Evidence of unconventional low-frequency dynamics in the normal phase of Ba(Fe1-xRhx)2As2 iron-based supercondutors

TL;DR

This study uses 75As NMR measurements to reveal unconventional low-frequency dynamics in the normal phase of Ba(Fe1-xRhx)2As2 superconductors, linked to nematic fluctuations and domain wall motion.

Contribution

It provides the first evidence of low-frequency activated dynamics in the normal phase of iron-based superconductors using NMR techniques.

Findings

1/T2 increases upon cooling indicating low-frequency dynamics.

Dynamic motion is enhanced with higher Rh content and suppressed by magnetic fields.

The observed dynamics are consistent with nematic fluctuations involving domain walls.

Abstract

This work presents 75As NMR spin echo decay rate (1/T2) measurements in Ba(Fe1-xRhx)2As2 superconductors, for 0.041 < x < 0.094. It is shown that 1/T2 increases upon cooling, in the normal phase, suggesting the onset of an unconventional very low-frequency activated dynamic. The correlation times of the fluctuations and their energy barriers are derived. The motion is favored at large Rh content, while it is hindered by the application of a magnetic field perpendicular to the FeAs layers. The same dynamic is observed in the spin-lattice relaxation rate, in a quantitatively consistent manner. These results are discussed in the light of nematic fluctuations involving domain wall motion. The analogies with the behaviour observed in the cuprates are also outlined.