Role of finite layer thickness in spin polarization of GaAs two-dimensional electrons in strong parallel magnetic fields

We report measurements and calculations of the spin polarization, induced by a parallel magnetic field, of interacting, dilute, two-dimensional electron systems confined to GaAs/AlGaAs heterostructures. The results reveal the crucial role the non-zero electron layer thickness plays: it causes a deformation of the energy surface in the presence of a parallel field, leading to enhanced values for the effective mass and g factor, and a nonlinear spin polarization with field.