Small-angle Shubnikov-de Haas measurements in a 2D electron system: The effect of a strong in-plane magnetic field

Measurements in magnetic fields applied at small angles relative Lo the electron plane in silicon MOS-FETs indicate a factor of 2 increase of the frequency of Shubnikov-de Haas oscillations ar N > H-sat. This signals the onset of full spin polarization above N-sat, the parallel field above which the resistivity saturates to a constant value. For N < N-sat, the phase of the second harmonic of the oscillations relative to the first is consistent with scattering events that depend on the overlap instead of thr sum of the spin-up and spin-down densities of stares. This unusual behavior may reflect the importance of many-body interactions.