Investigations of novel electronic and transport properties of correlated matter in thin films, at interfaces, and in nano- and heterostructures, in order to elucidate their potential for device applications

A major research goal of the TRR80 is the tailoring of the atomic and electronic structure on the nanoscale in order to realize novel electronic phases in correlated electronic materials, and to elucidate their potential for technological applications (devices). In this context, it is mandatory to understand the electronic structure of potential materials near interfaces, typically between different materials, and in heterostructures and superlattices. In particular, an essential aspect is the fact that electronic reconstruction may lead, on the one hand, to novel electronic phases at interfaces with properties not found in the bulk, and that such phases can be highly sensitive to external parameters like electric and magnetic fields, irradiation, pressure, and strain which, on the other hand, allows to control these artificial systems to a high degree. Prototypical examples are the interfaces of LaAlO3/SrTiO3 heterostructures that can become metallic although the bulk parent perovskites are band insulators, and of topological materials which are insulating bulk systems with protected currents at surfaces or interfaces. In addition, the influence of inhomogeneities and defects, omnipresent in real materials, need to be investigated. For example, it is still an open question under which conditions half-metallicity persists at surfaces and interfaces, and how the observed behaviour is influenced by electronic correlations.

Promising materials in this context are oxide heterostructures and Heusler compounds, which continue to be in the focus of research in Project Area G. The successful projects in this project area will be continued in the third funding period.  In turn, there are six projects in Project Area G, two of them experimental (G1 and G4), three combining experimental and theoretical efforts (G3, G5, G8), and one purely theoretical  (G7). The projects in area G are closely connected with each other, as well as with several projects in areas E and F as described in detail in the individual projects.

A variety of experimental techniques will be employed within the G-projects, e.g., x-ray scattering, molecular beam epitaxy (MBE), transmission electron microscopy, in-situ optical ellipsometry, x-ray magnetic circular dichroism, differential scanning calorimetry, pulsed laser deposition (PLD), RHEED, atomic force microscopy, charge and heat transport. Density functional theory (DFT) calculations within standard approximations such as the local density approximation (LDA), the generalized gradient approximation (GGA), as well as its extensions (LDA+U, GGA+U) to include local interaction effects, will continue to support most experimental investigations in the TRR80. However, extensions of the standard DFT methodology are needed to account for strong correlations in transport, e.g., by combining DFT with dynamical mean-field theory (DMFT). In addition, more sophisticated field-theoretical techniques are likely to be needed in order to describe phase transitions at interfaces, as well as topological aspects.