Non-adiabatic effects in exciton-mediated Raman scattering from first principles

We present a fully quantum mechanical, ab initio approach for the calculation of optical properties of solids, in particular resonant Raman scattering. Starting from the fundamental observable, we derive a fully general description of light scattering by matter beyond the commonly used semi-classical approximations for the electron-nuclei interaction. Our approach captures both direct and phonon-mediated light absorption as well as inelastic light scattering.

We provide a concrete computational recipe for the calculation of resonant Raman intensities beyond the approximation of static (adiabatic) phonons and including excitonic effects. Applying our approach to several materials, we discuss the effects of non-adiabaticity on the Raman intensity. The latter are not captured by frozen-phonon-based approaches [1,2] and so far could only be described by neglecting excitonic effects [3,4], which, however, are predominant in low-dimensional semi-conductors.

References:
[1] Y. Gillet, M. Giantomassi, and X. Gonze, Phys. Rev. B 88, 094305 (2013).
[2] H. P. C. Miranda, S. Reichardt, G. Froehlicher, A. Molina-Sánchez, S. Berciaud, and L. Wirtz, Nano Lett. 17, 2381 (2017).
[3] V. N. Popov and P. Lambin, Phys. Rev. B 73, 085407 (2006).
[4] S. Reichardt and L. Wirtz, Phys. Rev. B 95, 195422 (2017).