Ordering Phenomena in Transition Metal Oxides

Physical properties of artificially structured strongly correlated electron systems   

Interfaces between different materials provide the environment for many novel electronic phases and properties which are not available in bulk materials, and are important from a basic and possibly application point of view. Recent experimental developments have stimulated this field, most notably the metalic phase at Mott-insulator (MI) /band-insulator (BI) interfaces of LaTiO₃/SrTiO₃ and the electronic reconstruction for LaAlO₃ films on SrTiO₃ which even  show superconductivity. This talk presents theoretical work on correlation effects for the electronic behavior at BI/MI/BI heterostructures and arrays. Using the Kotliar-Ruckenstein slave-boson approach we discuss the mutual electron doping at the interface of the two insulators leading to a metallic phase. There are two obvious regimes of the electronic reconstruction at the interface: Hartree regime (weak correlation) and Mott regime (strong correlation). These regimes can be distinguish clearly in the charge redistribution and the optical conductivity. Correlation effects also play a role for thermopower of the metallic interface. Finally also ordered phases in the interface region will be addressed.