On-site Coulomb interaction and exchange splitting in Ni 2p photoemission of ferromagnetic nickel

The 2p photoemission of Ni metal displays a weak magnetic circular dichroism(MCD) with a complex structure over an energy range of more than 35 eV. Since a one-particle model clearly fails to explain this experimental result, we propose a final-state impurity model which assumes that the core-ionized atom can be described as an impurity state in a many-body approach. From this model we obtain the value of the on-site Coulomb interaction U without having to rely on assumptions concerning the nature of the ground state, which might be either localized or itinerant; The pd(8) satellite, which is much more pronounced in the MCD than in the isotropic spectrum, can be used to fix the value of U to similar to 5.15 eV. We demonstrate that an Anderson impurity model would require different values of U and transfer integral, T, in initial and final state. We further present the calculated spin-polarized Ni 2p photoemission. Its 2p(1/2) structure shows distinct differences with the MCD, which means that the 2p3d Coulomb interaction cannot be neglected with respect to the 2p spin-orbit interaction.