Ultra-high Q resonances governed by quasi-bound states in the continuum in all-dielectric THz metamaterials

Bound states in the continuum (BICs) have received increasing attention due to their ultra-sharp resonance in the field of ultra-sensitive sensing and trace amount detection in the terahertz (THz) regime. In this paper, we propose a new asymmetric all-dielectric THz metamaterial and show that quasi-BICs result in four ultra-high quality (Q) factor resonances observed in the transmission spectrum. The Q factors of resonances can be achieved up to 252248. Electromagnetic field distribution and multipolar decomposition of scattering power are performed to clarify the physical mechanism of quasi-BICs resonances. In addition, the spectra response to the analytes exhibited the ability of the proposed device as an ultra-sensitive sensor, and the maximum sensitivity is 482 GHz/RIU. We further find that the sensitivity of the metamaterial is proportional to the negative quadratic of the gap between structures and explain it by the area of the field enhancement in the metamaterial. Our work paves a novel way to design ultra-high Q resonance metamaterials and ultra-sensitive sensors at THz frequencies.