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arXiv · 2111.12725

Degenerate topological line surface phonons in quasi-1D double helix crystal SnIP

Bo Peng·Shuichi Murakami·Bartomeu Monserrat·Tiantian Zhang
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Abstract

Degenerate points/lines in the bulk 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 characterized, 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 and glide mirror symmetries $\mathcal{T}\bar{M}_y$. Our results indicate that surface degeneracies can be generically protected by symmetries such as $\mathcal{T}\bar{M}_y$, and phonons provide an ideal platform to explore such degeneracies.

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Bo Peng, Shuichi Murakami, Bartomeu Monserrat, Tiantian Zhang. 2021-11-24. Degenerate topological line surface phonons in quasi-1D double helix crystal SnIP. https://doi.org/10.1038/s41524-021-00667-6

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