Localized excitons in quantum wells show spin relaxation without coherence loss

The coherence in the secondary emission from quantum well excitons is studied using the speckle method. Analysing the different polarization channels allows to conclude that (i) no coherence loss occurs in the cross-polarized emission, favouring spin beating instead of spin dephasing, and that (ii) the underlying interface disorder has a preferential orientation. The experimental results are successfully compared with a microscopic model of exciton disorder eigenstates including exchange splitting.