Theoretical study of nuclear spin polarization and depolarization in self-assembled quantum dots

We investigate how the strain-induced nuclear quadrupole interaction influences the degree of nuclear spin polarization driven by optical pumping in self-assembled quantum dots. Our calculation shows that the achievable nuclear spin polarization in InₓGa_1-xAs quantum dots is related to the concentration of indium and the resulting strain distribution in the dots. The interplay between the nuclear quadrupole interaction and Zeeman splitting leads to interesting features in the magnetic field dependence of the nuclear spin polarization. Our results are in qualitative agreement with measured nuclear spin polarization by various experimental groups.