Nature of Orbital and Spin Rashba Coupling in the Surface Bands of SrTiO3 and KTaO3

TL;DR

This paper analyzes the surface electronic bands of SrTiO3 and KTaO3, revealing complex orbital and spin Rashba effects with linear and cubic momentum dependencies, derived through analytical and numerical methods.

Contribution

It introduces a unitary transformation technique to derive analytical expressions for cubic Rashba effects in surface bands of perovskite oxides.

Findings

Cubic Rashba effects depend on electric field strength and symmetry.

Analytical expressions match numerical calculations.

In-plane modulations due to C4v symmetry are observed.

Abstract

Tight-binding models for the recently observed surface electronic bands of SrTiO3 and KTaO3 are analyzed with a view to bringing out the relevance of momentum-space chiral angular momentum structures of both orbital and spin origins. Depending on the strength of electric field associated with inversion symmetry breaking at the surface, the orbital and the accompanying spin angular momentum structures reveal complex linear and cubic dependencies in the momentum k (linear and cubic Rashba effects, respectively) in a band-specific manner. Analytical expressions for the cubic orbital and spin Rashba effects are derived by way of unitary transformation technique we developed, and compared to numerical calculations. Due to the C4v symmetry of the perovskite structure the cubic Rashba effect appears as in-plane modulations.