Elasto-Raman scattering: arsenic optical phonon as a probe of nematicity in BaFe$_2$As$_2$

TL;DR

This study demonstrates how elasto-Raman scattering using arsenic phonons can effectively probe and monitor nematic order and susceptibility in BaFe$_2$As$_2$, revealing domain orientation and phase transition behavior under strain.

Contribution

It introduces a novel application of polarization-resolved arsenic phonon Raman scattering as a sensitive probe of nematicity and its fluctuations in iron-based superconductors under uniaxial strain.

Findings

Arsenic phonon intensity tracks nematic order parameter with temperature and strain.

Nematic domains are reversible and continuously oriented under variable strain.

Enhanced nematic susceptibility observed near the transition temperature.

Abstract

We report a Raman scattering study of nematic degrees of freedom in the iron-based superconductor parent compound BaFe$_2$As$_2$ under tunable uniaxial strain. We demonstrate that the polarization resolved arsenic (As) phonon intensity can be used to monitor the nematic order parameter as a function of both temperature and strain. At low temperature in the nematic ordered phase we use it to track the continuous and reversible orientation of nematic domains under variable strain. At higher temperature, the evolution of the As phonon intensity under strain reflects an enhanced nematic susceptibility close to the nematic transition $T_S$. Its temperature dependence under strong strain follows qualitatively the expected behavior of an Ising order parameter under a symmetry breaking field. Our elasto-Raman study illustrates the interest of combining selective anisotropic strain with a symmetry resolved probe like Raman scattering. Elasto-Raman scattering can be applied to a wide variety of quantum materials where uniaxial strain tunes electronic orders.