Ab Initio Approach to Second-order Resonant Raman Scattering Including Exciton-Phonon Interaction

TL;DR

This paper presents a first-principles method to compute second-order Raman spectra in crystalline solids, accounting for exciton-phonon interactions, and demonstrates its effectiveness on silicon with results matching experiments.

Contribution

The authors develop a novel ab initio approach to include exciton-phonon coupling in second-order Raman scattering calculations, advancing the understanding of resonance effects.

Findings

Excellent agreement with experimental Raman spectra for silicon.

Exciton-phonon interactions significantly influence resonance Raman features.

Method enables detailed analysis of vibrational and electronic interactions in solids.

Abstract

Raman spectra obtained by the inelastic scattering of light by crystalline solids contain contributions from first-order vibrational processes (e.g. the emission or absorption of one phonon, a quantum of vibration) as well as higher-order processes with at least two phonons being involved. At second order, coupling with the entire phonon spectrum induces a response that may strongly depend on the excitation energy, and reflects complex processes more difficult to interpret. In particular, excitons (i.e. bound electron-hole pairs) may enhance the absorption and emission of light, and couple strongly with phonons in resonance conditions. We design and implement a first-principles methodology to compute second-order Raman scattering, incorporating dielectric responses and phonon eigenstates obtained from density-functional theory and many-body theory. We demonstrate our approach for the case of silicon, relating frequency-dependent relative Raman intensities, that are in excellent agreement with experiment, to different vibrations and regions of the Brillouin zone. We show that exciton-phonon coupling, computed from first principles, indeed strongly affect the spectrum in resonance conditions. The ability to analyze second-order Raman spectra thus provides direct insight into this interaction.