Simultaneous Vanishing of the Nematic Electronic State and the Structural Orthorhombicity in NaFe_(1-x)Co_xAs Single Crystals

We have carried out in-plane resistivity measurements under a uniaxial pressure in NaFe$_{1-x}$Co$_x$As single crystals. A clear distinction of the in-plane resistivity $\rho_a$ and $\rho_b$ with the uniaxial pressure along $b$-axis was discovered in the parent and underdoped regime with the doping level up to about x=0.025$\pm$0.002. From the deviating point of $\rho_a$ and $\rho_b$, 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 in BaFe$_{2-x}$Co$_x$As$_2$, indicate a close relationship between nematicity and superconductivity.