Role of Berry curvature in the generation of spin currents in Rashba systems

TL;DR

This paper investigates how Berry curvature influences various spin currents in 2D Rashba systems and 3D noncentrosymmetric metals, revealing their dependence on Fermi energy, Zeeman interaction, and polarization characteristics.

Contribution

It introduces a modified spin current operator including anomalous velocity and details the behavior of spin currents in different regimes, highlighting the role of Berry curvature.

Findings

Background spin current saturates at high Fermi energy.

Linear spin current shows a plateau at the Zeeman gap.

Nonlinear spin currents peak at the gap edges and are enhanced by Zeeman strength.

Abstract

We study the background (equilibrium), linear and nonlinear spin currents in 2D Rashba spin-orbit coupled systems with Zeeman splitting and in 3D noncentrosymmetric metals using modified spin current operator by inclusion of the anomalous velocity. The linear spin Hall current arises due to the anomalous velocity of charge carriers induced by the Berry curvature. The nonlinear spin current occurs due to the band velocity and/or the anomalous velocity. For 2D Rashba systems, the background spin current saturates at high Fermi energy (independent of the Zeeman coupling), linear spin current exhibits a plateau at the Zeeman gap and nonlinear spin currents are peaked at the gap edges. The magnitude of the nonlinear spin current peaks enhances with the strength of Zeeman interaction. The linear spin current is polarized out of plane, while the nonlinear ones are polarized in-plane. We witness pure anomalous nonlinear spin current with spin polarization along the direction of propagation. In 3D noncentrosymmetric metals, background and linear spin currents are monotonically increasing functions of Fermi energy, while nonlinear spin currents vary non-monotonically as a function of Fermi energy and are independent of the Berry curvature. These findings may provide useful information to manipulate spin currents in Rashba spin-orbit coupled systems.