Nonlocal Screening Effect in Cu 4pσ- 1s Resonant X-ray Emission Spectra in Nd 2CuO 4

We theoretically study polarization and momentum-transfer dependence in Cu 4 p σ -1 s resonant X-ray emission spectra (RXES) of Nd 2 CuO 4 with exact diagonalization techniques, developing our previous report [T. Idé and A. Kotani, J. Phys. Soc. Jpn. 68 (1999) 3100]. We explain the experimental polarization and angular dependence of a charge-transfer excitation about 5.7 eV above the ground state. Comparing results calculated with single- and multi-Cu models, we confirm the essential contribution of the nonlocal screening effect in Cu 4 p σ -1 s RXES, together with the configuration dependence of d - p hybridization. We predict considerable dependence of a CT excitation at about 2 eV on momentum transfer along the CuO 2 planes, and the 5.7 eV excitation has less dependence.