Theoretical polarization dependence of the two-phonon double-resonant Raman spectra of graphene

TL;DR

This paper presents a comprehensive quantum perturbation theory model for the two-phonon Raman spectra of graphene, accurately predicting polarization dependence and intensity ratios, aligning well with experimental observations.

Contribution

It introduces a unified theoretical framework for two-phonon Raman spectra of graphene using density-functional-theory-based calculations.

Findings

Predicted polarization dependence of Raman bands matches experimental data.

Calculated intensity ratios between parallel and cross polarization are between 0.33 and 0.42.

Systematic analysis of overtone and combination two-phonon bands.

Abstract

The experimental Raman spectra of graphene exhibit a few intense two-phonon bands, which are enhanced through double-resonant scattering processes. Though there are many theoretical papers on this topic, none of them predicts the spectra within a single model. Here, we present results for the two-phonon Raman spectra of graphene calculated by means of the quantum perturbation theory. The electron and phonon dispersions, electronic lifetime, electron-photon and electron-phonon matrix elements, are all obtained within a density-functional-theory-based non-orthogonal tight-binding model. We study systematically the overtone and combination two-phonon Raman bands, and, in particular, the energy and polarization dependence of their Raman shift and intensity. We find that the ratio of the integrated intensities for parallel and cross polarized light for all two-phonon bands is between 0.33 and 0.42. Our results are in good agreement with the available experimental data.