Identification of the relative population of spin-orbit split states in the ground state of a solid

The authors introduce a method to investigate experimentally the relative populations of spin-orbit-split states in the ground state of a material. The method uses multiplet structure in X-ray absorption spectra and selection rules limit the subset of terms that can be reached in a given final-state configuration. This subset is dependent on the precise details of the ground state. A test of this method on Ce materials is presented. The results are consistent with an increase in the ratio of 4f 7 2/ 1 to 4f 5 2/ 1 contributions in the ground state with increasing hybridization between the 4f levels and the conduction states.