  Two phenomena have been recently observed in high-mobility Si MOS structures:
(1) strong enhancement of the metallic conduction at low temperatures, T < 2K,
and (2) the scaling behavior of the temperature and electric field dependences
of the resistivity. These results evidence for the true metal-insulator
transition in 2d, in apparent disagreement with the one-parameter scaling
theory. Here we present a model that explains both effects in the framework of
the spin-orbit interaction and provides a quantitative agreement with the
experimental data.
