Hourglass Charge-Three Weyl Phonons

Abstract

Unconventional Weyl point with nonlinear dispersion features higher topological charge $|\mathcal{C}|>1$ 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 $|\mathcal{C}|=3$ 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, $\alpha$-LiIO${}_3$ as the first realistic example with this unconventional Weyl point. Particularly, in the phonon spectra of $\alpha$-LiIO${}_3$, two Weyl points with $\mathcal{C}=-3$, 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 $\alpha$-LiIO${}_3$ and also show that the phonon spectra is a great platform for exploring unconventional topological states.

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• Triple hourglass Weyl phonons
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• Controllable Weyl Nodes and Fermi Arcs from Floquet Engineering Triple Fermions
• Chiral phonons in binary compounds $A$Bi ($A$ = K, Rb, Cs) with P2${}_1$/c structure
• Multiple types of unconventional quasiparticles in the chiral crystal CsBe${}_2$F${}_5$
• Phonon Weyl points and chiral edge modes with unconventional Fermi arcs in NbSi${}_2$
• Ferroelectrically Controlled Chirality Switching of Weyl Quasiparticles