关联外尔半金属的角分辨光电子能谱研究

Weyl semimetal states have become an important subject in condensed matter physics and materials science, due to their novel physical properties and potential applications. Previous experimental studies mainly focused on none- (or weak-) interaction systems. While the introduction of the electronic correlation effect can make the ground state of the system more sensitive to the internal and external parameters, leading to rich physical phenomena and inducing topological phase transitions between different quantum states. Based on our previous work, we propose a project to study the correlated Weyl semimetal states, like Weyl Kondo semimetals and so on. Using angle-resolved photoemission spectroscopy (ARPES), we focus on the candidate materials supported by recent theoretical or experimental evidences by accurately measuring all quantum numbers of electrons at both bulk and surface areas. Combined with theoretical calculations and other experimental methods, we explore the Weyl semimetal states from weak correlation to strong correlation regime and provide crucial experimental data to understand the intrinsic relationship between the topological property and correlation strength. By isovalent substitution, carrier doping and controlling temperature, we attempt to adjust the ground state of the system in order to realize novel the quantum states and topological phase transition. The primaeval experiments on candidates hosting emergent correlated topological quantum states are anticipated to make some distinctive and original achievements in the Weyl semimetal field.

外尔半金属的新奇物理性质和潜在应用价值，令其成为凝聚态物理和材料科学领域中一个前沿研究方向。前期实验研究主要集中于无(弱)相互作用系统，引入电子关联效应可使体系的基态对参数变化十分敏感，导致丰富的物理现象，诱导不同量子态间的拓扑相变。本项目拟开展对具有关联效应的外尔半金属的实验研究。通过角分辨光电子能谱，对一系列有理论或实验迹象支持的关联外尔半金属（如外尔近藤半金属等）候选材料进行探索，通过对其体内和表面电子的全部量子数的精确测量，结合理论计算和其它实验手段，探索处于不同关联强度区间内的外尔半金属材料的独特物性，揭示整体拓扑性质与关联效应等因素之间的本质联系，为系统研究关联外尔半金属态的奇特物性提供关键的实验数据。尝试通过元素替换、掺杂和温度变化，对关联外尔半金属进行调控，探索新的量子态和拓扑相变。本项目预期能在关联外尔半金属研究领域中取得有特色的原创性成果。

外尔半金属是近年来发现的一种新物态，具备许多独特的物理性质，在基础科学和应用科学领域都有重要意义。在外尔半金属可以通过破坏狄拉克半金属的时间/空间反演对称性来实现，引入关联效应可以使材料的整体拓扑性质发生变化，并可产生一系列新奇的相互作用，是凝聚态物理领域的重要课题。本项目利用体态敏感的同步辐射软x射线ARPES、表面敏感的同步辐射深紫外ARPES、自旋分辨ARPES、扫描电子显微镜等实验手段，结合第一性原理计算和理论模型分析，对一系列材料的电子结构进行了系统的研究，揭示了电子关联效应和拓扑性质之间的内在联系，获得成果包括：1）实验发现了鲁棒第二型外尔半金属WP2，证明自旋-轨道耦合导致手性相同的外尔点的劈裂；2）在NbSixTe2家族体系中发现一维无质量狄拉克费米子，并通过调节平移对称性实现对称性保证的弱拓扑绝缘体态；3）在kagome材料YCr6Ge6中观测到费米能附近共存的关联平带和狄拉克锥；4）在石墨烯基异质结中实现了大范围高阶摩尔效应，狄拉克锥的谷间相互作用可能导致关联摩尔平带。相关研究成果发表Nat. Mater.一篇、Phys. Rev. Lett.两篇、Phys. Rev. B两篇和Quantum Frontiers一篇。