CPM Seminar

Engineering electronic states at transition metal oxide interfaces: picoscale distortions and electronic correlations

Sohrab Ismail-Beigi

Department of Applied Physcis
Yale University

The atomic-scale structure and bonding topology in a material determines its resulting properties. Alterable or reversible bond distortions at the picometer length scale in turn modify a material's electronic configuration and can give rise to functional properties. Picoscale bond perturbations represent the ultimate length scale for materials engineering: any smaller and the effects are too small to matter; any larger and the bonds are completely broken so we are describing a different material. Using first principles theory based on density functional theory (DFT), I will present examples of metal oxide interfaces where picoscale distortions can control relative 3d orbital energies and electron occupancies. This approach permits one to answer questions such as “what does Ni³⁺ do when its orbital degeneracy is broken strongly?” or “can one make an atom behave partway between two neighboring atoms in the periodic table?”

Despite permitting us to make such advances in materials theory and engineering, the workhorse DFT approach has some serious shortcomings. While optimized atomic geometries, electron densities and mean orbital occupations from DFT are typically high quality, DFT-predicted electronic band structures often suffers from qualitative errors for materials with strong and localized electronic correlations such as transition metal oxides. I will give a short pedagogical introduction to how slave-boson methods go beyond band theory (i.e., DFT) to incorporate correlations, and then relate my work on developing slave-boson methods that describe dynamic electron fluctuations and band renormalizations.