Role of hyperfine interaction on electron spin optical orientation in charge-controlled InAs-GaAs single quantum dots

We report on electron spin physics in a single charge-tunable self-assembled InAs/GaAs quantum dot. The hyperfine interaction between the optically oriented electron and nuclear spins leads to the polarization of the quantum dot nuclei. The sign of the resulting Overhauser-shift depends on the trion state X+ or X, and remarkably its strength does not vanish in zero magnetic field. This explains the quenching of X+ spin relaxation under steady-state excitation polarization. (c) 2007 WILEYNCH Verlag GmbH & Co. KGaA, Weinheim.