Polarization memory in single Quantum Dots

TL;DR

This study investigates the polarization memory effects in single quantum dots, revealing how electron spins are preserved while hole spins dephase during optical transitions, supported by experimental measurements and a comprehensive model.

Contribution

It introduces a model explaining polarization spectra in quantum dots, highlighting differential spin preservation between electrons and holes during relaxation.

Findings

Electrons retain significant spin polarization during relaxation.

Holes undergo complete dephasing, losing initial spin orientation.

The model accurately predicts polarization spectra across different charge states.

Abstract

We measured the polarization memory of excitonic and biexcitonic optical transitions from single quantum dots at either positive, negative or neutral charge states. Positive, negative and no circular or linear polarization memory was observed for various spectral lines, under the same quasi-resonant excitation below the wetting layer band-gap. We developed a model which explains both qualitatively and quantitatively the experimentally measured polarization spectrum for all these optical transitions. We consider quite generally the loss of spin orientation of the photogenerated electron-hole pair during their relaxation towards the many-carrier ground states. Our analysis unambiguously demonstrates that while electrons maintain their initial spin polarization to a large degree, holes completely dephase.