  We develop a microscopic theory of spin relaxation of a two-dimensional
electron gas in quantum wells with anisotropic electron scattering. Both
precessional and collision-dominated regimes of spin dynamics are studied. It
is shown that, in quantum wells with noncentrosymmetric scatterers, the
in-plane and out-of-plane spin components are coupled: spin dephasing of
carriers initially polarized along the quantum well normal leads to the
emergence of an in-plane spin component even in the case of isotropic
spin-orbit splitting. In the collision-dominated regime, the
spin-relaxation-rate tensor is expressed in terms of the electric conductivity
tensor. We also study the effect of an in-plane and out-of-plane external
magnetic field on spin dephasing and show that the field dependence of electron
spin can be very intricate.
