PdSb $_2$中六重简并费米子的观测
Observation of sixfold degenerate fermions in PdSb$_2$
摘要：
在拓扑量子材料中，有三种费米子被广泛研究：狄拉克费米子、外尔费米子和马约拉纳费米子。除了高能物理中的基本费米子之外，奇异的费米子也可以存在于三重、六重或八重简并带交叉的凝聚态系统中。在这里，我们使用角分辨光电子能谱直接可视化三个双简并带PdSb $_2$。我们能够实现的能量分辨率允许在R点的所有六重简并带的确认，在显着的一致性与第一性原理计算。此外，我们发现，这种六重简并交叉具有二次色散的理论预测。最后，我们比较了六重简并费米子与先前确认的费米子，以证明这项工作的重要性：我们的研究表明，拓扑费米子超出了高能物理的限制。
英文摘要：
Three types of fermions have been extensively studied in topological quantum materials: Dirac, Weyl, and Majorana fermions. Beyond the fundamental fermions in high energy physics, exotic fermions are allowed in condensed matter systems residing in three-, six- or eightfold degenerate band crossings. Here, we use angle-resolved photoemission spectroscopy to directly visualize three-doubly-degenerate bands in PdSb$_2$. The ultrahigh energy resolution we are able to achieve allows for the confirmation of all the sixfold degenerate bands at the R point, in remarkable consistency with first-principles calculations. Moreover, we find that this sixfold degenerate crossing has quadratic dispersion as predicted by theory. Finally, we compare sixfold degenerate fermions with previously confirmed fermions to demonstrate the importance of this work: our study indicates a topological fermion beyond the constraints of high energy physics.
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