Bistability of the Nuclear Polarisation created through optical pumping in InGaAs Quantum Dots

TL;DR

This paper demonstrates that optical pumping in InGaAs quantum dots induces significant nuclear polarization with bistable behavior, depending on magnetic field and electron spin polarization, explained by a simple theoretical model.

Contribution

It reveals the bistability of nuclear polarization in quantum dots under optical pumping and provides a qualitative model to understand this phenomenon.

Findings

Maximum nuclear polarization of 40% at intermediate magnetic fields

Bistability observed in the Overhauser shift dependence

Nuclear fields are larger when anti-parallel to the external magnetic field

Abstract

We show that optical pumping of electron spins in individual InGaAs quantum dots leads to strong nuclear polarisation that we measure via the Overhauser shift (OHS) in magneto-photoluminescence experiments between 0 and 4T. We find a strongly non-monotonous dependence of the OHS on the applied magnetic field, with a maximum nuclear polarisation of 40% for intermediate magnetic fields. We observe that the OHS is larger for nuclear fields anti-parallel to the external field than in the parallel configuration. A bistability in the dependence of the OHS on the spin polarization of the optically injected electrons is found. All our findings are qualitatively understood with a model based on a simple perturbative approach.