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

The electronic structure of interfaces between LaAlO3 and SrTiO3 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 LaAlO3. 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 SrTiO3 and a splitting of Ti 3dxy orbitals, in AlO2-terminated bilayers the relaxation occurs primarily in LaAlO3 and results in an insulator-metal transition which has been observed experimentally with increasing thickness of the LaAlO3 layer.

Research Highlights► We study the structural relaxation in heterostructures LaAlO3/SrTiO3. ► The relaxation depends on the type of the structure and on its termination surface. ► In the sandwiches, the relaxation produces the electric polarization in SrTiO3. ► In the AlO2-terminated bilayers, the atomic displacements occur in LaAlO3. ► The relaxation in the bilayers leads to a metallic state for the thicker LaAlO3.