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

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

https://www.nature.com/articles/s41467-020-16133-8

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.

Abstract-Terahertz probe of photoexcited carrier dynamics in the Dirac semimetal Cd 3 As 2

Wei Lu, Jiwei Ling, Faxian Xiu, and Dong Sun

https://journals.aps.org/prb/accepted/bf077O78H3311337d63c5641b9f821c1375d6544c

The relaxation dynamics of photoexcited quasiparticles of three-dimensional (3D) Dirac semimetals are vital towards their application in high performance electronic and optoelectronic devices. In this work, the relaxation dynamics of photoexcited carriers of 3D Dirac semimetal Cd${}_3$As${}_2$ are investigated by transient terahertz spectroscopy. The visible pump-THz probe spectroscopy measurement shows clear biexponential decays with two characteristic time constants. According to the pump-power and temperature dependence, these two characteristic time constants are attributed to the electron phonon coupling (1-4 ps) and anharmonic decay of hot coupled phonons to electronic uncoupled phonons (2-9 ps), respectively. An anomalous electron-optical phonon coupling reduction and a bottleneck slowing of hot optical phonons relaxation are observed with higher excitation intensities similar to that in graphene. On the other hand, the electron-optical phonon coupling can be enhanced due to the phonon frequency broadening and softening at elevated lattice temperature. Furthermore, the transient THz spectrum response is strongly modified by the phonon assisted intraband absorption of hot carriers from a pure electronic Drude model, which is evidenced by a characteristic THz absorption dip in the transient THz absorption spectrum. This absorption dip is pinned by the mixing of discrete optical phonon energies that assist the intraband transition enabled by photoexcitation of hot carriers. 

Abstract-Terahertz Probe of Photoexcited Carrier Dynamics in Dirac Semimetal Cd3As2

Wei Lu, Jiwei Ling, Faxian Xiu, Dong Sun

https://arxiv.org/abs/1807.03049

The relaxation dynamics of photoexcited quasiparticles of three-dimensional (3D) Dirac semimetals are vital towards their application in high performance electronic and optoelectronic devices. In this work, the relaxation dynamics of photoexcited carriers of 3D Dirac semimetal Cd3As2 are investigated by transient terahertz spectroscopy. The visible pump-THz probe spectroscopy measurement shows clear biexponential decays with two characteristic time constants. According to the pump-power and temperature dependence, these two characteristic time constants are attributed to the electron phonon coupling (1-4 ps) and anharmonic decay of hot coupled phonons to electronic uncoupled phonons (2-9 ps), respectively. An anomalous electron-optical phonon coupling reduction and a bottleneck slowing of hot optical phonons relaxation are observed with higher excitation intensities similar to that in graphene. On the other hand, the electron-optical phonon coupling can be enhanced due to the phonon frequency broadening and softening at elevated lattice temperature. Furthermore, the transient THz spectrum response is strongly modified by the phonon assisted intraband absorption of hot carriers from a pure electronic Drude model, which is evidenced by a characteristic THz absorption dip in the transient THz absorption spectrum. This absorption dip is pinned by the discrete optical phonon energy that assists the intraband transition enabled by photoexcitation of hot carriers.

Abstract-Dynamic Terahertz Response in the Dirac Semimetal Cd3As2 Induced by Ultrafast Optical Excitation

Wei Lu, Jiwei Ling, Faxian Xiu, Dong Sun,

https://www.osapublishing.org/abstract.cfm?uri=CLEO_QELS-2018-JW2A.133

Hot electron relaxation and coupling in Cd3As2 is studied by employing ultrafast time-domain THz spectroscopy. The excited carriers enhance the absorption of THz and relax in ps-time scales, the cooling rules consistent with mid-IR spectroscopy.

© 2018 The Author(s)