A resonance in the cross section for Raman scattering of the incident photon accompanied by the emission of an intralayer phonon is observed in a series of p-type, quasi-two-dimensional metals formed by the electrochemical intercalation of graphite in sulfuric acid. The resonance in the cross section is observed to coincide with the inter-π-band absorption threshold, consistent with our theoretical calculations. The Raman matrix elements are calculated using the standard three-step scattering process. A rigid-band model is used for the carbon π states within a few eV of the Fermi level, and the electron-phonon interaction $V_{e\mathrm{-}\mathrm{ph}}$ is calculated in the deformation-potential approximation. The theory shows that the resonance is a general phenomenon which should be observable in all metals.

• Received 23 March 1987

DOI:https://doi.org/10.1103/PhysRevB.37.691