Electronic Structure of Nd_2-xCe_xCuO₄ and La_2-xSr_xCuO₄ Deduced from Cu 2 p Photoemission and Photoabsorption

Abstract

The electronic structures of Nd 2- x Ce x CuO 4 and La 2- x Sr x CuO 4 are studied using numerical diagonalization calculations for cluster models, Cu 5 O 16 , Cu 7 O 20 , and Cu 8 O 16 . The Fermi energy of Nd 2 CuO 4 used in the experiment is assumed to be pinned at the bottom of the upper Hubbard band, while that of La 2 CuO 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- x Ce x CuO 4 and La 2- x Sr x CuO 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 2 CuO 4 as well as in La 2 CuO 4 .