Resonant Raman scattering in metals at the interband absorption threshold

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-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.