Efficient dynamical nuclear polarization in quantum dots: Temperature dependence

We investigate in microphotoluminescence experiments dynamical nuclear polarization in individual InGaAs quantum dots. Experiments carried out in an applied magnetic field of 2 T show that the nuclear polarization achieved through the optical pumping of electron spins is increasing with the sample temperature between 2 and 55 K, reaching a maximum of about 50%. Analyzing the dependence of the Overhauser shift on the spin polarization of the optically injected electron as a function of temperature enables us to identify the main reasons for this increase.