Spin Polarization and g Factor of a Dilute GaAs Two-Dimensional Electron System

The effective g factor (g^*) of a dilute interacting two-dimensional electron system is expected to increase with respect to its bare value as the density is lowered, and to eventually diverge as the system makes a transition to a ferromagnetic state. We report here measurements of g^* in dilute (density 0.8 to 6.5×10¹⁰cm^-2), high-mobility GaAs two-dimensional electrons from their spin polarization in a parallel magnetic field. The data reveal a surprising trend. While g^* is indeed significantly enhanced with respect to the band g factor of GaAs, the enhancement factor decreases from about 6 to 3 as the density is reduced.