Tracking ultrafast change of multiterahertz broadband response functions in a photoexcited Dirac semimetal Cd${}_3$As${}_2$ thin film

Abstract

The electromagnetic response of Dirac semimetals in the infrared and terahertz frequency ranges is attracting growing interest for potential applications in optoelectronics and nonlinear optics. The interplay between the free-carrier response and interband transitions in the gapless, linear dispersion relation plays a key role in enabling novel functionalities. Here we investigate ultrafast dynamics in thin films of a photoexcited Dirac semimetal Cd${}_3$As${}_2$ by probing the broadband response functions as complex quantities in the multiterahertz region (10-45 THz, 40-180 meV, or 7-30 $\mu$m), which covers the crossover between the inter and intraband response. We resolve dynamics of the photoexcited nonthermal electrons which merge with originally existing carriers to form a single thermalized electron gas and how it is facilitated by high-density excitation. We also demonstrate that a large reduction of the refractive index by 80% dominates the nonequilibrium infrared response, which can be utilized for designing ultrafast switches in active optoelectronics.

arXiv comment20 pages

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Cited by in corpus (5)

• Disentangling the Competing Mechanisms of Light-Induced Anomalous Hall Conductivity in Three-Dimensional Dirac Semimetal
• Observation of Terahertz Spin Hall Conductivity Spectrum in GaAs with Optical Spin Injection
• Stimulated Rayleigh Scattering Enhanced by a Longitudinal Plasma Mode in a Periodically Driven Dirac Semimetal Cd${}_3$As${}_2$
• Anomalous Hall transport by optically injected isospin degree of freedom in Dirac semimetal thin film
• Correction of broadband terahertz electro-optic sampling with GaSe crystals