Theory of t2g electron-gas Rashba interactions

TL;DR

This paper develops a theoretical framework for Rashba spin splitting in t2g bands of 2D electron systems at cubic perovskite surfaces, highlighting the role of atomic spin-orbit interactions and lattice distortions.

Contribution

It introduces a model combining ab initio calculations and tight-binding theory to explain Rashba effects in t2g bands, emphasizing the impact of lattice distortions.

Findings

Rashba splitting arises from atomic-like on-site SO interactions.

Lattice distortions modify metal-oxygen-metal bond angles, enabling Rashba effects.

The theory explains Rashba splitting in perovskite 2DESs.

Abstract

The spin-degeneracy of Bloch bands in a crystal can be lifted when spin-orbit (SO) coupling is present and inversion symmetry is absent. In two-dimensional electron systems (2DES) spin-degeneracy is lifted by Rashba interaction terms - symmetry invariants that are scalar products of spin and orbital axial vectors. Rashba interactions are symmetry allowed whenever a 2DES is not invariant under reflections through the plane it occupies. In this paper, we use a tight-binding model informed by ab initio electronic structure calculations to develop a theory of Rashba splitting in the t2g bands of the two- dimensional electron systems formed at cubic perovskite crystal surfaces and interfaces. We find that Rashba splitting in these systems is due to atomic-like on-site SO interactions combined with processes in which t2g electrons change orbital character when they hop between metal sites. These processes are absent in a cubic environment and are due primarily to polar lattice distortions which alter the metal-oxygen-metal bond angle.