Single-pair Weyl points with the maximum charge number in acoustic crystals

To observe a Weyl point (WP) possessing the maximum charge number and to search for single-pair WPs in realistic materials are two challenges in topology physics. Here, we have successfully designed an acoustic crystal to realize single-pair WPs with the maximum charge number. Protected by time-reversal symmetry and point group symmetries, a WP with charge -4 and another WP with charge +4 are located at two different high-symmetry points of an acoustic crystal, without any other kinds of WPs. Moreover, the single-pair WPs obtained here are designed by the simplest two-band mode, and the related quadruple-helicoid surface arcs can be observed clearly in experiments, since they are not hybridized by other kinds of WPs. Our theoretical work puts forward an ideal acoustic crystal to study the topological properties of single-pair WPs with the maximum charge number.