PHOTOEMISSION ON HIGH TC SUPERCONDUCTORS

XPS and UPS photoemission results on the new high-Tc oxide superconductors La2−xMexCuO4 (Me=Sr, Ba) with a maximumTc≈40 K show the following: 1) the electronic density of states atE F is small (smaller than in pure Cu); the work function is metallic like with a value around 4.2 eV. 2) The Cu-2p spectra show hardly a possible small tendency to a mixed valent Cu3+/Cu2+state with increasing Me content, but smaller than expected from the Me2+ concentration suggesting that oxygen defects are responsible for the charge compensation. 3) The core level spectra of La, Me, and O show satellites which are at least partially related to O2− defects and which change in intensity with increasing surface sensitivity of the experiments. First core-level spectra on y1.2Ba0.8CuO4 with aTc ≈ K indicate a complicated composition of these new compounds.