Microscopic Theory of Light-Induced Coherent Phonons Mediated by Quantum Geometry

TL;DR

This paper develops a quantum-mechanical theory for light-induced coherent phonons, revealing their quantum geometric origin and demonstrating potential for ultrafast control of ferroelectric properties in semiconductors.

Contribution

It introduces a fully quantum framework based on Feynman diagrams to describe coherent phonon generation and uncovers the quantum geometric nature of electron-phonon interactions.

Findings

Identification of a dominant second-order, double-resonant process in noncentrosymmetric semiconductors.

Demonstration of light-induced modulation of ferroelectric polarization in BaTiO₃ and SnSe.

Revelation of the quantum geometric origin of coherent phonon generation.

Abstract

Light-induced coherent phonons provide a powerful platform for ultrafast control of material properties. However, the microscopic theory and quantum geometric nature of this phenomenon remain underexplored. Here, we develop a fully quantum-mechanical framework based on Feynman diagrams to systematically describe the generation of coherent phonons by light. We identify a dominant second-order, double-resonant process in noncentrosymmetric semiconductors that efficiently couples light to both electronic and phononic excitations. Crucially, we uncover the quantum geometric origin, encoded in the electron-phonon coupling (EPC) shift vector and the EPC quantum geometric tensor. Applying our theory to ferroelectric BaTiO$_3$ and SnSe, we demonstrate the potential for light-induced modulation of ferroelectric polarization driven by coherent phonons. This work provides fundamental insights for designing efficient optical control strategies for both coherent phonons and ferroelectric polarization.