Spin dynamics of quadrupole nuclei in InGaAs quantum dots

Photoluminescence polarization is experimentally studied for samples with (In,Ga)As/GaAs self-assembled quantum dots in transverse magnetic field (Hanle effect) under slow modulation of the excitation light polarization from fractions of Hz to tens of kHz. The polarization reflects the evolution of strongly coupled electron-nuclear spin systems in the quantum dots. Strong modification of the Hanle curves under variation of the modulation period is attributed to the peculiarities of the spin dynamics of quadrupole nuclei, which states are split due to deformation of the crystal lattice in the quantum dots. Analysis of the Hanle curves is fulfilled in the framework of a phenomenological model considering a separate dynamics of a nuclear field BNd determined by polarization of the ±1/2 nuclear spin states and of a nuclear field BNq determined by polarization of the split-off states ±3/2, ±5/2, etc. It is found that the characteristic relaxation time for the nuclear field BNd is of order a fraction of a second, while the relaxation of the field BNq is faster by about two orders of magnitude.