Overhauser effect in individual InP/GaInP dots

TL;DR

This study demonstrates significant nuclear spin polarization in individual InP/GaInP quantum dots induced by optical pumping, revealing feedback effects, bi-stability, and unusual Zeeman energy behavior due to the Overhauser field.

Contribution

It provides the first detailed observation of nuclear spin bi-stability and Overhauser effects in individual InP/GaInP quantum dots under varying magnetic fields.

Findings

Nuclear polarization up to 40% at 1.5T

Observation of nuclear spin bi-stability at low fields

Counter-intuitive increase in exciton Zeeman energy when Overhauser field cancels external field

Abstract

Sizable nuclear spin polarization is pumped in individual InP/GaInP dots in a wide range of external magnetic fields B_ext=0-5T by circularly polarized optical excitation. We observe nuclear polarization of up to ~40% at Bext=1.5T and corresponding to an Overhauser field of ~1.2T. We find a strong feedback of the nuclear spin on the spin pumping efficiency. This feedback, produced by the Overhauser field, leads to nuclear spin bi-stability at low magnetic fields of Bext=0.5-1.5T. We find that the exciton Zeeman energy increases markedly, when the Overhauser field cancels the external field. This counter-intuitive result is shown to arise from the opposite contribution of the electron and hole Zeeman splittings to the total exciton Zeeman energy.