Hybridization effect on the X-ray absorption spectra for actinide materials: Application to Pu B4

Studying the local moment and 5f-electron occupations sheds insight into the electronic behavior in actinide materials. X-ray absorption spectroscopy (XAS) has been a powerful tool to reveal the valence electronic structure when assisted with theoretical calculations. However, the analysis currently taken in the community on the branching ratio of the XAS spectra generally does not account for the hybridization effects between local f orbitals and conduction states. In this paper, we discuss an approach which employs the density functional theory plus Gutzwiller rotationally invariant slave boson method to obtain a local Hamiltonian for the single-impurity Anderson model, and calculates the XAS spectra by the exact diagonalization (ED) method. A customized numerical routine was implemented for the ED XAS part of the calculation. By applying this technique to the recently discovered 5f-electron topological Kondo insulator PuB4, we determined the signature of 5f-electronic correlation effects in the theoretical X-ray spectra. We found that the Pu 5f-6d hybridization effect provides an extra channel to mix the j=5/2 and 7/2 orbitals in the 5f valence. As a consequence, the resulting electron occupation number and spin-orbit coupling strength deviate from the intermediate-coupling regime.