Absence of pseudogap in heavily overdoped Bi2Sr2CaCu2O8+δ from tunneling spectroscopy of break junctions

We report tunneling spectroscopy of superconductor-insulator-superconductor break junctions on heavily overdoped Bi2Sr2CaCu2O8+delta with T-c=56K. At Tmuch less thanT(c), the junction conductances display well-defined quasiparticle peaks at +/-2Delta and in some cases a Josephson current at zero bias. Gap values as small as Delta=10.5 meV have been observed leading to 2Delta/kT(c) near the BCS limit for d(x 2-y 2) pairing. Temperature dependence of the gap magnitude, (DeltaT), follows the BCS relation and both the quasiparticle gap and Josephson current vanish for T>T-c. Above T-c, the tunneling conductance shows a at background without any indication of a pseudogap near the Fermi level.