Resonant Inelastic X-Ray Scattering from Valence Excitations in   Insulating Copper-Oxides
  We report resonant inelastic x-ray measurements of insulating La$_2$CuO$_4$ and Sr$_2$CuO$_2$Cl$_2$ taken with the incident energy tuned near the Cu K absorption edge. We show that the spectra are well described in a shakeup picture in 3rd order perturbation theory which exhibits both incoming and outgoing resonances, and demonstrate how to extract a spectral function from the raw data. We conclude by showing {\bf q}-dependent measurements of the charge transfer gap. 
P. Abbamonte, C. A. Burns, E. D. Isaacs, P. M. Platzman, L. L. Miller,   S. W. Cheong, and M. V. Klein