Pressure tuned superconductivity and normal state behavior in Ba(Fe${}_{0.943}$Co${}_{0.057}$)${}_2$As${}_2$ near the antiferromagnetic boundary

Abstract

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 $\ddot{I}=\ddot{I}{}_0+A{T}^n$ was studied under applied pressure up to 7.90 GPa. The parameter $n$ approaches a minimum value of $n\approx 1$ 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 $T_c$.

5pages, 4 figures