Nonlinear magneto-optical properties of Wannier excitons in GaAs are studied at 4 K using four-photon nearly degenerate parametric coupling. The results show a large enhancement in the nonlinear optical response related to a field-induced decrease in exciton mobility due to magnetic freezeout. High-resolution cw nonlinear spectroscopy is used to measure the relative strength of inter-Landau-level coupling and shows that the nonlinearity is dominated by Coulomb effects.

• Received 21 September 1993

DOI:https://doi.org/10.1103/PhysRevB.48.15476