All-electron theory of the coupling between laser-induced coherent phonons in bismuth

TL;DR

This paper presents a first-principles all-electron study of laser-induced coherent phonons in bismuth, revealing phonon-softening, anharmonicities, and mode coupling that explain experimental observations.

Contribution

It provides a comprehensive theoretical analysis of phonon dynamics in bismuth under laser excitation, including potential landscapes and mode interactions, unifying previous experimental results.

Findings

Observation of phonon-softening in bismuth

Detection of phonon-phonon coupling effects

Higher harmonics of phonons appear due to anharmonicities

Abstract

Using first principles, all-electron calculations and dynamical simulations we study the behavior of the A_1g and E_g coherent phonons induced in Bi by intense laser pulses. We determine the potential landscapes in the laser heated material and show that they exhibit phonon-softening, phonon-phonon coupling, and anharmonicities. As a consequence the E_g mode modulates the A_1g oscillations and higher harmonics of both modes appear, which explains recent isotropic reflectivity measurements. Our results offer a unified description of the different experimental observations performed so far on bismuth.