Exploring unconventional topological quasiparticles and their associated exotic physical properties has become a hot topic in condensed matter physics, thus stimulating extensive interest in recent years. Here, in contrast to the double-Weyl phonons (the topological chiral charge +2) in the trigonal and hexagonal crystal systems, we propose that the unconventional double-Weyl without counterparts in high-energy physics can emerge in the phonons of cubic structures, i.e., SrSi₂. Employing a two-band k ⋅ p Hamiltonian, we prove that the quadratic double-Weyl nodes are protected by the fourfold screw rotational symmetry \({\tilde{C}}_{4}\). Strikingly, we find that the surface arcs are terminated with the Weyl nodes that possess unequal topological charges with opposite sign (i.e., +2 and −1), leading to unique three-terminal Weyl complex (one quadratic double-Weyl and two linear single-Weyl) with double surface arcs in SrSi₂. In addition, we apply a uniaxial tensile strain along z-axis to examine the evolution of the three-terminal Weyl complex when the corresponding symmetries are broken. Our work not only provides an ideal candidate for the realization of the quadratic double-Weyl and the corresponding unique surface arc states, but also broadens the understanding of topological Weyl physics.

探索非常规的拓扑准粒子及其相关的奇异物理性质已成为凝聚态物理的一个热门话题，从而引起了近年来的广泛兴趣。在这里，与三角和六边形晶体系统中的双魏尔声子（拓扑手性电荷+2）相反，我们提出，高能物理中没有对应物的非常规双魏尔可以出现在立方结构的声子中，即，SrSi ₂。采用两波段ķ ⋅ p哈密顿量，我们证明了二次双外尔节点由四倍螺杆旋转对称保护\（{\代字号{C}} _ {4} \）。令人惊讶的是，我们发现表面弧终止于具有相反电荷（即+2和-1）的不等拓扑电荷的Weyl节点，从而导致唯一的三端Weyl络合物（一个二次双Weyl和两个线性单Weyl络合物） -Weyl）在SrSi _2中具有双表面弧。此外，我们沿z轴施加单轴拉伸应变，以检查当相应的对称性破坏时三端Weyl配合物的演化。我们的工作不仅为实现二次双Weyl和相应的独特表面弧态提供了理想的候选者，而且拓宽了对Weyl拓扑物理学的理解。