High Harmonic Generation in VO₂: First Principles Study

We studied the effect of High Harmonic Generation (HHG) in VO₂ in the insulating (M₁) phase by using Time-Dependent Density-Functional Theory (TDDFT) with the exchange-correlation (XC) potential obtained with Dynamical Mean-Field Theory (DMFT). In detail, we first studied the static properties of the system by using DFT+DMFT to take into account strong electron correlations and to derive an analytical (large-U limit) TDDFT XC potential. We used the resulting XC to analyze the HH spectrum of the system with a focus on the effects of electron-electron correlations. We have found that the odd harmonics, seen experimentally, are generated by correlations. It was also found that as correlation strength increases, the system generates a richer HH spectrum, with the spectrum weight shifted towards higher harmonics. In the limit of strong correlations and laser pulse frequencies <!--[if gte msEquation 12]> style='mso-bidi-font-style:normal'>~0.3
eV the spectrum demonstrates super-harmonics - an energy-periodic enhancement and suppression of certain harmonic orders. Obtained results may help to better understand the ultrafast and emissive properties of vanadium dioxide.