Nonlinear THz Optical Response Of 3D Topological Dirac/Weyl Semimetals

The optical nonlinearity of three-dimension (3D) topological Dirac/Weyl semimetals is studied by calculating its Kerr effect and high harmonic generation in THz regime [1]. Analytical expressions of third-order interband nonlinear optical conductivities are obtained based on a quantum mechanical formalism which couples 3D Dirac fermions with multiple photons. Our findings reveal that the massless Dirac fermions in 3D semi-metals retains strong optical nonlinearity in terahertz frequency regime, comparable to the case of the two-dimensional Dirac fermions in graphene. Since 3D topological Dirac/Weyl semimetals possess bulk structural advantage not found in the strictly two-dimensional graphene, it may offer greater design flexibility and ease-of-fabrication for photonic and optoelectronic device applications as a viable alternative to graphene nonlinear optics applications.