Spectroscopic measurement of large exchange enhancement of a spin-polarized 2D electron gas

Exchange enhancements of the spin-polarized 2D electron gas are determined for the first time by inelastic light scattering from spin-flip inter-Landau-level and intersubband excitations. In the magnetic quantum limit ν=1 the splitting between long wavelength magnetoplasmons and spin-flip inter-Landau-level excitations is a direct spectroscopic measurement of the enhanced exchange energy. At ν=1 the enhancements in GaAs quantum wells are in agreement with the Hartree-Fock approximation.