The Three-Dimensional Electronic Structure of LiFeAs: Strong-coupling Superconductivity and Topology in the Iron Pnictides

In the present discourse surrounding Fe-based superconductors, two broadly distinct research programs have evolved. While a considerable effort continues to be applied towards understanding the fundamentals of bulk superconductivity in this expansive family of materials, a nearly orthogonal avenue is directed towards the topic of topology. As a high purity material devoid of complications associated with disorder, magnetism and structural distortions, LiFeAs plays a central role in connection to both research programs.

However, the bulk electronic structure of LiFeAs reported in the literature is highly contentious. In this work, we combine polarization- and photon-energy dependent photoemission measurements with realistic numerical simulations thereof, to unravel the convoluted experimental signatures which have been interpreted previously towards conflicting descriptions of this material. Doing so, we identify an electronic structure which cannot easily be reconciled with the prevailing description of the bulk superconductivity in LiFeAs as a weak-coupling Fermi surface instability. At the same time, these results provide support and justification to intimations of a topological surface state in LiFeAs. Although tunnelling spectroscopy has indicated that any proximitized superconductivity on the surface state is topologically non-trivial, we provide a mechanism by which such topological superconductivity may be stabilized in LiFeAs.