Doping-insensitive density-of-states suppression in polycrystalline   iron-based superconductor SmO$_{1-x}$F$_{x}$FeAs
  We investigated the temperature dependence of the density-of-states in the iron-based superconductor SmO_1-xF_xFeAs (x=0, 0.12, 0.15, 0.2) with high resolution angle-integrated photoemission spectroscopy. The density-of-states suppression is observed with decreasing temperature in all samples, revealing two characteristic energy scales (10meV and 80meV). However, no obvious doping dependence is observed. We argue that the 10meV suppression is due to an anomalously doping-independent normal state pseudogap, which becomes the superconducting gap once in the superconducting state; and alert the possibility that the 80meV-scale suppression might be an artifact of the polycrystalline samples. 
H. W. Ou, Y. Zhang, J. F. Zhao, J. Wei, D. W. Shen, B. Zhou, L. X.   Yang, F. Chen, M. Xu, C. He, R. H. Liu, M. Arita, K. Sh...