Theory of resonant spectroscopies in nickel, cerium compounds and other systems

In this paper, we discuss theoretically information about electronic structures in strongly correlated systems obtained from resonant X-ray spectroscopies. From a many-body point of view on the basis of an impurity Anderson model or a cluster model including the intra-atomic multipole interaction between electrons, we calculate spectra by exactly diagonalizing our Hamiltonian. First, for ferromagnetic Ni. through an analysis of magnetic circular dichroism in 3d resonant photoemission spectroscopy (RPES) and resonant inverse photoemission spectroscopy (RIPES), it is shown that, in addition to 3d(9) and 3d(10), the 3d(8) configuration with weight of about 20% is contained as electron configuration of a Ni atom in Ni metal. The 3d(8) configuration is furthermore shown to be mainly composed of F-3 and its relation to the origin of ferromagnetism is discussed. Second, for mixed valent Ce compounds, including CeNi2, it is shown, through an analysis of RIPES, tht the 4f-conduction band hybridization must be reduced by the presence of a core hole. Third, for some 3d transition metal (TM) oxides, 3d RPES at TM ion 2p threshold is shown to be a powerful method for estimating the magnitude of 3d-3d interaction strength and the charge transfer energy. (C) 2001 Elsevier Science B.V. All rights reserved.