In the rapidly expanding field of topological materials there is growing interest in systems whose topological electronic band features can be induced or controlled by magnetism. Magnetic Weyl semimetals, which contain linear band crossings near the Fermi level, are of particular interest owing to their exotic charge and spin transport properties. Up to now, the majority of magnetic Weyl semimetals have been realized in ferro- or ferrimagnetically ordered compounds, but a disadvantage of these materials for practical use is their stray magnetic field which limits the minimum size of devices. Here we show that Weyl nodes can be induced by a helical spin configuration, in which the magnetization is fully compensated. Using a combination of neutron diffraction and resonant elastic x-ray scattering, we find that below T_N = 14.5 K the Eu spins in EuCuAs develop a planar helical structure which induces two quadratic Weyl nodes with Chern numbers C = ±2 at the A point in the Brillouin zone.

在快速扩展的拓扑材料领域，人们对拓扑电子能带特征可以通过磁性感应或控制的系统越来越感兴趣。磁性外尔半金属在费米能级附近包含线性带交叉，由于其奇异的电荷和自旋输运特性而受到特别关注。到目前为止，大多数磁性外尔半金属已经在铁磁或亚铁磁有序化合物中实现，但这些材料在实际应用中的缺点是它们的杂散磁场限制了器件的最小尺寸。在这里，我们展示了外尔节点可以通过螺旋自旋配置引起，其中磁化强度得到完全补偿。结合中子衍射和共振弹性 X 射线散射，我们发现低于T _N = 14.5 K，EuCuAs 中的 Eu 自旋形成平面螺旋结构， 在 A 点 产生两个陈数C = ±2 的二次 Weyl 节点在布里渊区。