Shielding of external magnetic field by dynamic nuclear polarization in (In,Ga)As quantum dots

TL;DR

This study demonstrates how dynamic nuclear polarization in (In,Ga)As quantum dots can effectively shield electrons from external magnetic fields, enabling control of internal magnetic environments through optical excitation and magnetic field tuning.

Contribution

It introduces a method to manipulate nuclear polarization and magnetic shielding in quantum dots using periodic optical excitation and magnetic field detuning.

Findings

Nuclear polarization can shield electrons from magnetic fields up to 1.3 T.

Electron spins can be locked into magnetic resonance via high-frequency optical excitation.

A model links nuclear polarization to magnetic field-dependent polarization rates.

Abstract

The dynamics of the coupled electron-nuclear spin system is studied in an ensemble of singly-charged (In,Ga)As/GaAs quantum dots (QDs) using periodic optical excitation at 1 GHz repetition rate. In combination with the electron-nuclei interaction, the highly repetitive excitation allows us to lock the electron spins into magnetic resonance in a transverse external magnetic field. Sweeping the field to higher values, the locking leads to an effective "diamagnetic" response of significant strength due to dynamic nuclear polarization, which shields the QD electrons at least partly from the external field and can even keep the internal magnetic field constant up to 1.3 T field variation. We model the effect through a magnetic field-dependent polarization rate of the nuclei, from which we suggest a strategy for adjusting the nuclear polarization through the detuning between optical excitation and electronic transition, in addition to tuning the magnetic field.