Unconventional electronic ground states and novel physical properties due to strong spin-orbit couplings and correlation effects in 5d oxides

分子和固体中的相对论效应最重要的结果之一是自旋和轨道自由度的耦合。在3D金属氧化物中，自旋-轨道耦合相对较弱，大多数有趣的物理学都建立在强电子关联的存在上。然而，当d轨道变得越来越长时，当进入更重的过渡金属元素，即4d和5d系统时，电子-电子相互作用变得越来越弱。另一方面，相对论的自旋-轨道耦合遵循相反的趋势：它逐渐增加。在5d金属化合物中，例如虹酸盐和橙酸盐，当这些相互作用在相同的能量尺度上相遇时，有趣的情况出现了。晶场效应、局域多重态物理、自旋轨道耦合和随后出现的位间跃迁之间的相互作用，为相关电子材料开辟了一个新的兴趣窗口，提供了新类型的关联基态和激发。更奇特的例子是虹酸盐中可能的拓扑态，如拓扑Mott绝缘体，以及可能实现长期寻求的具有键相关的自旋-自旋相互作用的Kitaev模型。该项目的目标是提供更深入的理论见解，以了解有趣的5d氧化物化合物的基本电子结构和磁性，如虹酸盐和橙酸盐。为此，我们将建立在波函数电子结构理论的概念和计算工具的基础上，特别是现代量子化学中的相关多参考方法和最近开发的固体嵌入技术。我们的工作将促进对固体中关联效应和自旋-轨道相互作用的相互作用的新视角。

One of the most important consequences of relativistic effects in molecules and solids is the coupling of spin and orbital degrees of freedom. In 3d-metal oxides, the spin-orbit coupling is relatively weak and most of the intriguing physics rests on the presence of strong electron correlations. Electron-electron interactions turn nevertheless progressively weaker when going to heavier transition-metal elements, i.e., 4d and 5d systems, as the d orbitals become more and more extended. The relativistic spin-orbit coupling, on the other hand, follows the opposite trend: it increases progressively. In 5d-metal compounds, e.g., iridates and osmates, the interesting situation arises where these interactions meet on the same energy scale. The interplay between crystal-field effects, local multiplet physics, spin-orbit couplings, and intersite hopping that subsequently emerges has opened up a new window of interest in correlated electronic materials, offering novel types of correlated ground states and excitations. The more exotic examples are possible topological states in iridates, such as the topological Mott insulator, and the possible realization of the long-sought Kitaev model with bond-dependent spin-spin interactions.The goal of this project is providing deeper theoretical insight into the basic electronic structure and magnetic properties of intriguing 5d oxide compounds such as the iridates and osmates. For this purpose, we will build on concepts and computational tools from wavefunction electronic-structure theory, in particular, correlated multireference methods from modern quantum chemistry and recently developed solid-state embedding techniques. Our work shall foster new perspectives over the interplay of correlation effects and spin-orbit interactions in solids.