High Q-factor toroidal resonances driven by bound states in the continuum in all-dielectric metamaterial at terahertz frequencies

• An all-dielectric metamaterial consisting a periodic array of split ring resonator is proposed for applications at terahertz frequencies. • Multipole approaches based on the bound states in the continuum theory are applied to excite toroidal dipole resonances. • Owing to high Q factors, the proposed metamaterial can serve as an optical sensing platform for the refractive index monitoring. Recently, the concept of bound states in the continuum (BICs) has been widely used in designing metamaterials with high quality factor resonances. In general, there are two approaches of implementing BICs in metamaterials, including tuning the structural parameters and breaking the rotational symmetry. Here, we report a significant process of exciting toroidal dipole resonances with high Q factors in all-dielectric metamaterial using both abovementioned approaches, which are realized by tuning the arc length or rotating the SRR subresonator with the respect to their central axis, respectively. The excitations of toroidal dipole resonances are confirmed by both the spatial distribution of induced electromagnetic fields and the multipole expansion of induced currents. Simulation results reveal that the excited toroidal dipole resonances are sensitive to the surrounding refractive index changes, yielding high sensitivities and large figure of merits (FoMs) simultaneously, which guarantee its potential applications as a platform of monitoring aerogel samples or biochemical analytes.