npj：铁磁外尔半金属CrP2O7—从杂化节点环到可调外尔费米子

来源：知社学术圈

外尔半金属是费米面附近存在能带二重简并交叉的拓扑电子态的新材料，具有表面费米弧、动量空间磁单极、负磁阻等新奇量子现象，有望应用于下一代小型化低能耗的电子器件中。与传统的非磁外尔半金属相比，磁性外尔半金属材料中磁性与拓扑之间的相互作用会产生更丰富的物理现象，如内禀磁矩增强的反常霍尔效应及可调的外尔点等等。但目前为止，磁性拓扑外尔半金属的候选材料仍为数不多。

来自南方科技大学的徐虎教授领导的团队，基于第一性原理计算和对称性分析，研究了铁磁材料CrP2O7 的拓扑能带结构。在考虑自旋轨道耦合的情况下，体系的杂化节点环缩减为不同类型的外尔点。通过外加磁场改变磁化方向，可以调节外尔点的数量和类型。此外，计算得到的费米弧和准粒子干涉图样非常有助于实验的进一步观测。该研究结果为深入研究磁性和拓扑之间的相互作用提供了一个理想候选材料，并且加深了人们对铁磁拓扑半金属材料的认识。

该文近期发表于npj Computational Materials 5: 74 (2019)，英文标题与摘要如下，点击左下角“阅读原文”可以自由获取论文PDF。

Tunable ferromagnetic Weyl fermions from a hybrid nodal ring 

Baobing Zheng, Bowen Xia, Rui Wang, Jinzhu Zhao, Zhongjia Chen, Yujun Zhao & Hu Xu

Realization of nontrivial band topology in condensed matter systems is of great interest in recent years. Using first-principles calculations and symmetry analysis, we propose an exotic topological phase with tunable ferromagnetic Weyl fermions in a half-metallic oxide CrP2O7. In the absence of spin–orbit coupling (SOC), we reveal that CrP2O7 possesses a hybrid nodal ring. When SOC is present, the spin-rotation symmetry is broken. As a result, the hybrid nodal ring shrinks to discrete nodal points and forms different types of Weyl points. The Fermi arcs projected on the (100) surface are clearly visible, which can contribute to the experimental study for the topological properties of CrP2O7. In addition, the calculated quasiparticle interference patterns are also highly desirable for the experimental study of CrP2O7. Our findings provide a good candidate of ferromagnetic Weyl semimetals, and are expected to realize related topological applications with their attracted features.