Electron Spin Dynamics and Hyperfine Interactions in Fe/Al_0.1Ga_0.9As/GaAs Spin Injection Heterostructures

TL;DR

This study investigates hyperfine interactions and nuclear spin polarization effects on electron spin dynamics in Fe/AlGaAs/GaAs heterostructures, revealing electrically driven NMR at low magnetic fields.

Contribution

It provides the first detailed analysis of electrically induced nuclear magnetic resonance and hyperfine interactions in spin injection heterostructures.

Findings

Nuclear polarization depends strongly on electron spin polarization.

Electrically modulated NMR observed at low magnetic fields.

Electron spin dynamics are influenced by polarized nuclei via hyperfine interactions.

Abstract

We have studied hyperfine interactions between spin-polarized electrons and lattice nuclei in Al_0.1Ga_0.9As/GaAs quantum well (QW) heterostructures. The spin-polarized electrons are electrically injected into the semiconductor heterostructure from a metallic ferromagnet across a Schottky tunnel barrier. The spin-polarized electron current dynamically polarizes the nuclei in the QW, and the polarized nuclei in turn alter the electron spin dynamics. The steady-state electron spin is detected via the circular polarization of the emitted electroluminescence. The nuclear polarization and electron spin dynamics are accurately modeled using the formalism of optical orientation in GaAs. The nuclear spin polarization in the QW is found to depend strongly on the electron spin polarization in the QW, but only weakly on the electron density in the QW. We are able to observe nuclear magnetic resonance (NMR) at low applied magnetic fields on the order of a few hundred Oe by electrically modulating the spin injected into the QW. The electrically driven NMR demonstrates explicitly the existence of a Knight field felt by the nuclei due to the electron spin.