TEMPERATURE-INDUCED TRANSITION FROM TUNNELING TO METALLIC BEHAVIOR OFBI(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-xPbxSr 2CanCun+1Oy (x=0.4, n=1 and n=2) break junctions. The gap values varie d from junction to junction displaying different temperature dependenc es but the same critical temperature. The observed effect can be inter preted as an indication for an intrinsic proximity effect associated w ith the layered structure of BiSrCaCuO:Pb superconductors and the vari able 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 modific ation of the I(V)-characteristic with temperature is explained by the presence of a localized state in the barrier.