Observation of quadruple Weyl point in hybrid-Weyl phononic crystals

TL;DR

This paper reports the first observation of a quadruple Weyl point with topological charge 4 in a phononic crystal, expanding the understanding of topological semimetals with multiple Weyl point types.

Contribution

It presents the experimental discovery of the highest topological charge quadruple Weyl point in phononic crystals, along with the coexistence of multiple Weyl point types.

Findings

Observation of quadruple Weyl point with charge 4

Presence of multiple Weyl point types in the system

Demonstration of quadruple-helicoid surface states

Abstract

The discovery of Weyl semimetals opens the door for searching topological semimetals in physical science. The Weyl points are generally recognized as conventional, quadratic, spin-1, and those of high topological charges. Here we report the observation of the quadruple Weyl point of charge 4, the highest topological charge a twofold degenerate node can carry. Besides the quadruple Weyl point, the phononic semimetal also hosts conventional, quadratic, and spin-1 Weyl points, which stands as a system with yet the richest types of Weyl points. The quadruple-helicoid surface states, specific to the quadruple Weyl point, are demonstrated. The finding of the high-charge Weyl point enriches the knowledge of Weyl semimetals and may stimulate related researches in other systems, such as photonic, mechanical and cold atom systems.