Superconductivity up to 30 K in the vicinity of the quantum critical point in BaFe2(As1-xPx)2

We report bulk superconductivity induced by an isovalent doping of phosphorus in BaFe2(As1-xPx)(2). The P-for-As substitution results in shrinkage of the lattice, especially for the FeAs block layers. The resistivity anomaly associated with the spin-density-wave (SDW) transition in the undoped compound is gradually suppressed by the P doping. Superconductivity with a maximum T-c of 30 K emerges at x = 0.32, coinciding with a magnetic quantum critical point (QCP) which is shown by the disappearance of SDW order and the linear temperature-dependent resistivity in the normal state. The T-c values were found to decrease with further P doping and no superconductivity was observed down to 2 K for x >= 0.77. The appearance of superconductivity in the vicinity of QCP hints at the superconductivity mechanism in iron-based arsenides.