Early study on the Dirac Fermion utilized two-dimensional (2D) systems like graphene, while more recent work on the subject has focused on three-dimensional Dirac semimetals (3D DSM). 3D DSM has a key structural advantage over graphene monolayer in that it shows linear band dispersion with a macroscopic thickness. Similar to graphene, the Dirac band structure of 3D DSM confers very high optical nonlinearities. Since Dirac physics describes charge carriers in both 2D and 3D DSM, 3D DSM should have similar optical properties to graphene, such as tunable optical conductivity, high nonlinear optical coefficients, and stronger light confinement. Also, 3D DSM is better for plasmonic waveguides than 2D graphene because it has a 3D structure, which gives it an extra degree of freedom. Based on these great qualities, 3D DSMs are a good replacement for 2D DSMs. Cadmium arsenide (Cd₃As₂) is a popular 3D DSM because of its chemical stability in air and exceptional optical properties.

In this comprehensive review (Recent Advances in Photonics of 3D Dirac Semimetal Cd₃As₂) accepted by Advanced Photonics Nexus, a sister journal of Advanced Photonics, Zhou et al. discussed photonic features of 3D DSM Cd₃As₂, including linear and nonlinear plasmonics, optical absorption, optical harmonic generation, and ultrafast dynamics. Additionally, they reviewed recent developments in Cd₃As₂ synthesis methods. Upon reviewing its optical properties, Cd₃As₂ stands out as a topological material, which has been extensively investigated both theoretically and experimentally. Reviewing its optical properties showed that Cd₃As₂ is a notable member of the class of materials called "topological materials," which have been studied a lot in both principles and application. There is no doubt that Cd₃As₂ contains well-defined 3D massless charge carriers.

Figure. A schematic shows a summary of the possible optical properties of 3D DSM Cd₃As₂

Without a doubt, 3D DSM will keep attracting attention and research effort. However, the fabrication of large-area, high-quality materials is constantly required for the development of large-scale devices as well as the exploration of fascinating topological physics. New ways of measuring and controlling must be developed in order to move forward. In fact, to properly comprehend many unique quantum states, new probes must be developed. It may be necessary to use a variety of strategies under extreme conditions to make the most of these new tools. The combination of electrical and optical techniques may also enable quantum control of the new physics, leading to real-world applications. It is very important to develop techniques tuned to the intriguing topological quantum physics at various frequencies, especially in the GHz and THz ranges.

Clearly, research into the unusual optical features of 3D DSM Cd₃As₂ is still in its early stages, and we could soon learn something that is far stranger than what we had anticipated. The authors hope that this article will serve as a succinct summary of recent developments in photonics in 3D DSM Cd₃As₂ and a handy reference for emerging scientists.