因为新奇而丰富的物理性质及广阔的应用前景，拓扑半金属成为继拓扑绝缘体之后又一广受凝聚态物理和材料科学关注的研究热点之一。拓扑半金属不同于拓扑绝缘体需要强的自旋轨道耦合作用以打开非平庸的带隙，其在像轻元素材料这类无自旋轨道耦合作用的体系中也可以实现。另外，在凝聚态固体材料中实现超出Dirac-Weyl范式的其他类型的费米子（比如，三重简并费米子），最近也引起了人们极大的研究兴趣。本项目拟重点探究轻元素材料中拓扑半金属新的拓扑分类以及三重简并费米子在轻元素材料和重元素材料中出现的对称性要求的区别和联系。通过系统的分析和研究，本项目不但可以进一步深化对拓扑半金属和三重简并费米子体系的理解，还可以为实验研究提供更好的理论指导和材料基础，以推动拓扑半金属领域的进一步发展。

Due to novel, abundant physical properties and great application potential, topological semimetals, following topological insulators, have become one of the hot research topics in condensed-matter physics and materials science. Topological semimetals are different from topological insulators which need strong spin-orbit coupling to induce non-trivial band gaps, they can also be realized in spinless systems like light-element materials. Besides, to acquire some new fermions beyond Dirac-Weyl paradigm (for instance, triply-degenerate fermion) in condensed-matter solid materials have also received a lot of research interests recently. The main purposes of this project are studying novel topological classifications of topological semimetals in light-element materials and the difference and correlations of symmetry constraints on the triply-degenerate fermions in light-element materials and heavy-element materials. Through the systematic analysis and studies, not only this project can enhance our understanding of topological semimetals and triply-degenerate fermion systems, but also can provide better theoretical guidance and materials foundation for experimental researches, and push forward the developments in the topological semimetals fields further.