Topological Fermi-arc surface state covered by floating electrons on a two-dimensional electride

Abstract

Two-dimensional electrides can acquire topologically non-trivial phases due to intriguing interplay between the cationic atomic layers and anionic electron layers. However, experimental evidence of topological surface states has yet to be verified. Here, via angle-resolved photoemission spectroscopy (ARPES) and scanning tunnelling microscopy (STM), we probe the magnetic Weyl states of the ferromagnetic electride [Gd2C]2+<middle dot>2e-. In particular, the presence of Weyl cones and Fermi-arc states is demonstrated through photon energy-dependent ARPES measurements, agreeing with theoretical band structure calculations. Notably, the STM measurements reveal that the Fermi-arc states exist underneath a floating quantum electron liquid on the top Gd layer, forming double-stacked surface states in a heterostructure. Our work thus not only unveils the non-trivial topology of the [Gd2C]2+<middle dot>2e- electride but also realizes a surface heterostructure that can host phenomena distinct from the bulk.,Electrides are an emerging family of materials with potential for hosting topological states. Here, the authors demonstrate the presence of Fermi-arc surface states in close proximity to the floating electron layer on the surface of an electride.,