Photoemission and inverse photoemission studies of La adatom interactions with YBa2Cu3O/sub 6.9/

The surface reactions that occur when adatoms of La are deposited onto the high-temperature superconductor YBa2Cu3O/sub 6.9/ have been studied using high-resolution synchrotron radiation photoelectron spectroscopy and inverse photoelectron spectroscopy. These adatoms lead to the depletion of oxygen from the substrate as La-O forms at low coverage. The process of oxygen withdrawal quickly becomes kinetically limited as the thickening overlayer impedes mass transfer. At the same time, Cu atoms released from the disrupted, no-longer- superconducting substrate outdiffuse into, and segregate to the top of, the growing La overlayer. The complex reacted interface, therefore, exhibits phases which are likely to be superconducting, insulating, and metallic