Sizable Residual Quasiparticle Density of States Induced by Impurity Scattering Effect in Ba(Fe1−xCox)2As2 Single Crystals

Low-temperature specific heat Cp is measured on Ba(Fe1–xCox)2As2 single crystals in a wide doping region. A sizeable residual specific heat coefficient γ0 is observed in the low temperature limit of all samples. The specific heat jump near Tc, i.e. ΔCp/T|\Tc, is also determined. It is found that –γ0, ΔCP/T|\Tc and Tc all share a similar evolution with doping. These can be well understood within the model of S± pairing symmetry when accounting for the cobalt-dopants as unitary scattering centers in the FeAs planes. Our results reveal a non-trivial impact of impurity scattering in FeAs-based superconductors.