Spin susceptibility, phase diagram, and quantum criticality in the electron-doped high Tc Superconductor Ba[Fe(1-x)Co(x)]2As2

TL;DR

This study investigates the electronic phase diagram of Ba[Fe(1-x)Co(x)]2As2, revealing how doping suppresses spin fluctuations and suggests a quantum critical point near optimal doping where spin order disappears.

Contribution

It provides a systematic analysis combining transport and NMR measurements to map the phase diagram and identify a quantum critical point in electron-doped high-Tc superconductor.

Findings

Doping suppresses spin susceptibility and fluctuations.

Superconductivity peaks at doping level x_c~0.08.

Evidence of a quantum critical point near optimal doping.

Abstract

We report a systematic investigation of Ba[Fe(1-x)Co(x)]2As2 based on transport and 75-As 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 x_c~0.08 when the tendency toward spin ordering completely diminishes. Our findings point toward the presence of a quantum critical point near x_c between the SDW (spin density wave) and superconducting phases.