Dirac semimetal terahertz metasurface for sensing and near-field imaging based on Q-BIC

The quasi-bound states in the continuum (Q-BIC) can excite an ultra-high radiation quality factor (Q-factor), enabling THz metasurface based on Q-BIC to achieve strong in-plane lightmatter interactions, which offers a feasible platform for developing highly sensitive THz sensors. By breaking the symmetry of the structure, we use multipole decomposition theory to analyze the dominant multipoles in resonance, explaining the origin of the Q-BIC resonance. Based on this, we propose a novel THz metasurface using Dirac semimetal (DS), achieving dynamic tunability of the Q-BIC resonance peak by altering the Fermi level of DS. In sensing applications, this structure realizes multi-peak sensing in the range of 4-5 THz, with a maximum sensitivity of up to 1080GHz/RIU, and the maximum Q-factor can reach 530.51, respectively. Additionally, this structure can be used for near-field imaging, as well as function as an optical switch, with a modulation depth of up to 86.7% for the Q-BIC resonance peak by adjusting DS's Fermi level from 20meV to 500meV. Our proposed structure holds promise as a high-performance sensor and an optical switch for applications in environmental monitoring, bio-recognition and Terahertz near-field imaging.