Optical Studies of the 2D Electron Gas in GaAs in High Magnetic Fields

We report optical emission and absorption spectra of modulation- doped GaAs multiple quantum wells to fields of 30T and temperatures >= 0.35K. Two regions are studied in detail. First, in the region of fractional filling factor nu = 2/3, we observe an unusual temperature dependence in the emission spectra associated with the many-body condensed state of the 2D e electron gas. Second, at integer filling factors, large changes in the emission and absorption spectra are seen, even at nu = 1 where new features appear as the lowest spin state begins to become unoccupied.