We report on spin quantum beats of excitonic kind in the time-resolved photoluminescence of quantum wells in a magnetic field. When this field is perpendicular to the growth direction, conditions for the manifestation of the electron or exciton spin precession in the circularly polarized components of the excitonic luminescence are obtained. These results lead to a direct measurement of the electron-hole exchange energy of the 2D exciton and give important insights into the exciton properties.

• Received 29 March 1996

DOI:https://doi.org/10.1103/PhysRevLett.78.1355