Dimensional Effect on the Lattice Anharmonicity in Graphene and Graphite

Dimensionality reduction is often expected to slow down the anharmonic decay of phonons since it drastically reduces the phase space for phonon-phonon interactions. However, the anharmonic scattering behavior of the Raman-active E_2g phonon in graphene deviates from this expectation when compared with graphite. Through systematic theoretical analysis, we reveal that this deviation arises from the dimensionality-reduction-induced enhancement of both phonon population and anharmonicity of flexural acoustic (also called ZA) phonons in graphene. This enhancement outweighs the reduced scattering phase space and results in a broader phonon linewidth. We further demonstrate that the anharmonicity of ZA phonons in graphite can be tuned by modifying the interlayer coupling. These results provide fundamental insight into lattice anharmonicity and highlight the critical role of dimensionality in the graphene-graphite system.