Structural relaxation and metal-insulator transition at the interface between SrTiO3 and LaAlO3

The electronic structure of interfaces between LaAlO${}_3$ and SrTiO${}_3$ is studied using local spin density approximation (LSDA) with intra-atomic Coulomb repulsion (LSDA+U). We find that the nature of the interface metallic states is strongly affected by the type of the structure (sandwich or bilayer) and by the termination surface of LaAlO${}_3$. In all structures the atomic relaxation plays a crucial role in the electronic properties of the system. While in sandwiches the structural relaxation produces a significant polarization in SrTiO${}_3$ and Jahn-Teller like splitting of Ti $3d_{xy}$ orbitals, in AlO${}_2$-terminated bilayers the relaxation occurs primarily in LaAlO${}_3$ and results in an insulator-metal transition which has been observed experimentally with increasing thickness of the LaAlO${}_3$ layer.