Related Experiment Video
Updated: Dec 24, 2025

Surface Mapping of Earth-like Exoplanets using Single Point Light Curves
Published on: May 10, 2020
Observation of quadratic Weyl points and double-helicoid arcs
Hailong He1, Chunyin Qiu2, Xiangxi Cai1
1Key Laboratory of Artificial Micro- and Nano-Structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan, 430072, China.
Abstract:
Novel quasiparticles beyond those mimicking the elementary high-energy particles such as Dirac and Weyl fermions have attracted great interest in condensed-matter physics and materials science. Here we report an experimental observation of the long-desired quadratic Weyl points by using a three-dimensional chiral metacrystal of sound waves. Markedly different from the newly observed unconventional quasiparticles, such as the spin-1 Weyl points and the charge-2 Dirac points featuring respectively threefold and fourfold band crossings, the charge-2 Weyl points identified here are simply twofold degenerate, and the dispersions around them are quadratic in two directions and linear in the third one. Besides the essential nonlinear bulk dispersions, we further unveil the exotic double-helicoid surface arcs that emanate from a projected quadratic Weyl point and terminate at two projected conventional Weyl points. This unique global surface connectivity provides conclusive evidence for the double topological charges of such unconventional topological nodes.
Related Concept Videos
Geometry of Hyperbolas
Gauss's Law: Planar Symmetry
Gauss's Law: Spherical Symmetry
Polar Equations of Conics
Gauss's Law: Cylindrical Symmetry
Eccentricity of an Ellipse

