Topological Weyl states in 2D ferromagnetic electride Gd₂C

Chan-young Lim

Two-dimensional (2D) electrides have interstitial anionic electron (IAE) layers that are separated from the surrounding atomic orbitals and localized in potential cages formed by cationic atoms. Recent studies have predicted topological phases in electride materials, where the topological surface states are expected to be related to these unique IAEs. However, the experimental evidence for the existence of topological states is still insufficient to verify their non-trivial nature, and there is a lack of information about the relationship between topological states and IAEs.

In this presentation, we report Weyl states in ferromagnetic [Gd₂C]²⁺·2e⁻ observed via angle-resolved photoemission spectroscopy (ARPES). Three-dimensional (3D) linear dispersions of Weyl cones and 2D Fermi arc surface states are obtained from photon energy dependent measurements. Our density functional theory (DFT) calculations indicate that the Fermi arc states are spatially confined to the topmost Gd atomic layer below the previously reported floating quantum electron liquid, forming a heterostructure of surface states. This unprecedented heterosurface state may lead to new physical phenomena beyond the bulk heterostructures, as the surface states have distinct properties that differ from those in the bulk.