Lattice relaxation effects on the interface electron states in the perovskite oxide heterostructures:: LaTiO3 monolayer embedded in SrTiO3

We have studied the effect of the lattice relaxation on the interface electronic structure of LaTiO3/SrTiO3, focusing in particular on the wedge-shaped potential, the interface sub-bands, and the orbital ordering, from density-functional calculations using the linearized augmented plane-wave and the linear muffin-tin orbital methods. We find that the extra screening due to the lattice relaxation is about as strong as the screening due to the electronic polarization alone, approximately doubling the value of the short-range dielectric constant as compared to the unrelaxed case. The additional screening reduces the interface electric field and spreads the two-dimensional electron gas further away from the interface, to about four to five layers into the SrTiO3 bulk on either side of the interface. The electronic band structure indicates distinct interface sub-bands, derived from the individual interface layers. The orbital-ordered state is quite interesting. While it consists of mainly the Ti(xy) orbitals oriented parallel to the interface for the first layer Ti, with or without the lattice relaxation, it switches to Ti(xz/yz) character as one goes beyond the first layer into the bulk.