镧系金属锑化物、铋化物的拓扑半金属态研究

The search of topological semimetal state in magnetic materials is an important and also challenging issue. While Dirac points are protected by inversion and time reversal symmetries, magnetic order or breaking of time reversal symmetry may destroy the robustness. Recently, research groups at home and abroad have reported several potential candidates, in which NdSb proposed by my group has solid evidence, i.e., chiral anomaly induced negative longitudinal magnetoresistance. In this project, we will focus on the magnetic and transport properties of lanthanide metal antimonides and bismuthides in the extreme conditions of high magnetic field and ultralow temperature. Electronic structures and carriers will be probed by high field magnetoresistance, Hall, and susceptibility measurements, and potential chiral anomaly will be checked by measurements of negative longitudinal magnetoresistance and planar Hall effect. This project will shed light on the origin of magnetic topological semimetal state, the nature of topological transition, and also the Dirac/Weyl quasiparticles tuned by different symmetries and spin degeneracies.

在磁性材料中实现拓扑半金属态一直以来都是非常重要且极具挑战的工作。由于磁序的存在，时间反演对称性破缺，原本受对称性保护的狄拉克点变得不稳定。近期，国内外的研究组陆续报道了一些潜在的磁性拓扑半金属材料，尤其是申请人研究组在NdSb中直接观测到手性反常导致的负磁阻现象，为拓扑半金属态的存在提供了坚实的证据。本项目将在前期工作的基础上，深入研究镧系金属锑化物、铋化物在强磁场、极低温等极端条件下的磁性与量子输运特性。我们将通过高场磁阻、霍尔系数、磁化率的测量以及量子振荡分析，研究能带结构与载流子特性；通过负磁阻效应与平面霍尔效应的测量，检验手性反常。本项目的实施，一方面有望阐明拓扑半金属态的形成机制以及拓扑相变的本质，另一方面有望得到不同对称性与自旋简并度对拓扑半金属准粒子的演化规律。

物质的拓扑性是近年来凝聚态物理最重要的课题之一。拓扑半金属是一类新型的拓扑材料，具有类似于基本粒子的低能激发态，在科学认知与实际应用方面都有重大意义。磁性拓扑半金属的发现对于完善拓扑半金属分类、检验拓扑半金属理论至为关键。本项目围绕磁性拓扑半金属开展了较深入的研究：制备了一系列磁性拓扑半金属的候选材料，实验验证了部分材料的拓扑奇异性，对拓扑半金属的平面霍尔效应、磁性拓扑半金属的临界相变行为进行了系统研究，较好的完成了计划任务书中的研究内容。此外，我们在新型二维半导体的光电特性方面取得了一些初步成果。在本项目支持下，课题组发表论文多篇，其中7篇发表在ACS Applied Materials & Interfaces，Journal of Materials Chemistry C，Applied Physics Letters， Physical Review B，Physical Review Materials等期刊上；受邀撰写专题综述”Materials and possible mechanisms of extremely large magnetoresistance: a review”；获得1项联合基金重点项目（子课题）和1项国家重点研发计划项目（参与）支持；支持了6名博士生的部分研究工作。