Electron spin orientation under in-plane optical excitation in GaAs quantum wells

TL;DR

This study investigates how the orientation of electron spins in GaAs/AlGaAs quantum wells depends on the direction of optical excitation, revealing significant differences between in-plane and growth-direction excitation.

Contribution

It provides a detailed experimental and theoretical analysis of electron spin polarization under different optical excitation directions in quantum wells, highlighting the role of excitonic absorption and band coupling.

Findings

Negligible electron spin polarization for in-plane excitation at heavy-hole transition

Nearly 100% electron spin polarization for growth-direction excitation at heavy-hole transition

Theoretical model accurately explains experimental results considering Coulomb correlations and band coupling

Abstract

We study the optical orientation of electron spins in GaAs/AlGaAs quantum wells for excitation in the growth direction and for in-plane excitation. Time- and polarization-resolved photoluminescence excitation measurements show, for resonant excitation of the heavy-hole conduction band transition, a negligible degree of electron spin polarization for in-plane excitation and nearly 100% for excitation in the growth direction. For resonant excitation of the light-hole conduction band transition, the excited electron spin polarization has the same (opposite) direction for in-plane excitation (in the growth direction) as for excitation into the continuum. The experimental results are well explained by an accurate multiband theory of excitonic absorption taking fully into account electron-hole Coulomb correlations and heavy-hole light-hole coupling.