NMR study of nematic spin fluctuations in a detwinned single crystal of underdoped Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$

TL;DR

This study uses NMR to investigate nematic spin fluctuations in detwinned underdoped Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$, revealing anisotropic relaxation rates and persistent glassy behavior, supported by a theoretical model.

Contribution

It demonstrates a method for combining mechanical detwinning with NMR and provides new insights into anisotropic spin fluctuations in underdoped iron pnictides.

Findings

Anisotropy of spin-lattice relaxation rate reaches 30% at T_N.

Glassy spin fluctuation behavior persists in detwinned crystals.

A theoretical model describes anisotropic nematic spin fluctuations.

Abstract

We report the experimental details of how mechanical detwinning can be implemented in tandem with high sensitivity nuclear magnetic resonance measurements and use this setup to measure the in-plane anisotropy of the spin-lattice relaxation rate in underdoped Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ with $x=0.048$. The anisotropy reaches a maximum of 30\% at $T_{N}$, and the recovery data reveal that the glassy behavior of the spin fluctuations present in the twinned state persist in the fully detwinned crystal. A theoretical model is presented to describe the spin-lattice relaxation rate in terms of anisotropic nematic spin fluctuations.