Charge transfer mechanism for the formation of metallic states at the KTaO${}_3$/SrTiO${}_3$ interface

The electronic and optical properties of the KTaO${}_3$/SrTiO${}_3$ heterointerface are analyzed by the full-potential linearized augmented plane-wave approach of density functional theory. Optimization of the atomic positions points at subordinate changes in the crystal structure and chemical bonding near the interface, which is due to a minimal lattice mismatch. The creation of metallic interface states thus is not affected by structural relaxation but can be explained by charge transfer between transition metal and oxygen atoms. It is to be expected that a charge transfer is likewise important for related interfaces such as LaAlO${}_3$/SrTiO${}_3$. The KTaO${}_3$/SrTiO${}_3$ system is ideal for disentangling the complex behavior of metallic interface states, since almost no structural relaxation takes place.

Figure 1

Schematic representation of the KTO/STO interface with the KTO on the left side and the STO on the right side. Large and medium spheres represent K/Sr and Ta/Ti atoms, respectively. Small spheres denote O atoms.

Figure 2

Projected Ti, Ta, and O densities of states obtained for the fully relaxed KTO/STO interface, as compared to the bulk KTO and STO compounds. In addition, the band structure of the interface system is shown.

Figure 3

Imaginary part of the dielectric function as well as reflectivity of the KTO/STO interface, as compared to bulk KTO and STO.