Absence of pseudogap in heavily overdoped Bi 2 Sr 2 CaCu 2 O 8 + δ from tunneling spectroscopy of break junctions

We report tunneling spectroscopy of superconductor-insulator-superconductor break junctions on heavily overdoped Bi 2 Sr 2 CaCu 2 O 8 + δ with T c = 56 K. At T << T c , the junction conductances display well-defined quasiparticle peaks at ±2Δ and in some cases a Josephson current at zero bias. Gap values as small as Δ = 10.5 meV have been observed leading to 2Δ/ kT c near the BCS limit for d x 2 − y 2 pairing. Temperature dependence of the gap magnitude, Δ( T ), 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 flat background without any indication of a pseudogap near the Fermi level.