YBCO thin films on sapphire with an epitaxial MgO buffer

The authors have developed a process for growing as-deposited c-axis YBCO thin films on R-plane sapphire using an epitaxial buffer of electron-beam-evaporated MgO. The authors discuss the structural and electrical properties of these films and describe the process parameters necessary for epitaxial growth of MgO on sapphire. A subsequent YBCO deposition yields a superconducting film with high transition temperature and critical current. While the YBCO is fully c-axis oriented, plane epitaxy is poor and so is RF surface resistance. Work in progress on a step-edge YBCO junction on MgO is mentioned.