Core-hole screening and plasmon satellites in calcium

The valence bands and the outermost p core levels of Ca metal have been studied by synchrotron radiation photoemission. High-resolution studies of the 3p core levels reveal three peaks and anomalously strong plasmon satellites. It is shown by the Z+1 approximation that empty states in Ca metal which are just above the Fermi level are pulled below EF by the core-hole potential and the core hole is screened by a 3d electron. Localization of the 3d electron at the core-hole site is confirmed by good agreement between the observed core-level structure and the calculated 3p⁵3d¹ multiplet. This conclusion is consistent with valence-band and core-level photoemission results for the Ca-Si interface and CaH₂. Studies of the Ba 5p core levels show structures which are ascribed to the multiplet of 5d-screened 5p⁵5d¹ final states. Possible effects of the poorly screened core-hole states (3p⁵3d⁰) on the plasmon satellites are discussed.