Superconductivity without magnetism in LiFeAs

TL;DR

This study reveals that LiFeAs superconducts without the typical Fermi surface nesting or magnetic order, highlighting alternative electronic conditions for superconductivity in iron-based materials.

Contribution

It demonstrates that superconductivity in LiFeAs occurs without Fermi surface nesting or magnetic fluctuations, challenging previous assumptions about their necessity.

Findings

Absence of Fermi surface nesting in LiFeAs

Strong band renormalization by a factor of three

High density of states at Fermi level due to Van Hove singularity

Abstract

The particular shape of the Fermi surface can give rise to a number of collective quantum phenomena in solids, such as density wave orderings or even superconductivity. In many new iron superconductors this shape, the 'nested' Fermi surface, is indeed observed, but its role in the formation of spin-density waves or superconductivity is not clear. We have studied the electronic structure of the non-magnetic LiFeAs (Tc~18K) superconductor using angle-resolved photoemission spectroscopy. We find a notable absence of the Fermi surface nesting, strong renormalization of the conduction bands by a factor of three, high density of states at the Fermi level caused by a Van Hove singularity, and no evidence for either a static or fluctuating order except superconductivity with in-plane isotropic energy gaps. Our observations set a new hierarchy of the electronic properties necessary for the superconductivity in iron pnictides and, possibly, in other materials.