Symmetry-Broken High-Q Terahertz Quasi-Bound States in the Continuum

Electromagnetic metasurfaces possess unique scattering effects that enable wavefront control. Relatively recently, metasurfaces have been shown to support an unconventional phenomenon known as bound states in continuum (BIC) modes. BICs enable the confinement of electromagnetic energy to a localized region without high radiation losses, thus manifesting as ultrahigh quality (Q) factor resonances. In this study, we investigate an all-dielectric metasurface composed of a suspended periodic array of asymmetric cylindrical resonators. Leveraging point group theory, we utilize a theoretical framework to explain how the introduced asymmetry leads to terahertz-active quasi-BIC modes. Our experimental findings reveal a high-Q mode near 600 GHz, boasting an unprecedented experimental Q factor of Q = 3700 ± 200. The symmetry-broken quasi-BIC metasurface offers a promising avenue toward achieving ultrahigh Q factor BIC resonances, presenting exciting possibilities in the field of artificial electromagnetic materials.