CopperMII,IIIx-ray-emission spectra of copper oxides and the bismuth cuprate superconductor

Photon-excited soft x-ray emission spectra for CuO, ${\mathrm{Cu}}_2$O, and bismuth cuprate in the region of the Cu 3d→3p transitions were measured to obtain bulk-sensitive electronic partial density-of-states information. For CuO and ${\mathrm{Cu}}_2$O transitions from the valence levels into the ${\mathit{M}}_{\mathrm{II}}$ and ${\mathit{M}}_{\mathrm{III}}$ levels were clearly resolved. The emission features were separated by the 2.3-eV spin-orbit interaction of the copper 3${\mathit{p}}_{1/2}$ and 3${\mathit{p}}_{3/2}$ states and appeared in the statistical intensity ratio. The copper ${\mathit{M}}_{\mathrm{III}}$ emission spectrum of the superconductor is broader than the spectra of CuO and ${\mathrm{Cu}}_2$O. For all three compounds the shape of the ${\mathit{M}}_{\mathrm{III}}$ emission spectrum extracted from the data is qualitatively similar to calculations of the copper single-particle local density of states. No evidence of multiplet structure was observed in the emission spectrum of CuO in spite of the open d shell in the ground state. The measurements are compared with published copper L emission data and photoemission results.