Exciton spin coherence and electromagnetically induced transparency in the transient optical response of GaAs quantum wells

We report experimental studies of electromagnetically induced transparency (EIT) arising from exciton spin coherence in the transient optical response of GaAs quantum wells. The exciton spin coherence, which is a direct result of Coulomb correlations between excitons with opposite spins, is induced via bound or unbound two-exciton states. Theoretical analyses based on a three-level model illustrate the manifestation of EIT in a transient regime and provide qualitative guidance for understanding the transient behaviors observed in the EIT experiments. Additional studies of the effects of exciton energy renormalization on optical Stark splitting also provide insights on how exciton many-body interactions can lead to unusual time-dependent asymmetric EIT line shapes.