Magnetoresistance of Si(001) MOSFETs with high concentration of electrons

We present an experimental study of electron transport in inversion layers of high-mobility Si(001) samples with occupied excited subbands. The second series of oscillations, observed in addition to the main series of Shubnikov-de Hass oscillations, is tentatively attributed to the occupation of a subband associated with the $E_{0'}$ level. Besides, a strong negative magnetoresistance and nonlinear field dependence of the Hall resistance accompany the novel oscillations at high carrier concentrations. The heating of the 2D electron layers leads to suppression of the observed anomalies.