Oxygen doping and temperature dependence of the tunneling spectroscopy on Bi₂Sr₂CaCu₂O_8+δ

Abstract

We present local probe tunneling spectroscopy of Bi₂Sr₂CaCu₂O_8+δ single crystals for different oxygen concentrations, from optimally doped (T_c=92.2 K) to highly overdoped (T_c=56.0 K) phases. With increasing oxygen overdoping, the superconducting gap (Δ_p) is reduced and the dip structure beyond Δ_p at negative sample bias¹ shifts toward the Fermi energy. Apart from the shift in energy of these features, the generic shape of the tunneling spectra remains unchanged. The gap roughly scales with T_c, and 2Δ_p/k_BT_c stays large even in the highly overdoped phase. We also present preliminary results on the temperature dependence of the tunneling spectra. They are consistent with a gap that is largely independent on temperature up to the vicinity of T_c