Discovery of topological Weyl fermion lines and drumhead surface states in a room temperature magnet

TLDR

Weyl semimetals (WSMs) host exotic Weyl fermions and require breaking either spatial inversion or time‑reversal symmetry; while inversion‑breaking WSMs have been identified, unambiguous evidence for time‑reversal‑breaking WSMs remains challenging. The authors probed Co₂MnGa with angle‑resolved photoemission spectroscopy, revealing drumhead surface states, and studied Co₃Sn₂S₂ complemented by scanning tunneling spectroscopy of Morali et al. Three groups now provide spectroscopic evidence for time‑reversal‑breaking WSMs in magnetic materials, and these states offer an ideal platform for exotic transport phenomena. References include Belopolski et al., Liu et al., and Science issue pages 1278, 1282, 1286, and 1248.

Abstract

Magnetic Weyl semimetals Weyl semimetals (WSMs)—materials that host exotic quasiparticles called Weyl fermions—must break either spatial inversion or time-reversal symmetry. A number of WSMs that break inversion symmetry have been identified, but showing unambiguously that a material is a time-reversal-breaking WSM is tricky. Three groups now provide spectroscopic evidence for this latter state in magnetic materials (see the Perspective by da Silva Neto). Belopolski et al. probed the material Co 2 MnGa using angle-resolved photoemission spectroscopy, revealing exotic drumhead surface states. Using the same technique, Liu et al. studied the material Co 3 Sn 2 S 2 , which was complemented by the scanning tunneling spectroscopy measurements of Morali et al. These magnetic WSM states provide an ideal setting for exotic transport effects. Science , this issue p. 1278 , p. 1282 , p. 1286 ; see also p. 1248