Charge and orbital order at head-to-head domain walls in PbTiO3

At ferroelectric longitudinal domain walls there is an uncompensated charge, which could form a two-dimensional electron gas in the insulator. However, the uncompensated charges can be accommodated by, e.g., defects or localized states that split off from the conduction band. We carried out density functional theory calculations to study these scenarios in PbTiO3 with and without consideration of strong correlation effects simulated via inclusion of a Hubbard parameter U. The optimized structure and electronic structure depend on the choice of this parameter: For vanishing U, a broad, conducting domain wall is obtained, while increasing U leads to localized Ti 3d states and an insulating, sharp domain wall. We also investigated the effects of varying the ferroelectric polarization on the electronic structure of these domain walls

Spin-orbit and exchange effects in the 2DEG of BiAlO3_{3} -based oxide heterostructures

We study the electronic properties of the BiAlO3/SrTiO3 (BAO/STO) interface and compare them to the well-studied LaAlO3/STO system. Due to the ferroelectricity of BAO it is possible to manipulate the carrier density at the interface. Using density functional theory, we investigate the spin-orbit coupling (SOC) effects in the two-dimensional electron gas (2DEG) in BAO/STO and its magnetic counterparts, the BAO/EuTiO3 and BAO/Sr2NiWO6 heterostructures. In the latter two structures, the proximity to ferroelectric insulators breaks the time-reversal symmetry in the 2DEG and can lead, in combination with inversion symmetry breaking and SOC to a single Fermi surface, analogous to the situation in topological insulators