Unusual photoemission resonances of oxygen-dopant induced states in   Bi$_{2}$Sr$_2$CaCu$_2$O$_{8+x}$
  We have performed an angular-resolved photoemission study of underdoped, optimally doped and overdoped Bi$_{2}$Sr$_2$CaCu$_2$O$_{8+x}$ samples using a wide photon energy range (15 - 100 eV). We report a small and broad non-dispersive A$_{1g}$ peak in the energy distribution curves whose intensity scales with doping. We attribute it to a local impurity state similar to the one observed recently by scanning tunneling spectroscopy and identified as the oxygen dopants. Detailed analysis of the resonance profile and comparison with the single-layered Bi$_{2}$Sr$_2$CuO$_{6+x}$ suggest a mixing of this local state with Cu via the apical oxygens. 
P. Richard, Z.-H. Pan, M. Neupane, A. V. Fedorov, T. Valla, P. D.   Johnson, G. D. Gu, W. Ku, Z. Wang and H. Ding