Fermi-liquid behavior in the electrical resistivity of ${\mathrm{K}}_3$${\mathrm{C}}_{60}$ and ${\mathrm{Rb}}_3$${\mathrm{C}}_{60}$

We report on the electrical resistivity of ${\mathrm{K}}_3$ ${\mathrm{C}}_{60}$ and ${\mathrm{Rb}}_3$ ${\mathrm{C}}_{60}$ thin films. These films, grown at elevated temperatures, are highly textured and consist of large single-crystal grains. The films exhibit metallic behavior up to 500 K, with residual resistivities of 1.2 mΩ cm. The low-temperature (T) resistivity exhibits a ${\mathit{T}}^2$ dependence. We suggest that it is dominated by electron-electron interactions, and we find quantitative agreement not only with estimates based on the electron density and the bandwidth, but also with other narrow band systems. The electron-phonon interactions only become important for the resistivity above room temperature, because these phonons correspond to high-frequency vibrations of the ${\mathrm{C}}_{60}$ molecule. Nevertheless, virtual excitations of these same high-energy phonons are responsible for the superconductivity. Using similar criteria of conventional organic superconductors, we find that these materials are dominated at all temperatures by electron-phonon interactions.