Electrical initialization of electron and nuclear spins in a single quantum dot at zero magnetic field

We demonstrate single quantum dot (p-type InGaAs quantum dot) electroluminescence (EL) with a circular polarization degree up to 35% at zero applied magnetic field, proving highly efficient electrical injection of spin polarized electrons [1]. It is achieved thanks to an ultrathin CoFeB electrode presenting Perpendicular Magnetic Anisotropy on top of a spin-LED. In addition, we measure an Overhauser shift of several micro-eV at zero magnetic field for the positively charged exciton (trion X+) EL emission, which changes sign as we reverse the injected electron spin orientation. This is a signature of dynamic polarization of the nuclear spins [1] in the quantum dot induced by the hyperfine interaction with the electrically injected electron spin. Both EL circular polarization and Overhauser shift follow the hysteresis cycle of the magnetic electrode. This study paves the way for electrical initialization of electron and nuclear spins in a single quantum dot without any external magnetic field. [1] F. Cadiz et al, Nano Letters 18 (4), 2381-2386 (2018)