Absence of large nanoscale electronic inhomogeneities in the Ba(Fe1-xCox)2As2 pnictide

TL;DR

This study uses NMR and susceptibility measurements to demonstrate that Co doping in Ba(Fe1-xCox)2As2 results in highly homogeneous electronic properties across nano to micrometer scales, contrasting with K doping effects.

Contribution

It provides evidence that Co substitution leads to uniform electronic doping in BaFe2As2, ruling out nanoscale inhomogeneities previously suggested.

Findings

Co doping is homogeneous within ±0.25%

NMR spectra show very narrow linewidths for H//ab

Electronic inhomogeneities are ruled out at nanometer scale

Abstract

75As NMR and susceptiblity were measured in a Ba(Fe1-xCox)2As2 single crystal for x=6% for various field H values and orientations. The sharpness of the superconducting and magnetic transitions demonstrates a homogeneity of the Co doping x better than +-0.25%. On the nanometer scale, the paramagnetic part of the NMR spectra is found very anisotropic and very narrow for H//ab which allows to rule out the interpretation of Ref.[6] in terms of strong Co induced electronic inhomogeneities. We propose that a distribution of hyperfine couplings and chemical shifts due to the Co effect on its nearest As explains the observed linewidths and relaxations. All these measurements show that Co substitution induces a very homogeneous electronic doping in BaFe2As2, from nano to micrometer lengthscales, on the contrary to the K doping.