Superconductivity at 22 K in Co-Doped BaFe 2 As 2 Crystals

Here we report bulk superconductivity in ${\mathrm{BaFe}}_{1.8}{\mathrm{Co}}_{0.2}{\mathrm{As}}_{2}$ single crystals below ${T}_{c}=22\text{ }\text{ }\mathrm{K}$, as demonstrated by resistivity, magnetic susceptibility, and specific heat data. Hall data indicate that the dominant carriers are electrons, as expected from simple chemical reasoning. This is the first example of superconductivity induced by electron doping in this family of materials. In contrast with cuprates, the ${\mathrm{BaFe}}_{2}{\mathrm{As}}_{2}$ system appears to tolerate considerable disorder in the FeAs planes. First principles calculations for ${\mathrm{BaFe}}_{1.8}{\mathrm{Co}}_{0.2}{\mathrm{As}}_{2}$ indicate the interband scattering…