Auger Spectra and Band Structure of La_1.85Sr_0.15CuO₄ and La_1.85Ba_0.15CuO₄

High-resolution Auger electron spectra of La_1.85Sr_0.15CuO₄ and La_1.85Ba_0.15CuO₄ have been measured. The experimental Auger line shapes of the oxygen KLL and copper L_2,3VV transitions are compared with those generated from local-density-approximation linear-muffin-tin-orbital band-structure calculations. An analysis based on this comparison is used to determine the Coulomb parameters U_p and U_d of the oxygen and copper atoms, respectively. For this purpose, an extended version of Cini and Sawatzky’s expression for the theoretical Auger line shape is used, taking into account the multiplet structure of the Auger final states and the point symmetry of the oxygen sites. We find U_p of approximately 5 and 7 eV for the planar and apical oxygen sites, respectively, and U_d of 7–8 eV for copper. An estimate of the effect of electron correlations on the band structure suggests a decrease of the anisotropy found in U_p.