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 interactions in very dilute 2D electron gases is revealed by inelastic light scattering in modulation-doped GaAs quantum wells. With increasing hydrostatic pressure the 2D electron density is continuously reduced down to values below 1×{}10¹⁰ 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×{}10¹⁰ cm^-2, which is attributed to a metal-non-metal transition of the electronic system. Exchange and correlation effects, on the contrary, remain significant even at very low carrier densities.