Elastoresistivity of heavily hole doped 122 iron pnictides superconductors

TL;DR

This study systematically investigates elastoresistivity in heavily hole-doped 122 iron pnictide superconductors, revealing divergent elastoresistance linked to electronic criticality rather than a separate nematic phase.

Contribution

It provides new insights into the relationship between elastoresistivity, Lifshitz transitions, and nematicity in heavily hole-doped iron pnictides, challenging previous interpretations.

Findings

Divergent elastoresistance observed along [110] direction upon cooling.

Elastoresistivity diverges with larger ion substitution or approaching Lifshitz transition.

Enhanced elastoresistivity linked to electronic criticality, not an independent nematic critical point.

Abstract

Nematicity in the heavily hole-doped iron pnictide superconductors remains controversial. Sizeable nematic fluctuations and even nematic orders far from a magnetic instability were declared in RbFe$_2$As$_2$ and its sister compounds. Here we report a systematic elastoresistance study of series of isovalent- and electron-doped KFe$_2$As$_2$ crystals. We found divergent elastoresistance upon cooling for all the crystals along their [110] direction. The amplitude of elastoresistivity diverges if K is substituted with larger ions or if the system is driven towards a Lifshitz transition. However, we conclude none of them necessarily indicates an independent nematic critical point. Instead, the increased nematicity can be associated with another electronic criticality. In particular, we propose a mechanism how elastoresistivity is enhanced at a Lifshitz transition.