Temperature dependence of the maximum Josephson current in V-V x O y -Pb tunnel junctions

Measurements of the temperature dependence of the maximum dc Josephson current in V-V_xO_y-Pb tunnel structures have been performed. Junctions exhibiting a vanadium critical temperature close to the bulk value and a uniform supercurrent density have been considered. In spite of the high quality of the samples, the results still differ markedly from the BCS calculation of Ambegaokar and Baratoff.This work is partially supported by the Consiglio Nazionale delle Ricerche under the Progetto Finalizzato Superconduttivitá.