Signatures of spin blockade in the optical response of a charged quantum dot

We model spin blockade for optically excited electrons and holes in a charged semiconductor quantum dot. We study the case where the quantum dot is initially charged with a single electron and is then filled with an additional, optically excited electron-hole pair, thus forming a charged exciton (trion). To make contact with recent experiments, we model an optical pump-probe setup, in which the two lowest quantum dot levels (s and p shells) are photo excited. Using the Lindblad master equation, we calculate the differential transmission spectrum as a function of the pump-probe time delay. Taking into account both spin conserving and spin-flip intraband relaxation processes, we find that the presence of the ground-state electron spin leads to an optical spin blockade at short delay times which is visible as a crossover between two exponential decays of the differential transmission. To make predictions for future experiments, we also study the dependence of the spin-blockade on an external magnetic field.