Eliashberg equations, pair symmetry and tunnel density of states in the optimally-doped high-Tc superconductor Bi2Sr2CaCu2O8+x

In this work, in order to compare the theoretical density of states (DOS) to the tunneling data in the optimally-doped high-Tc superconductor (HTS) Bi2Sr2CaCu2O8+x, we calculate the real-axis direct solution of the d-wave equations for the retarded electron-boson interaction in presence of half-filling and impurities. The use of a spectral function containing an isotropic part αs2F(Ω) and an anisotropic one αd2F(Ω) and the simple assumption: αd2F(Ω) = gdαs2F(Ω) where gd is a constant leads, for appropriate values of the isotropic coupling constant λs and the anisotropic one λd, to solutions with only d-wave symmetry for the order parameter Δ(ω) and only s-wave one for the renormalization function Z(ω). The results properly fit both the critical temperature and the DOS in the whole energy range, as recently determined in our break-junction tunneling experiments, but appear unable to do the same in the case of recent STM data.