Local nematic susceptibility in stressed BaFe$_2$As$_2$ from NMR electric field gradient measurements

TL;DR

This study uses NMR to measure the electric field gradient at the arsenic site in BaFe$_2$As$_2$, revealing how local nematicity responds to strain and diverges near the structural transition, providing a new method to probe nematic susceptibility.

Contribution

It introduces an NMR-based approach to measure local nematic susceptibility, which can be applied within the superconducting state, complementing existing bulk measurement techniques.

Findings

EFG asymmetry responds linearly to strain in the paramagnetic phase

Nematic susceptibility diverges near the structural transition

Method can be extended inside the superconducting state

Abstract

The electric field gradient (EFG) tensor at the $^{75}$As site couples to the orbital occupations of the As p-orbitals and is a sensitive probe of local nematicity in BaFe$_2$As$_2$. We use nuclear magnetic resonance to measure the nuclear quadrupolar splittings and find that the EFG asymmetry responds linearly to the presence of a strain field in the paramagnetic phase. We extract the nematic susceptibility from the slope of this linear response as a function of temperature and find that it diverges near the structural transition in agreement with other measures of the bulk nematic susceptibility. Our work establishes an alternative method to extract the nematic susceptibility which, in contrast to transport methods, can be extended inside the superconducting state.