Observation of incipient charge nematicity in Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$

TL;DR

This study uses electronic Raman spectroscopy to detect charge nematic fluctuations in Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, revealing an underlying charge nematic state that persists into superconducting phases, with weak lattice coupling.

Contribution

First direct measurement of charge nematic fluctuations in Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ using Raman spectroscopy, uncovering a hidden charge nematic state.

Findings

Charge nematic fluctuations are enhanced at low temperatures.

Charge nematic state extends into superconducting compositions.

Charge nematic fluctuations are weakly coupled to the lattice.

Abstract

Using electronic Raman spectroscopy, we report direct measurements of charge nematic fluctuations in the tetragonal phase of strain-free Ba(Fe$_{1-x}$Co$_{x})_{2}$As$_{2}$ single crystals. The strong enhancement of the Raman response at low temperatures unveils an underlying charge nematic state that extends to superconducting compositions and which has hitherto remained unnoticed. Comparison between the extracted charge nematic susceptibility and the elastic modulus allows us to disentangle the charge contribution to the nematic instability, and to show that charge nematic fluctuations are weakly coupled to the lattice.