COLLAPSE OF THE HARTREE TERM OF THE COULOMB INTERACTION IN A VERY DILUTE 2D ELECTRON-GAS

A novel many-body behavior of fundamental electron-electron interactio ns in very dilute 2D electron gases is revealed by inelastic light sca ttering in modulation-doped GaAs quantum wells. With increasing hydros tatic pressure the 2D electron density is continuously reduced down to values below 1 X 10(10) cm-2. A quantitative analysis of the energies of the elementary excitations of the electron gas shows the collapse of the Hartree term of the Coulomb interaction at densities of about 2 X 10(10) cm-2, which is attributed to a metal-nonmetal transition of the electronic system. Exchange and correlation effects, on the contra ry, remain significant even at very low carrier densities.