Unexpected weak spatial variation of local density of sates induced by   individual Co impurity atoms in Na(Fe{1-x}Cox)As as revealed by scanning   tunneling spectroscopy
  We use spatially resolved scanning tunneling spectroscopy in Na(Fe{1-x}Cox)As to investigate the impurity effect induced by Co dopants. The Co impurities are successfully identified, and the spatial distributions of local density of state at different energies around these impurities are investigated. It is found that the spectrum shows negligible spatial variation at different positions near the Co impurity, although there is a continuum of the in-gap states which lifts the zero-bias conductance to a finite value. Our results put constraints on the S+- and S++ models and sharpen the debate on the role of scattering potentials induced by the Co dopants. 
Huan Yang, Zhenyu Wang, Delong Fang, Sheng Li, Toshikaze Kariyado,   Genfu Chen, Masao Ogata, Tanmoy Das, A. V. Balatsky and...
cond-mat.supr-con