Raman response of stage-1 graphite intercalation compounds revisited

We present a detailed in situ Raman analysis of stage-1 KC₈, CaC₆, and LiC₆ graphite intercalation compounds to unravel their intrinsic fingerprint. Four main components were found between 1200 cm^-1 and 1700 cm^-1 and each of them were assigned to a corresponding vibrational mode. From a detailed line-shape analysis of the intrinsic Fano lines of the G- and D-line response we precisely determine the position (ωₚₕ), line width (Γₚₕ), and asymmetry (q) from each component. The comparison to the theoretical calculated line width and position of each component allows us to extract the electron-phonon coupling constant of these compounds. A coupling constant λₚₕ<0.06 was obtained. This highlights that Raman active modes alone are not sufficient to explain the superconductivity within the electron-phonon coupling mechanism in CaC₆ and KC₈.