Two-electron resonances in transition metals

We have studied experimentally the photoelectron spectra of Cr, Fe, and Co near the $3p$ excitation threshold. Comparison with earlier results in Ni and Cu yields a consistent picture for the behavior of the two-electron satellites. We show that resonance effects are observed in all materials with unfilled $3d$ bands, that the intensity of the resonance depends strongly on the number of $3d$ holes, and that the persistence of the satellite above the resonant energy in nickel, but not in the other transition metals, can be explained by a higher localization of the $3d$ electrons.