Eliashberg analysis of the optical conductivity in superconducting Pr₂CuO_x with x similar or equal to 4

Superconducting Pr₂CuO_x, x similar or equal to 4 films with T' structure and a T_c of 27 K have been investigated by millimeter-wave transmission and broadband (infrared-to-ultraviolet) reflectivity measurements in the normal and superconducting state. The results obtained by both experimental methods show a consistent picture of the superconducting condensate formation below T_c. An Eliashberg analysis of the data proves d-wave superconductivity and unitary-limit impurity scattering of the charge carriers below T_c. The derived electron-exchange boson interaction spectral function I²chi(omega) shows only marginal changes at the superconducting transition with the mass enhancement factor lambda, the first inverse moment of I²chi(omega), being equal to 4.16 at 30 K and to 4.25 at 4 K.