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

TL;DR

This study explores how exchange interactions influence dynamic nuclear polarization in Mn-doped InGaAs/GaAs quantum dots, revealing complex behaviors driven by electron-nucleus spin interactions under magnetic fields.

Contribution

It provides new insights into the role of exchange interactions in DNP processes within Mn-doped quantum dots, highlighting phenomena like multiple DNP sequences at different magnetic fields.

Findings

Efficient optical spin orientation in Mn-doped quantum dots.

Observation of DNP growth and abrupt vanishing at critical magnetic fields.

Multiple DNP sequences indicating complex exchange interactions.

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 circularly-polarized excitation. For the electron spin levels which are made quasi-degenerate by a magnetic field compensating the exchange interaction $\Delta_e$ 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.