# Population inversion and ultrafast terahertz nonlinearity of transient Dirac fermions in Cd$\_3$As$\_2$

Source: [Population inversion and ultrafast terahertz nonlinearity of transient Dirac fermions in Cd$\_3$As$\_2$](<https://www.sota2.com/research/paper/68fa47061e209131ce924e67>)

Collection index: [llms.txt](<https://www.sota2.com/research/llms.txt>)

Data updated: 2025-10-25T06:07:09.748Z

Authors: Changqing Zhu, Patrick Pilch, Renato M. A. Dantas, Anneke Reinold, Yunkun Yang, Faxian Xiu, Amilcar Bedoya-Pinto, Stuart S. P. Parkin, Roderich Moessner, Zhe Wang

Published: 2024-01-16T10:26:57.000Z

## Abstract

Harmonic generation provides an efficient tool for the study of ultrafast nonlinear dynamics. We report on time-resolved optical-pump terahertz-harmonic-generation spectroscopic investigation of ultrafast nonlinearity in a prototypical three-dimensional Dirac semimetal Cd$\_3$As$\_2$. A transient population inversion characterized by excessive nonthermal Dirac electrons and holes is found to be very sensitive and responsive to a periodic terahertz drive, leading to very efficient terahertz third-harmonic generation. Based on the Boltzmann transport theory, we analyze the terahertz field-driven kinetics of the transient Dirac fermions that is responsible for the observed strong terahertz nonlinearity.

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## Original sources and implementation

[Original paper](<https://arxiv.org/abs/2401.08257>)

[PDF](<https://arxiv.org/pdf/2401.08257.pdf>)