Strong terahertz third-harmonic generation by kinetic heavy quasiparticles in CaRuO$_3$

TL;DR

This study demonstrates strong terahertz third-harmonic generation in CaRuO$_3$, linked to heavy quasiparticles emerging from strong correlations, with implications for nonlinear terahertz spectroscopy of correlated materials.

Contribution

It reveals the nonlinear terahertz response due to heavy quasiparticles in CaRuO$_3$, combining experimental spectroscopy with a Boltzmann model to explain the third-harmonic generation.

Findings

Third-harmonic radiation observed up to 2.1 THz at low temperatures.

Deviation from Drude behavior linked to heavy quasiparticles.

Nonlinear kinetics explained by a time-dependent Boltzmann model.

Abstract

We report on time-resolved nonlinear terahertz spectroscopy of a strongly correlated ruthenate, CaRuO$_3$, as a function of temperature, frequency and terahertz field strength. Third-harmonic radiation for frequencies up to 2.1 THz is observed evidently at low temperatures below 80 K, where the low-frequency linear dynamical response deviates from the Drude model and a coherent heavy quasiparticle band emerges by strong correlations associated with the Hund's coupling.Phenomenologically, by taking an experimentally observed frequency-dependent scattering rate, the deviation of the field driven kinetics from the Drude behavior is reconciled in a time-dependent Boltzmann description, which allows an attribution of the observed third-harmonic generation to the terahertz field driven nonlinear kinetics of the heavy quasiparticles.