Electron-spin quantum-beat dephasing in quantum wells as a probe of the hole band structure

Time-resolved optical pumping experiments under transverse magnetic field at oblique incidence with respect to the growth axis have been performed on various quantum-well (QW) structures. When the incident photon energy is nonresonant with the heavy-hole exciton, the electron-spin quantum beats, which manifest the electron-spin Larmor precession, dephase with respect to the normal-incidence case. We show that the direction of the electron-spin precession can be deduced, which provides a method to determine unambiguously the sign of the conduction-electron g factor. Moreover, the amplitude of the dephasing is very sensitive to the mixing of the heavy- and light-hole states in the valence bands that are involved in optical transitions at a given photon energy. A theory of optical pumping of QWs under arbitrary incidence, based on the valence-band description in the effective-mass approximation, has been developed. It accounts quite well for the experimental observations.