Mechanism of orbital reconstruction at the interfaces of transition metal oxides

Orbital reconstruction at interfaces between YBa2Cu3O6 and SrO-terminated SrTiO3 is studied using local spin density approximation (LSDA) with intra-atomic Coulomb repulsion (LSDA+U). The change of population of interfacial Cu 3d orbitals results in stabilization of a new oxidation state $3d^8$ which involves an additional modification of orbital occupancies in the nearest SrO and TiO2 layers. We find that an increase of electron charge in Cu 3d_{x^2-y^2} states counterbalances a depopulation of 3d_{3z^2-r^2} orbitals which induces, on account of the onsite Coulomb repulsion U, a splitting of 3d_{3z^2-r^2} states at CuO2-SrO interfaces.