3presonance photoionization of the valence band in metallic Ca: Atomic and solid-state many-body effects

The valence-band photoemission of metallic Ca is shown to be resonantly enhanced in the region of $3p$ excitation. The general shape of the resonance profile can be explained as an atomic phenomenon, namely, a $3p-3d$ giant dipole resonance driving the valence-electron photoionization process. The metal aspects are revealed by the shape of the resonance, the asymmetry of which reflects the $3d$ character of the valence band, and by additional structure, which probably represents a coupling to shake-up processes.