Contrasting Spin Dynamics Between Underdoped and Overdoped Ba(Fe[1-x]Co[x])2As2

TL;DR

This study uses NMR to compare spin dynamics in underdoped and overdoped Ba(Fe[1-x]Co[x])2As2, revealing that suppression of antiferromagnetic fluctuations correlates with the loss of superconductivity.

Contribution

First NMR investigation of spin dynamics in overdoped Ba(Fe[1-x]Co[x])2As2, showing the link between spin fluctuations and superconductivity suppression.

Findings

Suppression of antiferromagnetic spin fluctuations for x > 0.15

Absence of inter-band transitions with large momentum transfer

Correlation between Tc and strength of Q(AF) spin fluctuations

Abstract

We report the first NMR investigation of spin dynamics in the overdoped non-superconducting regime of Ba(Fe[1-x]Co[x])2As2 up to x =0.26. We demonstrate that the absence of inter-band transitions with large momentum transfer Q(AF) ~ (pi, 0) between the hole and electron Fermi surfaces results in complete suppression of antiferromagnetic spin fluctuations for x > 0.15. Our experimental results provide direct evidence for a correlation between Tc and the strength of Q(AF) antiferromagnetic spin fluctuations.