Terahertz third-harmonic generation of lightwave driven Weyl fermions far from equilibrium

TL;DR

This study demonstrates room-temperature terahertz third-harmonic generation in Weyl semimetal TaP, revealing nonlinear optical responses driven far from equilibrium and tunable via polarization, with theoretical support from Boltzmann transport analysis.

Contribution

It provides the first experimental observation of terahertz third-harmonic generation in Weyl fermions at room temperature and offers a theoretical framework for understanding their nonlinear optical behavior.

Findings

Terahertz third-harmonic generation observed at room temperature.

Harmonic yield tunable by drive pulse polarization.

Theoretical modeling matches experimental results.

Abstract

We report on time-resolved ultrafast terahertz third-harmonic generation spectroscopy of nonequilibrium dynamics of Weyl fermions in a nanometer thin film of the Weyl semimetal TaP. Terahertz third-harmonic generation is observed at room temperature under the drive of a multicycle narrowband terahertz pulse with a peak field strength of down to tens of kV/cm. The observed terahertz third-harmonic generation exhibits a perturbative cubic power-law dependence on the terahertz drive. By varying the polarization of the drive pulse from linear to elliptical, we realize a sensitive tuning of the third harmonic yield. By carrying out theoretical analysis based on the Boltzmann transport theory, we can properly describe the experimental results and ascribe the observed THz nonlinearity to field-driven kinetics of the Weyl fermions.