Changes in the number of Weyl nodes in Weyl semimetals occur through merging processes, usually involving a pair of oppositely charged nodes. More complicated processes involving multiple Weyl nodes are also possible, but they typically require fine tuning and are thus less stable. In this Letter, we study how symmetries affect the allowed merging processes and their stability, focusing on the combination of a twofold rotation and time-reversal (𝐶2⁢𝒯) symmetry. We find that, counterintuitively, processes involving a merging of three nodes are more generic than processes involving only two nodes. Our Letter suggests that multi-Weyl merging may be observed in a large variety of quantum materials, and we discuss SrSi2 and bilayer graphene as potential candidates.

中文翻译：

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对称约束下 Weyl 节点合并过程的稳定性


外尔半金属中外尔节点数量的变化是通过合并过程发生的，通常涉及一对带相反电荷的节点。涉及多个 Weyl 节点的更复杂的过程也是可能的，但它们通常需要微调，因此不太稳定。在这封信中，我们研究了对称性如何影响允许的合并过程及其稳定性，重点关注双重旋转和时间反转 （C2T） 对称性的结合。我们发现，与直觉相反，涉及三个节点合并的流程比仅涉及两个节点的流程更通用。我们的信表明，在多种量子材料中可能会观察到多外尔合并，我们将 SrSi2 和双层石墨烯作为潜在的候选者进行讨论。