Spin polarization of two-dimensional electrons determined from Shubnikov-de Haas oscillations as a function of angle

Recent experiments in the two-dimensional electron systems in silicon metal-oxide-semiconductor field effect transistors have shown that the in-plane magnetic field H-sat required to saturate the conductivity to its high-field value, and the magnetic field H-s needed to completely align the spins of the electrons, are comparable. By small-angle Shubnikov-de Haas oscillation measurements that allow separate determinations of the spin-up and spin-down subband populations, we show to an accuracy 5% that H-sat H-s.