Ab initio theory of coherent phonon generation by laser excitation

TL;DR

This paper demonstrates that time-dependent density functional theory (TDDFT) can accurately model the generation of coherent optical phonons in solids under laser excitation, capturing key experimental phenomena.

Contribution

It shows that TDDFT can be used as a predictive ab initio method for coherent phonon generation, encompassing mechanisms like impulsive stimulated Raman scattering and displacive excitation.

Findings

Reproduces experimental polarization dependence

Captures strong growth at the direct band gap

Shows phase change from below to above the band gap

Abstract

We show that time-dependent density functional theory (TDDFT) is applicable to coherent optical phonon generation by intense laser pulses in solids. The two mechanisms invoked in phenomenological theories, namely impulsively stimulated Raman scattering and displacive excitation, are present in the TDDFT. Taking the example of crystalline Si, we find that the theory reproduces the phenomena observed experimentally: dependence on polarization, strong growth at the direct band gap, and the change of phase from below to above the band gap. We conclude that the TDDFT offers a predictive ab initio framework to treat coherent optical phonon generation.