A model and calculation of evolving tunneling spectra for the gap and pseudogap in Bi2Sr2CaCu2O8+δ

Abstract

By the intrinsic tunneling spectroscopy in Bi2Sr2CaCu2O8+δ (Bi2212), it is found that the superconducting coherence peak becomes greater and sharper and the pseudogap peak diminishes with the increase in doping. It is also found that these changes are accompanied by a significant almost exponential increase in the maximum Josephson current density Jc. In order to explain the experimental results, we propose a model, in which mobile carriers reside only in limited areas in the k-space, and are closely correlated with the d-wave superconducting order parameter. The range of the area in which mobile carriers reside depends on the doping level. Outside these areas the density of states is absent at the chemical potential and a semiconducting gap is assumed. Based on this model, the tunneling spectra are calculated at various doping levels to obtain the result that the superconducting peak increases from a cusp at the shoulder of the pseudogap to a dominantly strong peak as the doping increases. The results are in qualitatively good agreement with the experimental tunneling spectra observed.