  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.
