We analyze optical spectroscopy data of the electron-doped superconductor $\left({\text{Pr}}_{2-x}{\text{Ce}}_x\right){\text{CuO}}_4$ (PCCO) to investigate the coupling of the charge carriers to bosonic modes. The method of analysis is the inversion of the optical scattering rate ${\tau }_{\text{op}}^{-1}\left(\omega ,T\right)$ at different temperatures $T$ by means of maximum entropy technique combined with Eliashberg theory. We find that in the superconducting state the charge carriers couple to two dominant modes, one at $\sim 12\text{meV}$ and a second one at $\sim 45\text{meV}$ as well as to a high energy background. The low energy mode shows a strong temperature dependence and disappears at or slightly above the critical temperature $T_c$. The high energy mode exists above $T_c$ and moves toward higher energies with increasing temperatures. It becomes less prominent at temperatures $>100\text{K}$ above which it evolves into a typical spin-fluctuation background. In contrast to the hole-doped high-$T_c$ superconductors PCCO proves to be a superconductor close to the dirty limit.

• Received 23 February 2008

DOI:https://doi.org/10.1103/PhysRevB.78.134522