We report the experimental observation of a transient oscillatory behavior of magnetoexciton absorption in GaAs/AlGaAs heterostructures. We interpret these oscillations as absorption quantum beats of a coherent superposition of two excitonic spin states. Measurements of the oscillations period may be used as a new technique for accurately measuring the Landé g factor of excitons in semiconductors.

• Received 24 January 1991

DOI:https://doi.org/10.1103/PhysRevLett.66.2491