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

Abstract The quasi-bound states in the continuum (Q-BIC) can excite an ultra-high radiation quality factor ( Q -factor), enabling a terahertz (THz) metasurface based on Q-BIC to achieve strong in-plane light–matter interactions, which offer a feasible platform for developing highly sensitive THz sensors. In breaking the symmetry of the structure, we explain the origin of the Q-BIC resonance, using multipole decomposition theory to analyze the dominant multipoles in 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 1080 GHz RIU –1 , and the maximum Q -factor can reach 530.51. Additionally, this structure can be used for near-field imaging, and 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 20 meV to 500 meV. Our proposed structure holds promise as a high-performance sensor and an optical switch for applications in environmental monitoring, bio-recognition and THz near-field imaging.