Highly Confined Spin-Polarized Two-Dimensional Electron Gas in SrTiO3/SrRuO3 Superlattices

We report first-principles characterization of the structural and electronic properties of (SrTiO3)5/(SrRuO3)1 superlattices. We show that the system exhibits a spin-polarized two-dimensional electron gas, extremely confined to the 4d orbitals of Ru in the SrRuO3 layer. Every interface in the superlattice behaves as a minority-spin half-metal ferromagnet, with a magnetic moment of µ = 2.0µB/SrRuO3 unit. The shape of the electronic density of states, half-metallicity, and magnetism are explained in terms of a simplified tight-binding model, considering only the t2g orbitals plus (i) the bidimensionality of the system and (ii) strong electron correlations.