Eliashberg analysis of the optical conductivity in superconducting   Pr$_2$CuO$_{x}$ ($x \simeq 4$)
  Superconducting Pr$_2$CuO$_x$, $x\simeq 4$ films with $T^\prime$ 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 $I^2\chi(\omega)$ shows only marginal changes at the superconducting transition with the mass enhancement factor $\lambda$, the first inverse moment of $I^2\chi(\omega)$, being equal to 4.16 at 30 K and to 4.25 at 4 K. 
E. Schachinger, G. Chanda, R. P. S. M. Lobo, M. Naito, and A. V.   Pronin
cond-mat.supr-con cond-mat.str-el