Ultrafast Spin Dynamics in Optically Excited Bulk GaAs at Low Temperatures

TL;DR

This study investigates ultrafast electron spin dynamics in optically excited bulk GaAs at low temperatures, revealing how excitation conditions and doping influence spin dephasing times and mechanisms.

Contribution

It provides a comprehensive experimental and theoretical analysis of spin dephasing, including the breakdown of motional narrowing and the effects of screening and scattering.

Findings

Sub-nanosecond spin dephasing times observed across doping levels

Breakdown of motional narrowing under high excitation

Peak spin dephasing time linked to screening and scattering effects

Abstract

This paper presents a study of electron spin dynamics in bulk GaAs at low temperatures for elevated optical excitation conditions. Our time-resolved Faraday rotation measurements yield sub-nanosecond electron spin dephasing-times over a wide range of n-doping concentrations in quantitative agreement with a microscopic treatment of electron spin dynamics. The calculation shows the occurrence and breakdown of motional narrowing for spin dephasing under elevated excitation conditions. We also find a peak of the spin dephasing time around a doping density for which, under lower excitation conditions, a metal-insulator transition occurs. However, the experimental results for high excitation can be explained without a metal-insulator transition. We therefore attribute the peak in spin-dephasing times to the influence of screening and scattering on the spin-dynamics of the excited electrons.