Topological triply-degenerate point with double Fermi arcs

Abstract

Unconventional chiral particles have recently been predicted to appear in certain three dimensional (3D) crystal structures containing three- or more-fold linear band degeneracy points (BDPs). These BDPs carry topological charges, but are distinct from the standard twofold Weyl points or fourfold Dirac points, and cannot be described in terms of an emergent relativistic field theory. Here, we report on the experimental observation of a topological threefold BDP in a 3D phononic crystal. Using direct acoustic field mapping, we demonstrate the existence of the threefold BDP in the bulk bandstructure, as well as doubled Fermi arcs of surface states consistent with a topological charge of 2. Another novel BDP, similar to a Dirac point but carrying nonzero topological charge, is connected to the threefold BDP via the doubled Fermi arcs. These findings pave the way to using these unconventional particles for exploring new emergent physical phenomena.

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• Ideal Unconventional Weyl Point in a Chiral Photonic Metamaterial
• Observation of quadratic Weyl points and double-helicoid arcs
• 3D hinge transport in acoustic higher-order topological insulators
• Higher-order Dirac Semimetal in a Photonic Crystal
• Discovering topological surface states of Dirac points
• Corner states and topological transitions in two-dimensional higher-order topological sonic crystals with inversion symmetry
• Discovery of a maximally charged Weyl point
• Tracking valley topology with synthetic Weyl paths
• Single Pair of Weyl Points in Nonmagnetic Crystals
• Electronic Structure Studies of FeSi: A Chiral Topological System
• Classifying topology in photonic heterostructures with gapless environments
• Revealing Topology in Metals using Experimental Protocols Inspired by $K$-Theory
• Hidden-symmetry-enforced nexus points of nodal lines in layer-stacked dielectric photonic crystals
• Acoustic spin-1 Weyl semimetal
• High-degeneracy points protected by site-permutation symmetries
• Spin-1 Weyl Point and Surface Arc State in a Chiral Phononic Crystal
• 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
• Intrinsic triple degeneracy point bounded by nodal surfaces in chiral photonic crystal
• Probing and harnessing photonic Fermi arc surface states using light-matter interactions
• Observation of spin-tensor induced topological phase transitions of triply degenerate points with a trapped ion
• Unpaired topological triply degenerate point for spin-tensor-momentum-coupled ultracold atoms
• Moiré Band Engineering in Twisted Trilayer WSe2
• Observation of 1D Fermi arc states in Weyl semimetal TaAs
• Transmission properties of microwaves at an optical Weyl point in a three-dimensional chiral photonic crystal
• Dimensional hierarchy of topological bound states in the continuum
• Triply-degenerate point in three-dimensional spinless systems
• Topological Charges, Fermi Arcs, and Surface States of $K_4$ Crystal