# Large anisotropic spin relaxation time of exciton bound to donor states in triple quantum wells

## TL;DR

This study reveals a significant anisotropy in spin relaxation times for excitons bound to donors in triple quantum wells, influenced by internal magnetic fields and experimental conditions, advancing understanding of spin dynamics in semiconductor nanostructures.

## Contribution

It provides the first detailed measurement and modeling of anisotropic spin relaxation times in exciton-bound donor states in triple quantum wells, highlighting the role of internal magnetic fields.

## Key findings

- Spin relaxation time anisotropy up to a factor of 10.
- Internal magnetic field magnitude of a few millitesla.
- Dependence of anisotropy on temperature and optical power.

## Abstract

We have studied the spin dynamics of a dense two-dimensional electron gas confined in a GaAs/AlGaAs triple quantum well by using time-resolved Kerr rotation and resonant spin amplification. Strong anisotropy of the spin relaxation time up to a factor of 10 was found between the electron spins oriented in-plane and out-of-plane when the excitation energy is tuned to an exciton bound to neutral donor transition. We model this anisotropy using an internal magnetic field and the inhomogeneity of the electron g-factor. The data analysis allows us to determine the direction and magnitude of this internal field in the range of a few mT for our studied structure, which decreases with the sample temperature and optical power. The dependence of the anisotropic spin relaxation was directly measured as a function of several experimental parameters: excitation wavelength, sample temperature, pump-probe time delay, and pump power.