Terahertz harmonic generation across the Mott insulator-metal transition

TL;DR

This study explores terahertz harmonic generation across the Mott insulator-metal transition in rare-earth nickelates, revealing phase-dependent behaviors and underlying mechanisms using theoretical models, with implications for advanced material applications.

Contribution

It provides new insights into the phase-dependent mechanisms of THz harmonic generation in strongly correlated materials using Hubbard models.

Findings

Harmonic intensity increases with cooling in AFM and PM metallic phases.

Harmonic behavior reverses in the intermediate PM insulating phase.

Different physical mechanisms dominate harmonic generation in each phase.

Abstract

We demonstrate terahertz (THz) harmonic generation across the Mott insulator-metal transition in rare-earth nickelates (RNiO$_3$, R = rare-earth atom). The THz harmonic generation is observed in all the three different phases with distinct behaviors: the intensity of harmonics increases upon cooling in both the low-temperature antiferromagnetic (AFM) insulating and high-temperature paramagnetic (PM) metallic phases, while this trend is reversed in the intermediate PM insulating phase. Using single- and two-band Hubbard models, we find different dominant origins of THz harmonics in different phases: strong spin-charge and orbital-charge couplings in the AFM insulating phase, intraband currents from renormalized quasi-particles with frequency-dependent scattering rate in the PM metallic phase, and the reduction of the charge carrier density due to the opening of the Mott gap in the PM insulating phase. Our study offers strategies for efficient THz harmonic generation from Mott and other strongly correlated systems and insights into the fundamental physics of complex materials.