The spin state of holes bound to Mn acceptors in GaMnAs is investigated by optical spectroscopy. Concentrations of Mn from 10<sup>17</sup> to 10<sup>19</sup> cm<sup>-3</sup> were studied as a function of magnetic field and temperature. The photoluminescence from recombination of electrons with holes bound in the Mn-acceptor complex (MAC) displays multiple spectral peaks. The circular polarization of these peaks increases with increasing magnetic field and saturates at ρ ≈ 1/3. This value of polarization is expected from modeling the addition of spin angular momentum and interband optical transition matrix elements.
We present a review of our recent resonant inelastic light scattering research of the ultra-high
mobility two-dimensional electron gas in GaAs quantum wells. Spectroscopy of intersubband
excitations shows that exchange interactions are larger than previously anticipated. Light scattering
by large wavevector inter-Landau-level excitations displays the excitonic binding and roton minima
in the mode dispersions that are predicted by Hartree-Fock theories.