High-Harmonic Generation in Mott Insulators

TL;DR

This study uses Floquet dynamical mean-field theory to analyze high-harmonic generation in Mott insulators under AC fields, revealing distinct behaviors in strong and weak field regimes related to doublon-holon dynamics.

Contribution

It provides a detailed theoretical analysis of high-harmonic generation in Mott insulators, highlighting the role of Coulomb interactions and doublon-holon recombination processes, which was not previously well understood.

Findings

Multiple harmonic plateaus scale with Coulomb interaction and field strength.

Strong-field regime shows localized doublons and holons, with cutoff energies depending on $U$ and $E_0$.

Mott insulators exhibit stronger high-harmonic signals than comparable semiconductors.

Abstract

Using Floquet dynamical mean-field theory, we study the high-harmonic generation in the time-periodic steady states of wide-gap Mott insulators under AC driving. In the strong-field regime, the harmonic intensity exhibits multiple plateaus, whose cutoff energies $\epsilon_{\rm cut} = U + mE_0$ scale with the Coulomb interaction $U$ and the maximum field strength $E_0$. In this regime, the created doublons and holons are localized because of the strong field and the $m$-th plateau originates from the recombination of $m$-th nearest-neighbor doublon-holon pairs. In the weak-field regime, there is only a single plateau in the intensity, which originates from the recombination of itinerant doublons and holons. Here, $\epsilon_{\rm cut} = \Delta_{\rm gap} + \alpha E_0$, with $\Delta_{\rm gap}$ the band gap and $\alpha>1$. We demonstrate that the Mott insulator shows a stronger high-harmonic intensity than a semiconductor model with the same dispersion as the Mott insulator, even if the semiconductor bands are broadened by impurity scattering to mimic the incoherent scattering in the Mott insulator.