Two-Electron Resonance at the3pThreshold of Cu and Ni

A sharp $3d$-electron satellite excitation has been found for Cu which exhibits a strong resonant enhancement (∼ × 5) at the Cu $3p$-core-level threshold similar to the 6-eV resonant satellite observed previously in Ni. This satellite, which has two peaks at 11.8 and 14.6 eV below $E_{\mathrm{F}}$, is identified as a quasiatomic two-electron excitation with two $3d$ holes plus one $4s$ electron ($3d^{8}4s$). Present models for the Ni resonant satellite are not able to describe our Cu results.