Optical probing of spin dynamics of two-dimensional and bulk electrons in a GaAs/AlGaAs heterojunction system

TL;DR

This study uses time-resolved Kerr rotation to investigate spin dynamics of electrons in different layers of a GaAs/AlGaAs heterojunction, revealing layer-specific behaviors and the effects of pumping intensity and temperature.

Contribution

It introduces a method to distinguish electron spin populations in layered heterostructures based on their g-factors and dynamic responses, enhancing understanding of spin behavior in complex systems.

Findings

Different electron populations have distinct g-factors.

High pump intensities allow separation of signals from different layers.

Spin dynamics vary with temperature and layer type.

Abstract

We present time-resolved Kerr rotation measurements of electron spin dynamics in a GaAs/AlGaAs heterojunction system that contains a high-mobility two-dimensional electron gas (2DEG). Due to the complex layer structure of this material the Kerr rotation signals contain information from electron spins in three different layers: the 2DEG layer, a GaAs epilayer in the heterostructure, and the underlying GaAs substrate. The 2DEG electrons can be observed at low pump intensities, using that they have a less negative g-factor than electrons in bulk GaAs regions. At high pump intensities, the Kerr signals from the GaAs epilayer and the substrate can be distinguished when using a barrier between the two layers that blocks intermixing of the two electron populations. This allows for stronger pumping of the epilayer, which results in a shift of the effective g-factor. Thus, three populations can be distinguished using differences in g-factor. We support this interpretation by studying how the spin dynamics of each population has its unique dependence on temperature, and how they correlate with time-resolved reflectance signals.