六角结构的Sr4IrO6及相关4d/5d过渡金属氧化物的电子结构和物理性质研究

The comparable energy scales (such as spin-orbit coupling, electron correlation and Hund coupling) as well as the multiple degrees of freedom (such as charge, spin, orbit, and lattice) cooperate and compete with each other, leading to many novel properties, quantum phase and non-trivial topological electronic behavior in 4d/5d transition metal oxides, which have become the hot topics and difficult issues in the field of basic research in recent years. The present project plans to employ multiple theoretical methods and techniques, by studying the electronic structure, magnetic structure and electronic transport properties of hexagonal Sr4IrO6 and related 4d/5d transition metal oxides, to reach the following aims: (1) reveal the universal of the Jeff states, the existence of non-magnetic Jeff = 0 singlet and the nature of the insulation character of these system; (2) explore the microscopic effects of spin-orbit coupling, electron correlation, Hund coupling, magnetic exchange and crystal field splitting on the properties of materials; (3) establish the relations between physical properties of materials and the microstructure, octahedral stacking dimensionality, external electric field, magnetic field and other parameters; (4) probe possible new topological quantum states and novel quantum phase. The present project will enrich related condensed matter physics concepts and connotations, and provides the physical basis and theoretical guidance to design spin-orbit coupling functional material with the 4d/5d electrons.

由于存在自旋-轨道耦合、电子关联、洪特耦合等不同能量尺度以及电荷、自旋、轨道和晶格等多重自由度相互合作与竞争，4d/5d过渡金属氧化物展现许多新奇物性、奇异量子相和非平庸的拓扑电子行为，近年来成为基础研究领域的热点和难点课题。本项目计划综合运用多种理论方法与技术手段，通过研究六角结构的Sr4IrO6及相关4d/5d过渡金属氧化物的电子结构、磁结构，以及电子输运性质，揭示Jeff态的普适性、非磁性Jeff=0单重态的存在性以及体系的绝缘性本质，探索自旋-轨道耦合、电子关联、洪特耦合、磁性交换及晶体场劈裂等微观作用对材料性质的影响，建立材料物理性质与晶体微结构、八面体结构单元堆积的维度、外电场、磁场等参量之间的联系，探寻可能出现的新型拓扑量子态和新奇量子相，丰富相关凝聚态物理概念和内涵，为设计包含具有自旋-轨道耦合相对论作用的4d/5d电子功能材料提供一定的物理基础和理论指导。

本项目综合运用基于密度泛函理论的第一性原理计算、蒙特卡罗方法、动力学平均场理论、对称性分析、模型哈密顿函数以及格林函数等理论方法与技术手段，通过研究六角结构的六角结构的铱氧化物Sr3MIrO6 (M = Sr, Na and Li)及相关4d/5d过渡金属氧化物K0.75Na0.25IrO2，Na2RuO3和Ag3LiRu2O6的电子结构、磁基态，以及应变和压力诱导的结构相变、电子结构变化，揭示了Jeff态的普适性、非磁性Jeff=0单重态的存在性以及体系的绝缘性本质，探索了自旋-轨道耦合、电子关联、洪特耦合、磁性交换及晶体场劈裂等微观作用对材料性质的影响，建立了材料物理性质与晶体微结构、八面体结构单元堆积的维度、外加应变和压力等参量之间的联系，探寻了自旋轨道耦合纠缠态、结构二聚化和分子轨道等凝聚态物理现象。进一步的我们将研究对象从氧化物扩展到硫族化合物PdS2，PdSe2，PdSSe和NbS2，研究了高压和应力作用下的晶体结构相变、输运性质变化、铁弹性相变、电荷密度波和压致超导电性等物理现象和性质，丰富了相关凝聚态物理概念和内涵，基本实现了预期研究目标。发表学术论文15篇（被引用170次），培养研究生4人。