Magnetooptical studies of a single quantum dot:ffExcited states and spin flip of excitons

We report on microphotoluminescence experiments in magnetic fields on single quantum dots formed by width fluctuations in a narrow GaAs/${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As quantum well. The ground state as well as two excited states are discussed. We find a different diamagnetic shift and Zeeman spin splitting for these states. Resonantly exciting zero-dimensional excitons, we observe a strong magnetic-field dependence of the spin flip rates.