Observation of Weyl fermion states in 2D ferromagnetic electride Gd₂C via angle-resolved photoemission spectroscopy

Electrides are materials with interstitial anionic electrons (IAEs) decoupled from atomic orbitals and localized in potential cages formed by cationic atoms. The decoupling provides the possibility of pure electron state which is manifested as interesting properties, such as low work function and weak electron – phonon interaction. Recently, the formation of topological states with IAEs are expected for certain electride materials. 2D electride Gd₂C is one of the candidates of topological electrides, where Weyl semimetalic states are predicted due to ferromagnetism that breaks the time-reversal symmetry. However, such topological electronic structure of Gd₂C has not been investigated experimentally.

In this talk, we will report the observation of Weyl fermions in Gd₂C electronic structure captured with angle-resolved photoemission spectroscopy (ARPES). Weyl cones and Fermi arc states – key features of Weyl fermion state – are revealed with photon energy dependent ARPES measurements. Our calculation indicates that the Fermi arc surface state in Gd₂C mainly confined on the topmost Gd atomic layer. Still, there is a finite overlap between surface IAEs and the topmost Gd atoms, which could provide clues to topological states with IAEs – the electrons that are not bounded to the atomic orbital directly.