A new correlation for T_c from Cu 2p absorption

We studied the Cu 2p x-ray absorption spectra of the superconductor La2-xSrxCuO4 in the doping regime x=0-0.6 and found that the intensity of the satellite peak is a reliable measure of the doping-induced hole concentration. From the Cu 2p absorption spectra taken in this work on the La2-xSrxCuO4 system and from those published for other high-temperature superconductors, we found that the energy separation between the satellite peak and the main peak, which is the ligand-hole energy, increases with Tc. © 1991.