High harmonics from backscattering of delocalized electrons

Abstract

Electron backscattering is introduced as mechanism to enhance high-harmonic generation in solid-state like systems with broken translational symmetry. As a paradigmatic example we derive for a finite chain of N atoms the harmonic cut-off through backscattering of electrons in the conduction band from the edges of the chain. We also demonstrate a maximum in the yield of the high harmonics from the conduction band if twice the quiver amplitude of the driven electrons equals the length of the chain. High-harmonic spectra as a function of photon energy are shown to be equivalent if the ratio of chain length to the wavelength of the light is kept constant. Our quantum results are corroborated by a (semi-)classical trajectory model with refined spatial properties required to describe dynamics with trajectories in the presence of broken translational symmetry.

Correlation effects in high-harmonic generation from finite systems

“…1(a), an enhancement is found for the finite system, similar to the results of Ref. [30] where an uncorrelated chain was considered within a TDDFT approach. This enhancement peaks at the 16' to 20'th harmonic order, with an enhancement by a factor of 10 20 −10 25 .…”

“…In this work, we have used the laser-driven Hubbard model to examine the interplay between finite system and electron-electron correlation in HHG. Previously, an enhancement in finite systems was reported [30] when not accounting for beyond mean-field electronelectron correlation, i.e., U = 0 case of this study. The Hubbard was used earlier to demonstrate beyond mean-field electron-electron correlation effects of HHG enhancement, leading to an enhancement of the high frequency regime [2].…”

“…Recently, it was found that an enhancement of the HHG spectrum arises in finite lattices due to electrons backscattering on the edges of the lattice [30]. In the finite-size limit, however, electron-electron correlations are of importance as alluded to in HHG experiments with monolayer materials [21] and predicted for pump-probe HHG [31,32].…”