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磁性外尔半金属材料研究现状与展望

Magnetic Weyl semimetal materials

  • 摘要: 外尔半金属是拓扑半金属家族中的一员。理想的外尔半金属费米面附近有且仅有非简并价带和导带形成的孤立能带交叉点,其低能激发准粒子可以用描述手性外尔费米子的外尔方程来刻画。在三维固体中形成外尔半金属态需要破缺时间反演、中心反演以及它们的组合对称操作。外尔点(即能带交叉点)具有拓扑稳定性和确定的手性或磁荷,且左右手性外尔点需成对出现。非磁性外尔半金属TaAs家族材料的发现,使得研究具有手征性的电子态,及其导致的新物性、新现象成为可能。与非磁性外尔半金属相比,磁性外尔半金属可以仅仅具有一对外尔点,是最简单的外尔半金属,有利于物理机理的分析。磁性外尔半金属可用于实现具有本征磁性的量子反常霍尔效应,提供了通过外磁场来调控外尔点及其相关效应的新手段。文章介绍了磁性外尔半金属的理论模型、拓扑数计算等基本原理,简要回顾了一些典型材料的理论计算和实验研究进展,并介绍了磁性拓扑量子化学理论和磁性拓扑材料的高通量计算,最后讨论了磁性外尔半金属的发展前景和未来的研究方向。

     

    Abstract: A Weyl semimetal(WSM) is a member of the topological semimetal family. An ideal WSM has, and only has, isolated band crossing points formed by the nondegenerate valence and conduction bands near the Fermi level. The low energy excitation of its quasiparticles can be characterized by the Weyl equation describing the chiral Weyl fermions. The formation of WSM states in three- dimensional solids requires breaking of the time reversal symmetry, inversion symmetry, and their combined symmetry. The Weyl point, i.e., the band crossing point, has topological stability and definite chirality or magnetic charge, and the left- and right-handed chiral Weyl points must appear in pairs. The discovery of the nonmagnetic Weyl semimetal TaAs family of materials makes it possible to study the electronic states with chiral properties and the new physical properties and phenomena caused by them. Compared with nonmagnetic WSMs, magnetic Weyl semimetals can have one pair of Weyl points, which is the simplest type and is useful for the analysis of physical mechanism. They can be used to realize the quantum anomalous Hall effect with intrinsic magnetism, which provides a new means to control Weyl points and related effects through the outer magnetic field. In this work we introduce the basic principles of magnetic WSMs, including a theoretical model and calculation of the topological number, then review the theoretical predictions and experimental studies of some typical materials, as well as the latest developments in magnetic topological quantum chemistry and high-throughput calculations of magnetic topological materials. Finally, we discuss the prospects for magnetic WSMs and future research directions.

     

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