Simultaneous vanishing of nematic electronic state and structural orthorhombicity in NaFe1-x Cox As single crystals

We have carried out in-plane resistivity measurements under a uniaxial pressure on NaFe1-xCoxAs single crystals. A clear distinction of the in-plane resistivity ρa and ρb with the uniaxial pressure along the b axis was discovered in the parent and underdoped regime with a doping level of up to about x=0.025±0.002. From the deviating point of ρa and ρb, and the unique kinky structure of resistivity, together with the published data, we determined the temperatures for the nematic, structural, and antiferromagnetic transitions. It is clearly shown that the nematic electronic state vanishes simultaneously with the structural transition. The antiferromagnetic state disappears, however, at a lower doping level. Our results, in combination with the data on Ba(Fe1-xCox)2As2, indicate a close relationship between nematicity and superconductivity.