Pure dephasing induced by exciton-phonon interactions in GaAs quantum dots

Using three-pulse transient four-wave mixing (FWM), exciton dephasing in quantum dot-like islands in narrow GaAs quantum wells (QW) was compared with population decay rates. Results reveal a pure dephasing process which dominates excitonic dephasing at elevated temperatures but does not involve exciton population relaxation. The pure dephasing process arises from a mixing of excitonic states with a continuum of acoustic phonons and is enhanced by three-dimensional quantum confinement. The magnitude and temperature dependence of the pure dephasing rate is described by a theoretical model which generalizes the Huang-Rhys theory of F centers to include off-diagonal exciton-phonon coupling.