Nature of oxygen dopant-induced states in high-temperature Bi2Sr2CaCu2O8+x superconductors:: A photoemission investigation

We investigate the nature of oxygen dopant-induced electronic states in the high-temperature Bi2Sr2CaCu2O8+x superconductor by measuring photoemission spectra of underdoped, optimally doped, and overdoped samples using a wide photon energy range (15-100 eV). We find a small and broad nondispersive peak at -0.8 eV associated with oxygen dopants. Surprisingly, the detailed analysis of the resonance profile suggests a mixing with Cu states. Particularly, the A(1g) symmetry revealed by polarization-dependent experiments and the comparison with the single-layered Bi2Sr2CuO6+x indicates that the oxygen dopant-induced states are mixed to the superconducting CuO2 planes through the oxygen dopant-apical oxygen O2p(z)-Cu3d(3z2-r2) channel.