Emergence of a ZO Kohn anomaly in quasi-freestanding epitaxial graphene

Abstract

In neutral graphene, two prominent cusps known as Kohn anomalies are found in the phonon dispersion of the highest optical phonon at $q=\Gamma$ (LO branch) and $q=K$ (TO branch), reflecting a significant electron-phonon coupling to undoped Dirac electrons. In this work, high-resolution electron energy loss spectroscopy is used to measure the phonon dispersion around the $\Gamma$ point in quasi-freestanding graphene epitaxially grown on Pt(111). The Kohn anomaly for the LO phonon is observed at finite momentum $q\sim 2k_F$ from $\Gamma$, with a shape in excellent agreement with the theory and consistent with known values of the EPC and the Fermi level. More strikingly, we also observe a Kohn anomaly at the same momentum for the out-of-plane optical phonon (ZO) branch. This observation is the first direct evidence of the coupling of the ZO mode with Dirac electrons, which is forbidden for freestanding graphene but becomes allowed in the presence of a substrate. Moreover, we estimate the EPC to be even greater than that of the LO mode, making graphene on Pt(111) an optimal system to explore the effects of this new coupling in the electronic properties.

arXiv commentFinal version with journal reference. Significantly more experimental data was added to the main text and the supplemental material. 5 pages of main text + 6 of supplement

References in corpus (28)

• Electrochemically Top Gated Graphene: Monitoring Dopants by Raman Scattering
• First-principles study of the interaction and charge transfer between graphene and metals
• Kohn Anomalies and Electron-Phonon Interaction in Graphite
• Dirac Cones and Minigaps for Graphene on Ir(111)
• Non-adiabatic Kohn-anomaly in a doped graphene monolayer
• Electron-electron interactions and doping dependence of the two-phonon Raman intensity in graphene
• The phonon dispersion of graphite by inelastic x-ray scattering
• Phonon Linewidths and Electron Phonon Coupling in Nanotubes
• Electronic Cooling in Graphene
• Inelastic Scattering and Current Saturation in Graphene
• Transport properties of graphene in the high-current limit
• Theory of resonant multiphonon Raman scattering in graphene
• Energy Relaxation of Hot Dirac Fermions in Graphene
• Interplay of Coulomb and electron-phonon interactions in graphene
• Spontaneous parity breaking of graphene in the quantum Hall regime
• Mechanism for current saturation and energy dissipation in graphene transistors
• Energy Gaps and Kohn Anomalies in Elemental Superconductors
• Kohn anomaly and interplay of electron-electron and electron-phonon interactions in epitaxial graphene
• Kohn Anomalies in Graphene Nanoribbons
• Screening of electron-phonon coupling in graphene on Ir(111)
• Observation of the Kohn anomaly near the K point of bilayer graphene
• Effective Hamiltonian of Strained Graphene
• Spectroscopic characterization of graphene films grown on Pt (111) surface by chemical vapor deposition of ethylene
• Chirality-induced Dynamic Kohn Anomalies in Graphene
• Symmetries and selection rules in the measurement of the phonon spectrum of graphene and related materials
• Power law Kohn anomalies and the excitonic transition in graphene
• Power law Kohn anomaly in undoped graphene induced by Coulomb interactions
• Ising instability of a Holstein phonon mode in graphene

Cited by in corpus (10)

• Mapping momentum-dependent electron-phonon coupling and non-equilibrium phonon dynamics with ultrafast electron diffuse scattering
• Observation of the Breakdown of Optical Phonon Splitting in a Two-dimensional Polar Monolayer
• Spectroscopic investigations of phonons in epitaxial graphene
• Spontaneous mass generation due to phonons in a two-dimensional Dirac fermion system
• Emergent Chern-Simons excitations due to electron--phonon interaction
• Symmetry-breaking supercollisions in Landau-quantized graphene
• Electron-phonon Coupling and Kohn Anomaly due to the Floating 2D Electronic Bands on the Surface of ZrSiS
• In-plane optical phonon modes of current-carrying graphene
• Friedel oscillation near a van Hove singularity in two-dimensional Dirac materials
• Coexistence of spontaneous polarization and superconductivity in hole-doped oxyhydrides ATiO_2H (A=K, Rb, Cs): first-principles study