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

TL;DR

This study provides experimental evidence of topological Fermi-arc surface states on a two-dimensional electride, revealing their unique stacking beneath a floating electron liquid and advancing understanding of topological phases in electrides.

Contribution

First experimental verification of topological surface states in a 2D electride, demonstrating Fermi-arc states beneath a floating electron layer using ARPES and STM.

Findings

Identification of Weyl cones and Fermi-arc states via ARPES

Fermi-arc states exist beneath a floating electron liquid

Unveiling of non-trivial topology in the Gd-based 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 $[Gd_{2}$C]^{2+}\cdot2e^{-}$. 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 $[Gd_{2}$C]^{2+}\cdot2e^{-}$ electride but also realizes a surface heterostructure that can host phenomena distinct from the bulk.