Non-Markovian dephasing of excitons in GaAs quantum wells

We measured time-resolved photon echo signals by using the heterodyne detection technique on GaAs multiple quantum wells. Oscillation structure with a period of about 0.8 ps is observed when the time interval (delay time) of two pulses which generate the photon echo signal is shorter than 0.4 ps. The oscillating structure disappears when the delay time is longer than 0.6 ps. Temperature and excitation density dependence indicate that the origin of this oscillation is the interaction between a normal exciton and an exciton coupled with a specific acoustic phonon mode which is identified by calculating the Rytov model.