3d/5d过渡金属氧化物异质界面新奇电子态的理论研究

Transition metal oxides (TMOs) heterostructures and interfaces exhibit novel charge, spin, orbital, and lattice phases which do not exist in their bulk counterparts, and become a candidate of the next generation electronic devices with multi-functionality and low energy cost. Most of the research activities in this field have so far been focused either on the 3d/3d TMO-interfaces whose properties are dominated by the strong electron correlations, or on the low-dimensional 5d materials where the large spin-orbit coupling is playing a vital role. The 3d/5d interfaces, on the other hand, are less studied as they are largely regarded as simple structural extensions of these two systems. We have recently identified two unique properties at such interfaces, namely the 1) large charge-transfer effect, and 2) exotic interfacial electronic coupling. This proposed project will focus on how to employ these two effects to realize targeted design of novel properties that the community eagerly awaits, such as unconventional superconductivity that can be possibly realized by carrier doping in Sr2IrO4. Combining both model analysis and material calculations, we will study the microscopic mechanisms that can give rise to novel electronic phases and properties at the 3d/5d interfaces, and how different material combinations, lattice symmetries/orientations, dimensionality, epitaxial strains, and external fields can be utilized to achieve rational control of such properties. The ultimate goal of the project is to establish a unified theoretical framework for studying and exploring the novel electronic phases at the 3d/5d interfaces, which can serve as a guidance for future work in this field.

过渡金属氧化物异质界面呈现出本体中不存在的电荷、自旋、轨道、晶格及拓扑等新奇量子态，有望成为下一代多功能、低能耗电子器件的基础。目前绝大部分相关研究聚焦于具有强电子-电子相互作用的3d/3d氧化物异质界面，或者具有强自旋-轨道相互作用的低维5d电子体系；而3d/5d界面往往被当成材料上的简单拓展而被忽视。我们发现3d/5d过渡金属氧化物异质界面具有如下两种独有的特性：1）界面巨大电荷转移，2）界面奇异电子耦合。本项目将率先研究如何利用这两种特性来实现氧化物界面领域急切期待的一些新奇电子态，如界面电荷掺杂Sr2IrO4实现非常规超导态等。结合理论模型分析与材料计算来探索这些特性诱导新奇电子态的微观机理，通过材料组合、晶格、晶向、薄膜厚度、应力及外场等界面技术进行调控。最终目标是建立3d/5d氧化物界面新奇电子态的理论框架，引领这个研究方向。

过渡金属氧化物异质界面呈现出本体中不存在的电荷、自旋、轨道、晶格及拓扑等新奇量子态，有望成为下一代多功能、低能耗电子器件的基础。目前绝大部分相关研究聚焦于具有强电子-电子相互作用的3d/3d氧化物异质界面，或者具有强自旋-轨道相互作用的低维5d电子体系；而3d/5d界面往往被当成材料上的简单拓展而被忽视。我们发现3d/5d过渡金属氧化物异质界面具有如下两种独有的特性：1）界面巨大电荷转移，2）界面奇异电子耦合。本项目中我们研究了如何利用这两种特性来实现氧化物界面领域急切期待的一些新奇电子态。我们设计了具有中心反演对称性破缺的非对称氧化物异质界面，从而实现了并对其Rashba自旋轨道耦合作用的有效调控。我们构建了非极性的SrTiO3/SrRuO3异质界面，在界面上通过引入氧空位打破晶体结构的中心反演对称性，从而诱导出极化，且极化强度可达33.3μC/cm2，大于BaTiO3的25.5μC/cm2。我们提出一种带电荷氧空位稳定HfO2铁电相，从而产生铁电性的新机制。我们还通过第一性原理计算，证明了氧空位的电荷态能够剧烈影响HfO2结构相的热力学稳定性，因此通过改变氧空位电荷态能够稳定铁电相。此外，我们系统研究了镍基超导氧化物RNiO2的电子结构研究，并对镍基氧化物超导材料结构进行了理论预测。我们的研究有助于建立氧化物界面新奇电子态的理论框架，引领这个研究方向。