Eliashberg equations, pair symmetry and tunnel density of states in the optimally-doped high-T_c superconductor Bi_2Sr_2CaCu_2O_(8+x)

摘要

In this work, in order to compare the theoretical density of states (DOS) to the tunneling data in the optimally-doped high-T_c superconductor (HTS) Bi_2Sr_2CaCu_2O_(8+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 #alpha#_S~2F(#OMEGA#) and an anisotropic one #alpha#_d~2F(#OMEGA#) and the simple assumption: #alpha#_d~2f(#OMEGA#) = g_d#alpha#_s~2F(#OMEGA#) where g_d is a constant leads, for appropriate values of the isotropic coupling constant #lambda#_s and the anisotropic one #lambda#_d, to solutions with only d-wave symmetry for the order parameter triangle open(#omega#) and only s-wave one for the renormalization function Z(#omega#). 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.