What can we learn about the dynamics of transported spins by measuring shot noise in spin-orbit-coupled nanostructures?

TL;DR

This paper reviews how shot noise measurements in spin-orbit-coupled nanostructures reveal details about spin dynamics, decoherence, and the mechanisms behind the spin Hall effect, providing insights into spin transport phenomena.

Contribution

It generalizes the scattering theory of quantum shot noise to include full spin-density matrices and analyzes shot noise as a tool to differentiate intrinsic and extrinsic spin-orbit mechanisms.

Findings

Decoherence enhances the Fano factor of spin-polarized currents.

Shot noise distinguishes between intrinsic Rashba and extrinsic spin-orbit effects.

Pure spin Hall current shot noise reveals spin transport details.

Abstract

We review recent studies of the shot noise of spin-polarized charge currents and pure spin currents in multiterminal semiconductor nanostructures, while focusing on the effects brought by the intrinsic Rashba spin-orbit (SO) coupling and/or extrinsic SO scattering off impurities in two-dimensional electron gas (2DEG) based devices. By generalizing the scattering theory of quantum shot noise to include the full spin-density matrix of electrons injected from a spin-filtering electrode, we show how decoherence and dephasing in the course of spin precession can lead to substantial enhancement of the Fano factor (noise-to-current ratio) of spin-polarized charge currents. In four-terminal SO-coupled nanostructures, injection of unpolarized charge current through the longitudinal leads is responsible not only for the pure spin Hall current in the transverse leads, but also for nonequilibrium random time-dependent current fluctuations. The analysis of the shot noise of transverse pure spin Hall current and zero charge current, or transverse spin current and non-zero charge Hall current, driven by unpolarized or spin-polarized injected longitudinal charge current, respectively, reveals a unique experimental tool to differentiate between the intrinsic Rashba and extrinsic SO mechanisms underlying the spin Hall effect in 2DEG devices. Finally, we discuss the shot noise of transverse spin and zero charge currents in the quantum-interference-driven spin Hall effect in ballistic four-terminal Aharonov-Casher rings realized using high-mobility 2DEG with the Rashba SO coupling.