Absence of pseudogap in heavily overdoped from tunneling spectroscopy of break junctions

¹ Materials Science Division, Argonne National Laboratory - Argonne IL 60439, USA
² Department of Physics, Izmir Institute of Technology - TR-35437 Izmir, Turkey
³ Physics Division, Illinois Institute of Technology - Chicago IL 60616, USA
⁴ Naval Research Laboratory - Washington DC 20375, USA
⁵ Department of Applied Physics, Science University of Tokyo - Tokyo, Japan

Received: 29 September 2001
Accepted: 21 February 2002

Abstract

We report tunneling spectroscopy of superconductor-insulator-superconductor break junctions on heavily overdoped Bi₂Sr₂CaCu₂O with  K. At , 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  meV have been observed leading to 2 near the BCS limit for pairing. Temperature dependence of the gap magnitude, , follows the BCS relation and both the quasiparticle gap and Josephson current vanish for . Above , the tunneling conductance shows a flat background without any indication of a pseudogap near the Fermi level.