单斜半金属SrAs $_3$中Dirac节线的光电子能谱证据
Photoemission Spectroscopic Evidence for the Dirac Nodal Line in Monoclinic Semimetal SrAs$_3$
摘要：
具有奇异量子特性的拓扑线半金属在动量空间中表现出受量子保护的线接触体能带交叉。然而，在大多数已识别的拓扑结线化合物中，这些拓扑非平凡结线被费米能级处的复杂拓扑平凡态（$E_F$）所包围，这将给它们的识别和进一步的应用带来困难。利用角分辨光电子能谱和第一性原理计算，我们提供了令人信服的证据，狄拉克线费米子的存在，在单斜半金属SrAs $_3$，这是接近$E_F$和远离分心的复杂平凡的费米面或表面状态。计算结果表明，在$E_F$附近的\emph{Y}附近，两个宇称相反的能带发生反转，在$Γ$ - \emph{Y} - \emph{S}平面上形成单节环，自旋轨道耦合效应可以忽略.我们跟踪这些带交叉，然后明确地确定了完整的节环定量，这提供了一个关键的实验支持的预测在CaP $_3$家庭的材料的线费米子。SrAs $_3$在$E_F$周围具有简单的拓扑非平凡体电子态，且不干扰自然解理面上的表面态，有望成为拓扑量子态研究和应用的潜在平台。
英文摘要：
Topological nodal-line semimetals with exotic quantum properties are characterized by symmetry-protected line-contact bulk band crossings in the momentum space. However, in most of identified topological nodal-line compounds, these topological non-trivial nodal lines are enclosed by complicated topological trivial states at the Fermi energy ($E_F$), which would perplex their identification and hinder further applications. Utilizing angle-resolved photoemission spectroscopy and first-principles calculations, we provide compelling evidence for the existence of Dirac nodal-line fermions in the monoclinic semimetal SrAs$_3$, which are close to $E_F$ and away from distraction of complex trivial Fermi surfaces or surface states. Our calculation indicates that two bands with opposite parity are inverted around \emph{Y} near $E_F$, which results in the single nodal loop at the $Γ$-\emph{Y}-\emph{S} plane with a negligible spin-orbit coupling effect. We track these band crossings and then unambiguously identify the complete nodal loop quantitatively, which provides a critical experimental support to the prediction of nodal-line fermions in the CaP$_3$ family of materials. Hosting simple topological non-trivial bulk electronic states around $E_F$ and no interfering with surface states on the natural cleavage plane, SrAs$_3$ is expected to be a potential platform for topological quantum state investigation and applications.
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