0 Tunneling conductance of SIN junctions with different gap symmetries and non - magnetic impurities by direct solution of real - axis Eliashberg equations

We investigate the effect of various symmetries of the superconducting order parameter ∆(ω) on the normalized tunneling conductance of SIN junctions by directly solving the real-axis Eliash-berg equations (EEs) for a half-filled infinite band, with the simplifying assumption µ * = 0. We analyze six different symmetries of the order parameter: s, d, s + id, s + d, extended s and anisotropic s, by assuming that the spectral function α 2 F (Ω) contains an isotropic part α 2 F (Ω)is and an anisotropic one, α 2 F (Ω)an, such that α 2 F (Ω)an=g · α 2 F (Ω)is, where g is a constant. We compare the resulting conductance curves at T = 2 K to those obtained by analytical continuation of the imaginary-axis solution of the EEs, and we show that the agreement is not equally good for all symmetries. Then, we discuss the effect of non-magnetic impurities on the theoretical tunneling conductance curves at T = 4 K for all the symmetries considered. Finally, as an example, we apply our calculations to the case of optimally-doped high-Tc su-perconductors. We compare the theoretical conductance curves calculated at T = 4 K to the results of various tunneling measurements performed on Bi2Sr2CaCu2O 8+δ , La2−xSrxCuO4, YBa2Cu3O 7−δ , Tl2Ba2CuO 6+δ , HgBa2CuO 4+δ single crystals, and we discuss the results.