Tunneling observation of the coexistence of two distinct gaps in Bi2Sr2CaCu2O8+delta

Temperature, T and doping dependent tunneling spectroscopy on Bi2Sr2CaCu2O8 +delta/natural barrier/Zn thin film (Bi2212/I/Zn) junctions has been invest igated systematically. For most of the junctions, the tunneling conductance shows one superconducting gap (SG) at low T and a discontinuous transforma tion from the SG to the pseudogap (PG) at T-c For some junctions studied, t he conductance reveal two distinct gaps: an inner gap which closes when T a pproaches to T-c with BCS-like T-dependence, and an outer gap, coexisting w ith the inner gap for T below T-c, which is almost T-independent below abou t 120 K. We discuss the possible origins of the coexistence of the two gaps , including the coexistence of the SG and PG and the gaps resulting from el ectronic or doping inhomogeneity. (C) 2001 Elsevier Science B.V. All rights reserved.