Electric-field induced spin excitations in two-dimensional spin-orbit coupled systems

TL;DR

This paper derives coupled spin-charge drift-diffusion equations for 2D systems with spin-orbit coupling under electric fields, revealing spin wave excitations, their dispersion, and electric field amplification via spin injection.

Contribution

It introduces a rigorous analytical framework for spin excitations in 2D spin-orbit coupled systems, connecting space-charge wave methods to spin eigenmodes.

Findings

Identification of dispersion relations for spin excitations.

Demonstration of long-lived spin wave excitation by electric fields.

Showcase of electric field amplification through spin injection.

Abstract

Rigorous coupled spin-charge drift-diffusion equations are derived from quantum-kinetic equations for the spin-density matrix that incorporate effects due to k-linear spin-orbit interaction, an in-plane electric field, and the elastic scattering on nonmagnetic impurities. The explicit analytical solution for the induced magnetization exhibits a pole structure, from which the dispersion relations of spin excitations are identified. Applications of the general approach refer to the excitation of long-lived field-induced spin waves by optically generated spin and charge patterns. This approach transfers methods known in the physics of space-charge waves to the treatment of spin eigenmodes. In addition, the amplification of an oscillating electric field by spin injection is demonstrated.