Superconductivity induced by Ni doping in BaFe 2 As 2 single crystals

A series of 122 phase BaFe 2− x Ni x As 2 ( x =0, 0.055, 0.096, 0.18 and 0.23) single crystals was grown by the self-flux method and a dome-like Ni doping dependence of the superconducting transition temperature was discovered. The transition temperature T c on reaches a maximum of 20.5 K at x =0.096, and it drops to below 4 K as x ⩾0.23. The negative thermopower in the normal state indicates that the electron-like charge carrier indeed dominates in this system. This Ni-doped system provides another example of superconductivity induced by electron doping in the 122 phase.