Coordination Complex extensions of Dynamical Mean-Field Theory for (negative) Charge Transfer Transition Metal Oxides

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The proposed project is focused on the theoretical treatment of strongly correlated electron materials. Specifically, we will study transition metal oxides (TMOs) which belong to the class of (negative) charge transfer systems. Our motivation originates in the systems’ rich phase diagrams and partially exotic ground states (including, e.g. high temperature superconductivity). Many materials which belong to this class are already used as functional devices even though a thorough theoretical understanding (i.e. predictive power) is missing. The problems for a microscopic theory of these systems originate in the strong hybridization of transition metal d- and oxygen p- states, which prohibit a clean separation of their respective Hilbertspaces. For the materials studies we propose a specific conceptional extension of cluster dynamical mean-field theory. This extension is closely linked to the so called ligand field theory of coordination complexes in chemistry and will allow us to treat transition metal d- and oxygen p- states simultaneously and on equal footing. In our proposal we show with test cases the technical feasibility of our method and outline the plan for the materials studies. In the initial phase we will study the so-called Emery model for high Tc cuprates. It presents one of the simplest non-trivial models for a charge transfer system and will allow us to benchmark our results. A central goal of our calculations is also the computation of the two-particle magnetic response function (i.e. the dynamic magnetic susceptibility). With this observable we will be able to address a very specific unsolved puzzle of the magnetic response in cuprates measured by NMR experiments. Following we will turn to two other material families which belong to the (negative) charge transfer class: high valence chromium oxides and rare-earth nickelates. Both material families display exciting phase transitions (to magnetically- and orbital- ordered phases) as well as strong indications for the importance of an explicit treatment of the oxygen degrees of freedom.