Journal
SCIENTIFIC REPORTS
Volume 7, Issue -, Pages -Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/s41598-017-07682-y
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Funding
- Fonds National de la Recherche Scientifique (FNRS, Belgium)
- ESF through the ESF/Psi-k2 programme
- Fonds de la Recherche Scientifique de Belgique (FRS-FNRS)
- Walloon Region [1117545]
- compute cluster DUNE at the Humboldt-Universitat of Berlin
- Einstein Foundation Berlin
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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 affects the spectrum in resonance conditions. The ability to analyze second-order Raman spectra thus provides direct insight into this interaction.
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