Fabrication and tunneling measurements of YBa/sub 2/Cu/sub 3/O/sub x//CaF/sub 2//Nb thin film tunnel junctions
The heteroepitaxial growth of YBa/sub 2/Cu/sub 3/O/sub x/(YBCO)/CaF/sub 2/ has been studied and this structure has been applied to tunnel junctions. The CaF/sub 2/ thin film were epitaxially grown with [111] orientation on YBCO[110] films. The tunneling measurements of YBCO[110]/CaF/sub 2//Nb junctions exhibited that the differential conductance curves have pronounced gap-like structures with sharp peaks at the energy gap edge. The temperature dependence of the energy gap was well fitted to the scaled BCS curve. The 2 Delta /kTc of about eight was derived from the energy gap of 15 meV and T/sub c/ of 45 K obtained by the fitting. This 2 Delta /kTc value was consistent with the infrared reflectivity data reported for the direction parallel to the Cu-O planes.<<ETX>>