## Abstract

Topological Dirac and Weyl semimetals not only host quasiparticles analogous to the elementary fermionic particles in high-energy physics, but also have a non-trivial band topology manifested by gapless surface states, which induce exotic surface Fermi arcs ^{1,2} . Recent advances suggest new types of topological semimetal, in which spatial symmetries protect gapless electronic excitations without high-energy analogues ^{3-11} . Here, using angle-resolved photoemission spectroscopy, we observe triply degenerate nodal points near the Fermi level of tungsten carbide with space group P 6 m 2 (no. 187), in which the low-energy quasiparticles are described as three-component fermions distinct from Dirac and Weyl fermions. We further observe topological surface states, whose constant-energy contours constitute pairs of 'Fermi arcs' connecting to the surface projections of the triply degenerate nodal points, proving the non-trivial topology of the newly identified semimetal state.

Original language | English |
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Pages (from-to) | 349-354 |

Number of pages | 6 |

Journal | Nature Physics |

Volume | 14 |

Issue number | 4 |

DOIs | |

Publication status | Published - 1 Apr 2018 |

Externally published | Yes |