We report on the dynamic nuclear polarization of a single charge-tunable self-assembled $\mathrm{InAs}∕\mathrm{GaAs}$ quantum dot in a longitudinal magnetic field of $\sim 0.2\mathrm{T}$. The hyperfine interaction between the optically oriented electron and nuclear spins leads to the polarization of the quantum dot nuclei measured by the Overhauser shift of the singly charged excitons ($X^{+}$ and $X^{-}$). When going from $X^{+}$ to $X^{-}$, we observe a reversal of this shift, which reflects the average electron spin optically written in the quantum dot either in the $X^{+}$ state or in the final state of $X^{-}$ recombination. We discuss a theoretical model which indicates an efficient depolarization mechanism for the nuclei limiting their polarization to $\sim 10\%$.

• Received 12 July 2005

DOI:https://doi.org/10.1103/PhysRevB.74.081306