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 1 g 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.