EPITAXIAL CEO2 BUFFER LAYERS AND CROSSOVERS FOR YBA2CU3O7 THIN-FILMS

We have grown epitaxial trilayer structures of YBa2Cu3O7/CeO2/YBa2Cu3O7 using pulsed laser deposition. The thin films were grown on a CeO2 buffer layer deposited on R-plane sapphire. The crystal quality and orientation of the CeO2 and the YBa2Cu3O7 layers has been determined using x-ray diffraction and transmission electron microscope cross-sections. All of the constituent films of the trilayer structure grow epitaxially and have sharp interfaces at an atomic level. The films have Tc above 88K, resistance ratios between 2.5 and 3.0 and surface resistances at 31 GHz and 77K, which are lower than that of copper.