Terahertz Polarization Conversion from Optical Dichroism in a Topological Dirac Semimetal

Topological Dirac semimetals (TDSM) such as Cd3As2 and Na3Bi are attractive for nanophotonic applications in the terahertz (THz) frequency regime and exhibit strong optical dichroism with contrasting dielectric permittivity along different crystal axes and. However, such optical dichroism is often overlooked in the computational works of TDSM-based optoelectronic devices, and whether such optical dichroism can lead to unique functionalities not found under the isotropic approximation remains an open question thus far. My talk will present our recent findings that starkly different THz responses between isotropic and anisotropic media based on TDSM metasurface. Using finite-difference time-domain simulations, we demonstrate that such optical dichroism can lead to an unexpected THz wave polarization conversion even if the metasurface structure remains four-fold rotationally symmetric, a useful feature not achievable under the isotropic model of TDSM. I will also discuss why such optical dichroism in TDSM leads to a contrast response compared to the isotropic case, such as the high Q-factor and asymmetric transmission spectra.