Nature of orbital and spin Rashba coupling in the surface bands of SrTiO3 and KTaO3

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 characters. 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 a unitary transformation technique we developed, and compared to numerical calculations. The cubic Rashba effect appears as in-plane modulations due to the C4v symmetry of the perovskite structure.