CuKα resonant x-ray emission spectroscopy of high- Tc -related cuprates

The pre-edge structure of Cu1s excitations of high Tc cuprates reflects the lowest-lying unoccupied electronic states in these materials, and thus it is directly relevant to the interesting low-energy excitations and their nonlocal characters. We have performed theoretical calculations of the CuKα resonant x-ray emission spectroscopy (RXES) in the pre-edge region of La2 CuO4 with a Cu5 O16 cluster model in order to analyze recent experimental data. The Cu1s to on-site Cu3d excitation by the electric quadrupole transition and the Cu1s to off-site Cu3d excitation by the electric dipole transition are taken into account, confirming that the off-site transition is indeed visible but that it is split due to the effect of both the local and the nonlocal components of screening. The calculated results of RXES spectra, as well as of x-ray absorption spectra by partial fluorescence yield method, are in reasonable agreement with the experimental data. The influence of the low-energy tail of Cu4p states and the effects of doping electrons and holes are also calculated and discussed. Calculations are made for CuKα RXES of one-dimensional corner and edge sharing cuprates and compared to new experimental results for Sr2 CuO3 and GeCuO3.