Theory of Cu 2p X-Ray Emission Spectroscopy in CuO and La2CuO4

Soft X-ray emission spectroscopy due to the Cu 3d→2p electronic transition (Cu 2p-XES) is one of the powerful tools for investigating the local nature of the Cu 3d state in high-Tc superconductors. We theoretically investigate Cu 2p-XES for CuO and La2CuO4 based upon the impurity Anderson model and the formula of the second order optical process. Justification for this model is given by that available experimental data of Cu 2P-XES, 2P-XPS, 2p-XAS and 3d-XPS are satisfactorily reproduced in a unified way. According to Cu 2p-XES experiments so far made, a shoulder structure appears on the high energy side of the main peak in La2CuO4 and also in high-Tc superconductors, but it is absent in CuO. It is shown that the appearance of the shoulder structure originates from the stronger hybridization for the a1g symmetry states in La2CuO4 than in CuO due to the existence of the apical oxygen.