Electronic structure of domain walls in strontium titanate

At low temperatures, SrTiO₃ transforms from cubic to tetragonal, and twin domain boundaries form. We present density functional calculations of this system, focusing on the conduction-band states bound to the domain walls. Spin-orbit coupling strongly modifies the low-energy states. Two types of domain walls form which have different relative phases of the rotation of the oxygen octahedra in the bulk regions. The two types of domain walls have significantly different electronic states. The importance of the domain walls on electron pairing without superconductivity in this system will be discussed.