Nuclear spin polarization in single self-assembled In0.3Ga0.7As quantum dots by electrical spin injection

Abstract

For a single In${}_{0.3}$Ga${}_{0.7}$As quantum dot in a spin light-emitting diode, we compare the nuclear spin polarization created by a spin polarized electrical current with the nuclear spin polarization originating from optically generated spin polarized carriers. As detection method we employ high-resolution optical spectroscopy of the Overhauser shift. We find that optically and electrically generated electron spin populations in the quantum dot result in a nuclear spin polarization of comparable magnitude, provided the injected electrons have the same spin polarization degree in both excitation modes. An asymmetric dependence of nuclear spin polarization on electron spin polarization is observed, consistent with the theoretical treatment. The results imply that nuclear spin polarization degrees of $\ensuremath{\sim}$58% can be achieved by purely electrical means in self-assembled quantum dots.