EuCd $_2$ As $_2$自旋倾斜结构中的单对Weyl节点
Single pair of Weyl nodes in the spin-canted structure of EuCd$_2$As$_2$
摘要：
时间反演对称性破缺Weyl半金属是唯一的Weyl材料中，允许最小数量的Weyl点，从而提供相关物理的最清晰的签名。在这里，我们提出的中子衍射，密度泛函理论和输运测量的结果表明，EuCd $_2$ As $_2$，在环境场，应变和压力下，是这样一个材料的单对Weyl点。我们的工作揭示了一个磁结构（磁空间群$C2'/m'$）与Eu矩指向沿[210]方向在平面内和倾斜的$\sim$ 30 $^{\circ}$面外。使用这种结构的密度泛函理论计算表明，观察到的倾斜大大改变了相关的电子带，相对于平面内的顺序，导致一组定义良好的外尔点。此外，我们发现倾斜角可以调节费米能级以上外尔点的距离，并且在小倾斜角时外尔点的距离最小。最后，传输测量的异常霍尔效应和纵向磁电阻表现出的手征异常，从而支持的中子散射和DFT的结果表明EuCd $_2$作为$_2$接近外尔“氢原子“的理想情况。
英文摘要：
Time reversal symmetry breaking Weyl semimetals are unique among Weyl materials in allowing the minimal number of Weyl points thus offering the clearest signatures of the associated physics. Here we present neutron diffraction, density functional theory and transport measurement results which indicate that EuCd$_2$As$_2$ , under ambient field, strain and pressure, is such a material with a single pair of Weyl points. Our work reveals a magnetic structure (magnetic space group $C2'/m'$) with Eu moments pointing along the [210] direction in-plane and canted $\sim$ 30$^{\circ}$ out-of-plane. Density functional theory calculations using this structure show that the observed canting drastically alters the relevant electronic bands, relative to the in-plane order, leading to a single set of well defined Weyl points. Furthermore, we find the canting angle can tune the distance of the Weyl points above the Fermi level, with the smallest distance at low canting angles. Finally, transport measurements of the anomalous Hall Effect and longitudinal magnetoresistance exhibit properties indicative of a chiral anomaly, thus supporting the neutron scattering and DFT results suggesting EuCd$_2$As$_2$ is close to the ideal situation of the Weyl "Hydrogen atom".
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