Phonon self-energy corrections to non-zero wavevector phonon modes in single-layer graphene

TL;DR

This study investigates non-zero wavevector phonon modes in single-layer graphene using gate-modulated Raman scattering, revealing unique phonon self-energy effects that differ from zone-center behaviors and identifying specific phonon modes near the K point.

Contribution

The paper provides experimental evidence and theoretical analysis of phonon self-energy corrections for non-zero wavevector modes in graphene, expanding understanding beyond zone-center phonons.

Findings

Observed phonon renormalization effects differ from zone-center cases.

Identified G* Raman feature as arising from q ≠ 0 modes near the K point.

Resolved the phonon modes contributing to the G* feature, including iTO+LA and 2iTO modes.

Abstract

Phonon self-energy corrections have mostly been studied theoretically and experimentally for phonon modes with zone-center (q = 0) wave-vectors. Here, gate-modulated Raman scattering is used to study phonons of a single layer of graphene (1LG) in the frequency range from 2350 to 2750 cm-1, which shows the G* and the G'-band features originating from a double-resonant Raman process with q \not= 0. The observed phonon renormalization effects are different from what is observed for the zone-center q = 0 case. To explain our experimental findings, we explored the phonon self-energy for the phonons with non-zero wave-vectors (q \not= 0) in 1LG in which the frequencies and decay widths are expected to behave oppositely to the behavior observed in the corresponding zone-center q = 0 processes. Within this framework, we resolve the identification of the phonon modes contributing to the G* Raman feature at 2450 cm-1 to include the iTO+LA combination modes with q \not= 0 and the 2iTO overtone modes with q = 0, showing both to be associated with wave-vectors near the high symmetry point K in the Brillouin zone.