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 MOSFETs 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 that $H_{sat}=H_s$ to an accuracy of 5% for electron densities $n_s > 3 \times 10^{11}$ cm$^{-2}$.