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

TL;DR

This study clarifies the electronic structure of LiFeAs using advanced ARPES techniques and simulations, revealing surface effects, topological states, and challenging existing theories of its superconductivity.

Contribution

It combines comprehensive ARPES measurements with simulations to resolve conflicting interpretations of LiFeAs's electronic structure and topological properties.

Findings

Identification of surface-related issues affecting ARPES data

Evidence supporting topologically non-trivial states in LiFeAs

Incompatibility of observed states with spin-fluctuation-driven superconductivity

Abstract

Amongst the iron-based superconductors, LiFeAs is unrivalled in the simplicity of its crystal structure and phase diagram. However, our understanding of this canonical compound suffers from conflict between mutually incompatible descriptions of the material's electronic structure, as derived from contradictory interpretations of the photoemission record. Here, we explore the challenge of interpretation in such experiments. By combining comprehensive photon energy- and polarization- dependent angle-resolved photoemission spectroscopy (ARPES) measurements with numerical simulations, we establish the providence of several contradictions in the present understanding of this and related materials. We identify a confluence of surface-related issues which have precluded unambiguous identification of both the number and dimensionality of the Fermi surface sheets. Ultimately, we arrive at a scenario which supports indications of topologically non-trivial states, while also being incompatible with superconductivity as a spin-fluctuation driven Fermi surface instability.