Hourglass Charge-Three Weyl Phonons

Abstract

Unconventional Weyl point with nonlinear dispersion features higher topological charge ∣C∣>1|{\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 ∣C∣=3|{\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, α\rm\alpha-LiIO3_3 as the first realistic example with this unconventional Weyl point. Particularly, in the phonon spectra of α\rm\alpha-LiIO3_3, two Weyl points with C=−3{\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 α\rm\alpha-LiIO3_3 and also show that the phonon spectra is a great platform for exploring unconventional topological states

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