Electronic Properties of Some Novel Mott Insulators

在这项材料合成与加工计划的资助下，我们将研究两类新型Mott绝缘体的电子结构：冠醚电体和层状过渡金属氧化物。尽管这些氧化物被认为是由Hubbard模型解释的传统Mott绝缘体，但实际上该模型的基态与实验中的Bragg中子散射严重不一致。这个模型的假设将被检验，目的是找到一个合适的替代来描述观察到的自旋密度和激发态。冠醚电子的一个新特征是阴离子本身就是定域电子。对孤立的冠醚分子的计算表明，定域电子将沿着它们的谱系追踪到由未配对的电子占据的高度扩散的里德堡式轨道。这些分子电子的扩散特性可能会使它们局限在分子离子之间形成的空穴中。这一命题以及过渡金属氧化物中有序磁矩的空间分布将用从头算Hartree-Fock理论和多带Hubbard模型结合变分和微扰两种方法进行研究。理论研究将作为材料合成和加工倡议的一部分进行。主要焦点将放在对一类新的带电材料--冠醚--的理论解释上。这些材料是在密歇根州立大学合成的，需要一个坚实的理论解释。此外，还将对一种相关材料--过渡金属氧化物进行研究，这是高温超导体的重要先驱体材料。

Electronic structure of two classes of novel Mott insulators will be studied under this Materials Synthesis and Processing Initiative grant: the crown-ether electrides and the layered transition metal oxides. Although these oxides are believed to be traditional Mott insulators explained by the Hubbard model, in fact the ground state of that model disagrees seriously with experimental Bragg neutron scattering. The assumptions of this model will be examined with the objective of finding an appropriate replacement that will describe the observed spin density as well as the excited states. A novel feature of the crown-ether electrides is that the anions are simply the localized electrons themselves. Calculations on isolated crown-ether molecules suggests that the localized electrons will trace their lineage to a highly diffuse Rydberg-like orbital occupied by the unpaired electron. The diffuse character of these molecular electrons may permit them to become localized in the cavities formed "between" the molecular ions. This proposition, as well as the spatial distribution of the ordered magnetic moment in the transition metal oxides, will be explored using ab initio Hartree-Fock theory as well as multi-band Hubbard models using both variational and perturbation methods. %%% Theoretical research will be conducted as part of the Materials Synthesis and Processing Initiative. The primary focus will be on a theoretical explanation of a new class of electride materials - the crown-ethers. These materials have been synthesized at Michigan State and a firm theoretical explanation is required. In addition, research will be conducted on a related material, the transition metal oxides, which is important as the precursor material for high temperature superconductors.