Ultrafast Relaxation Dynamics of Photoexcited Dirac Fermion in The Three Dimensional Dirac Semimetal Cadmium Arsenide

TL;DR

This study investigates the ultrafast relaxation dynamics of photoexcited carriers in the 3D Dirac semimetal cadmium arsenide, revealing slower carrier cooling compared to graphene due to lower optical phonon energies.

Contribution

It provides the first systematic ultrafast transient reflection measurements of Cd3As2, demonstrating carrier dynamics and phonon coupling differences in this stable Dirac semimetal.

Findings

Carrier cooling in Cd3As2 is slower than in graphene.

Dynamical evolution of carriers can be modeled by a two-temperature model.

Carrier relaxation depends on doping, probe wavelength, pump power, and temperature.

Abstract

Three dimensional (3D) Dirac semimetals which can be seen as 3D analogues of graphene have attracted enormous interests in research recently. In order to apply these ultrahigh-mobility materials in future electronic/optoelectronic devices, it is crucial to understand the relaxation dynamics of photoexcited carriers and their coupling with lattice. In this work, we report ultrafast transient reflection measurements of the photoexcited carrier dynamics in cadmium arsenide (Cd3As2), which is one of the most stable Dirac semimetals that have been confirmed experimentally. By using low energy probe photon of 0.3 eV, we probed the dynamics of the photoexcited carriers that are Dirac-Fermi-like approaching the Dirac point. We systematically studied the transient reflection on bulk and nanoplate samples that have different doping intensities by tuning the probe wavelength, pump power and lattice temperature, and find that the dynamical evolution of carrier distributions can be retrieved qualitatively by using a two-temperature model. This result is very similar to that of graphene, but the carrier cooling through the optical phonon couplings is slower and lasts over larger electron temperature range because the optical phonon energies in Cd3As2 are much lower than those in graphene.