Experimental Observation of Dirac Nodal Links in Centrosymmetric Semimetal TiB2
Experimental Observation of Dirac Nodal Links in Centrosymmetric Semimetal TiB2
复制标题
中心对称半金属TiB2狄拉克节点连杆的实验观察
DOI：
10.1103/physrevx.8.031044
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发表时间：
2018-08-17
影响因子：
12.5
通讯作者：
Wang, Shancai
中科院分区：
文献类型：
--
作者：
Liu, Zhonghao;Lou, Rui;Wang, Shancai
作为各种拓扑量子相的沃土的拓扑节线半金属态，当特定的保护对称性被打破时，可以实现拓扑绝缘体、狄拉克半金属或魏尔半金属，但只在很少的材料中进行了实验研究。与离散节点相比，具有丰富拓扑结构的节线可以导致更多不寻常的输运现象。利用角分辨光电子能谱和第一性原理计算，我们提供了中心对称半金属TiB_2中节线费米子的有力证据，其自旋-轨道耦合效应可以忽略不计。利用费米能级以下的能带交叉点，可以清楚地观察到两组Dirac节环，一组在水平镜面的布里渊区(BZ)角附近，另一组在垂直镜面的BZ中心附近，没有任何其他能带的干扰。形成狄拉克节环的线性色散宽达2 eV。我们进一步观察到，这两组节点环沿着$\Gamma$-$K$方向连接在一起，构成了节点-链接构型。以狄拉克节点链为主的费米面的简单电子结构表明，TiB$2是研究和应用与节线费米子相关的新物理性质的一个很好的平台。
The topological nodal-line semimetal state, serving as a fertile ground for various topological quantum phases, where a topological insulator, Dirac semimetal, or Weyl semimetal can be realized when the certain protecting symmetry is broken, has only been experimentally studied in very few materials. In contrast to discrete nodes, nodal lines with rich topological configurations can lead to more unusual transport phenomena. Utilizing angle-resolved photoemission spectroscopy and first-principles calculations, here, we provide compelling evidence of nodal-line fermions in centrosymmetric semimetal TiB$_2$ with a negligible spin-orbit coupling effect. With the band crossings just below the Fermi energy, two groups of Dirac nodal rings are clearly observed without any interference from other bands, one surrounding the Brillouin zone (BZ) corner in the horizontal mirror plane $\sigma_h$ and the other surrounding the BZ center in the vertical mirror plane $\sigma_v$. The linear dispersions forming Dirac nodal rings are as wide as 2 eV. We further observe that the two groups of nodal rings link together along the $\Gamma$-$K$ direction, composing a nodal-link configuration. The simple electronic structure with Dirac nodal links mainly constituting the Fermi surfaces suggests TiB$_2$ as a remarkable platform for studying and applying the novel physical properties related to nodal-line fermions.