Enhancement of coherent LO phonons by quantum beats of excitons in GaAs/AlAs multiple quantum wells

We have investigated the dynamical properties of the coherent GaAs-like longitudinal optical (LO) phonon and the quantum beat of excitons in GaAs/AlAs multiple quantum wells with different splitting energies of the heavy-hole and light-hole excitons by using a reflection-type pump–probe technique. It has been found that the coherent GaAs-like LO phonon in the multiple quantum well is remarkably enhanced as the splitting energy approaches to the LO phonon energy of GaAs. The pump-energy dependence of the intensity of the coherent GaAs-like LO phonon is similar to that of the excitonic quantum beat in the multiple quantum wells with the splitting energy nearly equal to the LO phonon energy of GaAs. We conclude that the enhancement of the coherent LO phonon is induced by the coupling of the excitonic quantum beat with the coherent GaAs-like LO phonon through the longitudinal polarization.