Observation of quadratic Weyl points and double-helicoid arcs

Abstract

Very recently, 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 science1-9. Here we report the first experimental observation of the long-desired quadratic Weyl points10 by using a three-dimensional chiral metacrystal of sound waves. Markedly different from the newly observed unconventional quasiparticles5-9, such as the spin-1 Weyl points and the charge-2 Dirac points that are featured respectively with 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 one10. 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 through Fourier transformation of the scanned surface fields. This unique global surface connectivity provides conclusive evidence for the double topological charges of such unconventional topological nodes.

arXiv comment4 figures

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Cited by in corpus (19)

• Topological acoustics
• Symmetry-Enforced Weyl Phonons
• Ideal Unconventional Weyl Point in a Chiral Photonic Metamaterial
• Acoustic Higher-Order Weyl Semimetal with Bound Hinge States in the Continuum
• Observation of a charge-2 photonic Weyl point in the infrared
• Magnetic higher-order nodal lines
• Single Pair of Weyl Points in Nonmagnetic Crystals
• Tracking valley topology with synthetic Weyl paths
• Hourglass Charge-Three Weyl Phonons
• Non-Abelian charged nodal links in dielectric photonic crystal
• Weyl points on non-orientable manifolds
• Observation of Single Pair of Type-III Weyl Points in Sonic Crystals
• Weyl-triplons in SrCu2(BO3)2
• Intertwined Weyl phases emergent from higher-order topology and unconventional Weyl fermions via crystalline symmetry
• Protection of all nondefective twofold degeneracies by anti-unitary symmetries in non-Hermitian systems
• Intrinsic triple degeneracy point bounded by nodal surfaces in chiral photonic crystal
• $Z_2$ Dirac points with topologically protected multihelicoid surface states
• Parallel and anti-parallel helical surface states for topological semimetals
• Topological excitations in quasi two-dimensional quantum magnets with weak interlayer interactions