Orbital mapping of energy bands and the truncated spin polarization in three-dimensional Rashba semiconductors

TL;DR

This study uses first-principles calculations and a multi-orbital model to reveal how spin-orbit coupling induces complex spin polarization in 3D Rashba semiconductors through orbital hybridization, advancing understanding of spin textures.

Contribution

It uncovers the orbital hybridization mechanism behind spin polarization in Rashba systems, extending the understanding beyond simple models and suggesting new material design strategies.

Findings

Spin polarization arises from SOC-induced hybridization between spin and multiple orbitals.

Orbital textures are key to understanding spin polarization effects.

The mechanism applies broadly to Rashba systems, including those with inversion symmetry.

Abstract

Associated with spin-orbit coupling (SOC) and inversion symmetry breaking, Rashba spin polarization opens a new avenue for spintronic applications that was previously limited to ordinary magnets. However, spin polarization effects in actual Rashba systems are far more complicated than what conventional single-orbital models would suggest. By studying via first-principles DFT and a multi-orbital k.p model a 3D bulk Rashba system (free of complications by surface effects) we find that the physical origin of the leading spin polarization effects is SOC-induced hybridization between spin and multiple orbitals, especially those with nonzero orbital angular momenta. In this framework we establish a general understanding of the orbital mapping, common to the surface of topological insulators and Rashba system. Consequently, the intrinsic mechanism of various spin polarization effects, which pertain to all Rashba systems even those with global inversion symmetry, is understood as a manifestation of the orbital textures. This finding suggests a route for designing high spin-polarization materials by considering the atomic-orbital content.