TEMPERATURE-INDUCED TRANSITION FROM TUNNELING TO METALLIC BEHAVIOR OF BI(2-X)PB(X)SR2CA(N)CU(N+1)O(Y) (X=0.4, N=1 AND N=2) BREAK JUNCTIONS

A distinct gap feature has been observed in polycrystalline Bi2-xPbxSr2CanCun+1Oy (x=0.4, n=1 and n=2) break junctions. The gap values varied from junction to junction displaying different temperature dependences but the same critical temperature. The observed effect can be interpreted as an indication for an intrinsic proximity effect associated with the layered structure of BiSrCaCuO:Pb superconductors and the variable properties of the fracture surface. The properties of the surface barrier affect also the current flow across the contact. We observed a temperature-induced transition from a current-voltage characteristic with tunnelling behaviour to one with metallic behaviour. The modification of the I(V)-characteristic with temperature is explained by the presence of a localized state in the barrier.