Tunneling in cuprate and bismuthate superconductors

Tunneling measurements using a point-contact technique are reported for the following high temperature superconducting oxides: Ba1-xKxBiO3(BKBO), Nd2-xCexCuO4 (NCCO), Bi2Sr2CaCu2O7 (BSCCO) and Tl2Ba2CaCu2Ox (TBCCO). For the bismuthate, BKBO, ideal, S-I-N tunneling characteristics are observed using a Au tip. The normalized conductance is fitted to a BCS density of states and thermal smearing only proving there is no fundamental limitation in BKBO for device applications. For the cuprates, the normalized conductance displays BCS-like characteristics, but with a broadening larger than from thermal smearing. Energy gap values are presented for each material. For BKBO and NCCO the Eliashberg functions, α2F(ω), obtained from the tunneling are shown to be in good agreement with neutron scattering results. Proximity effect tunneling studies are reported for Au/BSCCO bilayers and show that the energy gap of BSCCO can be observed through Au layers up to 600 A thick