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

TL;DR

This paper models spin blockade effects in the optical response of a charged quantum dot, revealing how electron spin influences the differential transmission spectrum in pump-probe experiments and how magnetic fields affect this phenomenon.

Contribution

It introduces a detailed theoretical model of spin blockade in charged quantum dots using the Lindblad master equation, including spin relaxation effects and magnetic field dependence.

Findings

Spin blockade causes a crossover in exponential decay of differential transmission.

External magnetic fields modulate the spin blockade effect.

The model aligns with recent experimental observations.

Abstract

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.