Effects of Excess or Deficiency of Oxygen Content on the Electronic Structure of High-T_c Cuprates

摘要

Band structure calculations are presented for large supercells of Ba_2CuO_4 (BCO) with O-vacancies in planar or apical positions, and of superoxygenated La_2CuO_4 (LCO) with oxygen interstitials in the La_2O_2 layers. It is found that apical oxygen vacancies in BCO act as electron dopants and makes the electronic structure similar to that of hole doped LCO. Excess oxygen interstitials forming wires in the La_2O_2 layers of LCO are shown to yield a much larger density-of-states at the Fermi energy than for the stoichiometric compound related with a segmentation of the Fermi surface. Antiferromagnetic (AFM) spin fluctuations are strengthened by O-vacancies in BCO as well as by oxygen interstitials in LCO, but are strongly suppressed in O-deficient LCO. Our results indicate the complexity of doping by O-vacancies, and by ordered defects that are a significant factor controlling the electronic properties of cuprates.