Exchange enhancement of the spin gap of a spin-polarized 2D electron gas determined by optical absorption spectroscopy

Abstract

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 ν = 1. When the Fermi energy is located between the spin split electron slates 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. Knowledge of the temperature-dependent occupations of the spin-up (0 +) and spin-down (0 −) electron levels leads to a thermodynamic measure of the spin splitting energy and exchange enhancement. Analysis of the temperature dependence reveals an exchange enhancement of the electron g-factor of ~ 9.