  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.
