Spin Susceptibility, Phase Diagram, and Quantum Criticality in the Electron-Doped High Tc Superconductor Ba(Fe1-xCox)2As2

Abstract

We report a systematic investigation of Ba(Fe1��xCox)2As2 based on transport and 75As NMR measurements, and establish the electronic phase diagram. We demonstrate that doping progressively suppresses the uniform spin susceptibility and low frequency spin fluctuations. The optimum superconducting phase emerges at xc ~ 0.08 from a non-Fermi-liquid which exhibits T-linear resistivity. Our findings point toward the presence of a quantum critical point near xc between the SDW (spin density wave) and superconducting phases.