Superconductivity induced by Ni doping in BaFe${}_2$As${}_2$

Abstract

A series of 122 phase BaFe${}_{2-x}$Ni${}_x$As${}_2$ ($x$ = 0, 0.055, 0.096, 0.18, 0.23) single crystals were grown by self flux method and a dome-like Ni doping dependence of superconducting transition temperature is 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 $x$ $\ge$ 0.23. The negative thermopower in the normal state indicates that 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.

7 pages, 5 figures, revised version, added EDX result, accepted for special issue of NJP