Nature of oxygen dopant-induced states in high-temperature Bi_2Sr_2CaCu_2O_(8+x) superconductors: A photoemission investigation

摘要

We investigate the nature of oxygen dopant-induced electronic states in the high-temperature Bi_2Sr_2CaCu_2O_(8+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 Bi_2Sr_2CuO_(6+x) indicates that the oxygen dopant-induced states are mixed to the superconducting CuO_2 planes through the oxygen dopant—apical oxygen O2p_z—Cu3d_(3z~2-r~2) channel.