Absence of nematic instability in LiFeAs

TL;DR

This study investigates nematic fluctuations in LiFeAs, a superconductor lacking structural or magnetic transitions, and finds no evidence of nematic instability even with doping, challenging previous suggestions of nematic states.

Contribution

The paper provides the first elastoresistance measurements showing LiFeAs is far from nematic instability, clarifying its electronic state compared to other FeSCs.

Findings

LiFeAs shows no signs of nematic instability.

Doping with Co or V does not induce nematic fluctuations.

LiFeAs differs from other FeSCs with nematic order.

Abstract

The relationship between unconventional superconductivity, antiferromagnetism and nematic order in iron-based superconductors (FeSCs) is still highly debated. In many FeSCs superconductivity is in proximity of a nematically and magnetically ordered state. LiFeAs is an exceptional stoichiometric FeSC becoming superconducting below 18 K, without undergoing a structural or magnetic transition. However, some recent experimental studies suggested the existence of finite nematic fluctuations and even a nematic superconducting state. In this study, we employ elastoresistance as a measure of nematic fluctuations in pristine LiFeAs and compare the findings with the elastoresistance of LiFeAs at low Co and V doping levels as well with that of magnetically and nematically ordering NaFeAs. We find LiFeAs and cobalt-doped LiFeAs far away from a nematic instability.