Complex oxides with 4d and 5d transition-metal ions recently emerged as a new paradigm in correlated electron physics, due to the interplay between spin–orbit coupling and electron interactions. For 4d and 5d ions, the spin–orbit coupling, ζ, can be as large as 0.2–0.4 eV, which is comparable with and often exceeds other relevant parameters such as Hund’s coupling J_H, noncubic crystal field splitting Δ, and the electron hopping amplitude t. This gives rise to a variety of spin–orbit-entangled degrees of freedom and, crucially, non-trivial interactions between them that depend on the d-electron configuration, the chemical bonding, and the lattice geometry. Exotic electronic phases often emerge, including spin–orbit assisted Mott insulators, quantum spin liquids, excitonic magnetism, multipolar orderings and correlated topological semimetals. This paper provides a selective overview of some of the most interesting spin–orbit-entangled phases that arise in 4d and 5d transition-metal compounds.

中文翻译：

---

4d和5d过渡金属化合物的自旋轨道纠缠电子相

由于自旋轨道耦合和电子相互作用之间的相互作用，具有4 d和5 d过渡金属离子的复合氧化物最近成为相关电子物理学的新范例。对于4 d和5 d离子，自旋-轨道耦合ζ可以大到0.2–0.4 eV，这可以与并且经常超过其他相关参数，例如洪德耦合J _H，非立方晶场分裂Δ和电子跳跃幅度t。这就产生了各种自旋轨道纠缠的自由度，并且至关重要的是，它们之间依赖于d的非平凡相互作用。-电子构型，化学键和晶格几何形状。奇异的电子相经常出现，包括自旋轨道辅助的Mott绝缘子，量子自旋液体，激子磁，多极有序和相关的拓扑半金属。本文提供了一些有关4 d和5 d过渡金属化合物中最有趣的自旋轨道纠缠相的概述。