Optical Phonon Anomaly in Bilayer Graphene with Ultrahigh Carrier Densities

Abstract

Electron-phonon coupling (EPC) in bilayer graphene (BLG) at different doping levels is studied by first-principles calculations. The phonons considered are long-wavelength high-energy symmetric (S) and antisymmetric (AS) optical modes. Both are shown to have distinct EPC-induced phonon linewidths and frequency shifts as a function of the Fermi level $E_F$. We find that the AS mode has a strong coupling with the lowest two conduction bands when the Fermi level $E_F$ is nearly 0.5 eV above the neutrality point, giving rise to a giant linewidth (more than 100 cm${}^{-1}$) and a significant frequency softening ($\sim$ 60 cm${}^{-1}$). Our \emph{ab initio} calculations show that the origin of the dramatic change arises from the unusual band structure in BLG. The results highlight the band structure effects on the EPC in BLG in the high carrier density regime.

5 pages, 4 figures

References in corpus (16)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• The electronic properties of graphene
• Controlling electron-phonon interactions in graphene at ultra high carrier densities
• Excitonic Effects on the Optical Response of Graphene and Bilayer Graphene
• Non-adiabatic Kohn-anomaly in a doped graphene monolayer
• Determination of the electronic structure of bilayer graphene from infrared spectroscopy results
• Phonon dispersions and vibrational properties of monolayer, bilayer, and trilayer graphene
• Velocity Renormalization and Carrier Lifetime in Graphene from Electron-Phonon Interaction
• Optical conductivity of bilayer graphene with and without an asymmetry gap
• Electron-Phonon Interactions in Graphene, Bilayer Graphene, and Graphite
• Observation of Anomalous Phonon Softening in Bilayer Graphene
• Observation of Distinct Electron-Phonon Couplings in Gated Bilayer Graphene
• Doped graphene as tunable electron-phonon coupling material
• Anisotropic Electron-Phonon Coupling and Dynamical Nesting on the Graphene Sheets in CaC6
• Electron-Phonon Interactions for Optical Phonon Modes in Few-Layer Graphene
• Enhanced Optical Conductivity Induced by Surface States in ABC-stacked Few-Layer Graphene