Interface properties of YBa2Cu3O7-x/I/metal junctions with native and artificial tunnelling barriers

Tunnelling spectroscopy was used to study interface properties of YBa2Cu3O7 -x (YBCO)/artificial barrier/normal-metal and YBCO/native barrier/normal-me tal tunnel junctions. As artificial tunnelling barriers, YBCO + 2% Co and C eO2 thin films were used. The native tunnel barrier of YBCO was prepared by a surface treatment to create a YBCO layer with oxygen deficiency. Tunnell ing characteristics of the junctions were obtained as a rule, but the corre sponding differential characteristics indicate suppression of the pair pote ntial in YBCO near the barrier. Peculiarities like a linear dependence of t he differential conductance versus voltage, smeared gap-like structures, an d increase of the differential conductance close to zero bias voltage for t hese junctions were observed. These phenomena are discussed within the mode l of complex structure creation in the tunnel junction as a result of YBCO degradation near the contact with the metal, as well as pronouncedly inelas tic processes in the degraded YBCO.