节线拓扑半金属拥有非平庸的鼓膜状表面态、丰富的电磁输运行为等特点，在量子输运、高温超导等领域拥有潜在应用。当前大部分节线拓扑半金属发现于同时具有中心反演和时间反演对称性的材料体系中，然而这些节线在体系强自旋轨道耦合的作用下会打开较大能隙（最高可达200meV），极大破坏节线电子的本征特性。针对这一问题，本项目提出利用电子晶体中传导电子被局域在晶格空位中而本征呈现弱的自旋轨道耦合的特点，基于电子晶体开发具有小自旋轨道耦合能隙节线拓扑半金属的构想。依据我们大量符合预期的前期结果，本项目项目将以X2Y（X=Ca，Sr，Ba；Y=As，Sb，Bi）系列电子晶体为切入点，旨在：1）开发与合成若干种具有自旋轨道耦合能隙小于10meV、节线电子特性显著的节线拓扑半金属，并对其物性展开研究；2）通过对它们电子结构、基本物性、以及电子晶体与拓扑节线融合点的研究，建立起开发电子晶体型节线拓扑半金属的一般方法。

Topological nodal line semimetals, which possesses many appealing properties such as nontrivial drumhead surface states and rich transport characters, have potential applications in the fields of quantum transports and high-temperature superconductivity. Currently, most realistic topological nodal line semimetals are proposed in materials where the inversion symmetry and the time reversal symmetry coexist. However, nodal lines in these materials will be gapped when spin-orbit coupling is taken into account. Especially, when containing heavy elements, the spin-orbit coupling gap can as large as 200 meV, which will greatly destroy the intrinsic properties of nodal lines. On concerning this issue, we proposes to develop topological nodal line semimetals with small spin-orbit coupling gap by using electrides as the platform. In electrides, the conduction electrons are mostly localized in the interstitial sites of the lattice. These electrons are not constrained by the nuclei electric field, thereby intrinsically manifest weak spin-orbit coupling. Based on our extensive work upfront, our project will start from the family of X2Y (X=Ca, Sr, Ba; Y=As, Sb, Bi) electrides, and the targets of our project are: 1) design and prepare several ideal topological nodal line semimetals with small spin-orbit coupling gap (< 10 meV) and pronounced nodal line characters; 2) based on the investigations on their electronic structures, physical properties and the combination point of electride and nodal line, we finally develop the general rules for exploring ideal topological nodal line semimetals from electrides.