Spin and symmetry in optical studies of individual semiconductor quantum dots

Abstract

The talk summarizes results of our recent optical studies related to spin states in II-VI and III-V semiconductor quantum dot (QD) systems. First the influence of in-plane anisotropy on the QD excitonic spin states is recalled. Then various ways of circumventing, compensating, or exploiting this influence are discussed. Short lifetime of neutral excitons (governed by inter-dot tunneling) allowed us to transfer their spin polarization to another QD before its destruction by the anisotropic exchange interaction. This spin polarization, as well as single carrier spin memory effects in quantum dots are demonstrated using trion states, negligibly perturbed by the anisotropy. Modification of the anisotropy by external perturbations (electric and magnetic field) is shown. In particular, full compensation of the anisotropy by in-plane electric field is demonstrated using optical orientation of neutral excitons. Finally, the influence of the anisotropy will be exploited to achieve circular-to-linear and linear-to-circular polarization conversion in single QDs and in coupled QD pairs.