Low-Field Optical Polarization in Type-II Quantum Dots via Nuclear-Driven Dark State Mixing

TL;DR

This paper explores how weak magnetic fields can control light polarization in type-II quantum dots, offering a new approach for creating compact sources of circularly polarized light.

Contribution

The study introduces low-field optical polarization in type-II quantum dots via nuclear-driven dark state mixing.

Findings

Low magnetic fields as low as 0.17 T enable optical polarization in type-II In(Ga)As/GaAsSb QDs.

Nuclear spin interactions mediate in-plane electron spin precession, confirmed by polarization recovery measurements.

A theoretical model accurately reproduces the observed mirror-symmetric luminescence helicity.

Abstract

Semiconductor quantum dots (QDs) offer a rich landscape
for spin
control and quantum light emission. While most studies have focused
on type-I band alignment, the potential of type-II systems remains
underexplored. Here, we report low-field optical polarization in type-II
In­(Ga)­As/GaAsSb QDs, enabled by hyperfine-induced mixing between bright
and dark excitons via level anticrossing under magnetic fields as
low as 0.17 T. The weak-field regime arises from the suppressed wave
function overlap, yielding a reduced electron–hole exchange
interaction. A theoretical model based on the spin Hamiltonian and
the spin-split state populations accurately captures the observed
mirror-symmetric luminescence helicity, reproducing the experimental
polarization response. Additionally, polarization recovery measurements
confirm the role of nuclear spin interactions in mediating the in-plane
electron spin precession. Our work demonstrates an alternative route
for light polarization control using weak magnetic fields and nonresonant
linear excitation, establishing type-II QDs as promising platforms
for compact sources of circularly polarized light.

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