Realization of the Single-pair-Weyl Phonons with the Maximum Charge Number in Acoustic Crystals

TL;DR

This paper reports the design of an acoustic crystal that hosts a unique pair of Weyl phonons with maximum charge, providing a platform for experimental study of topological properties in acoustic systems.

Contribution

The authors successfully designed an acoustic crystal with a single pair of Weyl phonons having maximum charge, using a simple two-band mode, and demonstrated their topological properties theoretically.

Findings

Weyl phonons with charge ±4 are located at high-symmetry points.

The designed Weyl phonons are isolated from other bands and hybridizations.

The structure is suitable for experimental observation of topological phenomena.

Abstract

To observe the Weyl phonon (WP) with the maximum charge and to design a realistic material structure containing only single-pair-WPs have long been considered two challenges in the field of topology physics. Here we have successfully designed an acoustic crystal to realize the single-pair-WPs with the maximum charge for the first time. Our theoretical simulations on acoustic band dispersions demonstrate that protected by the time-reversal symmetry ($\cal T$) and the point group symmetries, a WP with the charge -4 ($\mathcal{C}=-4$) and another WP with $\mathcal{C}=+4$ are located at the high-symmetry point $\Gamma$ and R, respectively, with the absence of any other kinds of WPs. Moreover, the singe-pair-WPs obtained here are designed by the simplest two-band mode, and the related quadruple-helicoid Fermi acrs can be observed clearly in experiments, since they aren't covered by any bulk bands and hybridized by other kinds of WPs. Our theoretical results provide a reliable acoustic crystal to study the topological properties of the single-pair-WPs with the maximum charge for experimentalists in this field.