Analysis of Breit-Wigner line shapes in the Raman spectra of graphite intercalation compounds

Abstract

We perform an analysis of the ∼ 1500 ${\mathrm{cm}}^{-1\mathrm{}}$ Breit-Wigner interference feature in the Raman spectra of stage-1 (${\mathrm{C}}_{8}X$, $X=\mathrm{K},\mathrm{R}\mathrm{b},\mathrm{C}\mathrm{s}$) graphite-alkali-metal intercalation compounds based on new ${\mathrm{C}}_8$Cs data found a wider frequency range. Unlike previous studies of this interference feature we take into account the frequency dependence of the continuum scattering. Our analysis of the ${\mathrm{C}}_8$Cs spectrum strongly suggests that the Breit-Wigner resonance at ∼ 1500 ${\mathrm{cm}}^{-1\mathrm{}}$ in these ${\mathrm{C}}_{8}X$ donor compounds is due to an interference of a continuum with an in-plane carbon-layer vibration corresponding to the $\Gamma$-point mode of pristine graphite, rather than to the graphitic zone-folded $M$-point mode suggested previously.