Degenerate topological line surface phonons in quasi-1D double helix crystal SnIP
Degenerate topological line surface phonons in quasi-1D double helix crystal SnIP
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DOI：
10.1038/s41524-021-00667-6
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发表时间：
2021-11
影响因子：
9.7
通讯作者：
Bo Peng;S. Murakami;B. Monserrat;Tiantian Zhang
中科院分区：
文献类型：
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作者：
Bo Peng;S. Murakami;B. Monserrat;Tiantian Zhang
晶体能带结构中的简并点/线已经成为越来越多的拓扑材料的主食。体-边界对应提供了体拓扑和表面状态之间的关系。虽然线简并体激发已被广泛的特点，线简并的表面状态没有得到很好的理解。我们发现，SnIP，准一维的双螺旋晶体结构的货车范德华材料，表现出拓扑节环/线的体声子模式和相应的表面状态。结合第一性原理计算、基于量子化学的指示剂理论和Zak相位分析，我们发现两个相邻的体节环在其鼓面状表面态中形成双简并线，这是由时间反演的对称性和滑移镜对称性的结合所保护的.我们的研究结果表明，表面简并可以一般的对称性，如保护，声子提供了一个理想的平台，探索这种简并。
Degenerate points/lines in the band structures of crystals have become a staple of the growing number of topological materials. The bulk-boundary correspondence provides a relation between bulk topology and surface states. While line degeneracies of bulk excitations have been extensively characterised, line degeneracies of surface states are not well understood. We show that SnIP, a quasi-one-dimensional van der Waals material with a double helix crystal structure, exhibits topological nodal rings/lines in both the bulk phonon modes and their corresponding surface states. Using a combination of first-principles calculations, symmetry-based indicator theories and Zak phase analysis, we find that two neighbouring bulk nodal rings form doubly degenerate lines in their drumhead-like surface states, which are protected by the combination of time-reversal symmetryand glide mirror symmetry. Our results indicate that surface degeneracies can be generically protected by symmetries such as, and phonons provide an ideal platform to explore such degeneracies.