| The confinement of electrons on the nano-scale and the control of their spin is leading to both new physics and to novel devices with functionality at the quantum level. In III-V semiconductors where manipulation of a single electron spin has been possible in nano-structures, new challenges and opportunities arise due to the hyperfine interaction with the spin reservoir of lattice nuclei. In this work we show that by illuminating an InGaAs/GaAs self-assembled quantum dot with circularly polarized light, the nuclei of the tens of thousands of atoms constituting an InGaAs island can be driven into a bistable regime, in which either a threshold-like enhancement or reduction of the local nuclear field by up to 3 Tesla can be generated by varying the intensity of light. We show that such a nuclear spin "switch" can be controlled by both external magnetic and electric fields, thus offering the prospects for the accurate manipulation of nuclear spins on the nano-scale. The switch is shown to arise from the strong feedback of the nuclear spin polarization on the dynamics of spin transfer from electrons to the nuclei of the dot. |
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