Electronic structure of Nd _2-xCe _xCuO ₄ and La _2-xSr _xCuO ₄ deduced from Cu 2 _p photoemission and photoabsorption

The electronic structures of Nd _2-xCe _xCuO ₄ and La _2-xSr _xCuO ₄ are studied using numerical diagonalization calculations for cluster models, Cu ₅O ₁₆, Cu ₇O ₂₀, and Cu ₈O ₁₆. The Fermi energy of Nd ₂CuO ₄ used in the experiment is assumed to be pinned at the bottom of the upper Hubbard band, while that of La ₂CuO ₄ is assumed to be pinned at the top of the Zhang Rice singlet band. This assumption enables us to consistently understand the doping dependence of the Cu 2 _p photoemission and photoabsorption spectra in Nd _2-xCe _xCuO ₄ and La _2-xSr _xCuO ₄ on the basis of the so-called "crossing the gap" picture. The present calculation of Cu 2 _p photoemission spectrum also shows that core hole screening caused by charge transfer between neighboring CuO ₄ plaquettes, in other words, nonlocal screening (NLS), is important in Nd ₂CuO ₄ as well as in La ₂CuO ₄.