The strong nonlinearity optical calculation of 3D Dirac semimetals.*

The optical nonlinearity of novel Dirac materials, such as graphene, have been extensively studied theoretically and experimentally in recent years. Due to the exceptionally strong light-matter interactions, Dirac material is promising in revolutionizing the functionality of photonic and optoelectronic device technology. In this work, we study the nonlinear optical response generated by the massless Dirac quasiparticles residing around the topologically-protected Dirac nodal points in three-dimensional (3D) Dirac topological semimetals in the terahertz frequency regime. Analytical expressions of third-order interband nonlinear optical conductivities are obtained based on semiclassical Boltzmann equation and quantum mechanical Floquet theory. Using Cd3As2 as an example, we demonstrate that the optical nonlinearity of 3D Dirac semimetal at terahertz frequency is comparable to that of the two-dimensional Dirac fermions in graphene. Importantly, the additional degree of freedom of 3D Dirac semimetal shall offer additional optical device design flexibility not found in atomically-thin graphene.