A highly asymmetric dynamic nuclear spin pumping is observed in a single self assembled InGaAs quantum dot subject to resonant optical pumping of the neutral exciton transition leading to a large maximum polarization of 54%. This dynamic nuclear polarization is found to be much stronger following pumping of the higher energy Zeeman state. Time-resolved measurements allow us to directly monitor the buildup of the nuclear spin polarization in real time and to quantitatively study the dynamics of the process. A strong dependence of the observed dynamic nuclear polarization on the applied magnetic field is found, with resonances in the pumping efficiency being observed for particular magnetic fields. We develop a model that fully accounts for the observed behaviour, where the pumping of the nuclear spin system is due to hyperfine-mediated spin flip transitions between the states of the neutral exciton manifold.
@article{arxiv.1007.2145,
title = {Asymmetric optical nuclear spin pumping in a single uncharged quantum dot},
author = {F. Klotz and V. Jovanov and J. Kierig and E. C. Clark and M. Bichler and G. Abstreiter and M. S. Brandt and J. J. Finley and H. Schwager and G. Giedke},
journal= {arXiv preprint arXiv:1007.2145},
year = {2010}
}