Persistence of slow fluctuations in the overdoped regime of Ba(Fe1-xRhx)2As2 superconductors

TL;DR

This study provides nuclear magnetic resonance evidence that very slow spin fluctuations persist into the overdoped regime of Ba(Fe$_{1-x}$Rh$_x$)$_2$As$_2$ superconductors, indicating complex magnetic dynamics beyond optimal doping.

Contribution

It reveals the persistence of slow spin fluctuations in overdoped iron-based superconductors, involving domain wall motions, which was previously unreported.

Findings

Slow spin fluctuations extend into the overdoped regime.

Fluctuations involve short-range diffusive domain wall dynamics.

Fluctuations are weakly affected by external magnetic fields.

Abstract

We present nuclear magnetic resonance evidence that very slow ($\leq 1$ MHz) spin fluctuations persist into the overdoped regime of Ba(Fe$_{1-x}$Rh$_{x}$)$_2$As$_2$ superconductors. Measurements of the $^{75}$As spin echo decay rate, obtained both with Hahn Echo and Carr Purcell Meiboom Gill pulse sequences, show that the slowing down of spin fluctuations can be described by short-range diffusive dynamics, likely involving domain walls motions separating $(\pi/a,0)$ from $(0,\pi/a)$ correlated regions. This slowing down of the fluctuations is weakly sensitive to the external magnetic field and, although fading away with doping, it extends deeply into the overdoped regime.