Andreev reflection in BSCCO/Pb tunneling junctions

We have studied the zero bins conductance peak (ZBCP) due to Andreev reflec tion in BSCCO/Db and BSCCO/Ag tunneling junctions. According to the convent ional BTK theory, the normalized peak height is always less than 2. Surpris ingly, the ZBCP in our junctions can be as high as 5. Even more interesting , the ZBCP exhibits unexpected behavior as the normal electrode (Pb) become s superconducting. We find that the ZBCP will split if the peak is broad, o therwise it will decrease in height. None of these phenomena is observed in BSCCO/Ag junctions, for which Ag remains normal in the whole temperature r ange. (C) 1998 Elsevier Science Ltd. All rights reserved.