Phonon-driven decoherence of high-harmonic generation in the solid-state

TL;DR

This study demonstrates that incoherent phonons caused by thermal lattice fluctuations significantly reduce high-harmonic generation efficiency in solids, confirmed through experiments on silicon and supported by a theoretical model.

Contribution

It provides the first direct experimental evidence linking temperature-driven incoherent phonons to decoherence in solid-state high-harmonic generation.

Findings

Harmonic yield increases as temperature decreases.

Theoretical model reproduces temperature-dependent harmonic changes.

Incoherent phonons are identified as a key decoherence source.

Abstract

High-harmonic generation in solids has emerged as a powerful probe of ultrafast electron dynamics and lattice motion, and recent theoretical work has suggested that thermally driven lattice fluctuations can act as an effective source of decoherence in the harmonic-generation process. However, a direct experimental link between high-harmonic emission and temperature-driven incoherent phonons has remained unclear. Here, we investigate the temperature dependence of high-harmonic generation in ultrapure silicon using reflection-geometry measurements over a wide temperature range. We observe that the harmonic yield increases significantly with decreasing temperature. To interpret these results, we introduce a one-dimensional atomic-chain model in which finite temperature is represented by random lattice displacements that mimic incoherent phonon fluctuations. The simulations reproduce the magnitude of temperature-dependent change of the harmonic signal and support a picture in which thermally induced lattice disorder enhances electron-hole decoherence, thereby reducing high-harmonic emission. Our results establish incoherent phonons as an important source of decoherence in solid-state high-harmonic generation.