Terahertz Dynamics of Excitons in GaAs/AlGaAs Quantum Wells

By monitoring changes in excitonic photoluminescence that are induced by far-infrared (FIR) radiation, we observed resonant FIR absorption by magnetoexcitons in GaAs/AlGaAs quantum wells. The dominant resonance is assigned to the $1s\to {2p}^{+}$ transition of the heavy-hole exciton, and agrees well with theory. At low FIR and interband excitation intensities, the $1s\to {2p}^{+}$ absorption feature is very narrow and broadens as either of these intensities is increased. The $1s\to {2p}^{+}$ absorption feature persists even when the FIR electric field is comparable to the electric field which binds the exciton.