4d、5d关联电子体系中复自旋-轨道序和自旋-轨道激发的理论研究

较强的自旋-轨道耦合使得“自旋序”、“轨道序”和相应的准粒子激发不足以描述4d、5d关联电子体系的物性。因此，我们引入能够体现自旋-轨道耦合这一能量尺度的量子序和准粒子激发-“复自旋-轨道序”和“自旋-轨道激发”来表征它们的性质。本项目以Ca2-xSrxRuO4、Sr2IrO4及Sr2YIrO6(Ba2YIrO6)等氧化物为载体，利用密度泛函理论+动力学平均场方法结合线性响应函数及多体微扰方法研究4d、5d体系中自旋-轨道耦合相对于晶体场、Hund耦合、能带宽度等在决定复自旋-轨道序和自旋-轨道激发时的重要程度以及自旋-轨道耦合与这些能量尺度之间的耦合关系。同时发展新的计算方法来更好地处理低温条件下4d、5d体系中和自旋-轨道耦合相关的问题。这项研究不仅有助于理解或证实一系列有别于3d体系的新奇物理现象，还有助于探索铜基高温超导的机理。

Relatively stronger spin-orbit coupling makes concepts “orbital ordering”, “spin ordering” and corresponding quasi-particle excitations insufficient to describe the properties of 4d and 5d correlated electron systems. Therefore, to characterize these systems, we introduce new concepts, “complex spin-orbit ordering”, “spin-orbit excitation” which can embody the energy scale of spin-orbit coupling. By applying multiple techniques, density functional theory + dynamical mean field theory, linear response theory, and many-body perturbation theory on typical compounds, Ca2-xSrxRuO4, Sr2IrO4 and Sr2YIrO6 (Ba2YIrO6), we investigate the relative role of spin-orbit coupling to crystal field splitting, Hund coupling and bandwidth in determining the complex spin-orbit orderings and spin-orbit excitations of 4d and 5d correlated electron systems. At the same time, we study the interplay between these energy scales. The outcomes of this project can help not only to understand or confirm a series of novel phenomena different from those of 3d electron systems, but also to explore the mechanism of superconductivity in cuprates.