MULTIPLE RESONANCES INVOLVING MAGNETOEXCITONS IN A GAAS AL0.30GA0.70AS QUANTUM-WELL/

The excitonic states in an undoped GaAs/Al0.30Ga0.70As single quantum well have been studied by magnetophotoluminescence excitation spectros copy at T=4.2 K. A series of regularly spaced steplike features is obs erved in the magnetic field dispersions of the transition energies of the excited heavy-hole excitons nshh, n=2,3,4. Correspondingly, the sp litting between the two circular polarizations of the 2shh exciton sho ws pronounced oscillations as a function of magnetic field. We suggest that these features originate from the coupling of the transition bet ween the ground state 1shh exciton and each of the excited states of t he exciton with another excitation in the system. The energy differenc e between the features, which is about 7.5 meV, suggests that the exci tation may be a transverse acoustic phonon with nonzero wave number ne ar the zone boundary. [S0163-1829(98)01936-5].