标题： 候选外尔氢原子K$_2$Mn$_3$(AsO$_4$)$_3$的绝缘基态和2-k磁结构 显示英文标题

标题： Insulating ground state and 2-k magnetic structure of candidate Weyl Hydrogen atom K$_2$Mn$_3$(AsO$_4$)$_3$

摘要： 理想Weyl '氢原子' 半金属仅在费米能级处表现出一对Weyl节点和其他非平庸态。 这种材料将在Weyl准粒子的研究中成为万灵药，允许直接明确地观察其拓扑性质。 类似alluaudite的 K$_2$Mn$_3$(AsO$_4$)$_3$化合物最近被提出作为这种材料。 在这里，我们使用全面的实验工作和第一性原理计算来评估这一预测。 我们发现 K$_2$Mn$_3$(AsO$_4$)$_3$在$C2/c$对称性下结晶，具有准1D Mn亚晶格，以小针状晶体生长。 块体性质测量显示在$\approx$8 和$\approx$4 K 发生磁性转变，中子散射实验表明这些对应于两种不同的磁性有序，首先是 8 K 时部分有序的铁磁结构$\mathbf{k_1}$= (0, 0, 0)，其次是 4 K 时的$\mathbf{k_2}$= (1, 0, 0) 转变为完全有序状态。在第二次转变以下，两个序矢量都是描述具有调制自旋大小的复杂磁结构所必需的。本工作中找到的两个最佳拟合磁结构都被发现破坏了生成外尔节点所需的对称性，尽管由$\mathbf{k_1}$允许的一种磁结构保持了这种对称性。然而，晶体是光学透明的，椭圆偏振测量显示有大的带隙，这与半金属行为的预期相矛盾。密度泛函理论计算预测了一个绝缘反铁磁基态，与之前的报道相反，并表明磁子晶格上可能存在潜在的挫折。鉴于所有奥迪特结构的广泛可调性，我们考虑了将系统推向半金属态的方法。 显示英文摘要

摘要： The ideal Weyl 'Hydrogen-atom' semi-metal exhibits only a single pair of Weyl nodes and no other trivial states at the Fermi energy. Such a material would be a panacea in the study of Weyl quasi particles allowing direct unambiguous observation of their topological properties. The alluaudite-like K$_2$Mn$_3$(AsO$_4$)$_3$ compound was recently proposed as such a material. Here we use comprehensive experimental work and first principle calculations to assess this prediction. We find K$_2$Mn$_3$(AsO$_4$)$_3$ crystallizes in the $C2/c$ symmetry with a quasi-1D Mn sublattice, growing as small needle-like crystals. Bulk properties measurements reveal magnetic transitions at $\approx$ 8 and $\approx$ 4 K which neutron scattering experiments show correspond to two distinct magnetic orders, first a partially ordered ferrimagnetic $\mathbf{k_1}$= (0, 0, 0) structure at 8 K and a second transition of $\mathbf{k_2}$= (1, 0, 0) at 4 K to a fully ordered state. Below the second transition, both ordering vectors are necessary to describe the complex magnetic structure with modulated spin magnitudes. Both of the best-fit magnetic structures in this work are found to break the symmetry necessary for the generation of the Weyl nodes, though one of the magnetic structures allowed by $\mathbf{k_1}$ does preserve this symmetry. However, the crystals are optically transparent and ellipsometry measurements reveal a large band-gap, undermining expectations of semi-metallic behavior. Density functional theory calculations predict an insulating antiferromagnetic ground state, in contrast to previous reports, and suggest potential frustration on the magnetic sublattice. Given the wide tunability of the alluaudite structure we consider ways to push the system closer to semi-metallic state.