  Resonant optical excitation of lowest-energy excitonic transitions in
self-assembled quantum dots lead to nuclear spin polarization that is
qualitatively different from the well known optical orientation phenomena. By
carrying out a comprehensive set of experiments, we demonstrate that nuclear
spin polarization manifests itself in quantum dots subjected to finite external
magnetic field as locking of the higher energy Zeeman transition to the driving
laser field, as well as the avoidance of the resonance condition for the lower
energy Zeeman branch. We interpret our findings on the basis of dynamic nuclear
spin polarization originating from non-collinear hyperfine interaction and find
an excellent agreement between the experimental results and the theoretical
model.

Mesoscale and Nanoscale Physics