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

提出的项目重点是强相关电子材料的理论处理。具体来说，我们将研究过渡金属氧化物（TMOs）属于一类（负）电荷转移体系。我们的动机源于系统丰富的相图和部分奇异的基态（包括，例如高温超导）。许多属于这一类的材料已经被用作功能器件，即使缺乏彻底的理论理解（即预测能力）。这些系统的微观理论的问题源于过渡金属d-态和氧p-态的强杂化，这使得它们各自的希尔伯特空间无法完全分离。对于材料的研究，我们提出了簇动力平均场理论的具体概念扩展。这种扩展与化学中所谓的配位配合物的配体场理论密切相关，并将使我们能够同时平等地处理过渡金属d-态和氧p-态。在我们的提案中，我们用测试案例展示了我们方法的技术可行性，并概述了材料研究的计划。在初始阶段，我们将研究高Tc铜酸盐的所谓金刚砂模型。它为电荷传递系统提供了一个最简单的非平凡模型，并允许我们对结果进行基准测试。我们计算的一个中心目标也是计算两粒子磁响应函数（即动态磁化率）。有了这一观察结果，我们将能够解决一个非常具体的未解决的谜题，即通过核磁共振实验测量铜酸盐的磁响应。下面我们将转向另外两个属于（负）电荷转移类的材料族：高价氧化铬和稀土镍酸盐。这两种材料族都表现出令人兴奋的相变（向磁有序相和轨道有序相转变），以及明确处理氧自由度的重要性的强烈迹象。

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.