Transition of a 2D spin mode to a helical state by lateral confinement

TL;DR

This paper experimentally demonstrates how lateral confinement in a 2D electron gas induces a transition to a long-lived helical spin mode, significantly enhancing spin lifetime in GaAs quantum wells with strong spin-orbit interaction.

Contribution

It provides the first visualization of the transition from a 2D spin mode to a helical state due to lateral confinement in a GaAs quantum well.

Findings

Formation of a helical spin mode in non-quantized channels

Spin-lifetime enhancement consistent with theory

Lateral confinement as a practical method for high spin lifetimes

Abstract

Spin-orbit interaction (SOI) leads to spin precession about a momentum-dependent spin-orbit field. In a diffusive two-dimensional (2D) electron gas, the spin orientation at a given spatial position depends on which trajectory the electron travels to that position. In the transition to a 1D system with increasing lateral confinement, the spin orientation becomes more and more independent on the trajectory. It is predicted that a long-lived helical spin mode emerges. Here we visualize this transition experimentally in a GaAs quantum-well structure with isotropic SOI. Spatially resolved measurements show the formation of a helical mode already for non-quantized and non-ballistic channels. We find a spin-lifetime enhancement that is in excellent agreement with theoretical predictions. Lateral confinement of a 2D electron gas provides an easy-to-implement technique for achieving high spin lifetimes in the presence of strong SOI for a wide range of material systems.