Unusual photoemission resonances of oxygen-dopant induced states in Bi₂Sr₂CaCu₂O_{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.