Correlation effects in high-harmonic generation from finite systems

TL;DR

This study investigates how electron-electron correlations influence high-harmonic generation in finite and bulk systems using the Hubbard model, revealing size-dependent enhancements and correlation-driven spectral changes.

Contribution

It demonstrates the impact of electron-electron interactions on HHG spectra, highlighting finite-size effects and correlation-induced enhancements in high-frequency regimes.

Findings

Finite-size enhancement of HHG signal due to electron backscattering.

Increased electron-electron correlation enhances high-frequency HHG components.

Threshold for correlation dominance decreases with stronger correlations, approaching the Mott insulator limit.

Abstract

Using the Hubbard model we study how the process of high-order harmonic generation (HHG) is modified by beyond mean-field electron-electron correlation for both finite and bulk systems. A finite-size enhancement of the HHG signal is found and attributed to electrons backscattering off the lattice edges. Additionally, with increasing strength of the electron-electron correlation an enhancement of the high-frequency regime of the HHG spectrum is found. This is attributed to the on-site Coulomb repulsion between electrons giving rise to a localized quiver motion of the electrons. The finite-lattice enhancement dominates the HHG spectra from a few harmonic orders until a threshold from which the correlational enhancement dominates. This threshold is determined by the degree of correlation and decreases into the low-frequency regime for increasing electron-electron correlation. This infers that as the Mott insulator limit of high electron-electron correlation is approached, the finite-size effect on the electron dynamics becomes negligible.