Electron-phonon coupling in AA-stacked multilayer graphene: First-principles calculations

Chih-Wei Hsu^1,2*, Mei-Yin Chou^1,2

¹Physics, National Taiwan University, Taipei, Taiwan
²Institute of Atomic and Molecular Sciences, Academic Sinica, Taipei, Taiwan

* Presenter:Chih-Wei Hsu, email:r13222008@ntu.edu.tw

It has been discovered that in several twisted graphene systems exhibiting superconductivity, the charge density of low-energy electrons is localized in the AA-stacked regions. Therefore, the electron-phonon coupling in these regions is of particular interest. In this work, we investigate the vibrational properties and electron–phonon interactions of AA-stacked multilayer graphene using first-principles calculations. In AA-stacked bilayer graphene, the in-plane optical phonons at both the zone center and the zone corner split into two branches with an opposite layer parity. Owing to the bonding–antibonding nature of the low-energy electronic states in AA-stacked bilayer graphene, the layer-symmetric mode exhibits vanishing electron–phonon coupling, whereas the antisymmetric mode retains finite coupling—behavior well captured by a tight-binding model and consistent with symmetry-based selection rules. Although the overall magnitude of the coupling matrix elements is smaller than that in monolayer graphene, the nearly perfect intra- and inter-valley Fermi-ring nesting in AA-stacked bilayers leads to a pronounced enhancement of the phonon linewidth for layer-antisymmetric modes.
As the number of layers increases, the in-plane phonons further split into multiple modes with distinct vibrational symmetries, and the phonon-linewidth contributions are redistributed among them through additional intra- and inter-cone scattering channels. In particular, the linewidths of the layer-alternating antisymmetric modes increase significantly with the layer number due to enhanced Dirac-cone pair-scattering processes. Our findings identify AA-stacked graphene as a platform for exploring strong electron–phonon coupling in layered graphene systems and provide a theoretical foundation for future studies of both aligned and twisted graphene multilayers.

Keywords: Electron-phonon coupling, AA-stacked multilayer graphene, Fermi-surface nesting