# Non-adiabatic exciton-phonon coupling in Raman spectroscopy of layered materials

## TL;DR

This paper introduces an ab initio computational method to analyze resonant Raman intensities in layered materials, accounting for excitonic and non-adiabatic effects, revealing quantum interference phenomena affecting exciton behavior.

## Contribution

It develops a novel diagrammatic approach for calculating resonant Raman intensities including excitonic and non-adiabatic effects in layered materials.

## Key findings

- Quantum interference causes strong redistribution of oscillator strength in h-BN.
- Spin-orbit splitting suppresses quantum interference effects in MoS2.
- The approach enables detailed analysis of exciton-phonon interactions in layered materials.

## Abstract

We present an ab initio computational approach for the calculation of resonant Raman intensities, including both excitonic and non-adiabatic effects. Our diagrammatic approach, which we apply to two prototype, semiconducting layered materials, allows a detailed analysis of the impact of phonon-mediated exciton-exciton scattering on the intensities. In the case of bulk hexagonal boron nitride, this scattering leads to strong quantum interference between different excitonic resonances, strongly redistributing oscillator strength with respect to optical absorption spectra. In the case of MoS$_2$, we observe that quantum interference effects are suppressed by the spin-orbit splitting of the excitons.