Two-dimensional analysis of the double-resonant 2D Raman mode in bilayer graphene

TL;DR

This paper provides a comprehensive first-principles analysis of the double-resonant 2D Raman mode in bilayer graphene, revealing the dominance of inner processes and the importance of phonon splitting for accurate lineshape description.

Contribution

It introduces a first-principles computational approach including electron-electron interactions to analyze the 2D Raman mode, highlighting the significance of inner processes and phonon splitting.

Findings

Inner processes dominate the 2D-mode in bilayer graphene.

The 2D-mode lineshape is governed by three main resonances near the K point.

Phonon splitting of up to 12 cm$^{-1}$ significantly affects the lineshape.

Abstract

By computing the double-resonant Raman scattering cross-section completely from first principles and including electron-electron interaction at the $GW$ level, we unravel the dominant contributions for the double-resonant 2D-mode in bilayer graphene. We show that, in contrast to previous works, the so-called inner processes are dominant and that the 2D-mode lineshape is described by three dominant resonances around the $K$ point. We show that the splitting of the TO phonon branch in $\Gamma-K$ direction, as large as 12 cm$^{-1}$ in $GW$ approximation, is of great importance for a thorough description of the 2D-mode lineshape. Finally, we present a method to extract the TO phonon splitting and the splitting of the electronic bands from experimental data.