Triple hourglass Weyl phonons

TL;DR

This paper predicts and confirms the existence of triple hourglass Weyl phonons with high topological charge in chiral space groups, revealing unique surface arcs and proposing LiIO$_3$ as a candidate material.

Contribution

It introduces symmetry enforced triple hourglass Weyl phonons with Chern number ±3 and demonstrates their realization in LiIO$_3$, expanding the understanding of topological phonons.

Findings

THWPs with Chern number ±3 identified in LiIO$_3$

Unique sextuple-helicoid surface arcs observed

Six equivalent SWPs emerge due to symmetry constraints

Abstract

Unconventional Weyl phonons with higher topological charges in crystalline solids have attracted increasing attention. By symmetry analysis and low-energy $k.p$ effective Hamiltonian, we propose the symmetry enforced triple hourglass Weyl phonons (THWPs) with Chern number $\mathcal C$ = $\pm$ 3 protected by $6_3$ screw rotation symmetry in chiral space groups 173 ($P6_3$) and 182 ($P6_322$). We take LiIO$_3$ with space group 173 as a candidate and confirm that it possesses THWP with linear and quadratic dispersions along the $k_z$ direction and in the $k_x$-$k_y$ plane, respectively. Due to the constraints of crystal symmetry and topological charge conservation, six equivalent single Weyl phonons (SWPs) emerge and lie in the $k_z$ = 0 plane. Therefore, the unique phonon surface arcs connect the projections of two THWPs and six SWPs, leading to nontrivial sextuple-helicoid surface arcs on the (001) surface Brillouin zone. Our work proposes a class of topological phonons and realizes it in realistic materials, providing a perfect platform for experimental observation of THWPs. We expect our work to provide a new idea for detection of unconventional quasiparticles.