Fig. 1. Cu $L_3$ x-ray absorption spectra, reprinted from Bianconi {\it et al.}. For the upper two curves, the solid line corresponds to La$_2$CuO$4$ and the dashed line to La$_{1.85}$Sr$_{0.15}$CuO$_4$. Note that there is no change in the leading edge or main peak, which are sensitive to empty $3d$ states. Doping enhances the absorption on the high-energy side, corresponding to O $2p$ holes. The empty $3d$ states are pulled down in energy relative to these by the potential of the x-ray-induced core hole.

Fig. 2. (a) Oxygen $K$ edge x-ray absorption spectra measured by fluorescence yield on ceramic samples of LSCO for various dopings. (b) Expanded view of the pre-edge peaks, after subtraction of the solid curve indicated in (a). From Chen {\it et al.}