1 2 A ug 2 00 9 Superconductivity up to 30 K in the vicinity of quantum critical point in BaFe 2 ( As 1 − x P x ) 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 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 the maximum Tc of 30 K emerges at x=0.32, coinciding with a magnetic quantum critical point (QCP) which is evidenced by the disappearance of SDW order and the linear temperature-dependent resistivity in the normal state. The Tc 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 to the superconductivity mechanism in iron-based arsenides. (Some figures in this article are in colour only in the electronic version) PACS numbers: 74.70.Dd; 74.25.Dw; 74.62.Dh; 73.43.Nq Submitted to: J. Phys.: Condens. Matter as a FAST TRACK COMMUNICATIONS § Corresponding author. E-mail address: [email protected] Superconductivity up to 30 K in BaFe2(As1−xPx)2 2