The effective mass and the g -factor of the strongly correlated 2D electron fluid. Evidence for a coupled-valley state in the Si system

The effective mass m *, and the Landé g -factor of the uniform 2D electron system (2DES) are calculated as a function of the spin polarization ζ, and the density parameter r s , using a non-perturbative analytic approach. Our theory is in good accord with the susceptibility data for the simple 2DES, and in excellent agreement with the two-valley Si-2DES data of Shashkin et al. While g * is enhanced in GaAs, m * is enhanced in Si. The two-valley susceptibility is treated within a coupled-mode (coupled-valley) approach. The coupled-valley model is confirmed by comparison with the Quantum Monte Carlo results for a 4-component 2DES.