Pressure-tuned superconductivity and normal-state behavior in Ba(Fe0.943Co0.057)2As2 near the antiferromagnetic boundary

Superconductivity in iron pnictides is unconventional and pairing may be mediated by magnetic fluctuations in the Fe-sublattice. Pressure is a clean method to explore superconductivity in iron based superconductors by tuning the ground state continuously without introducing disorder. Here we present a systematic high pressure transport study in Ba(Fe$_{1-x}$Co$_{x}$)$_2$As$_2$ single crystals with $x=$ 0.057, which is near the antiferromagnetic instability. Resistivity $rho=rho_0+AT^{n}$ was studied under applied pressure up to 7.90 GPa. The parameter $n$ approaches a minimum value of $napprox 1$ at a critical pressure $P_c =$ 3.65 GPa. Near $P_c$, the superconducting transition temperature $T_c$ reaches a maximum value of 25.8 K. In addition, the superconducting diamagnetism at 2 K shows a sudden change around the same critical pressure. These results may be associated with a possible quantum critical point hidden inside the superconducting dome, near optimum $T_c$.