Hourglass Charge-Three Weyl Phonons

TL;DR

This paper predicts the first realistic material, $ meta$-LiIO$_3$, hosting hourglass charge-3 Weyl phonons with unique topological features, using first-principles calculations and theoretical analysis.

Contribution

It reports the discovery of hourglass charge-3 Weyl phonons in $ meta$-LiIO$_3$, a novel topological state not previously observed in real materials.

Findings

Identification of two Weyl points with C=-3 in $ meta$-LiIO$_3$ phonon spectra

Observation of symmetry-protected triple- and sextuple-helicoid surface arc states

Uncovering the topological character of $ meta$-LiIO$_3$ phonons

Abstract

Unconventional Weyl point with nonlinear dispersion features higher topological charge $|{\cal{C}}|>1$ and multiple topologically protected Fermi arc states at its boundary. As a novel topological state, it has been attracting widespread attention. However, the unconventional Weyl point with $|{\cal{C}}|=3$ has not yet been reported in realistic materials, even though it has been theoretically proposed for more than a decade. In this work, based on first-principles calculations and theoretical analysis, we predict the existing material, $\rm\alpha$-LiIO$_3$ as the first realistic example with this unconventional Weyl point. Particularly, in the phonon spectra of $\rm\alpha$-LiIO$_3$, two Weyl points with ${\cal{C}}=-3$, connected by time-reversal symmetry, appear at the neck crossing-point of a hourglass-type band, leading to two hourglass charge-3 Weyl phonons. The symmetry protection and the associated novel triple- and sextuple-helicoid surface arc states of the hourglass charge-3 Weyl phonons are revealed. Our results uncover a hidden topological character of $\rm\alpha$-LiIO$_3$ and also show that the phonon spectra is a great platform for exploring unconventional topological states.