Theory of exciton doublet structures and polarization relaxation in singlequantum dots

The mechanism of exciton doublet structures in quantum dots is identified a s the long-range part of the electron-hole exchange interaction which is em phasized by the anisotropic shape of quantum dots. The physical origin of t he energetic order of the orthogonally polarized exciton states of each dou blet is clarified by inspecting the spatial distribution of the exciton pol arization. The key concepts to understand the energetic order are the node configuration of the distribution function of exciton polarization and the dipole-dipole interaction energy originating from the long-range electron-h ole exchange interaction. The population relaxation and the polarization re laxation of excitons are studied and the extremely slow polarization relaxa tion within exciton doublet states is predicted. It is also found that the inter-doublet cross-relaxation between orthogonally polarized exciton state s occurs as efficiently as the population relaxation.