Non-perturbative terahertz high-harmonic generation in the three-dimensional Dirac semimetal Cd3As2

Sergey Kovalev,Jiwei Ling,Faxian Xiu,Semyon Germanskiy,Renato M A Dantas,Zhe Wang,Paul H M Van Loosdrecht,Jan-Christoph Deinert,Takashi Oka,Nilesh Awari,Mohammed Bawatna,Bertram Green,Igor Ilyakov,Min Chen,Piotr Surówka

doi:10.1038/s41467-020-16133-8

Abstract

Harmonic generation is a general characteristic of driven nonlinear systems, and serves as an efficient tool for investigating the fundamental principles that govern the ultrafast nonlinear dynamics. Here, we report on terahertz-field driven high-harmonic generation in the three-dimensional Dirac semimetal Cd3As2 at room temperature. Excited by linearly-polarized multi-cycle terahertz pulses, the third-, fifth-, and seventh-order harmonic generation is very efficient and detected via time-resolved spectroscopic techniques. The observed harmonic radiation is further studied as a function of pump-pulse fluence. Their fluence dependence is found to deviate evidently from the expected power-law dependence in the perturbative regime. The observed highly non-perturbative behavior is reproduced based on our analysis of the intraband kinetics of the terahertz-field driven nonequilibrium state using the Boltzmann transport theory. Our results indicate that the driven nonlinear kinetics of the Dirac electrons plays the central role for the observed highly nonlinear response.

Highlights

Harmonic generation is a general characteristic of driven nonlinear systems, and serves as an efficient tool for investigating the fundamental principles that govern the ultrafast nonlinear dynamics
In a distinctly different context of a three-dimensional Dirac semimetal, we report on experimental observation of high-harmonic generation up to the seventh order driven by strong-field terahertz pulses
We report on time-resolved detection of non-perturbative THz High-harmonic generation (HHG) in the 3D Dirac semimetal Cd3As2, and a real-time theoretical analysis of the THz-field driven kinetics of the Dirac fermions that is directly linked to the linear dispersion relation

Summary

Introduction

Harmonic generation is a general characteristic of driven nonlinear systems, and serves as an efficient tool for investigating the fundamental principles that govern the ultrafast nonlinear dynamics. In a distinctly different context of a three-dimensional Dirac semimetal, we report on experimental observation of high-harmonic generation up to the seventh order driven by strong-field terahertz pulses. High-harmonic generation (HHG) in two-dimensional Dirac semimetals (single-layer graphene[14,16,17] and 45-layer graphene7) has been reported very recently for pump pulses both in the terahertz (1012 Hz, 1 THz ∼4 eV)[7,16] and mid-infrared or nearinfrared (0.2–0.8 eV) ranges[14,17]. We report on time-resolved detection of non-perturbative THz HHG in the 3D Dirac semimetal Cd3As2, and a real-time theoretical analysis of the THz-field driven kinetics of the Dirac fermions that is directly linked to the linear dispersion relation. Our results show that the THz-field driven nonlinear kinetics of the Dirac electrons is the mechanism responsible for the efficient generation of highharmonic radiation, as well as for its non-perturbative fluence dependence in Cd3As2

Methods

Results

Conclusion