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

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Phenomena

Background:

• Two-dimensional (2D) electrides exhibit unique electronic properties due to layered structures of cations and electrons.
• Topologically non-trivial phases in 2D electrides are theoretically predicted but experimentally underexplored.
• Experimental verification of topological surface states in magnetic electrides is lacking.

Purpose of the Study:

• To experimentally investigate the magnetic Weyl states in the ferromagnetic electride [Gd2C]2+·2e−.
• To provide evidence for topological surface states, specifically Weyl cones and Fermi arcs.
• To explore the formation and characteristics of surface heterostructures in 2D electrides.

Main Methods:

• Angle-resolved photoemission spectroscopy (ARPES) with varying photon energies.
• Scanning tunnelling microscopy (STM) for surface imaging and characterization.
• Comparison of experimental findings with theoretical band structure calculations.

Main Results:

• Demonstrated the presence of Weyl cones and Fermi-arc states in [Gd2C]2+·2e− using ARPES.
• Experimental results align with theoretical band structure predictions.
• STM revealed Fermi-arc states beneath a quantum electron liquid, forming double-stacked surface states.

Conclusions:

• The study unveils the non-trivial topology of the [Gd2C]2+·2e− electride.
• A novel surface heterostructure with distinct phenomena from the bulk has been realized.
• This work opens avenues for exploring exotic quantum phenomena in engineered electride heterostructures.