Spin injection into a single self-assembled quantum dot

We demonstrate spin injection into a single self-assembled CdSe/ZnSe quantum dot using a semimagnetic BeMnZnSe spin aligner. Comparing quasiresonant excitation of the single quantum dot to excitation above the spin-aligner band gap, spin injection is evidenced by a strong increase of the polarization degree of the single quantum dot photoluminescence emission even at small magnetic fields. A spin injection efficiency into a single quantum dot of about 70% can be estimated. From a detailed analysis of the polarization degree, we derive an exciton spin-relaxation time from the upper to the lower Zeeman level of about a nanosecond in the quantum dot, independent of magnetic field.