Direct Observation of the Electron Spin Relaxation Induced by Nuclei in Quantum Dots

Abstract

We have studied the electron spin relaxation in semiconductor $\mathrm{InAs}/\mathrm{GaAs}$ quantum dots by time-resolved optical spectroscopy. The average spin polarization of the electrons in an ensemble of $p$-doped quantum dots decays down to $1/3$ of its initial value with a characteristic time $T_{\Delta }\approx 500\mathrm{ps}$, which is attributed to the hyperfine interaction with randomly oriented nuclear spins. We show that this efficient electron spin relaxation mechanism can be suppressed by an external magnetic field as small as 100 mT.