Role of Cu 4s Band in Cu 2p-XPS of Nd_2−xCe_xCuO₄

Abstract

The role of the Cu 4s band in the Cu 2p-XPS of Nd_2−xCe_xCuO₄ is investigated on the basis of the impurity Anderson model. The model consists of the impurity Cu 3d shell and the conduction and valence bands formed from the O 2p and Cu 4s bands under the tight-binding approximation. Because of the symmetry of the crystal, the 3d states couple weakly to the Cu 4s band so that the effect of the 4s band on the Cu 2p-XPS is very small in general. However, in the case where the 4s band is lower by a few eV in energy than that estimated by the first-principle calculation, the 4s state is important in the electron doping process in Nd_2−xCe_xCuO₄ because the doped electron enters this state.