Unveiling the Role of Electron-Phonon Scattering in Dephasing High-Order Harmonics in Solids

TL;DR

This paper investigates how electron-phonon scattering causes dephasing in high-order harmonic generation in solids, combining experiments and simulations to reveal a momentum-dependent dephasing time and its implications.

Contribution

It introduces the concept of momentum-dependent dephasing time in HHG and identifies electron-phonon scattering as the main dephasing mechanism in solids.

Findings

Electron-phonon scattering is the dominant dephasing mechanism.

Dephasing time depends on electron momentum.

Experimental and simulation results agree on the dephasing role.

Abstract

High-order harmonic generation (HHG) in solids is profoundly influenced by the dephasing of the coherent electron-hole motion driven by an external laser field. The exact physical mechanisms underlying this dephasing, crucial for accurately understanding and modelling HHG spectra, have remained elusive and controversial, often regarded more as an empirical observation than a firmly established principle. In this work, we present comprehensive experimental findings on the wavelength-dependency of HHG in both single-atomic-layer and bulk semiconductors. These findings are further corroborated by rigorous numerical simulations, employing ab initio real-time, real-space time-dependent density functional theory and semiconductor Bloch equations. Our experimental observations necessitate the introduction of a novel concept: a momentum-dependent dephasing time in HHG. Through detailed analysis, we pinpoint momentum-dependent electron-phonon scattering as the predominant mechanism driving dephasing. This insight significantly advances the understanding of dephasing phenomena in solids, addressing a long-standing debate in the field. Furthermore, our findings pave the way for a novel, all-optical measurement technique to determine electron-phonon scattering rates and establish fundamental limits to the efficiency of HHG in condensed matter.