Discovery of a Weyl fermion semimetal and topological Fermi arcs

TLDR

Weyl physics, involving massless half‑integer‑spin particles, is expected to appear as collective excitations in Weyl semimetals whose band structure features discrete Weyl points, as highlighted by studies of Xu et al. and Lu et al. The authors used photoemission spectroscopy to detect Weyl points in TaAs and a photonic crystal, confirming Weyl semimetal behavior. The observation of Weyl points in TaAs and a photonic crystal demonstrates Weyl physics and may enable discovery of exotic fundamental phenomena.

Abstract

Weyl physics emerges in the laboratory Weyl fermions—massless particles with half-integer spin—were once mistakenly thought to describe neutrinos. Although not yet observed among elementary particles, Weyl fermions may exist as collective excitations in so-called Weyl semimetals. These materials have an unusual band structure in which the linearly dispersing valence and conduction bands meet at discrete “Weyl points.” Xu et al. used photoemission spectroscopy to identify TaAs as a Weyl semimetal capable of hosting Weyl fermions. In a complementary study, Lu et al. detected the characteristic Weyl points in a photonic crystal. The observation of Weyl physics may enable the discovery of exotic fundamental phenomena. Science , this issue p. 613 and 622