Exchange interaction-driven dynamic nuclear polarization in Mn-doped InGaAs/GaAs quantum dots

Abstract

We investigated optical spin orientation and dynamic nuclear polarization (DNP) in individual self-assembled InGaAs/GaAs quantum dots (QDs) doped by a single Mn atom, a magnetic impurity providing a neutral acceptor A 0 with an effective spin J = 1. We find that the spin of an electron photo-created in such a quantum dot can be efficiently oriented by a quasi-resonant circularlypolarized excitation. For the electron spin levels which are made quasi-degenerate by a magnetic field compensating the exchange interaction ∆e with A 0 , there is however a full depolarization due the anisotropic part of the exchange. Still, in most studied QDs, the spin polarized photo-electrons give rise to a pronounced DNP which grows with a longitudinal magnetic field until a critical field where it abruptly vanishes. For some QDs, several replica of such DNP sequence are observed at different magnetic fields. This striking behavior is qualitatively discussed as a consequence of different exchange interactions experienced by the electron, driving the DNP rate via the energy cost of electron-nucleus spin flip-flops.

Readout of a dopant spin in the anisotropic quantum dot with a single magnetic ion

“…As we show, the simple picture is invalidated by the interplay between optical orientation of the exciton and the non-trivial dependence of the TM ion spin on the selection rules in anisotropic quantum dots. Our considerations will be showcased using a particular system of a CdSe/ZnSe QD with single Fe 2+ ion [14], but the same reasoning should be valid also for all other known systems of that kind [20][21][22].…”