Observation of Distinct Electron-Phonon Couplings in Gated Bilayer Graphene

TL;DR

This study uses Raman spectroscopy to observe how electron-phonon interactions in gated bilayer graphene cause splitting and shifts in vibrational modes, revealing layer-specific couplings influenced by charge transfer.

Contribution

It provides the first detailed experimental evidence of distinct electron-phonon couplings for symmetric and anti-symmetric phonons in gated bilayer graphene.

Findings

Raman G-band splits into two components with gating.

Symmetric and anti-symmetric phonons couple differently to electrons.

Charge transfer induces inversion symmetry breaking.

Abstract

A Raman study of a back gated bilayer graphene sample is presented. The changes in the Fermi level induced by charge transfer splits the Raman G-band, hardening its higher component and softening the lower one. These two components are associated with the symmetric (S) and anti-symmetric vibration (AS) of the atoms in the two layers, the later one becoming Raman active due to inversion symmetry breaking. The phonon hardening and softening are explained by considering the selective coupling of the S and AS phonons with interband and intraband electron-hole pairs.