Performing an analysis within density functional theory, we develop insight
into the structural and electronic properties of the oxide heterostructure
LaAlO3/SrTiO3. Electrostatic surface effects are decomposed from the internal
lattice distortion in order to clarify their interplay. We first study the
interface relaxation by a multi-layer system without surface, and the surface
effects, separately, by a substrate-film system. While elongation of the TiO6
octahedra at the interface enhances the metallicity, reduction of the film
thickness has the opposite effect due to a growing charge depletion. The
interplay of these two effects, as reflected by the full lattice relaxation in
the substrate-film system, however, strongly depends on the film thickness. An
inversion of the TiO6 distortion pattern for films thinner than four LaAlO3
layers results in an insulating state.Comment: 10 pages, 7 figures, accepted by Europhysics Letter
