Theory of spin-orbit coupling at LaAlO3/SrTiO3 interfaces and SrTiO3 surfaces

The theoretical understanding of the spin-orbit coupling (SOC) effects at LaAlO3/SrTiO3 interfaces and SrTiO3 surfaces is still in its infancy. We perform first-principles density-functional-theory calculations and derive from these a simple tight-binding Hamiltonian, through a Wannier function projection and group theoretical analysis. We find striking differences to the standard Rashba theory for spin-orbit coupling in semiconductor heterostructures due to multiorbital effects: By far the biggest SOC effect is at the crossing point of the xy and yz (or zx) orbitals, and around the point a Rashba spin splitting with a cubic dependence on the wave vector k is possible.