Weyl半金属中的电子关联效应及其在电/磁场中的性质调控

Weyl semimetal, as a new topological quantum state, has been theoretically predicted and experimentally observed in several materials. These materials almost contain transition-metal elements and most of them show obvious electronic correlation effects. The electronic correlation even play an important role in the ground-state stability of some Weyl semimetals (such as pyrochlore iridates). In addition, since the scattering between two Weyl nodes with opposite chirality is very weak, the transport with low power consumption may be realized at room temperature. It has great potential for the application of room-temperature low-energy electric devices. In this proposal we perform our researches in following two aspects: (1) Through introducing the electron-electron interaction into the single-particle model of Weyl semimetal, we focus on the role of electric correlation in the topological stability and the response of topological properties to external electric and magnetic fields so that the formation mechanism of Weyl semimetal can be revealed. (2) We employ first-principles method and dynamical mean-field theory to study the electronic correlation effects of realistic Weyl semimetal materials and its transport properties in external electric and magnetic fields. According to the topological surface state and transport properties, we design spintronic devices.

Weyl半金属作为一种新型拓扑量子态已经在多种材料中被理论预言或实验观测到，这些材料几乎都含有过渡金属元素，并且相当一部分具有明显的电子关联效应，甚至在Weyl半金属基态稳定性上起到至关重要的作用（如烧绿石结构的铱氧化物）。另外，在Weyl半金属中两个具有相反手性的Weyl电子态之间的散射很弱，可以在室温下通过外加电/磁场实现极低能耗的电子输运，对室温低能耗电子学器件的应用具有重要价值。本项目从两方面展开研究：(1)在Weyl半金属的单粒子近似模型中引入电子间相互作用，重点研究电子关联在拓扑稳定性上所起到的作用，以及体系在外加电/磁场中的响应特征，进而揭示Weyl半金属基态的形成机理。(2)选取实际Weyl半金属材料，利用第一性原理结合动力学平均场理论深入研究电子关联效应以及在外加电/磁场中体系的输运性质，并利用其拓扑表面态和输运特征设计自旋电子学器件。

该项目原计划对Weyl半金属中的电子关联效应及其在外场中的性质调控进行详细研究，在获得国家自然科学基金青年项目的资助后，该项目进展顺利。我们已经系统地研究了Weyl半金属体系的新奇拓扑性质，绘制出电子关联-化学势相图，特别是在吸引相互作用情况下，Weyl半金属和超导配对之间的竞争诱导出丰富的相变过程；通过施加外场我们呈现了拓扑边界态的演化特征，为设计自旋过滤器和自旋扭转器等器件提供了有效的理论信息。此外，我们还基于第一性原理、紧束缚近似模型和动力学平均场理论等进一步研究了实际拓扑材料，包括第四主族二维拓扑材料、1T-TaS2和MoS2等，研究结果展现出了丰富的物态性质，我们对其进行了物理解释，阐明了第四主族二维材料中的拓扑相变物理机制、1T-TaS2中电子关联效应和轨道密度波机制以及单层MoS2中超导穹顶现象背后的物理原因。在三年的项目资助期间，项目负责人以第一作者身份发表SCI论文5篇（包括3篇已发表，2篇已接收）。