Exchange Enhancement of the Spin-gas of a Spin-polarized 2D Electron Gas Determined by Optical Absorption Spectroscopy

A large exchange enhancement of the spin-splitting of a two-dimensional electron gas has been determined from optical spectroscopy. Band gap transmission spectra of modulation-doped GaAs-(AlGa)As multiple quantum wells in high magnetic fields show a striking temperature dependence at filling factors near v = 1. When the Fermi energy is located between the spin-split electron states of the lowest Landau level, the temperature dependence of optical transitions to both spin levels monitors changes in the distribution function, yielding a direct measure of the occupation.