Metal-insulator transitions in strongly correlated oxides

Strongly correlated materials exhibit many interesting features that make them attractive for various applications. For example, correlations between electrons might increase the efficiency of solar cells [1]. Other potential applications such as transistors, sensors, or data storage rely on the ability of these materials to exhibit metal-insulator transitions, characterized by an abrupt change in resistance, which can be triggered by external influences such as temperature, stress, or applied voltage.

The term “strong correlations” here means the motion of the electrons is correlated, which causes established methods such as density-functional theory to fail. We simulate these strongly correlated materials with a combination of density-functional theory (DFT) (see also our other research areas: Multiferroic materials and beyond, Materials for permanent magnets, Searching for hidden order, Searching for dark matter) to describe the uncorrelated behavior and dynamical mean-field theory (DMFT) to accurately account for the strong correlations. This behavior occurs frequently in materials with open electronic d or f shells.

The strength of correlations can be quantified by two material-dependent parameters, which can lead to very different physics: the screened Coulomb repulsion U (which penalizes electrons on the same atom) and the Hund’s exchange interaction J (which favors spin alignment on the same site according to Hund’s first rule).

1. F. Petocchi, S. Beck, C. Ederer, and P. Werner, external page Hund excitations and the efficiency of Mott solar cells, Phys. Rev. B 100, 075147 (2019)