Electron-electron correlation-induced generation of super-harmonics in the high harmonic spectrum in perovskites*

High Harmonic Generation (HHG) is a powerful experimental technique for examining the impact of electron-light interactions and the dynamics of electrons in solids and other systems. Using the time-dependent density-functional theory with the exchange-correlation (XC) kernel obtained by using dynamical mean-field theory, we analyze the role of effects of strong electron-electron correlations in the high-harmonic (HH) spectrum of perovskite BaTiO₃ excited by a laser pulse. As we show, the correlation effects considerably alter the HH spectrum,

moving it to higher frequencies, and when the correlation strength (magnitude of the XC kernel) exceeds a critical value, the HH spectrum demonstrates super-harmonics – an energy-periodic enhancement and suppression of certain harmonic orders.  The results are stable to the varying strength of the pulse field, its length, and laser frequency. Applications of the found effect may help to analyze the importance of correlation effects and optical response of perovskites and other strongly correlated materials.