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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.