Orbital-Angular-Momentum Based Origin of Rashba-Type Surface Band Splitting

TL;DR

This paper introduces a novel explanation for Rashba-type surface band splitting, emphasizing the role of local orbital angular momentum and electric dipole interactions rather than Zeeman effects, supported by first-principles calculations.

Contribution

It proposes a new model linking local orbital angular momentum and electric dipoles to Rashba splitting, challenging the traditional Zeeman-based explanation.

Findings

First-principles calculations confirm the model's predictions.

The spin texture direction is opposite to traditional Rashba theory.

Electric dipole interactions drive the band splitting.

Abstract

We propose that existence of local orbital angular momentum (OAM) on the surfaces of high-Z materials play a crucial role in the formation of Rashba-type surface band splitting. Local OAM state in a Bloch state produces asymmetric charge distribution (electric dipole). Presence of surface electric field aligns the electric dipole and results in chiral OAM states and the relevant Rashba- type splitting. Therefore, the band splitting originates from electric dipole interaction, not from the Zeeman splitting as proposed in the original Rashba picture. The characteristic spin chiral structure of Rashba states is formed through the spin-orbit coupling and thus is a secondary effect to the chiral OAM. Results from first principles calculations on a single Bi layer under an external electric field verify the key predictions of the new model, including the direction of the spin textures which is predicted to be in opposite direction in the Rashba picture.