Electron correlation effects play a prominent role in 3d transition metal oxides leading to a plethora of functionalities like magnetism, multiferroicity, and unconventional superconductivity. Going to 5d materials, correlations are expected to become less important, while spin-orbit coupling effects become increasingly stronger. One thus could be led to consider spin-orbit coupling effects and electron correlations to be essentially disjoint phenomena in transition metal oxides. However, in particular the possibilities of strain engineering and heterostructuring in thin films and superlattices allow to create situations where electron correlations and spin-orbit coupling become entangled in intriguing ways. In this project we intend to fabricate such samples by pulsed laser deposition and study their chemical and electronic structure by state-of-the-art electron and x-ray spectroscopies with particular emphasis on controlled surface and interface sensitivity. Particularly interesting aspects are added by the perspective to induce topologically non-trivial states, which build on specific lattice symmetries, and the possibility to electrostatically dope these systems by gating or the effects of electronic reconstruction. Our search for novel quantum phases will be spurred by both model-oriented and material-specific theory predictions in and outside of the SFB.
 W. Witczak-Krempa et al., Annu. Rev. Condens. Matter Phys. 5, 57 (2014).