Millisecond-range electron spin memory in singly-charged InP quantum dots

We report millisecond-range spin memory of resident electrons in an ensemble of InP quantum dots (QDs) under a small magnetic field of 0.1 T applied along the optical excitation axis at temperatures up to about 5 K. A pump-probe photoluminescence (PL) technique is used for optical orientation of electron spins by the pump pulses and for study of spin relaxation over the long time scale by measuring the degree of circular polarization of the probe PL as a function of pump-probe delay. Dependence of spin decay rate on magnetic field and temperature suggests two-phonon processes as the dominant spin relaxation mechanism in this QDs at low temperatures.