FERMI VELOCITY MISMATCH EFFECTS IN TUNNELING CHARACTERISTICS OF HIGH-TC SUPERCONDUCTORS

We present a comparative study of the tunneling characteristics of poi nt contacts in which one electrode was a superconducting single crysta l of Bi2Sr2CaCu2Ox and the other electrode was either a normal metal ( N-HTSC point contact), or a non-superconducting rare earth metallic ox ide (REMO-HTSC point contact), or another crystal of the same supercon ductor (HTSC'-HTSC point contact). We show that the mismatch of the Fe rmi velocities of the electrons is in part responsible for the irrepro ducibility of most of the tunneling conductance curves obtained in hig h temperature superconductors.