Ultrafast dynamics of superconducting ${\mathrm{K}}_3{\mathrm{C}}_{60}$ and ${\mathrm{Rb}}_3{\mathrm{C}}_{60}$

We report the results of a detailed experimental and theoretical study of the ultrafast relaxation processes in superconducting ${\mathrm{K}}_3{\mathrm{C}}_{60}$ and ${\mathrm{Rb}}_3{\mathrm{C}}_{60}$ films. Room temperature pump-probe spectra were obtained for different pump and probe wavelengths. Low-temperature measurements through the phase transition temperature $T_c$ were performed to monitor the quasiparticle dynamics in the superconducting state. For comparison we performed measurements on ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$ under similar conditions. An intuitive model is presented to explain the temperature and wavelength dependence of our experimental results for both the superconducting and normal phases.