二维拓扑节线半金属及其多场调控的理论研究

Two-dimensional (2D) materials and topological semimetals have become the focus of intensive research in condensed matter physics, materials science, and so on, owing to their wide range of pronounced properties and potential applications. In spite of extensive efforts so far, most of the known topological semimetals are in three dimensions, 2D topological semimetals are rarely reported and the realistic host materials with excellently physical properties are in high demand. In particular, a gap opens when spin-orbit coupling is included in 2D topological nodal-line semimetals, but the nodal line should survive for good candidates. In this proposal, based on the current research progress and our previous works, we will focus on the basic theory and material exploring of 2D topological nodal-line semimetals. The underlying origins for 2D topological nodal-line semimetals will be discussed. To predict and devise good 2D topological nodal-line semimetals with spin-orbit coupling, we will explore the 2D layered materials, quantum wells, and lateral heterostructures. In addition, we will investigate the tuning of the 2D topological nodal-line semimetals by magnetic, electric, and strain fields, and map out the corresponding topological phase diagram. Related exotic characters will also be studied. Such studies are expected to broaden the understanding of 2D topological nodal-line semimetals, as well as to offer theoretical foundations and good materials for further experimental studies and device applications.

二维材料和拓扑半金属均具有丰富的电子物性和巨大的应用价值，是凝聚态物理和材料科学等领域的研究热点。然而，二维拓扑半金属的研究却相对较少，⾼品质的宿主材料还非常匮乏。特别是二维拓扑节线半金属，目前报道的材料均为忽略自旋轨道耦合的情况，即并未实现真正的二维拓扑节线半金属。结合当前的研究现状和已有的工作基础，本项目将开展二维拓扑节线半金属的理论和计算研究。深入理解二维拓扑节线半金属的形成机制，揭示在⼆维层状材料、量子阱、横向异质结中二维拓扑节线半金属的设计原理和规律，预言几种性能优良的含有自旋轨道耦合的二维拓扑节线半金属材料；系统地研究分析磁场、电场、应变场等对二维拓扑节线半金属的影响和作用规律，给出相应的拓扑相图，揭示与之相关的新奇物理现象。总之，通过系列研究，丰富人们对二维拓扑节线半金属的理解和认识，为其进一步的实验研究和器件应用等提供理论依据和材料基础。

拓扑量子态和拓扑量子材料是当前凝聚态物理和材料科学等领域的研究热点。磁性拓扑材料中不同磁构型与对称性之间的复杂相互作用为研究对称性保护的拓扑序提供了理想平台，为无耗散或低耗散自旋电子器件的设计与应用提供了新视野。本项目通过第一性原理计算和理论分析，探索新的磁性拓扑节线半金属和拓扑绝缘体材料, 提供设计磁性调控的拓扑相变新方案并揭示与之相关的新奇物理现象。在本研究的支持下，项目负责人及研究组全面完成了项目研究任务，达成了项目研究目标，发表SCI学术论文10篇，其中包括Phys. Rev. Lett.、Mater. Horiz.、Nano Lett.等。取得的主要成果有: (1) 发现了磁方向调控的拓扑节线半金属和拓扑绝缘物态之间的拓扑相变和有效调控，并首次在二维磁性体系中实现了拓扑晶体绝缘体和拓扑绝缘体相的共存，拓展了现有的理论认识，在拓扑自旋电子学器件中具有重要的应用价值。（2）揭示了晶体对称性保护的二维反铁磁拓扑绝缘体的形成机制，并给出了实现二维反铁磁拓扑绝缘体的有效模型和SrMnPb、RbMnBi等十余种较为理想的材料体系。将反铁磁拓扑绝缘体的概念引入到二维，实现了不同于量子反常霍尔效应的二维磁性拓扑绝缘物态，为进一步的实验研究和自旋电子学器件应用与发展等提供了材料基础。（3）提出了高阶拓扑绝缘体的新机制，据此发现了高鲁棒性的磁性二阶拓扑绝缘体，并实现了磁方向调控的高阶拓扑绝缘体和拓扑晶体绝缘体间的拓扑相变，极大地丰富人们对拓扑物态的理解和认识。