Three-component fermions with surface Fermi arcs in topological semimetal tungsten carbide

TL;DR

This paper reports the discovery of three-component fermions in tungsten carbide, characterized by triply-degenerate nodal points and unique surface Fermi arcs, revealing a new class of topological semimetals protected by spatial symmetries.

Contribution

It introduces a new topological semimetal state with triply-degenerate nodal points and surface Fermi arcs, expanding the understanding of fermionic quasiparticles in condensed matter.

Findings

Observation of triply-degenerate nodal points near the Fermi level in WC

Detection of surface Fermi arcs connecting the projections of TPs

Confirmation of nontrivial topological surface states

Abstract

Topological Dirac and Weyl semimetals not only host quasiparticles analogous to the elementary fermionic particles in high-energy physics, but also have nontrivial band topology manifested by exotic Fermi arcs on the surface. Recent advances suggest new types of topological semimetals, in which spatial symmetries protect gapless electronic excitations without high-energy analogy. Here we observe triply-degenerate nodal points (TPs) near the Fermi level of WC, in which the low-energy quasiparticles are described as three-component fermions distinct from Dirac and Weyl fermions. We further observe the surface states whose constant energy contours are pairs of Fermi arcs connecting the surface projection of the TPs, proving the nontrivial topology of the newly identified semimetal state.