Polarization-sensitive symmetry-protected bound states in the continuum in Dirac semimetal metasurface: a comparative study and application to refractive index sensing

We have designed an actively tunable, polarization-sensitive, symmetry-protected quasi-BIC metasurface based on Dirac semimetals (DS), featuring a silicon dioxide (SiO₂) substrate and a resonant unit of three DS strips. A comparative study was conducted on three distinct methods of breaking symmetry. We initially examined the evolution from BIC to quasi-BIC across different polarizations under these symmetry-breaking conditions, achieving a maximum Q-factor of 7624. Furthermore, by selecting three representative parameters, we calculated the electric field distribution and surface current density and performed multipole decompositions, confirming that the quasi-BIC state is primarily origin in electric dipole oscillations. Subsequently, by adjusting the Fermi energy of the DS strips within the 0.16-0.24 eV range, we actively tuned the resonant frequencies to 1.802-1.826 THz, 1.811-1.822 THz, and 1.805-1.825 THz for <i>x</i>-polarization, and 1.259-1.280 THz, 1.270-1.281 THz, and 1.269-1.284 THz for <i>y</i>-polarization. Coating the metasurface with analyte of diverse refractive indices, we've measured sensing sensitivities and FOM of up to 0.406 THz/RIU and 418.8 RIU^-1 for <i>x</i>-polarization, 0.267 THz/RIU and 232.6 RIU^-1 for <i>y</i>-polarization, highlighting its potential in manipulating electromagnetic waves and applications in hazard detection and biomedical diagnostics.