Josephson Effects and Tunnelling Spectroscopy in Yttrium Barium Copper Oxide Materials.

Tunneling and proximity effect measurements were undertaken with narrow constrictions (microbridges) fabricated in bulk ceramic, melt processed thick films and thin films of the high-T_{rm c} superconductor, rm YBa_2Cu_3O _{7-delta}, in order to provide detailed information on the nature of the superconducting state in these different forms of this new material. Since pure Josephson behaviour is expected for bridges whose width is of the order of the superconducting coherence length, which is only of the order of 1 nm, and impossible to fabricate with present technology, our larger bridges were doped with rm Y_2BaCuO_5 which gave rise to a number of interesting effects. These effects are Josephson junction like, SQUID-like, involve chaotic behaviour and non-linear characteristics in the measured CVCs for the high voltage regime. These experimentally observed effects are analysed in terms of the basic BCS -Ginsburg-Landau phenomenology.