Experimental analysis of the spin-orbit coupling dependence on the drift velocity of a spin packet

TL;DR

This study investigates how spin-orbit interactions in a two-dimensional electron gas depend on drift velocity, revealing velocity-dependent changes in spin-orbit coupling that impact spin transistor operation.

Contribution

It provides the first experimental analysis of the velocity dependence of spin-orbit fields in a 2D electron gas under drift conditions.

Findings

Cubic Dresselhaus term increases significantly with velocity.

Rashba coupling decreases as drift velocity increases.

High spin mobility and long spin lifetimes observed.

Abstract

Spin transport was studied in a two-dimensional electron gas hosted in a wide GaAs quantum well occupying two subbands. Using space and time Kerr rotation microscopy to image drifting spin packets under an in-plane accelerating electric field, optical injection and detection of spin polarization were achieved in a pump-probe configuration. The experimental data exhibited high spin mobility and long spin lifetimes allowing to obtain the spin-orbit fields as a function of the spin velocities. Surprisingly, above moderate electric fields of 0.4V/cm with velocities higher than 2$\mu$m/ns, we observed a dependence of both bulk and structure-related spin-orbit interactions on the velocity magnitude. A remarkable feature is the increase of the cubic Dresselhaus term to approximately half of the linear coupling when the velocity is raised to 10$\mu$m/ns. In contrast, the Rashba coupling for both subbands decreases to about half of its value in the same range. These results yield new information for the application of drift models in spin-orbit fields and about limitations for the operation of spin transistors.