Electron charge and spin delocalization revealed in the optically probed longitudinal and transverse spin dynamics in $n$-GaAs

TL;DR

This study uses advanced optical spectroscopy to explore how electron charge and spin behavior in n-GaAs change from localized to delocalized states, revealing key differences in spin relaxation and dephasing.

Contribution

It demonstrates the impact of electron delocalization on spin dynamics and uncovers a novel relation between transverse dephasing time and longitudinal relaxation time in n-GaAs.

Findings

Increased $T_2^*$ with delocalization due to motional narrowing

Difference in spin relaxation rates between localized and metallic phases

Constant product of $T_2^*$ and $T_1$ explained by spin diffusion effects

Abstract

The evolution of the electron spin dynamics as consequence of carrier delocalization in $n$-type GaAs is investigated by the recently developed extended pump-probe Kerr/Faraday rotation spectroscopy. We find that isolated electrons localized on donors demonstrate a prominent difference between the longitudinal and transverse spin relaxation rates in magnetic field, which is almost absent in the metallic phase. The inhomogeneous transverse dephasing time $T_2^*$ of the spin ensemble strongly increases upon electron delocalization as a result of motional narrowing that can be induced by increasing either the donor concentration or the temperature. An unexpected relation between $T_2^*$ and the longitudinal spin relaxation time $T_1$ is found, namely that their product is about constant, as explained by the magnetic field effect on the spin diffusion. We observe a two-stage longitudinal spin relaxation which suggests the establishment of spin temperature in the system of exchange-coupled donor-bound electrons.