论文标题
1651个磁性空间组和528个磁性层组中的所有沙漏玻色子激发
All hourglass bosonic excitations in the 1651 magnetic space groups and 528 magnetic layer groups
论文作者
论文摘要
小组的不可还原表示之间的兼容性关系所施加的带连接性会产生由四个带和五个带横梁（BCS）组成的异国沙漏样形状。这样的沙漏频带连接可以强制实施诸如Weyl Fermion，Dirac Fermion甚至超越它们之外的非平凡激发的出现。另一方面，玻色子（如声子，镁质和光子）也被证明具有非平凡的拓扑结构，而沙漏玻色子激发的全面对称性分类对材料设计和设备应用都具有重要意义。在这里，我们首先列出了布里群区域（BZ）中与小组的所有混凝土位置和表示，分别适用于所有1651个磁性空间组和528个磁性磁层组，分别适用于三维（3D）和两个维度（2D）系统。发现255（42）个MSG（MLG）基本上托管了这样的沙漏BCS：这里``基本上''意味着，只要在相应的MSG/MLG中结晶的系统结晶，Bosonic Hourglass BC绝对存在。我们还对数百种3D非磁性材料进行了第一原理计算本质上是托管沙漏声子，并提出2D材料Ali可以托管沙漏声子。我们选择辅助（x = br和i）作为说明性示例，以证明两种材料的两个必需的沙漏带结构可以在声子光谱中共存，而对于AUBR来说，发现了一个意外的频带交叉粘贴两个小型镜。我们针对沙漏玻色弹性激发的对称条件的结果可以为使用沙漏玻色子激发设计人工结构提供有用的指南。
The band connectivity as imposed by the compatibility relations between the irreducible representations of little groups can give rise to the exotic hourglass-like shape composed of four branches of bands and five band crossings (BCs). Such an hourglass band connectivity could enforce the emergence of nontrivial excitations like Weyl fermion, Dirac fermion or even beyond them. On the other hand, the bosons, like phonons, magnons, and photons, were also shown to possess nontrivial topology and a comprehensive symmetry classification of the hourglass bosonic excitations would be of great significance to both materials design and device applications. Here we firstly list all concrete positions and representations of little groups in the Brillouin zone (BZ) related with the hourglass bosonic excitations in all the 1651 magnetic space groups and 528 magnetic layer groups, applicable to three dimensional (3D) and two dimensional (2D) systems, respectively. 255 (42) MSGs (MLGs) are found to essentially host such hourglass BCs: Here ``essentially'' means that the bosonic hourglass BC exists definitely as long as the studied system is crystallized in the corresponding MSG/MLG. We also perform first-principles calculations on hundreds of 3D nonmagnetic materials essentially hosting hourglass phonons and propose that the 2D material AlI can host hourglass phonons. We choose AuX (X=Br and I) as illustrative examples to demonstrate that two essential hourglass band structures can coexist in the phonon spectra for both materials while for AuBr, an accidental band crossing sticking two hourglasses is found interestingly. Our results of symmetry conditions for hourglass bosonic excitations can provide a useful guide of designing artificial structures with hourglass bosonic excitations.
