect to the one usually observed in III–V zinc-blende QW ( τ ^s _⊥ = 2 τ ^s _∥ ). This dependence stems from the nonlinear contributions of the k -dependent conduction band spin splitting terms which begin to play the dominant spin relaxing role while the linear Dresselhaus terms are compensated by the Rashba ones through the applied bias. A spin density matrix model for the conduction band spin splitting including both linear and cubic terms of the Dresselhaus Hamiltonian is used which allows a quantitative description of the measured electric field dependence of the spin relaxation anisotropy. The existence of an isotropic point where the spin relaxation tensor reduces to a scalar is predicted and confirmed experimentally. The spin splitting compensation electric field and collision processes type in the QW can be likewise directly extracted from the model without complementary measurements.