  The spin susceptibility of a two-dimensional electron system is calculated by
determining the spin-polarization dependence of the ground-state energy within
the self-consistent mean-field theory of Singwi et al. (STLS). Results are
presented for three different devices, viz. the Si (100) inversion layer, the
AlAs quantum well, and the GaAs heterojunction-insulated gate field-effect
transistor. We find a fairly good agreement with experiments for the Si (100)
system, on most of the experimental density range, whereas the agreement for
the AlAs and GaAs systems is less satisfactory; in all cases, however, it is
vital to include the characteristic device parameters like the valley
degeneracy, the finite transverse thickness, etc. Further, the STLS theory
predicts an abrupt spin-polarization transition at a sufficiently low electron
density irrespective of the valley degeneracy and/or the finite thickness, with
the partially spin-polarized states remaining unstable. Moreover, in the Si
(100) inversion layer, the spin-polarization transition is preceded by the
simultaneous valley- and spin- polarization; for its zero thickness model,
these transitions however grossly disagree with the recent quantum Monte Carlo
simulations. This drawback of the STLS theory is traced to its inaccuracy in
treating electron correlations, which in turn become more and more important as
the number of independent components (spin and valley) increases.
