High Q Chiroptical Responses Driven by Toroidal Dipole Resonance in All-Dielectric Metasurfaces

Chiral metasurfaces with enhanced chiroptical effects have drawn extensive attentions due to their potential applications from chiral molecule detection to low-threshold chiral emission. However, pursuing strong circular dichroism (CD) and high quality (Q) factors of chiroptical resonances simultaneously still remains problematic. Here, we present a novel design of all-dielectric chiral metasurface which supports enhanced chiroptical responses driven by toroidal dipole (TD) resonances. By introducing geometrical perturbations and breaking the in-plane mirror symmetry, the proposed chiral metasurface can excite high-Q factor ($\sim 2938$) chiroptical resonance with maximal CD ($\sim -0.995$) at terahertz frequencies. Interestingly, the magnitude of CD signals can be freely modulated via tuning geometrical parameters, while the value of Q factor almost remains stable. These results may pave a new avenue for manipulating chiroptical responses for potential applications which require strong CDs accompanied by enhanced light-matter interaction.