Dynamical Magnetic and Nuclear Polarization in Complex Spin Systems: Semi-magnetic II-VI Quantum Dots

TL;DR

This paper investigates how optical excitation can induce and control magnetic and nuclear polarization in complex spin systems, specifically in quantum dots with magnetic impurities, through exact time-evolution calculations.

Contribution

It introduces a detailed theoretical framework for studying optically induced dynamical polarization in quantum dots with magnetic and nuclear spins, including exact calculations of spin transfer processes.

Findings

Magnetization of magnetic impurity builds up through exciton spin transfer.

Nuclear spin polarization occurs alongside impurity magnetization.

Dark excitons influence the competition between different spin transfer pathways.

Abstract

Dynamical magnetic and nuclear polarization in complex spin systems is discussed on the example of transfer of spin from exciton to the central spin of magnetic impurity in a quantum dot in the presence of a finite number of nuclear spins. The exciton is described in terms of the electron and heavy hole spins interacting via exchange interaction with magnetic impurity, via hypeprfine interaction with a finite number of nuclear spins and via dipole interaction with photons. The time-evolution of the exciton, magnetic impurity and nuclear spins is calculated exactly between quantum jumps corresponding to exciton radiative recombination. The collapse of the wavefunction and the refilling of the quantum dot with new spin polarized exciton is shown to lead to build up of magnetization of the magnetic impurity as well as nuclear spin polarization. The competition between electron spin transfer to magnetic impurity and to nuclear spins simultaneous with the creation of dark excitons is elucidated. The technique presented here opens up the possibility of studying optically induced Dynamical Magnetic and Nuclear Polarization in Complex Spin Systems.