Here we systematically investigate the structure, phase stability, half-metallicity, and topological electronic structure for a topological spintronic material $\mathrm{Na}{\mathrm{V}}_2{\mathrm{O}}_4$. The material has a tetragonal structure with excellent dynamical and thermal stabilities. It shows a half-metallic ground state, where only the spin-up bands are present near the Fermi level. These bands are demonstrated to form a nodal line with the double degeneracy on the $k_z=0$ plane. The nodal line is robust against spin-orbit coupling, under the protection of the mirror symmetry. The nodal line band structure is very clean, thus the drumhead surface states can be clearly identified. Remarkably, the nodal line and drumhead surface states have the $100\%$ spin polarization, which are highly desirable for spintronics applications. In addition, by shifting the magnetic field in-plane, we find that the nodal line can transform into a single pair of Weyl nodes. The nodal-line and Weyl-node fermions in the bulk, as well as the drumhead fermions on the surface are all fully spin-polarized, which may generate interesting physical properties and promising applications.

中文翻译：

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化合物NaV2O4中的结构，相稳定性，半金属性和完全自旋极化的Weyl态：拓扑自旋电子材料的示例

在这里，我们系统地研究拓扑自旋电子材料的结构，相稳定性，半金属性和拓扑电子结构 $娜{\mathrm{V}}_2{\mathrm{Ø}}_4$。该材料具有良好的动态和热稳定性的四方结构。它显示了一种半金属基态，其中在费米能级附近仅存在自旋带。这些波段被证明形成了一条带有双重简并的节点线。${ķ}_{ž}=0$飞机。在镜面对称性的保护下，节点线对于自旋轨道耦合具有鲁棒性。节点线带结构非常干净，因此可以清楚地识别鼓面的表面状态。值得注意的是，结线和鼓面的表面状态具有$100％$自旋极化，这对于自旋电子学应用是非常需要的。另外，通过在平面内移动磁场，我们发现节点线可以转换为一对Weyl节点。本体中的节点线和Weyl节点费米子，以及表面上的鼓面费米子都被完全自旋极化，这可能会产生令人感兴趣的物理特性和有希望的应用。